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Identifying multiple stressor controls on phytoplankton dynamics in the River Thames (UK) using high-frequency water quality data
Abstract
River phytoplankton blooms can pose a serious risk to water quality and the structure and function of aquatic ecosystems. Developing a greater understanding of the physical and chemical controls on the timing, magnitude and duration of blooms is essential for the effective management of phytoplankton development. Five years of weekly water quality monitoring data along the River Thames, southern England were combined with hourly chlorophyll concentration (a proxy for phytoplankton biomass), flow, temperature and daily sunlight data from the mid-Thames. Weekly chlorophyll data was of insufficient temporal resolution to identify the causes of short term variations in phytoplankton biomass. However, hourly chlorophyll data enabled identification of thresholds in water temperature (between 9 and 19°C) and flow (<30m(3)s(-1)) that explained the development of phytoplankton populations. Analysis showed that periods of high phytoplankton biomass and growth rate only occurred when these flow and temperature conditions were within these thresholds, and coincided with periods of long sunshine duration, indicating multiple stressor controls. Nutrient concentrations appeared to have no impact on the timing or magnitude of phytoplankton bloom development, but severe depletion of dissolved phosphorus and silicon during periods of high phytoplankton biomass may have contributed to some bloom collapses through nutrient limitation. This study indicates that for nutrient enriched rivers such as the Thames, manipulating residence time (through removing impoundments) and light/temperature (by increasing riparian tree shading) may offer more realistic solutions than reducing phosphorus concentrations for controlling excessive phytoplankton biomass.
... Blooming algae: diatom growth and silica depletion Diatoms are the dominant phytoplankton in the River Thames and give rise to pronounced spring algal blooms when river-water chlorophyll-a reaches maximum concentrations 34 . During these diatom blooms, dissolved reactive silica (SiO 2 ) is assimilated to form the diatom outer shells (siliceous frustules), resulting in depletion in river-water SiO 2 concentrations 35 , and a negative relationship between chlorophyll-a and SiO 2 concentrations (Fig. 5a). ...
... Phytoplankton blooms are highly dynamic, responding to changes in physio-chemical conditions on daily and sub-daily timescales 34 and monthly monitoring is insufficient to characterize these dynamics. Recent higherresolution monitoring has shown that, with an overabundance of P and N in the River Thames, water temperature during the spring is a key driver of diatom blooms in the River Thames 34,38,39 , among other multiple controls on bloom dynamics, including light 40 . ...
... From this, we identified an ecological range in water temperature of 9.6 to 18.25 o C that is favourable for spring diatom blooms in the lower River Thames at Teddington. This range is consistent with estimates of the ecological range in water temperatures favourable for diatom blooms at other locations within the River Thames 34,40 . ...
Eutrophication and proliferation of nuisance and harmful algal blooms are a major cause of water-quality impairment globally. Here, we analyze the world’s longest continuous (150-year) river water-quality dataset for the River Thames, U.K. (including biological oxygen demand, chloride, phosphorus and silica), to explore the impacts of urbanization, wastewater discharges and agricultural intensification. Over the last 40 years, improvements in wastewater treatment and agricultural management have reduced phosphorus loads by ~80%. However, this has been insufficient to curtail river algal blooms because nutrient concentrations remain above limiting levels. Over the last 50–60 years, rising water temperatures have increased the number of days with water temperatures favourable for diatom blooms in March-April and for cyanobacterial growth in July-August. These results highlight the challenges of eutrophication management in a warming climate and a strategic need to redouble efforts in further reducing nutrient emissions to control nuisance and increasingly harmful algal blooms.
... Nutrient concentrations often vary seasonally within any given temperate river, although the exact pattern depends on the nutrient constituent and watershed of interest. For instance, NO 3 [24][25][26][27][28] and PO 4 [27,[29][30][31] concentrations in temperate rivers are often lowest during the summer. On the other hand, SiO 4 concentrations have been shown to be generally (although not always) lower in spring and early summer, and higher in late summer and fall [27,[29][30][31][32][33], but see [24] for an exception. ...
... For instance, NO 3 [24][25][26][27][28] and PO 4 [27,[29][30][31] concentrations in temperate rivers are often lowest during the summer. On the other hand, SiO 4 concentrations have been shown to be generally (although not always) lower in spring and early summer, and higher in late summer and fall [27,[29][30][31][32][33], but see [24] for an exception. ...
... For instance, in the Yukon River, SiO 4 increased continuously from May to September [29] and in the Yangtze River, China, SiO 4 was higher in the summer [30]. In the River Thames, UK, dissolved SiO 4 is lowest around May and reaches a maximum in August-September [31]. This previous research indicates that, generally speaking, summer is when dissolved nutrients are least abundant in large, temperate rivers. ...
Nutrient limitation of phytoplankton is common but by no means universal in large temperate rivers. Previous field studies in the Columbia River, USA, are suggestive of nutrient limitations of phytoplankton, especially during summer, but this has never been tested experimentally. We therefore undertook monthly 5-day nutrient amendment incubation experiments from May–September 2018 using Columbia River water collected at Vancouver, Washington, USA. We compared replicate treatment bottles containing natural microplankton assemblages and amended nutrients (NO3, PO4 and SiO4 in combination) with replicate control bottles containing natural microplankton assemblages and ambient nutrients. Phytoplankton abundance and biomass were compared between treatments and controls on each day of each experiment, and microplankton assemblage structure was evaluated using Permutational Multivariate Analysis of Variance and Non-Metric Multi-Dimensional Scaling ordination on Day 0 (ambient) and Day 5 of each experiment. Nutrient amendment significantly affected phytoplankton abundance and biomass, particularly in June–August, although this varied between taxa (e.g., cyanobacteria, dinoflagellates, flagellates and ciliates showed more frequent positive responses than chlorophytes and diatoms did). Abundance-based microplankton assemblage structure was significantly correlated with PO4, SiO4 and NO3 concentrations, and BIOENV procedure in R revealed that the best subset of explanatory variables included SiO4 and NO3 concentrations. Biomass-based assemblage structure was significantly correlated with SiO4 and NO3, although BIOENV explanatory variables included only SiO4. These results are suggestive of summertime nutrient control of phytoplankton abundance and biomass, as well as microplankton composition, in the lower Columbia River, at least during some months. Since eutrophication is increasing in the watershed, this could have important implications for higher level consumers (e.g., zooplankton and out-migrating juvenile salmon).
... Residence time varied from 9 to 112 h at 90 th and 10 th percentile flows, respectively. A favorable combination of light availability, high temperatures, and long residence times during mid-spring to mid-summer causes excessive phytoplankton production, which results in large fluctuations in river DO levels (Bowes et al. 2016;Pathak et al. 2021). ...
... Light availability, as commonly observed (Bott et al. 1985;Mulholland et al. 2001), increases the GPP with increase in photosynthetic production. High GPP occurred at mid-temperatures (Fig. 6), which is similar to the findings of Bowes et al. (2016) and Pathak et al. (2021), who reported optimum temperature ranges (~11-18 C) for high phytoplankton growth in the lower River Thames. An opposing interaction between 1/k b T and SRP (Fig. 6) shows that GPP increases with water temperature, but only at low SRP levels. ...
... An opposing interaction between 1/k b T and SRP (Fig. 6) shows that GPP increases with water temperature, but only at low SRP levels. SRP depletion with increased GPP (Fig. S8) indicates biomass uptake (Bowes et al. 2016). Hence, we believe that the opposing interaction between 1/k b T and SRP is more of a causal effect that occurs during the growing season when phytoplankton utilizes SRP and peaks with increase in temperature. ...
High‐resolution monitoring of water quality and ecosystem functioning over large spatial scales in expansive lowland river catchments is challenging. Therefore, we need modeling tools to predict these processes at locations where observations are absent. Here, we present a new approach to estimate ecosystem metabolism underpinned by a high‐resolution, process‐based model of in‐stream flows and water quality. The model overcomes the current challenges in metabolism modeling by accounting for oxygen transport under varying flows and oxygen transformations due to biogeochemical processes. We implement the model in a 62‐km‐long stretch of the River Thames, England, using observations spanning 2 yr. Model outputs suggest that the river is primarily autotrophic from mid‐spring to mid‐summer due to high biomass during low‐flow periods, and is heterotrophic during the rest of the year. Ecosystem respiration in upstream reaches is driven mainly by biochemical oxygen demand, autotrophic respiration, and nitrification processes, whereas downstream sites also show a control of benthic oxygen demand in addition to the aforementioned processes. Using empirical modeling, we analyze the sensitivity of our estimated metabolism rates to multiple environmental stressors. Results demonstrate that empirical models could be useful for rapid river health assessments, but need improvements to reproduce peak metabolism rates. The process‐based model, although more complex than existing in situ approaches to metabolism quantification, allows inference when gaps in continuous observations are present. The model offers additional benefits for predicting metabolism rates under future scenarios of environmental change incorporating multiple stressor effects.
... But now the blooms are also frequently reported in rivers (Mckay et al., 2018), especially in impounded rivers (Bormans et al., 2004) and in urban, industrial, and agricultural watersheds (Paerl et al., 2018). Therefore, it is vital to understand the processes and the causes of phytoplankton growth along rivers, in order to efficiently reduce the risk of algae blooms (Bowes et al., 2016). Whereas, compared to research in lake systems, it is less studied how the phytoplankton communities vary in river systems (Dolph et al., 2017). ...
... Furthermore, except for the effects of nutrients availability on river eutrophication, there are a growing number of studies that suggest that physical factors also play an important role in phytoplankton variations (Minaudo et al., 2017). For example, in the nutrient-enriched Thames River, water residence time and light were critical physical factors associated with the risk of excessive algal growth (Bowes et al., 2012(Bowes et al., , 2016. The study in River Lambourn also found that reducing light intensity could be an important management tool to reduce river periphyton biomass (McCall et al., 2017). ...
... In river systems, nutrients distribution, water temperature, sunlight and hydraulic condition are the main physicochemical factors associated with phytoplankton growth (Bowes et al., 2016;Haakonsson et al., 2017;Lurling et al., 2018;Nguyen et al., 2019). In this study, during warm seasons, from April to October, temperature and light were not the main limitation factors in the 13th impoundment, while TP and discharge (represents the variation of hydrodynamic conditions) were the key drivers determining Chl a concentrations of the phytoplankton communities (Fig. 7). ...
Rubber dams are widely used in urban rivers for landscape construction and flood control. However, the increased water residence time by dams usually causes phytoplankton accumulation. Developing a greater understanding of the phytoplankton dynamics and the effecting factors is essential for the eutrophication control of dammed rivers. Here, we investigated the variations in biomass and structure of phytoplankton communities along an urban landscape river with 30 rubber dams, and the main controlling factors during a 2-yr field monitoring. The biomass of phytoplankton significantly increased from 12.7 μg/L-Chl a and 1.14 × 107 ind./L-cells at the natural river part above dams to 65.2 μg/L-Chl a and 1.16 × 108 ind./L-cells at the 30th dam on average. There were different dominant taxa of phytoplankton between river sections with and without dams in different seasons. As Bacillariophyta dominated at the natural river part above dams throughout the year, accounting for 64.6% on average, and dominated at the 13th and 30th dams during the cold seasons (69.6% on average). But during the warm seasons, Cyanophyta and Chlorophyta increased obviously in the dammed river sections and became dominant taxa at the 30th dam, accounting for 55.9% and 34.7% respectively. The α-diversity of phytoplankton decreased along the series of dams. While the β-diversity between river sections with and without dams increased because of species replacement. Redundancy analysis revealed that nutrients, flow velocity and temperature were the main factors influencing the spatial-temporal variation in phytoplankton community structure in this river. High-frequency monitoring data further indicated that phosphorus and discharge explained most of the variations in phytoplankton biomass within the 13th dam impoundment. It suggested that management strategies should focus on reducing the phosphorus input concentration under 0.164 mg/L and increase the discharge higher than 0.64 m3/s during warm seasons, to prevent phytoplankton bloom and further eutrophication problems in this dammed river.
... Given their critical role in the hydrological and ecological connectivity of surface waters, analyses of eutrophication responses by rivers are still desperately needed (Dodds and Smith, 2016). Relative to lakes, river ecosystems are spatially and temporally dynamic, with complex interacting factors driving water quality changes (Basu and Pick, 1995;Bowes et al., 2016;Hutchins and Hitt, 2019). Water temperature, water residence time (discharge), transparency (light), and pH have all been found to be correlated with temperate river phytoplankton biomass in previous studies, in addition to nutrients (Basu and Pick, 1996;Balbi, 2000;Bukaveckas et al., 2011;Bowes et al., 2016). ...
... Relative to lakes, river ecosystems are spatially and temporally dynamic, with complex interacting factors driving water quality changes (Basu and Pick, 1995;Bowes et al., 2016;Hutchins and Hitt, 2019). Water temperature, water residence time (discharge), transparency (light), and pH have all been found to be correlated with temperate river phytoplankton biomass in previous studies, in addition to nutrients (Basu and Pick, 1996;Balbi, 2000;Bukaveckas et al., 2011;Bowes et al., 2016). Variation in run-off and erosion patterns, as well as anthropogenic land use changes in the watershed, can further influence these processes (Bennett et al., 2001;Walsh et al., 2005). ...
... Thus, detecting long-term responses to eutrophication remediation not only requires sufficient data across years to detect net changes, but also sufficient data within years (particularly during the growing season) to assess whether the frequency and intensity of individual bloom events is also changing. This requirement for higher-frequency data is particularly critical for understanding the eutrophication recovery of flowing systems, such as river networks, which are inherently spatially and temporally dynamic (Balbi, 2000;Minaudo et al., 2015;Bowes et al., 2016). ...
Despite massive financial investment in mitigation, eutrophication remains a major water quality problem and management priority. Eutrophication science—well established for lakes—is not as well developed for rivers, and scientific understanding of how rivers respond to eutrophication management is far more limited. Long-term data are required to evaluate progress, but such datasets are relatively rare for rivers. We analyzed 23 years of water quality data for the Charles River, a major urban river system in the northeastern U.S.A., to examine nutrient and phytoplankton biomass (chl-a) responses to decades of phosphorus (P) management. Using the more novel and robust approach of quantile regression, we identified statistically and ecologically significant declines in both total phosphorus (TP) and chl-a over time, but only for middle percentiles. Statistically high concentrations of TP and chl-a persist—the segments of the data of greatest concern to managers and the public—and yet this critical result is concealed by statistical tests often employed in eutrophication studies that only evaluate mean changes. TP, temperature, precipitation, and river segment jointly explain the most chl-a variation observed at the decadal scale. Spatial variation is also considerable: despite a significant decline in TP, the impounded lower river exhibits no long-term trend in chl-a and continues to experience annual blooms of harmful cyanobacteria—a lagging response comparable to that of a recovering eutrophic lake. Despite long-term successes in reducing P, chl-a, and cyanobacteria in the Charles River system, we did not detect any significant, long-term change in the attainment of statutory compliance, illustrating the protracted and complex nature of the river's response. Our analysis demonstrates the need for high-frequency, long-term water quality data to evaluate the progress of eutrophication management in urban rivers, and the utility of quantile regression for detecting critical trends in the occurrence of statistically low-frequency but ecologically high-impact events, including blooms of harmful cyanobacteria.
... Phytoplankton is characterized by circadian variability, as well as by diurnal rhythms and seasonal variability, driven by physical and biological factors such as light intensity, water temperature, wind, water level, nutrients, species, and size (Carstensen et al., 2007;Moore et al., 2008;Leal et al., 2009;Zhang et al., 2012;Jindal and Thakur, 2013;de Tezanos Pinto and O' Farrel, 2014;Bowes et al., 2016). For this reason, lake routine monitoring and water quality assessment with conventional sampling techniques, such as boat based sampling with filtration of water samples followed by laboratory analysis Exploiting high frequency monitoring and satellite imagery for assessing chlorophyll-a dynamics in a shallow eutrophic lake N o n -c o m m e r c i a l u s e o n l y (e.g., solvent extraction of chlorophyll-a and spectrophotometric determination), are challenged to provide insights into the complex relationship between biological, chemical and physical processes (Kaplan et al., 2003;Polat et al., 2005;Bresciani et al., 2013, Klemas et al., 2013Kiefer et al., 2015;Huang et al., 2015). ...
... For this reason, lake routine monitoring and water quality assessment with conventional sampling techniques, such as boat based sampling with filtration of water samples followed by laboratory analysis Exploiting high frequency monitoring and satellite imagery for assessing chlorophyll-a dynamics in a shallow eutrophic lake N o n -c o m m e r c i a l u s e o n l y (e.g., solvent extraction of chlorophyll-a and spectrophotometric determination), are challenged to provide insights into the complex relationship between biological, chemical and physical processes (Kaplan et al., 2003;Polat et al., 2005;Bresciani et al., 2013, Klemas et al., 2013Kiefer et al., 2015;Huang et al., 2015). An appropriate spatial and temporal characterization of phytoplankton blooms together with information on rapidly changing temperature, light, water discharge, precipitation, and nutrients are still a challenge in aquatic ecosystems (Bowes et al., 2016;Brentrup et al., 2016;Vargas-Lopez et al., 2021). ...
... The measurement of the diurnal variation of Chl-a concentration is a fundamental factor to investigate short-term dynamics, because the phytoplankton blooms can grow and dissipate within a few days (growth rate of 0.1-0.86 d −1 as reported by Reynolds, 2006). This short-term variability can influence the seasonal structure and phenology of phytoplankton distribution (Woods et al., 2021), and therefore the monitoring needs also to detect annual variations in bloom magnitude and timing over a medium-long term period (Bowes et al., 2016). One of the main approaches to determine Chl-a concentration is based on the Chl-a fluorescence used in both in situ continuous fluorimetry measurements (Laney, 2010;Pan and Qiu, 2019), and in optical sensors that indirectly estimate in situ fluorescence and, in addition, allow the assessment of phytoplankton abundance at large spatial scale (Huot and Babin, 2010;Ha et al., 2017). ...
Freshwater ecosystems are challenged by cultural eutrophication across the globe, and it is a priority for water managers to implement water quality monitoring at different spatio-temporal scales to control and mitigate the eutrophication process. Phytoplankton abundance is a key indicator of the trophic and water quality status of lakes. Phytoplankton dynamics are characterized by high spatio-temporal variation, driven by physical, chemical and biological factors, that challenge the capacity of routine monitoring with conventional sampling techniques (i.e., boat based sampling) to characterise these complex relationships. In this study, high frequency in situ measurements and multispectral satellite data were used in a synergistic way to explore temporal (diurnal and seasonal) dynamics and spatial distribution of Chlorophyll-a (Chl-a) concentration, a proxy of phytoplankton abundance, together with physico-chemical water parameters in a shallow fluvial-lake system (Mantua Lakes). A good agreement was found between Chl-a retrieved by remote sensing data and Chl-a fluorescence data recorded by multi-parameters probes (R2 = 0.94). The Chl-a maps allowed a seasonal classification of the Mantua Lakes system as eutrophic or hypertrophic. Along the Mantua lakes system an increasing gradient in Chl-a concentration was recorded following the transition from a fluvial to lacustrine system. There was significant seasonal heterogeneity among the sub-basins, probably due to different hydrodynamics, influenced also by macrophyte stands. High-frequency data revealed the importance of rainfall events in the timing and growth dynamics of phytoplankton, particularly for spring and late summer blooms. Combining temporal and spatial data at high resolution improves the understanding of complex fluvial-lake systems. This technique can allow managers to target blooms in near-real time as they move through a system and guide them to localized hot spots enabling timely management action in ecosystems of high conservation and recreational value.
... Based on this finding, the seasons with poorer water quality did not show an increase in cell density of the phytoplankton community. Bowes et al. (2016) found that the manipulation of light and water temperature offered more realistic solutions to controlling excessive phytoplankton biomass. These two photo-thermal factors reach their highest values in summer, when the phytoplankton has the fastest growth rate under these circumstances (Pan et al., 2012). ...
... Therefore, the effect of phosphorus on the phytoplankton community was predominant rather than nitrogen (Huo et al., 2019;Wang et al., 2019). Bowes et al. (2016) found that a reduction in nutrient concentrations and the manipulation of residence time may be conducive to eutrophication prevention and phytoplankton biomass control. After autumn harvest, bare farmlands along the riversides are more susceptible to soil erosion (Ouyang et al., 2010), which is accompanied by the high levels of nutrient runoff (Weijters et al., 2009). ...
... The phytoplankton community characteristics (e.g. diversity indexes, index of biotic integrity, trophic diatom index, the relative abundance of diatom and cyanobacteria, the appearance or absence of a species) were usually defined by a unified quantitative criteria for the indication for eutrophication and disturbance of human activities (Kane et al., 2009;Katsiapi et al., 2012;Bowes et al., 2016;Vadeboncoeur and Power, 2017). In this study, parts of the phytoplankton community characteristics exhibited linear response to the environmental factors. ...
Knowledge of the phytoplankton community dynamics is fundamentally important for river ecological management. Disentangling the relative impacts of co-occurring factors is critical to understanding the community responses to environmental heterogeneity, as well as anthropogenic activities. Taking phytoplankton community as the indicative variable, this study aimed at elucidating the impacts of driving forces (local factors: water environments; regional factors: land-use, fertilizers application, and socio-economic factors) on the phytoplankton community dynamics. We found that spatial and seasonal processes played a vital role in structuring the phytoplankton community, with Bacillariophyta and Chlorophyta accounting for>79.0% of taxa composition. Bacillariophyta had the highest cell density (>41%), followed by Cyanophyta (>20%) and Chlorophyta (>11%), which mainly contributed to the spatial and seasonal differences in the composition and abundance of the phytoplankton community. Meanwhile, local factors (such as total phosphorus, permanganate index, flow velocity, transparency, and stream depth) and regional factors (the application of phosphate fertilizers) (p < 0.05) were the dominant factors that influenced the phytoplankton community. Here, the phosphorus related factors interfered with the phytoplankton community on both local and regional scales. On the whole, the local factors (including nutrients and hydrology factors) have a more direct impacts on the phytoplankton community in a temperate river. It is of guiding significance for river ecology monitoring and improvement in north China, while paying attention to terrestrial influences, the eutrophication of the river itself still needs to be focused on accompanied with the hydrology factors.
... Phytoplankton biomass in rivers have shown to respond to rapid changes in its environmental controls (M. Bowes et al., 2016), and thus, it is crucial to understand these shorter scale dynamics to predict phytoplankton growth and bloom timings more accurately. ...
... These studies, however, have shown limited predictive ability in modeling large and rapidly developing phytoplankton biomass, suggesting that there is still a need to better understand process interactions (M. Bowes et al., 2016). For example, there has been uncertainty as to which phytoplankton groups dominate the response. ...
... Some studies found green algae to be dominant during peaks in the summer (Lack, 1971;Ruse & Love, 1997) yet subsequent studies have found cool water diatoms to predominate with peaks instead during spring and autumn seasons (M. Bowes et al., 2016;Read et al., 2014). The daily time-step Quality Evaluation and Simulation Tool for River-systems (QUESTOR) model (Boorman, 2003a) has been developed to simulate phytoplankton (M. ...
High‐resolution river modeling is valuable to study diurnal scale phytoplankton dynamics and understand biomass response to short‐term, rapid changes in its environmental controls. Based on theory contained in the Quality Evaluation and Simulation Tool for River‐systems model, a new river model is developed to simulate hourly scale phytoplankton growth and its environmental controls, thus allowing to study diurnal changes thereof. The model is implemented along a 62 km stretch in a lowland river, River Thames (England), using high‐frequency water quality measurements to simulate flow, water temperature, dissolved oxygen, nutrients, and phytoplankton concentrations for 2 years (2013–2014). The model satisfactorily simulates diurnal variability and transport of phytoplankton with Nash and Sutcliffe Efficiency (NSE) > 0.7 at all calibration sites. Even without high‐frequency data inputs, the model performs satisfactorily with NSE > 0.6. The model therefore can serve as a powerful tool both for predictive purposes and for hindcasting past conditions when hourly resolution water quality monitoring is unavailable. Model sensitivity analysis shows that the model with cool water diatoms as dominant species with an optimum growth temperature of 14°C performs the best for phytoplankton prediction. Phytoplankton blooms are mainly controlled by residence time, light and water temperature. Moreover, phytoplankton blooms develop within an optimum range of flow (21–63 m ³ s ⁻¹ ). Thus, lowering river residence time with short‐term high flow releases could help prevent major bloom developments. The hourly model improves biomass prediction and represents a step forward in high‐resolution phytoplankton modeling and consequently, bloom management in lowland river systems.
... A simplified version of the methodology presented in Mzyece et al. (2024) for expert elicitation was used to determine P uptake for the four catchments for four seasons. We selected 6 key papers describing UK-led experiments on this topic (Bowes et al., 2016;Jarvie et al., 2002;Stutter et al., 2021Stutter et al., , 2010Wade et al., 2001;Withers and Jarvie, 2008), and invited four authors of these papers to contribute to our elicitation exercise as experts who have published on the topic of P uptake in rivers. Three accepted, one declined. ...
... Furthermore, the experts suggested that visual aids such as photos of the river corridor could assist in estimating uptake, allowing the approximate width and depth of ditches and rivers to be estimated, as well as the presence of submerged and emergent vegetation and algae to be assessed. This is especially important because increased riparian vegetation and algae can lead to decreased dissolved P concentrations (Bowes et al., 2016;Chase et al., 2016). The distributions obtained were used in each catchment model to calculate the instream P load reduction (Eq. ...
A Bayesian Network (BN) aimed at calculating stream phosphorus (P) concentrations in agricultural catchments was previously parametrized with high-frequency data in a pilot study. To test model transferability, the BN was applied to three further agriculture-dominated catchments in Ireland with varying land use, hydrology, and P pressures, all monitored through the Agricultural Catchments Programme (ACP) of the Irish Agriculture and Food Development Authority. While the pilot catchment Ballycanew was dominated by poorly drained grassland, the further three catchments were dominated by well-drained grassland (Timoleague), well-drained arable (Castledockrell), and moderately-drained arable (Dunleer), respectively. In all four catchments, the main P source came from agriculture and (minimal) domestic inputs, whilst the well-drained arable catchment also contained Sewage Treatment Works (STWs).
To best fit the characteristics of the catchments, a total of six different BN structures were developed. The models were parametrized using a range of methods, including bootstrapping of high-frequency data to obtain fitted distributions, distribution fitting of literature data, and expert elicitation to quantify in-stream P uptake processes. Model transferability and fit were evaluated using a suit of approaches, including 1) calculating percentage bias between simulated and observed distributions fitted to the observed stream Total Reactive P (TRP) concentration, 2) comparing modelled concentration quantiles and means to the observed, and 3) visually comparing the posterior distributions by plotting them against daily observations.
The original BN structure developed in the pilot study was found to best fit the poorly and moderately drained catchments, irrespective of the dominant land use (78% ≤ PBIAS ≤ 81%), not as well in the groundwater-dominated catchments. This confirms that the initial BN represents the catchment-specific process understanding whereby transport via quick-flow dominates P processes in these catchments. In contrast, the well-drained catchments required more complex BN structures to perform well. The additional processes included groundwater Total Dissolved P (TDP) loads, derived from observed concentrations from piezometer data, STWs loads, and in-stream P uptake calculations. These more complex model implementations yielded good results in Castledockrell and Timoleague (-5% ≤ PBIAS ≤ 14%). In all four catchments, the additional in-stream P removal process improved the model performance, however, it remains a second-order mechanism.
Overall, the unique monitoring programme allowed pilot-testing BN transferability, a research avenue that needs to be further explored across catchment typologies and scales.
... However, the change in water quality is a discrete process, thus improper sampling timing and frequency make it difficult to understand the real situation of the water body. The high-frequency water quality monitoring provides the potential to develop a much greater understanding of the controls on eutrophication (Bowes et al., 2016;Castrillo and García, 2020). As an illustration, some studies have discovered the drift pattern of algae through hourly scale monitoring (Huang et al., 2015;Xue et al., 2023), and the results indicate that the phytoplankton biomass in the lake center is the lowest during high-temperature periods of a day (12:00-16:00) under the influence of lake breeze, which is consistent with the results of this study (Fig. 7). ...
... Our analysis of hourly scale wind speed data from lakeside meteorological stations also confirms this viewpoint point (Supplementary Fig. S1). In addition, other studies have pointed out that the growth rate of chlorophyll-a in lakes is highest with a daily sunlight duration of 11-12 h (Bowes et al., 2016). It is readily apparent that these findings cannot be obtained from weekly or monthly scale monitoring. ...
... Of the rare studies on true river phytoplankton (sensu Reynolds & Descy, 1996), most compare phytoplankton biomass to growth (e.g., nutrients, light, and temperature) or transport conditions in isolation (Basu & Pick, 1996;Bowes et al., 2016;Bukaveckas et al., 2011;Dolph et al., 2017;Graham et al., 2018;Soballe & Kimmel, 1987). The resulting relationships are weak and inconsistent (Lucas et al., 2009), and thus few studies have successfully used environmental factors to predict the timing of river phytoplankton blooms. ...
... Phytoplankton blooms in rivers are therefore controlled by both export rates (transport conditions) and growth conditions. Most previous attempts to predict river phytoplankton blooms use growth or transit conditions alone (e.g., Basu & Pick, 1996;Bukaveckas et al., 2011;Bowes et al., 2016;Dolph et al., 2017;Graham et al., 2018;Soballe & Kimmel, 1987;however, see Lucas et al., 2009 for a unifying conceptual model). Here, we demonstrate how T=Q, which instead combines the state of transport and growth conditions, outperforms either of its components when predicting river phytoplankton blooms. ...
In rivers, phytoplankton populations are continuously exported by unidirectional, advective flow. Both transport and growth conditions determine periods of excess phytoplankton growth, or blooms, in a given reach. Phytoplankton abundance, however, has mainly been compared to the state of either growth or transport conditions alone rather than in tandem. Previous studies have not yielded consistent driver–response relationships, limiting our ability to predict the timing of riverine phytoplankton blooms based on environmental factors. Here, we derive a simple joint metric that combines the state of growth and transport conditions, specifically the ratio of temperature and discharge (T/Q T/Q ). We then compare the metric to biomass abundance data (daily, sensor‐based chlorophyll a [chl a] data) from a mid‐sized Great Plains river (the Kansas). T/Q T/Q was an excellent predictor of low to high biomass, outperforming either variable alone. However, it could not differentiate between very high biomass values, values well above the biomass threshold designating bloom conditions. Our findings of reduced performance at the highest values of T/Q indicated that T/Q T/Q could predict the occurrence (timing) but not magnitude of phytoplankton blooms, and we used T/Q to correctly predict 71% of days when bloom conditions occurred. Analyzing chl a abundance with T/Q T/Q also revealed likely switching from transport and temperature to nutrient control. T/Q T/Q offers a simple tool for (1) predicting the timing of river phytoplankton blooms, (2) forecasting how river ecosystems will respond to surrounding environmental changes, and (3) determining which environmental factors shape phytoplankton blooms at specific locations along a river.
... WT showed a significant positive correlation with most phytoplankton, especially Cyanophyta ( Figure 5a), due to several reasons. First, light and WT are two important environmental factors for the growth of phytoplankton [28]. Since these two factors peak in summer, phytoplankton grows the fastest in summer, and Cyanophyta especially prefers high WT, making the WT of the Yitong River suitable for Cyanophyta growth in summer. ...
... WT showed a significant positive correlation with most phytoplankton, especially Cyanophyta (Figure 5a), due to several reasons. First, light and WT are two important environmental factors for the growth of phytoplankton [28]. Since these two factors peak in summer, phytoplankton grows the fastest in summer, and Cyanophyta especially prefers high WT, making the WT of the Yitong River suitable for Cyanophyta growth in summer. ...
To explore how environmental factors affected the plankton structure in the Yitong River, we surveyed the water environmental factors and plankton population in different seasons. The results showed high total nitrogen concentrations in Yitong River throughout the year, while the total phosphorus, water temperature (WT), and chemical oxygen demand in summer were significantly higher than those in other seasons (p < 0.05), and the dissolved oxygen (DO) concentrations and TN/TP ratio were significantly lower (p < 0.01) than those in other seasons. There was no significant seasonal change in other environmental factors. Cyanophyta, Chlorophyta, and Bacillariophyta were the main phytoplankton phylum, while Protozoa and Rotifera were the main zooplankton phylum. The abundance and biomass of zooplankton and phytoplankton in the summer were higher than those in other seasons. Non-Metric Multidimensional scaling methods demonstrated obvious seasonal variation of phytoplankton in summer compared to spring and winter, while the seasonal variation of the zooplankton community was not obvious. The results of the redundancy analysis showed that WT, DO and nitrate nitrogen were the main environmental factors affecting phytoplankton abundance. In contrast to environmental factors, phytoplankton was the main factor driving the seasonal variation of the zooplankton community structure. Cyanophyta were positively correlated with the changes in the plankton community.
... Therefore, land use change will affect eutrophication trajectories through changes in nutrient inputs, source areas, and transport pathways [4]. Climate change threatens to worsen eutrophication through increased precipitation intensity, increasing nutrient loss, and lower summer precipitation, causing lower flows which, in turn, reduce effluent dilution [5][6][7]. ...
... This has been ascribed to local factors typically, including internal loading of P that maintains high P concentrations in the reach or lake water column [71], long residence times of NO 3 − -N stored in groundwater-dominated catchments [68,72], and the complexity of aquatic ecology in which many factors, including planned and inadvertent species introductions, affect the ecosystem. Reach-scale and lake light and temperature regimes have also been found to be as, if not more, important for primary production than nutrient concentrations in some cases [7,73]. Thus, whilst moves to more sustainable production will likely reduce freshwater N and P concentrations, the ecological response is far less predictable, as demonstrated here where the modelled lake nutrient and chl-a concentrations are far more variable than those in the stream water. ...
Recent studies have demonstrated that projected climate change will likely enhance nitrogen (N) and phosphorus (P) loss from farms and farmland, with the potential to worsen freshwater eutrophication. Here, we investigate the relative importance of the climate and land use drivers of nutrient loss in nine study catchments in Europe and a neighboring country (Turkey), ranging in area from 50 to 12,000 km2. The aim was to quantify whether planned large-scale, land use change aimed at N and P loss reduction would be effective given projected climate change. To this end, catchment-scale biophysical models were applied within a common framework to quantify the integrated effects of projected changes in climate, land use (including wastewater inputs), N deposition, and water use on river and lake water quantity and quality for the mid-21st century. The proposed land use changes were derived from catchment stakeholder workshops, and the assessment quantified changes in mean annual N and P concentrations and loads. At most of the sites, the projected effects of climate change alone on nutrient concentrations and loads were small, whilst land use changes had a larger effect and were of sufficient magnitude that, overall, a move to more environmentally focused farming achieved a reduction in N and P concentrations and loads despite projected climate change. However, at Beyşehir lake in Turkey, increased temperatures and lower precipitation reduced water flows considerably, making climate change, rather than more intensive nutrient usage, the greatest threat to the freshwater ecosystem. Individual site responses did however vary and were dependent on the balance of diffuse and point source inputs. Simulated lake chlorophyll-a changes were not generally proportional to changes in nutrient loading. Further work is required to accurately simulate the flow and water quality extremes and determine how reductions in freshwater N and P translate into an aquatic ecosystem response.
... As a region with no seasonal ice cover, phytoplankton communities within the Trent are more exposed to cool winter conditions which may become the limiting factor on algae population size. These results correspond with previous findings in the UK [53] where algal growth was inhibited at temperatures below 10 °C. In contrast, during cooler conditions in the Beaver catchment, ice cover frequently topped with snow shields phytoplankton communities from extreme temperature conditions; and instead, restricts light which may then become a primary limiting factor during winter [54]. ...
... First, high frequency datasets were selected for the calibration of the study catchments, as lower temporal resolution data such as monthly grab samples have been demonstrated to be insufficient to identify causes of variations in phytoplankton biomass [53]. Using these data, assessment of model accuracy can be performed to a more management-relevant timescale, e.g., weekly or daily. ...
Process-based models are commonly used to design management strategies to reduce excessive algal growth and subsequent hypoxia. However, management targets typically focus on phosphorus control, under the assumption that successful nutrient reduction will solve hypoxia issues. Algal responses to nutrient drivers are not linear and depend on additional biotic and abiotic controls. In order to generate a comprehensive assessment of the effectiveness of nutrient control strategies, independent nutrient, dissolved oxygen (DO), temperature and algal models must be coupled, which can increase overall uncertainty. Here, we extend an existing process-based phosphorus model (INtegrated CAtchment model of Phosphorus dynamics) to include biological oxygen demand (BOD), dissolved oxygen (DO) and algal growth and decay (INCA-PEco). We applied the resultant model in two eutrophied mesoscale catchments with continental and maritime climates. We assessed effects of regional differences in climate and land use on parameter importance during calibration using a generalised sensitivity analysis. We successfully reproduced in-stream total phosphorus (TP), suspended sediment, DO, BOD and chlorophyll-a (chl-a) concentrations across a range of temporal scales, land uses and climate regimes. While INCA-PEco is highly pa-rameterized, model uncertainty can be significantly reduced by focusing calibration and monitoring efforts on just 18 of those parameters. Specifically, calibration time could be optimized by focusing on hydrological parameters (base flow, Manning's n and river depth). In locations with significant inputs of diffuse nutrients, e.g., in agricultural catchments, detailed data on crop growth and nutrient uptake rates are also important. The remaining parameters provide flexibility to the user, broaden model applicability, and maximize its functionality under a changing climate.
... This deviation is possibly connected to a suspended algae or benthic/epiphytic community bloom stimulated by favorable spring light conditions that particular year and would require an additional dedicated biomass stock in the model. Similar ecological events have been witnessed in other streams with high nutrient levels at similar periods of the year, with, for instance, phytoplankton blooms during the spring period in [80,81] in England. Another algae bloom was also observed at the stream's source Sjael Lake in August 2019 (visual inspection). ...
... The simulation of DO concentrations at the sub-daily time step highlights the need for improved characterization of the influence of the aquatic plant biomass, both in terms of spatial coverage but also in terms of autotroph group dynamics, to fully capture the overall dynamics of DO in small peri-urban streams. This task, however, may need to rely on more spatially detailed and high-frequency data, very often not available [81,100]. ...
Holistic water quality models to support decision-making in lowland catchments with competing stakeholder perspectives are still limited. To address this gap, an integrated system dynamics model for water quantity and quality (including stream temperature, dissolved oxygen, and macronutrients) was developed. Adaptable plug-n-play modules handle the complexity (sources, pathways) related to both urban and agricultural/natural land-use features. The model was applied in a data-rich catchment to uncover key insights into the dynamics governing water quality in a peri-urban stream. Performance indicators demonstrate the model successfully captured key water quantity/quality variations and interactions (with, e.g., Nash-Sutcliff Efficiency ranging from very good to satisfactory). Model simulation and sensitivity results could then highlight the influence of stream temperature variations and enhanced heterotrophic respiration in summer, causing low dissolved oxygen levels and potentially affecting ecological quality. Probabilistic uncertainty results combined with a rich dataset show high potential for ammonium uptake in the macrophyte-dominated reach. The results further suggest phosphorus remobilization from streambed sediment could become an important diffuse nutrient source should other sources (e.g., urban effluents) be mitigated. These findings are especially important for the design of green transition solutions, where single-objective management strategies may negatively impact aquatic ecosystems.
... This may be particularly true for prediction of CyanoHABs, as phytoplankton dynamics are often characterized by uncertainty and stochasticity (McGowan et al 2017). Phytoplankton can respond very rapidly to the changing environment, such as sudden changes in nutrient levels, temperature or flows (Bowes et al 2016), and their populations can fluctuate over an order of magnitude within days (Fang et al 2019). In addition, the monitoring data of CyanoHABs are often incomplete and imbalanced (Choi et al 2019), which strengthens the variability of the time-series observations. ...
... On the other hand, with the advent of emerging monitoring technologies, high-frequency sensors provide enormous and consecutive time series that minimize the often lengthy time between sample collection, data analysis and response action. This feature provides researchers and managers with the ability to better capture temporal variability and elucidate bloom-related factors (Bowes et al 2016). However, it may be prudent to undergo scrutiny of the dataset before blindly using them to develop predictive models of CyanoHABs for two main reasons. ...
Cyanobacterial harmful algal blooms (CyanoHABs) threaten ecosystem functioning and human health at both regional and global levels, and this threat is likely to become more frequent and severe under climate change. Predictive information can help local water managers to alleviate or manage the adverse effects posed by CyanoHABs. Previous works have led to various approaches for predicting cyanobacteria abundance by feeding various environmental variables into statistical models or neural networks. However, these models alone may have limited predictive performance owing to their inability to capture extreme situations. In this paper, we consider the possibility of a hybrid approach that leverages the merits of these methods by integrating a statistical model with a deep-learning model. In particular, the autoregressive integrated moving average (ARIMA) and long short-term memory (LSTM) were used in tandem to better capture temporal patterns of highly dynamic observations. Results show that the proposed ARIMA-LSTM model exhibited the promising potential to outperform the state-of-the-art baseline models for CyanoHAB prediction in highly variable time-series observations, characterized by nonstationarity and imbalance. The predictive error of the mean absolute error and root mean square error, compared with the best baseline model, were largely reduced by 12.4% and 15.5%, respectively. This study demonstrates the potential for the hybrid model to assist in cyanobacterial risk assessment and management, especially in shallow and eutrophic waters.
... As a region with no seasonal ice cover, phytoplankton communities within the Trent are more exposed to cool winter conditions which may become the limiting factor on algae population size. These results correspond with previous findings in the UK [53] where algal growth was inhibited at temperatures below 10 °C. In contrast, during cooler conditions in the Beaver catchment, ice cover frequently topped with snow shields phytoplankton communities from extreme temperature conditions; and instead, restricts light which may then become a primary limiting factor during winter [54]. ...
... First, high frequency datasets were selected for the calibration of the study catchments, as lower temporal resolution data such as monthly grab samples have been demonstrated to be insufficient to identify causes of variations in phytoplankton biomass [53]. Using these data, assessment of model accuracy can be performed to a more management-relevant timescale, e.g., weekly or daily. ...
... As a region with no seasonal ice cover, phytoplankton communities within the Trent are more exposed to cool winter conditions which may become the limiting factor on algae population size. These results correspond with previous findings in the UK [53] where algal growth was inhibited at temperatures below 10 °C. In contrast, during cooler conditions in the Beaver catchment, ice cover frequently topped with snow shields phytoplankton communities from extreme temperature conditions; and instead, restricts light which may then become a primary limiting factor during winter [54]. ...
... First, high frequency datasets were selected for the calibration of the study catchments, as lower temporal resolution data such as monthly grab samples have been demonstrated to be insufficient to identify causes of variations in phytoplankton biomass [53]. Using these data, assessment of model accuracy can be performed to a more management-relevant timescale, e.g., weekly or daily. ...
Process-based models are commonly used to design management strategies to reduce excessive algal growth and subsequent hypoxia. However, management targets typically focus on phosphorus control, under the assumption that successful nutrient reduction will solve hypoxia issues. Algal responses to nutrient drivers are not linear and depend on additional biotic and abiotic controls. In order to generate a comprehensive assessment of the effectiveness of nutrient control strategies, independent nutrient, dissolved oxygen (DO), temperature and algal models must be coupled, which can increase overall uncertainty. Here, we extend an existing process-based phosphorus model (INtegrated CAtchment model of Phosphorus dynamics) to include biological oxygen demand (BOD), dissolved oxygen (DO) and algal growth and decay (INCA-PEco). We applied the resultant model in two eutrophied mesoscale catchments with continental and maritime climates. We assessed effects of regional differences in climate and land use on parameter importance during calibration using a generalised sensitivity analysis. We successfully reproduced in-stream total phosphorus (TP), suspended sediment, DO, BOD and chlorophyll-a (chl-a) concentrations across a range of temporal scales, land uses and climate regimes. While INCA-PEco is highly parameterized, model uncertainty can be significantly reduced by focusing calibration and monitoring efforts on just 18 of those parameters. Specifically, calibration time could be optimized by focusing on hydrological parameters (base flow, Manning’s n and river depth). In locations with significant inputs of diffuse nutrients, e.g., in agricultural catchments, detailed data on crop growth and nutrient uptake rates are also important. The remaining parameters provide flexibility to the user, broaden model applicability, and maximize its functionality under a changing climate.
... This is open to further data and reliability issues as the early automatic water quality monitors were liable to routine breakdown and maintenance issues. Recent improvements in technology have significantly improved this situation (Bowes et al., 2016). However, this approach cannot predict future water quality based on from forecasts of catchment rainfall and temperature. ...
... Studies on the Berounka River (Czech Republic) from 2002 to 2007 indicated a significant increase in chlorophyll-a concentrations related to water temperature [58]. In the Thames River, high phytoplankton biomass and growth rates were observed when both flow and temperature conditions (ranging from 9 • C to 19 • C) aligned with long periods of sunlight [59]. ...
In the context of ongoing environmental changes, particularly against the backdrop of global warming, significant attention is being given to areas of exceptional natural value that, in many aspects, retain a pristine character. One such area is the Biebrza River in northeastern Poland, which, together with the wetlands in its basin, forms one of the most valuable ecosystems of its kind in Europe. This study analyses the changes in the thermal and ice regime for two hydrological stations, Sztabin and Burzyn, in the period from 1959 to 2023. It was found that the average annual water temperature in this period for the Biebrza River increased by 0.28 • C/decade, and in the case of ice phenomena, statistically significant changes for both stations showed a decline, with an acceleration of the ice cover disappearance by an average of 3 days/decade. These recorded changes should be considered unfavourable, as they will affect the transformation of both the biotic and abiotic characteristics of the river itself, as well as the natural elements associated with it.
... While all the BBNs achieved good performance in predicting the marginal mean concentrations across the four catchments during the baseline period (Table 1), the BBNs did not represent seasonality well in Ballycanew and Dunleer [23]. However, the ability to reproduce seasonal variation in discharge, and therefore dilution correctly during ecological sensitive periods is important, for example, to determine algal bloom development and persistence [15,43], which is relevant to developing mitigation strategies under anticipated climate change impacts. ...
Climate-induced changes in precipitation and river ows are expected to cause changes in river phosphorus loadings. The uncertainty associated with climate-induced changes to water quality is rarely represented in models. Bayesian Belief Networks (BBNs) are probabilistic graphical models incorporating uncertainty in their model parameters, making them ideal frameworks for communicating climate risk. This study presents a set of catchment-speci c BBNs to simulate total reactive phosphorus (P) concentrations in four agricultural catchments under projected climate change. Six climate models (ve models plus the ensemble mean) across two objective functions (NSE vs log NSE), two Representative Concentration Pathways (RCP 4.5 and 8.5), and three time periods (the 2020s, the 2040s, and the 2080s) were used to create discharge scenarios as model inputs. The simulated monthly mean P concentrations show no obvious trends over time or differences between the two RCP scenarios, with the model ensemble essentially replicating the results obtained for the baseline period. However, the P concentration distributions simulated using the outputs from the HadGEM2-ES model rather than the ensemble, showed differences from the baseline in drier months. A sensitivity analysis demonstrated that this difference occurred because the catchment-speci c BBNs were sensitive to changes in the mean total monthly discharge which were captured in the HadGEM2-ES projections but not by the ensemble mean.
... Aquatic systems respond in a holistic way to climate change with different pressures having additive, synergistic or antagonistic interactions. The major disaster in the river Oder in 2022 was a multifactorial event with the climatic factors of high solar irradiance, drought and low flows likely concentrating existing pressures such as industrial saline discharges and nutrients to promote rapid growth of an invasive brackish algae (Prymnesium parvum) the toxins of which killed fish over 100s of kilometers (Bowes et al., 2016;Free et al., 2023;Nordstrom, 2009). Timing is also crucial, for example compounded events like the two successive rainfall events in May 2023 that led to the disastrous flooding in Emilia-Romagna (Italy) caused 12 categories of environmental impact (Arrighi and Domeneghetti, 2023). ...
The Water Framework Directive (WFD) sets the fundamental structure for assessing the status of water bodies in the European Union. Its implementation is currently entering its fourth six-year cycle assisted by a total of 38 guidance documents. The principal objective is to ensure good status for surface and ground waters. The functioning of the WFD is based on detecting the impact of human pressures on biological, physico-chemical, or hydromorphological parameters, and reducing these causal pressures through a program of measures to achieve good status. Climate change can exert a significant influence on ecological status by directly altering parameters monitored, pressure interactions, or influencing the effectiveness of programs of measures. Aquatic systems respond holistically to climate change with different pressures having additive, synergistic, or antagonistic interactions. The challenge is how to adapt the framework to manage aquatic systems in the context of climate change while maintaining focus on implementing measures to tackle key pressures. This paper examines potential approaches, including reassignment of waterbody type, quantifying the portion of Ecological Quality Ratio (EQR) driven by climate change, and creating an assessment module of climatic pressures and ecological responses. The overall purpose is to stimulate discussion and explore ways to incorporate climate change into the WFD structure.
... This is open to further data and reliability issues as the early automatic water quality monitors were liable to routine breakdown and maintenance issues. Recent improvements in technology have significantly improved this situation (Bowes et al., 2016). However, this approach cannot predict future water quality based on from forecasts of catchment rainfall and temperature. ...
Increasingly scarce water resources and growing global populations have exacerbated the problems of water quality in river systems and freshwaters in general. New monitoring methodologies and tools to democratize access to water quality information are needed if we are to reach ambitious societal objectives such as the UN Sustainable Development Goals and the European Green Deal. Here we present a cloud-based system for producing publicly accessible real time water quality forecasts coupled to novel biosensor technology. Short term forecasts of water quality impairments, e.g., as cyanobacteria blooms, sediment plumes and toxic pollution incidents are increasingly relevant both to citizens and stakeholders. Here, we present a new cloud based system that utilizes satellite data to produce real time forecasts of flow and water quality using a chain of dynamic catchment-scale models at multiple locations in a river network. We demonstrate this new system using two case studies: the River Thames and the Essex Colne River (United Kingdom). These rivers are key water supply sources for London and South-East England, respectively and are of high interest to recreational water users. We show how the new system can predict and forecast water quality, estimate toxicity and connect to citizen science observations using an App (www.aquascope.com) for information synthesis and delivery.
... Recent developments in high-frequency water quality measurements have brought new insights into mechanistic understanding of abiotic and biotic catchment and stream processes which are increasingly used to evaluate the effectiveness of water monitoring and management efforts. Application areas so far include (1) evaluation of concentration−discharge relationships to identify solute/particulate mobilization and delivery patterns, 12−15 (2) estimation of travel time distributions and identification of flow pathways in catchments using tracers, 16−19 (3) development and validation of catchment hydrogeological and hydrochemical models, 20,21 (4) improved estimation of pollutant loads and concentrations to comply with statutory requirements, 22,23 (5) evaluation of diel cycles and estimation of stream metabolism based on dissolved oxygen (DO) sensors, 24−27 (6) impact assessment of multiple stressors on stream biota 28,29 and impact of stream biota on water quality, 30 (7) evaluation of feedbacks between biogeochemical cycles and hydrology, 31,32 (8) evaluation of trade-offs between different ecosystem services and management solutions, 4,33 (9) development of proxies for difficult-to-measure water quality parameters based on readily available sensor data, 34,35 (10) online water quality monitoring for drinking water and wastewater treatment optimization, 36,37 and (11) combining high-frequency data with artificial intelligence tools to develop early detection systems for water contamination and algal bloom outbreaks. 38,39 In this paper we explore and discuss the current state-of-theart methods and potential future developments in highfrequency water quality measurements and their contributions to our understanding of hydrological, biogeochemical, and ecological processes. ...
High-frequency water quality measurements in streams and rivers have expanded in scope and sophistication during the last two decades. Existing technology allows in situ automated measurements of water quality constituents, including both solutes and particulates, at unprecedented frequencies from seconds to subdaily sampling intervals. This detailed chemical information can be combined with measurements of hydrological and biogeochemical processes, bringing new insights into the sources, transport pathways, and transformation processes of solutes and particulates in complex catchments and along the aquatic continuum. Here, we summarize established and emerging high-frequency water quality technologies, outline key high-frequency hydrochemical data sets, and review scientific advances in key focus areas enabled by the rapid development of high-frequency water quality measurements in streams and rivers. Finally, we discuss future directions and challenges for using high-frequency water quality measurements to bridge scientific and management gaps by promoting a holistic understanding of freshwater systems and catchment status, health, and function.
... Durant la période productive, si le débit est faible, le temps de résidence des particules augmente laissant plus de temps aux populations phytoplanctoniques pour croître. La biomasse s'accumule, les efflorescences se déclenchent (Bowes et al., 2016), permettant ainsi l'augmentation des concentrations en toxines lors des HABs par exemple (Bargu et al., 2016). D'autres systèmes peuvent présenter la dynamique inverse avec l'augmentation des efflorescences et de la consommation des nutriments associées à une augmentation du temps de résidence (Beaver et al., 2013; 6. Discussion générale Koch et al., 2004), comme décrit ci-après au niveau de la baie de Seine. ...
Depuis les années 2000, sur le continuum Estuaire - Baie de la Seine les apports en phosphores (P) ont été réduit contrairement à ceux en azote (N) qui sont restés élevés. Cette réduction entraîne donc un déséquilibre de la stoechiométrie N:P affectant les communautés phytoplanctoniques. L'écart à l'équilibre optimal de Redfield (N:P = 16) est appelé dystrophie. Pour qualifier et quantifier l'effet de la dystrophie sur le phytoplancton les méthodes de fluorimétrie variable et de cytométrie en flux sont employées pour étudier les production primaire, la structure des communautés et leurs interactions. Dans l'estuaire, au-delà de la limitation en lumière les communautés phytoplanctoniques sont affectées par la distribution des sels nutritifs, les déséquilibres N:Si et P:Si provoquent la succession des communautés. Une dynamique complexe de la production primaire a également été mis en évidence avec un rôle important du temps de résidence mais également l'influence de certains facteurs encore mal identifiés. Les expériences en milieux contrôlés et l'étude d'une efflorescence dans la baie montrent que la baie est co-limitée par le N et le P en fonction du rapport N:P, rendant nécessaire l'établissement d'un nouveau calcul "d'efficacité d'utilisation de la ressource (RUE)" adapté à la dystrophie, le RUE NP. La dystrophie va affecter négativement les paramètres photosynthétiques et la production primaire, et accroître des indicateurs de stress physiologiques [activité de la phosphatase alcaline et les excrétions de carbone (TEP)]. Cette dystrophie influence aussi la structure des communautés en entraînant une baisse de la diversité fonctionnelle et modification de la taille des communautés. La prise est compte de l’effet de la dystrophie sur le phytoplancton associé à celui du changement climatique est ainsi essentiel pour la gestion des écosystèmes côtiers et la scénarisation de trajectoires dans le continuum dans un contexte de gestion de l’eau est donc majeure.
... Varieties in reclaimed water quality in rivers were mainly affected by the growth and reproduction of phytoplankton (He et al., 2017). Several studies attributed phytoplankton growth and reproduction to excessive nutrient inputs (Carpenter and Bennett., 2011;Némery et al., 2016), in addition, suitable sunlight and temperature can promote phytoplankton growth through photosynthesis and cell division, respectively (Bowes et al., 2016;Lurling et al., 2018). In the previous studies of our group, temperature and sunlight determined the distribution of phytoplankton in the vertical direction of the river, but the flow velocity was the most critical factor for phytoplankton growth and reproduction along the flow direction (He et al., 2017), similar to the construction of dams that significantly promoted the phytoplankton reproduction by slowing down the water flow rate (Némery et al., 2016). ...
The reuse of reclaimed water (RW) for river ecological restoration in global water-shortage regions has inevitably brought some potential risks for groundwater. However, little is known about the effects of reclaimed water on the hydrochemical evolution of groundwater especially under long-term infiltration conditions. Herein, 11-years monitoring data (2007–2018) of reclaimed water and groundwater were adopted to analyze the characteristics and genesis of groundwater hydrochemical evolution under long-term infiltration of reclaimed water from Jian River to Chaobai River in Beijing. The results showed that the hydrochemical components in groundwater totally performed a significant increase in Na⁺, Cl–, and K⁺ and decrease in Ca²⁺, Mg²⁺, and HCO3– concentration after long-term infiltration of reclaimed water. Meanwhile, a significant hydrochemical evolution difference between the groundwater of Jian River and Chaobai River was observed. In Jian River, the hydrochemical type in groundwater shifted gradually from HCO3–Ca·Mg to the type of HCO3·Cl–Na·Ca approaching reclaimed water. In contrast, the hydrochemical evolution in the Chaobai River shows an obvious opposite trend from HCO3–Ca·Mg to HCO3·Cl–Na·Mg and finally deviating reclaimed water type of Cl·HCO3·SO4–Na. PHREEQC simulation indicated that the differences in hydrochemical evolution were mediated synergically by sediment thickness and geochemical processes (e.g. mixing and sulfate reduction). In such mediators, thinner sediment and strong mixing in the Jian River were confirmed to be the genesis of groundwater hydrochemical evolution progressively approaching reclaimed water. Different from the Jian River, multiple regression analyses revealed that the genesis of groundwater hydrochemical evolution in the Chaobai River was divided into two stages according to the increase of sediment thickness. Reclaimed water quality and infiltration amount are the leading proposed cause in the initial stage (2007–2008) due to thinner sediment formation, contributing 53.5% and 29.8% within the 95% confidence interval, respectively. Subsequently, the rise in sediment thickness is proved to play a crucial role in groundwater hydrochemical evolution trend away from reclaimed water (2009–2018), with a contribution of 41.6% within the 95% confidence interval. It is mainly attributed to the reduced reclaimed water infiltration rate and favorable sulfate reduction conditions. These findings advance our understanding on groundwater hydrochemical evolution under long-term infiltration of reclaimed water and also guide future prediction of evolution trends.
... The water quality problem is well pronounced in megacities due to the high population density together with the vast amount of pollutant sources. It has been investigated in many megacities all over the world: Jakarta (Costa et al., 2016), Delhi (Parween et al., 2017), Kolkata (Zaman et al., 2018), Beijing (Zhang et al., 2017), Shanghai (Zhao et al., 2016), Shenzhen (Wang et al., 2004), Tokyo (Kido et al., 2009;Saito et al., 2020), Seoul (Chang, 2005), Bangkok (Areerachakul & Sanguansintukul, 2010), Ho Chi Minh City (Vo, 2007), Istanbul (van Leeuwen & Sjerps, 2016), London (Bowes et al., 2016;Whitehead et al., 2013), Paris (Billen et al., 2001), Kinshasa (Kayembe et al., 2018), Cairo (Abdel-Satar, 2005), Buenos Aires (Rigacci et al., 2013), Rio de Janeiro (Ribeiro & Kjerfve, 2002;Villas-Boas et al., 2017), Mexico (Espinosa-García et al., 2015), New York (Mehaffey et al., 2005), and others. Moscow is the largest megacity in Europe with a population of about 12.6 million inhabitants (Demographics, 2021) and is located on the Moskva River, which experiences high anthropogenic pressure from the city's industrial enterprises, water carriage, wastewater treatment facilities, municipal wastewater, etc. Landscape components where Moscow's pollutants accumulate (soil, road dust, sediment, snow cover, rain, and atmospheric aerosols) have been recently well studied. ...
This study aims to identify the main patterns of distribution and sources of pollutants in the Moskva River and their influence on river water quality under different levels of anthropogenic stress caused by the largest megacity in Europe – Moscow. For this study, we determined concentrations of 18 trace elements, nutrient elements and major ions, chemical and biochemical oxygen demand, and physical parameters of water at 45 stations on the Moskva River and 20 stations on its tributaries during spring flood and low water of 2019 and 2020 to identify the extent and mechanisms of urban impact on its water chemistry. Chemical elements concentrations have been determined using ICP–MS and ICP–AES methods. Mn, Al, Cu, Sr, Zn, B, Mo, and inorganic nitrogen were outlined as key pollutants according to various drinking water and environmental guidelines. Using correlation and factor analysis, five groups of elements were identified, corresponding to different drivers controlling their unequal distribution within the watershed: mineral sources (Sr, Li, B, Mo, Ca), sewage and road runoff (TN, TP, Sb, Ni, N–NO2, BOD5, COD, V, Zn), impact of acidic wetlands (Al, COD, Zr, Bi), groundwater and landfills leachate (V, As, Pb, U, Sb), and industrial activities (Zn, Cu). Water quality in the Moskva Basin on the whole is good according to the CCME Water Quality Index. Local deterioration of water quality to marginal and even fair (depending on the reference water quality guideline) is confined to the Moskva River part downstream from the Kuryanovo aeration station to the Moskva mouth and to the mouths of several heavily contaminated tributaries.
... The succession of microalgae community is influenced by the bottom-up controls of environmental factors such as temperature, nutrients and light Bowes et al., 2016;Zhang et al., 2018) and top-down controls such as the grazing activities of zooplankton (Lofton et al., 2020). Water temperature affects the physiological activities of microalgae and their efficiency of nutrient utilization (Zhao et al., 2015). ...
The construction of cascade reservoirs increases eutrophication and exacerbates algal blooms and thus threatens water quality. Previous studies on the microalgae in reservoir have mainly focused on the spatio-temporal patterns of surface microalgae communities at the horizontal scale, while few studies have simultaneously considered the successions of microalgae in vertical profiles including the sediments and the effects of the nutrients release and microalgae in sediments on microalgae in upper waters. In this study, we investigated the effects of microalgae and physico-chemical parameters in waters and sediments on the successions of vertical microalgae communities in Xipi Reservoir, Southeast China. The seasonal variations in microalgae compositions decreased gradually from the surface water (the dominance of Cryptophyta and Chlorophyta in spring, Chlor-ophyta and Cyanophyta in summer, and relatively uniform in autumn and winter) to the sediment (the dominance of Bacillariophyta throughout the year), which was influenced by the variations of physico-chemical factors in different layers. The spatio-temporal variations in microalgae communities in waters was attributing to not only the heterogeneities of the stratification, and the physico-chemical factors such as water temperature, pH, and nutrient concentrations, especially for phosphorus in the water column, but also the combinations of phosphorus release and microalgae composition in sediments. Environmental changes would be especially problematic for microalgae groups such as Cryptophyta, Dinophyta and Chlorophyta that were sensitive to the changes of temperature and nutrients. Our results are helpful for an extensive understanding of the dynamics of microalgae communities in reservoir, and contribute to reservoir management for ensuring the safety of drinking water.
... Ideally, a monitoring program should be extensive for long-term data is necessary to evaluate the effects of climate and large-scale phenomena [4,5], and also intensive, for only high-frequency sampling can account for the significant biomass fluctuations that the phytoplankton may exhibit in a matter of days [6,7]. Such a complete monitoring program is rarely achieved, however, because of the costs that are related to sampling [8]. ...
By monitoring the chlorophyll a concentration (chla), it is possible to keep track of the eutrophication status of a lake and to describe the temporal dynamics of the phytoplankton biomass. Such monitoring must be both extensive and intensive to account for the short- and long-term biomass variations. This may be achieved by the remote estimation of chla through an orbital sensor with high temporal resolution. In this study, we used MODIS imagery to produce 21-year time series of chla for three strategic lakes of the Brazilian semi-arid region: Eng. Armando Ribeiro Gonçalves, Castanhão, and Orós. We used data collected in 13 lakes of the region to test new and published regression models for chla estimation. The selected model was validated and applied to daily MODIS images for the three largest lakes. The resulting chla time series revealed that the temporal dynamics of the phytoplankton biomass is associated with the hydraulic regime of the lakes, with chla plummeting upon intense water renewal and keeping high during persistent dry periods. The intense rainy season of 2004 reduced the phytoplankton biomass and its effects even extended to the subsequent years. Our results encourage the exploration of the MODIS archived imagery in limnological studies.
... In addition, the drainage rate of cascade reservoirs significantly modulated species composition and biovolume of phytoplankton indicating the role of hydraulic stability to phytoplankton (Beaver et al., 2013;Silva and Costa, 2015). The findings showed that increased residence time, low sediment content, and high levels of nutrients increase phytoplankton abundance and biovolume (Bowes et al., 2016;Rao et al., 2018). Furthermore, the findings indicate that sediment content reduced abundance and biovolume of phytoplankton, and increased the diversity index of phytoplankton in the studied cascade reservoirs. ...
Previous studies report significant changes on biotic communities caused by cascade reservoir construction. However, factors regulating the spatial–temporal plankton patterns in alpine cascade reservoir systems have not been fully explored. The current study explored effects of environmental factors on the longitudinal plankton patterns, through a 5-year-long study on the environmental factors and communities of phytoplankton and zooplankton in an alpine cascade reservoir system located upstream of Yellow River region. The findings showed that phytoplankton and zooplankton species numbers in the studied cascade reservoir system were mainly regulated by the hydrological regime, whereas nutrient conditions did not significantly affect the number of species. Abundance and biovolume of phytoplankton in cascade reservoirs were modulated by the hydrological regime and nutrient conditions. The drainage rate, N:P ratio, and sediment content in cascade reservoirs were negatively correlated with abundance and biovolume of phytoplankton. Abundance and biovolume of zooplankton were not significantly correlated with the hydrological regime but showed a strong positive correlation with nutrient conditions in cascade reservoirs. Shannon–Wiener index (H’) and the Pielou index (J) of phytoplankton were mainly regulated by the hydrological regime factors, such as drainage rate and sediment content in cascade reservoirs. However, temperature and nutrient conditions were the main factors that regulated the Shannon–Wiener index (H’) and the Pielou index (J) of zooplankton. Species number, abundance, and biovolume of phytoplankton showed a significant positive correlation with those of zooplankton. Hydrodynamics and nutrient conditions contributed differently in regulating community structure of phytoplankton or zooplankton. These findings provide an understanding of factors that modulate longitudinal plankton community patterns in cascade reservoir systems.
... Although high-frequency data has become more available with increasing technology (Bowes et al. 2016;Miller et al. 2017;Leigh et al. 2019), monitoring plans remain limited by several conditions, such as those related to sample collection, integrity, and laboratory analysis. Furthermore, data acquisition through sensors and remote sensing techniques is often limited due to calibration and validation issues, presence of interference, and spectral resolution (Gholizadeh et al. 2016). ...
Limited water quality data is often responsible for incorrect model descriptions and misleading interpretations in terms of water resources planning and management scenarios. This study compares two hybrid strategies to convert discrete concentration data into continuous daily values for one year in distinct river sections. Model A is based on an autoregressive process, accounting for serial correlation, water quality historical characteristics (mean and standard deviation), and random variability. The second approach (model B) is a regression model based on the relationship between flow and concentrations, and an error term. The generated time series, here referred to as synthetic series, are propagated in time and space by a deterministic model (SihQual) that solves the Saint-Venant and advection-dispersion-reaction equations. The results reveal that both approaches are appropriate to reproduce the variability of biochemical oxygen demand and organic nitrogen concentrations, leading to the conclusion that the combination of deterministic/empirical and stochastic components are compatible. A second outcome arises from comparing the results for distinct time scales, supporting the need for further assessment of statistical characteristics of water quality data - which relies on monitoring strategies development. Nonetheless, the proposed methods are suitable to estimate multiple scenarios of interest for water resources planning and management.
Graphical Abstract
... At a UK scale, it is estimated that the number of months per year exceeding this temperature threshold will increase from <1 under baseline conditions to approximately 1 under a +2°C warming scenario, and 2 under a +4°C scenario. Additional thresholds for higher bloom risk have been identified (flows of <30 m 3 s -1 , >20 h sunshine during previous 5 days, Bowes et al., 2016) and these could be used to refine projections of bloom exceedance. There is currently insufficient evidence to place an economic value on these changes. ...
The CCRA is a comprehensive assessment of the risks to the UK from climate change, as required by Act of Parliament every 5 years (Climate Change Act)
... By contrast, other stressors acting on ecosystems but manifested from large-scale drivers, such as climate change, may be impossible for catchment managers to control. Stressors driven by anthropogenic activities operating at different scales can also interact; for example, changes in temperature and flushing rate can alter ecological responses to nutrient loading in rivers (Bowes et al. 2016) and lakes (Carvalho et al. 2012). Many mechanisms exist through which the effects of climate change may be moderated in lakes and rivers, including geographically distinct projections in weather patterns and the influence of ecosystem morphology and other stressors, including nutrient enrichment (Adrian et al. 2009). ...
Interactions between stressors in freshwater ecosystems, including those associated with climate change and nutrient enrichment, are currently difficult to detect and manage. Our understanding of the forms and frequency of occurrence of such interactions is limited; assessments using field data have been constrained as a result of varying data forms and quality. To address this issue, we demonstrate a statistical approach capable of assessing multiple stressor interactions using contrasting data forms in 3 European catchments (Loch Leven Catchment, UK: assessment of phytoplankton response in a single lake with time series data; Pinios Catchment, Greece: macroinvertebrate response across multiple rivers using spatial data; and Lepsämänjoki Catchment, Finland: phytoplankton response across multiple rivers using spatiotemporal data). Statistical models were developed to predict the relative and interactive effects of climate change and nutrient enrichment sensitive indicators (stressors) on indicators of ecological quality (ecological responses) within the framework of linear mixed effects models. In all catchments, indicators of nutrient enrichment were identified as the primary stressor, with climate change-sensitive indicators causing secondary effects (Loch Leven: additive, total phosphorus [TP] × precipitation; Pinios: additive, nitrate × dissolved oxygen; Lepsämänjoki: synergistic, TP × summer water temperature), the intensity of which varied between catchments and along the nutrient stressor gradient. Simple stressor change scenarios were constructed for each catchment and used in combination with mechanistic models to explore potential management responses. This approach can be used to explore the need for multiple stressor management in freshwaters, helping practitioners navigate a complex world of environmental change.
... Automatic telemetric monitoring stations in surface water bodies can provide nowcasting and early warning services, essential for pollution mitigation and preparation against extreme events [1][2][3][4][5]. Automatic monitoring provides very large volumes of data in high temporal and spatial resolution, allowing the detection of both short-term events and long-term changes, thus contributing significantly to environmental research [6][7][8]. ...
The monitoring of surface waters is of fundamental importance for their preservation under good quantitative and qualitative conditions, as it can facilitate the understanding of the actual status of water and indicate suitable management actions. Taking advantage of the experience gained from the coordination of the national water monitoring program in Greece and the available funding from two ongoing infrastructure projects, the Institute of Inland Waters of the Hellenic Centre for Marine Research has developed the first homogeneous real-time network of automatic water monitoring across many Greek rivers. In this paper, its installation and maintenance procedures are presented with emphasis on the data quality checks, based on values range and variability tests, before their online publication and dissemination to end-users. Preliminary analyses revealed that the water pH and dissolved oxygen (DO) sensors and produced data need increased maintenance and quality checks respectively, compared to the more reliably recorded water stage, temperature (T) and electrical conductivity (EC). Moreover, the data dissemination platform and selected data visualization options are demonstrated and the need for both this platform and the monitoring network to be maintained and potentially expanded after the termination of the funding projects is highlighted.
... Low frequency may limit our understanding of the actual dynamics and prevent capture of real behavior ( Jørgensen and Bendoricchio, 2001 ). Data frequency has relatively little impact on the predicted nitrogen and phosphorus concentrations in water bodies ( Bowes et al., 2016 ). The high-frequency input data (e.g., hourly meteorological data and flow data) can improve the accuracy of the hydrodynamic module as shown in our case study. ...
Understanding the limiting factors of phytoplankton growth and competition is crucial for the restoration of aquatic ecosystems. However, the role and synergistic effect of co-varying environmental conditions, such as nutrients and light on the succession of phytoplankton community remains unclear. In this suty, a hydrodynamic-ecological modeling approach was developed to explore phytoplankton growth and succession under co-varying environmental conditions (nutrients, total suspended solids (TSS) and variable N:P ratios) in a large shallow lake called Lake Chagan, in Northeast China. A phytoplankton bloom model was nested in the ecological modeling approach. In contrast to the traditonal ecological modeling, competition between phytoplankton species in our study was modeled at both the species/functional group and phenotype levels. Six phytoplankton functional groups, namely diatoms, green algae, Anabaena, Microcystis, Aphanizomenon and Oscillatoria and each of them with three limitation types (i.e., light-limitation, nitrogen-limitation and phosphorus-limitation) were included in the bloom model. Our results demonstrated that the average biomass proportion of the three limitation types (light-limitation, nitrogen-limitation and phosphorus-limitation) in the six phytoplankton function groups accounted for approximately 50%, 37% and 23% of the total phytoplankton biomass, respectively. TSS suppressed the growth of diatoms and green algae, but favored the dominance of cyanobacteria in Lake Chagan, especially in the turbid water phase (TSS ≥ 60 mg/L). In addition, it was reported that the potential of either N-fixing or non-N-fixing cyanobacterial blooming along the gradients of N:P ratios could exist under the influence of the co-environmental factors in the lake. The proportion of non-N-fixing cyanobacteria (i.e., Microcystis and Oscillatoria) exceeded the proportion of N-fixing cyanobacteria (i.e., Anabaena and Aphanizomenon) when the N:P ratios exceeded 20. Non-N-fixing cyanobacteria would become dominant at higher TSS concentrations and lower light intensities in the turbid water. N-fixing cyanobacteria favored lower N:P ratios and higher light intensities in the clearwater phase (where TSS ≤ 60 mg/L). To sustain a good ecological status in the lake, our results suggest that nutrient and TSS levels in the lake should be maintained at or below the thresholds (TN ≤ 1.5 mg/L; TP ≤ 0.1 mg/L; N:P ratios between 15 and 20; and TSS ≤ 60 mg/L). These findings can help improve water quality management practices to restore aquatic ecosystems.
Dolichospermum spp. and Microcystis spp. are two common cyanobacteria that form blooms in the Changjiang (Yangtze) River basin, but the environmental conditions for their succession in large lakes are still unclear. Based on daily monitoring data from Meiliang Bay in Taihu Lake from March to June, 2016–2018, we studied the environmental conditions necessary for the succession of these two cyanobacteria. Results show that from March to June, the dominant genera of cyanobacteria experienced succession and co-dominated with Microcystis. The succession process included three stages. In Stage I, the biomass of Dolichospermum and Microcystis was similar (March), but Dolichospermum was dominant for most of the period. In Stage II, dominance alternated between Dolichospermum and Microcystis (April to mid-May). In Stage III, the biomass of Microcystis dominated (mid-May to June). In addition, temperature and nutrients across the three stages varied significantly. The average temperature increased continuously from 10.9 to 18.4, and to 24.2 °C. The total nitrogen content decreased from 2.87 to 2.40, and to 1.86 mg/L. The total phosphorus content increased from 0.08 to 0.09, and to 0.12 mg/L. Correlation analysis revealed that Microcystis biomass was positively correlated with temperature and total phosphorus. Dolichospermum biomass was positively correlated with total nitrogen. Classification and regression tree displays that when the temperature was below 18.1 °C, Dolichospermum dominated; above 18.1 °C, Microcystis took over. Further analysis revealed that when temperature reached 18 °C, the biomass of Microcystis increased exponentially, and the biomass of Dolichospermum exhibited a Gaussian distribution trend. This finding indicated that temperature was the key factor in the succession of Dolichospermum and Microcystis in nutrient-rich shallow lakes. As nitrogen and phosphorus concentrations decrease, the dominant species of cyanobacteria will diversify its development. The results of this study provide a foundation for risk prediction and control strategies for cyanobacterial blooms in lakes and reservoirs.
Understanding the relative impact of nutrients and related environmental variables on phytoplankton biomass changes in urban rivers is important for river management. In this study, we explored the long-term dynamic changes and driving factors of phytoplankton biomass in the process of urbanization from the perspective of time and space, and provided a scientific support to water ecological health assessment and management of urban rivers. From 2012 to 2021, the phytoplankton community composition in Taiyuan section of Fenhe River was found to be dominated by Cyanophyta, Chlorophyta, and Bacillariophyta. Among them, cyanobacteria were the main contributors to the total abundance, green algae ranked second, and diatoms were the least. The biomass of phytoplankton in different groups showed different decreasing trends. Based on 10 environmental factors to explain the changes of three main phytoplankton groups (cyanobacteria, green algae, diatoms), we found that chemical oxygen demand and water temperature had a high explanation rate for the abundance changes of the three main phytoplankton groups, which were important environmental factors affecting their biomass changes. The random forest model was used to analyze the changes in the total biomass of phytoplankton. It was found that the permanganate index had a higher contribution to the total biomass of phytoplankton in time. The contribution of air temperature to the total biomass of phytoplankton was higher in space.
Monitoring the environmental status along the Veleka River (Strandzha Mtn, Bulgaria) is an essential measure for avoiding the dangers of ecological catastrophes and for preserving the unique biological diversity in this region. A system for monitoring some of the main parameters of surface waters, soils and air, as well as the sunlight levels, has been designed and initially tested. For this purpose, an automatic, remote measuring station was developed, intended for installation on the shore, near the riverbed. It has been designed not only for collecting and archiving information about the physico-chemical status of the river, but also periodically sends the data to a communication server. The developed system of several automatic measuring stations will enable us not only to analyze the current status, but also to generate an early warning in case of danger health ecosystem decline.
Antimicrobial resistance (AMR) is a global health hazard. Although clinical and agricultural environments are well-established contributors to the evolution and dissemination of AMR, research on wastewater treatment works (WwTWs) has highlighted their potential role as disseminators of AMR in freshwater environments. Using metagenomic sequencing and analysis, we investigated the changes in resistomes and associated mobile genetic elements within untreated wastewater influents and treated effluents of five WwTWs, and sediments collected from corresponding river environments in Oxfordshire, UK, across three seasonal periods within a year. Our analysis demonstrated a high diversity and abundance of antimicrobial resistance genes (ARGs) in untreated wastewater influents, reflecting the varied anthropogenic and environmental origins of wastewater. WwTWs effectively reduced AMR in the final effluent, with an average 87 % reduction in normalised ARG abundance and an average 63 % reduction in richness. However, wastewater effluents significantly impacted the antimicrobial resistome of the receiving rivers, with an average 543 % increase in ARG abundance and a 164 % increase in richness from upstream sediments to downstream sediments. The normalised abundance of the human gut-associated bacteriophage crAssphage was highly associated with both ARG abundance and richness. We observed seasonal variation in the resistome of raw influent which was not found in the effluent-receiving sediments. We illustrate the potential of WwTWs as focal points for disseminating ARGs and resistance-selecting chemicals, contributing to the elevation of environmental AMR. Our study emphasises the need for a comprehensive understanding of the anthropogenic impacts on AMR evolution and dissemination in wastewater and river environments, informing efforts to mitigate this growing public health crisis.
Biogeochemical catchment models are often developed for a single catchment and, as a result, often generalize poorly beyond this. Evaluating their transferability is an important step in improving their predictive power and application range. We assess the transferability of a recently developed Bayesian Belief Network (BBN) that simulated monthly stream phosphorus (P) concentrations in a poorly-drained grassland catchment through application to three further catchments with different hydrological regimes and agricultural land uses. In all catchments, flow and turbidity were measured sub-hourly from 2009 to 2016 and supplemented with 400–500 soil P test measurements. In addition to a previously parameterized BBN, five further model structures were implemented to incorporate in a stepwise way: in-stream P removal using expert elicitation, additional groundwater P stores and delivery, and the presence or absence of septic tank treatment, and, in one case, Sewage Treatment Works. Model performance was tested through comparison of predicted and observed total reactive P (TRP) concentrations and percentage bias (PBIAS). The original BBN accurately simulated the absolute values of observed flow and TRP concentrations in the poorly and moderately drained catchments (albeit with poor apparent percentage bias scores; 76 % ≤ PBIAS≤94 %) irrespective of the dominant land use, but performed less well in the groundwater-dominated catchments. However, including groundwater total dissolved P (TDP) and Sewage Treatment Works (STWs) inputs, and in-stream P uptake improved model performance (−5 % ≤ PBIAS≤18 %). A sensitivity analysis identified redundant variables further helping to streamline the model applications. An enhanced BBN model capable for wider application and generalisation resulted.
Excessive phytoplankton concentrations in rivers can result in the loss of plant and invertebrate communities, and threaten drinking water supplies. Whilst the physicochemical controls on algal blooms have been identified previously, how these factors combine to control the initiation, size, and cessation of blooms in rivers is not well understood. We applied flow cytometry to quantify diatom, chlorophyte, and cyanobacterial group abundances in the River Thames (UK) at weekly intervals from 2011 to 2022, alongside physicochemical data. A niche modeling approach was used to identify thresholds in water temperature, flow, solar radiation, and soluble reactive phosphorus (SRP) concentrations required to produce periods of phytoplankton growth, with blooms only occurring when all thresholds were met. The thresholds derived from the 2011 to 2018 dataset were applied to a test data set (2019–2022), which predicted the timing and duration of blooms at accuracies of > 80%. Diatoms and nano‐chlorophyte blooms were initiated by flow and water temperature, and usually terminated due to temperature and flow going out of the threshold range, or SRP and Si becoming limiting. Cyanobacterial bloom dynamics were primarily controlled by water temperature and solar radiation. This simple methodology provides a key understanding of phytoplankton community succession and inter‐annual variation and can be applied to any river with similar water quality and phytoplankton data. It provides early warnings of algal and cyanobacterial bloom timings, which support future catchment management decisions to safeguard water resources, and provides a basis for modeling changing phytoplankton bloom risk due to future climate change.
Biogeochemical catchment models are typically developed for single catchments and, as a result, often generalize poorly beyond this specific context. Therefore, evaluating their transferability is an important step in improving their predictive power and application range. We assess the transferability of a recently developed Bayesian Belief Network (BBN) that simulated monthly stream phosphorus (P) in a poorly drained grassland catchment through application to three further catchments with different hydrological regimes and agricultural land uses. In all catchments, flow and stream water P concentrations were measured sub-hourly from 2009 to present day and supplemented with 400 – 500 soil P test measurements. In addition to the original BBN, five further model structures were implemented to incorporate in a stepwise way: in-stream P removal using expert elicitation, additional groundwater P stores and delivery, and the presence or absence of septic tank treatment, and, in one case, sewage treatment works. Model performance was tested through direct comparison of predicted and observed total reactive P (TRP) concentrations and using percentage bias. The original BBN simulated the observed flow and TRP concentrations well in the poorly and moderately drained catchments, irrespective of the dominant land use (74%≤PBIAS≤81%) but performed less well in the groundwater-dominated catchments. The inclusion of groundwater total dissolved P (TDP), Sewage Treatment Works (STWs) inputs, and in-stream P uptake improved model performance (-4%≤PBIAS≤16%) in the groundwater-dominated catchments. A sensitivity analysis identified redundant parameters in some of the non- catchment specific data used. The original BBN structure could be transferred effectively only between catchments with similar hydrology. For application elsewhere, the BBN structure required modification to include representation of in-stream P removal, groundwater P concentrations, and sewage treatment works inputs. Thus, inclusion of these processes is recommended to accurately determine monthly P concentrations and aid widespread application of the proposed BBN model.
Meteorological and hydrological forcings influence phytoplankton at very short-time scales. The effect of turbulence, dilution, light, and nutrients are highly dynamic. Yet, our knowledge of short-term phytoplankton dynamics associated with discharge disturbances and nutrient inputs remains elusive, especially in large rivers. Based on every three-day monitoring, we studied phytoplankton in the middle Loire River (France) and related to the daily variations in water discharge and the physical and chemical parameters. We focused on summer phytoplankton (2013 and 2014), where dissolved inorganic phosphorus concentration was potentially limiting growth. We identified eight discharge events, which increased suspended matter concentration and decreased chlorophyll-a concentration. The most significant environmental drivers of phytoplankton composition were discharge and water temperature, a sensitive proxy for meteorological forcing at short-time scale. The phytoplankton composition responded to changes in hydrology along with three distinct assemblage types, where even small water discharge increase induced a community response. Meroplanktic algae being able to withstand sedimentation and resuspension could take advantage of hydrological peaks, following the benthic retention hypothesis. Our results suggest that short-term dynamics are crucial to understanding community organization and functioning in large river plankton, with meroplankton playing a decisive role in maintaining phytoplankton diversity and ecosystem functioning.
Interactions between plant roots and rhizosphere bacteria modulate nitrogen (N)-cycling processes and create habitats rich in low molecular weight compounds (exudates) and complex organic molecules (decaying root litter) compared to those of bulk soil. Microbial N-cycling is regulated by edaphic conditions and genes from many interconnected metabolic pathways, but most studies of soil N-cycling gene expression have focused on single pathways. Currently, we lack a comprehensive understanding of the interplay between soil N-cycling gene regulation, spatial habitat, and time. We present results from a replicated time series of soil metatranscriptomes; we followed gene expression of multiple N transformations in four soil habitats (rhizosphere, detritusphere, rhizo-detritusphere, and bulk soil) during active root growth for the annual grass, Avena fatua . The presence of root litter and living roots significantly altered the trajectories of N-cycling gene expression. Upregulation of assimilatory nitrate reduction in the rhizosphere suggests that rhizosphere bacteria were actively competing with roots for nitrate. Simultaneously, ammonium assimilatory pathways were upregulated in both rhizosphere and detritusphere soil, which could have limited N availability to plants. The detritusphere supported dissimilatory processes DNRA and denitrification. Expression of nitrification genes was dominated by three phylotypes of Thaumarchaeota and was upregulated in bulk soil. Unidirectional ammonium assimilation and its regulatory genes (GS/GOGAT) were upregulated near relatively young roots and highly decayed root litter, suggesting N may have been limiting in these habitats (GS/GOGAT is typically activated under N limitation). Our comprehensive analysis indicates that differences in carbon and inorganic N availability control contemporaneous transcription of N-cycling pathways in soil habitats.
IMPORTANCE
Plant roots modulate microbial nitrogen (N) cycling by regulating the supply of root-derived carbon and nitrogen uptake. These differences in resource availability cause distinct micro-habitats to develop: soil near living roots, decaying roots, near both, or outside the direct influence of roots. While many environmental factors and genes control the microbial processes involved in the nitrogen cycle, most research has focused on single genes and pathways, neglecting the interactive effects these pathways have on each other. The processes controlled by these pathways determine consumption and production of N by soil microorganisms. We followed the expression of N-cycling genes in four soil microhabitats over a period of active root growth for an annual grass. We found that the presence of root litter and living roots significantly altered gene expression involved in multiple nitrogen pathways, as well as tradeoffs between pathways, which ultimately regulate N availability to plants.
Cytotoxic CD8+ T lymphocytes (CTLs) are key players of adaptive anti-tumor immunity based on their ability to specifically recognize and destroy tumor cells. Many cancer immunotherapies rely on unleashing CTL function. However, tumors can evade killing through strategies which are not yet fully elucidated. To provide deeper insight into tumor evasion mechanisms in an antigen-dependent manner, we established a human co-culture system composed of tumor and primary immune cells. Using this system, we systematically investigated intrinsic regulators of tumor resistance by conducting a complementary CRISPR screen approach. By harnessing CRISPR activation (CRISPRa) and CRISPR knockout (KO) technology in parallel, we investigated gene gain-of-function as well as loss-of-function across genes with annotated function in a colon carcinoma cell line. CRISPRa and CRISPR KO screens uncovered 187 and 704 hits respectively, with 60 gene hits overlapping between both. These data confirmed the role of interferon‑γ (IFN-γ), tumor necrosis factor α (TNF-α) and autophagy pathways and uncovered novel genes implicated in tumor resistance to killing. Notably, we discovered that ILKAP encoding the integrin-linked kinase-associated serine/threonine phosphatase 2C, a gene previously unknown to play a role in antigen specific CTL-mediated killing, mediate tumor resistance independently from regulating antigen presentation, IFN-γ or TNF-α responsiveness. Moreover, our work describes the contrasting role of soluble and membrane-bound ICAM-1 in regulating tumor cell killing. The deficiency of membrane-bound ICAM-1 (mICAM-1) or the overexpression of soluble ICAM-1 (sICAM-1) induced resistance to CTL killing, whereas PD-L1 overexpression had no impact. These results highlight the essential role of ICAM-1 at the immunological synapse between tumor and CTL and the antagonist function of sICAM-1.
Temporal and spatial water quality data are essential to evaluate human health risks. Understanding the interlinking variations between water quality and socio-economic development is the key for integrated pollution management. In this study, we applied several multivariate approaches, including trend analysis, cluster analysis, and principal component analysis, to a 15-year dataset of water quality monitoring (1999 to 2013) in the Thi Vai estuary, Southern Vietnam. We discovered a rapid improvement for most of the considered water quality parameters (e.g., DO, NH4, and BOD) by step trend analysis, after the pollution abatement in 2008. Nevertheless, the nitrate concentration increased significantly at the upper and middle parts and decreased at the lower part of the estuary. Principal component (PC) analysis indicates that nowadays the water quality of the Thi Vai is influenced by point and diffuse pollution. The first PC represents soil erosion and stormwater loads in the catchment (TSS, PO4, and Fetotal); the second PC (DO, NO2, and NO3) determines the influence of DO on nitrification and denitrification; and the third PC (pH and NH4) determines point source pollution and dilution by seawater. Therefore, this study demonstrated the need for stricter pollution abatement strategies to restore and to manage the water quality of the Thi Vai Estuary.
Limited water quality data is often responsible for incorrect model description and misleading interpretation in water resources planning and management scenarios. This study compares two hybrid strategies to convert discrete concentration data into continuous daily values for one year in different river sections. Model A is based on an autoregressive process, accounting for serial correlation, water quality historical characteristics (mean and standard deviation) and random variability; the second approach (model B) is a regression model, based on the relationship between monitoring flow and concentrations, plus an error term. The generated series (here referred to as synthetic series) are propagated in time and space by a full deterministic model (SihQual), that solves the Saint-Venant and advection-dispersion-reaction equations. Results reveal that both approaches are appropriate to reproduce the variability of biochemical oxygen demand and organic nitrogen concentrations, leading to the conclusion that the combination of deterministic/empirical and stochastic components are compatible. A second outcome arises from the comparison of results in different time scales, supporting the need for further assessment of statistical characteristics of water quality data - which relies on monitoring plans. Nonetheless, the proposed methods are suitable to estimate multiple scenarios of interest in water resources planning and management.
A need for multi-functional assessment tools evaluating trade-offs and co-benefits for various types of Nature-Based Solutions (NBS) has been increasingly identified in recent years. Methodologically, concepts for a tool are presented which include quantifying the demand and potential for NBS to enhance ecosystem service (ES) provision, and linking ESs to readily quantifiable and legislatively-relevant environmental quality indicators (EQIs). The objective of tool application is to identify optimal NBS placement across a diverse set of socio-environmental indicators, whilst also incorporating issues of relative location of areas of implementation and benefit accrual. Embedded within the tool is the importance of evaluating outcomes in terms of economic benefits and of sustainable development goals. The concepts are illustrated with simplified examples, relating to the case of implementing urban forestry as an exemplar NBS. By summarising the knowledge base it is demonstrated that benefits of NBS are substantially scale-dependent in two main respects; those of extent and proximity to receptors. Evaluation tools should be capable of quantifying scale-dependence. The substantive importance of these considerations and how their dynamics vary between indicators and services is illustrated graphically through schematic functions. When developed, the tool should be used as a focus for consultation and co-design to pinpoint the size of NBS necessary to achieve a sufficient level of benefit for a particular receptor. This could be measured against target levels of benefit for each indicator, distinguishing between primary intended outcomes and those co-benefits or trade-offs that are secondary or unintended.
Understanding the relative role of anthropogenic and environmental drivers on the timing, magnitude and composition of algal and cyanobacterial blooms is vitally important for the effective management of river catchments. Whilst taxonomic identification and enumeration of algal species can provide valuable insights, the time and specialist skills needed for this approach makes it prohibitive for high frequency and multiple-site studies. Other proxies for phytoplankton, such as total chlorophyll concentration provide little information on community composition. Here we demonstrate the use of flow cytometry (FCM) as a viable alternative approach for monitoring the changing seasonal patterns of abundance, composition and biovolume of phytoplankton in rivers. A FCM assay was set up and calibrated using a range of pure algal cultures and then applied to a year-long, weekly sampling campaign on the River Thames at Wallingford, UK. Ten groups of phytoplankton representing diatoms, chlorophytes, cryptophytes and cyanobacteria were monitored over the course of the year and examined in relation to river physiochemical parameters. Major diatom blooms occurred in spring and autumn, correlating with depletion of soluble reactive phosphorus and dissolved silicon concentrations and we also observed a significant and sustained cyanobacteria bloom between July and October. Pico-chlorophytes (0.2-2.0 μm in diameter) dominated the community throughout the summer period but were not detected using traditional colorimetric chlorophyll analysis, suggesting underestimates of actual phytoplankton standing stocks by traditional methods. We demonstrate high resolution sampling and FCM as a sensitive method for river ecosystem monitoring and that FCM data may be used as an indicator of riverine health.
This paper introduces new insights into the hydrochemical functioning of lowland river systems using field-based spectrophotometric and electrode technologies. The streamwater concentrations of nitrogen species and phosphorus fractions were measured at hourly intervals on a continuous basis at two contrasting sites on tributaries of the River Thames - one draining a rural catchment, the River Enborne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly complex dynamics under storm conditions dependent on the antecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in controlling the streamwater phosphorus and nitrogen concentrations at low flows, even at a distance of 7 km from the nearest sewage treatment works in the rural River Enborne. The time of sample collection is important when judging water quality against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and multiple septic tank sources during storm events was evident and load estimation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual reduction in the phosphorus mass entering the stream during events. The results highlight the utility of sub-daily water quality measurements and the discussion considers the practicalities and challenges of in situ, sub-daily monitoring.
The catchment of the River Thames, the principal river system in southern England, provides the main water supply for London but is highly vulnerable to changes in climate, land use and population. The river is eutrophic with significant algal blooms with phosphorus assumed to be the primary chemical indicator of ecosystem health. In the Thames Basin, phosphorus is available from point sources such as wastewater treatment plants and from diffuse sources such as agriculture. In order to predict vulnerability to future change, the integrated catchments model for phosphorus (INCA-P) has been applied to the river basin and used to assess the cost-effectiveness of a range of mitigation and adaptation strategies. It is shown that scenarios of future climate and land-use change will exacerbate the water quality problems, but a range of mitigation measures can improve the situation. A cost-effectiveness study has been undertaken to compare the economic benefits of each mitigation measure and to assess the phosphorus reductions achieved. The most effective strategy is to reduce fertilizer use by 20% together with the treatment of effluent to a high standard. Such measures will reduce the instream phosphorus concentrations to close to the EU Water Framework Directive target for the Thames.
The seasonal succession of plankton is an annually repeated process of com-munity assembly during which all major external factors and internal inter-actions shaping communities can be studied. A quarter of a century ago, the state of this understanding was described by the verbal plankton ecology group (PEG) model. It emphasized the role of physical factors, grazing and nutrient limitation for phytoplankton, and the role of food limitation and fish predation for zooplankton. Although originally targeted at lake ecosystems, it was also adopted by marine plankton ecologists. Since then, a suite of eco-logical interactions previously underestimated in importance have become research foci: overwintering of key organisms, the microbial food web, par-asitism, and food quality as a limiting factor and an extended role of higher order predators. A review of the impact of these novel interactions on plank-ton seasonal succession reveals limited effects on gross seasonal biomass patterns, but strong effects on species replacements.
Soluble reactive phosphorus (SRP) concentrations in the River Thames, south east England, have significantly decreased from an annual maximum of 2100 mu g l(-1) in 1997 to 344 in 2010, primarily due to the introduction of phosphorus (P) removal at sewage treatment works within the catchment. However, despite this improvement in water quality, phytoplankton biomass in the River Thames has greatly increased in recent years, with peak chlorophyll concentrations increasing from 87 mu g l(-1) in the period 1997 to 2002, to 328 mu g l(-1) in 2009. A series of within-river flume mesocosm experiments were performed to determine the effect of changing nutrient concentrations and light levels on periphyton biomass accrual. Nutrient enrichment experiments showed that phosphorus, nitrogen and silicon were not limiting or co-limiting periphyton growth in the Thames at the time of the experiment (August-September 2010). Decreasing ambient SRP concentration from 225 mu g l(-1) to 173 mu g l(-1) had no effect on periphyton biomass accrual rate or diatom assemblage. Phosphorus limitation became apparent at 83 mu g SRP l(-1), at which point a 25% reduction in periphyton biomass was observed. Diatom assemblage significantly changed when the SRP concentration was reduced to 30 mu g l(-1). Such stringent phosphorus targets are costly and difficult to achieve for the River Thames, due to the high population density and intensive agriculture within the Thames basin. Reducing light levels by shading reduced the periphyton accrual rate by 50%. Providing shading along the River Thames by planting riparian tree cover could be an effective measure to reduce the risk of excessive algal growth. If the ecology of the Thames is to reach the WFD's "good ecological status", then both SRP concentration reductions (probably to below 100 mu g l(-1)) and increased shading will be required. Crown Copyright (c) 2011 Published by Elsevier B.V. All rights reserved.
Nitrogen and phosphorus are the primary nutrients that affect water quality in streams in the midwestern USA and high concentrations
of these nutrients tend to increase algal biomass. However, how nutrients interact with physical controls in regulating algal
biomass is not well known in agricultural streams. Eighteen streams in east-central Illinois (USA) were sampled during June
and September 2003 to analyze factors possibly regulating algal biomass. Additionally, two shaded and two non-shaded sites
in the Embarras River in east-central Illinois were sampled intensively from June to December 2003. Both sestonic and periphytic
chlorophyll-a (chl-a) were analyzed, and periphytic chl-a was assessed on natural substrata and unglazed ceramic tiles. Although high concentrations of nutrients were found in these
streams (mean total P = 0.09–0.122mgl−1 and mean NO3-N=4.4–8.4mgl−1), concentrations of sestonic chl-a were low among all sites and both sampling periods (<18mgm−3, median values of 5 and 3 in June and September, respectively). Filamentous algae were an important component of the algal
communities in streams with stable substrata. Periphytic chl-a was generally not related to the concentration of N or P in the water column, and in non-shaded streams periphyton appeared
at times to be light-limited due to turbid water. Turbidity was found to be an important factor controlling chl-a on ceramic tiles across the 18 sites and for the Embarras River sites; chl-a decreased exponentially in concentration (132–0mgm−2) as turbidity increased from 4 to 39 NTU (r
2 = 0.80). In general, the interaction between hydrology and light (turbidity) likely controlled algal biomass in these nutrient-rich,
agricultural streams.
Climate change will probably increase the frequency and intensity of low river flows, affecting both water quantity and water quality. Although climate change impacts on water quantity are widely recognised, the impacts on water quality are less known. The aim of this paper is to assess the effects of droughts on the water quality of the river Meuse in western Europe, based on analysis of existing water quality data. Time series of water quality were investigated at two monitoring stations during two severe drought periods, occurring in the years 1976 and 2003. Water quality during these droughts was investigated and compared to water quality during reference periods, representing common hydrological conditions and similar chemical pollution. A total amount of 24 water quality parameters were involved in the analysis, which can be divided into four groups: (1) general water quality variables (water temperature, chlorophyll-a, pH, dissolved oxygen and suspended solids), (2) nutrients, (3) major elements (e.g. chloride, fluoride) and (4) heavy metals and metalloids. To assess the effects of changes in discharge and water temperature on the concentration of chemical substances, empirical relations have been established between concentration and discharge, and between concentration and water temperature. The results indicate a general deterioration of the water quality of the Meuse river during droughts, with respect to water temperature, eutrophication, major elements, and some heavy metals and metalloids. This decline in water quality is primarily caused by favourable conditions for the development of algae blooms (high water temperatures, long residence times, high nutrient concentrations) and a reduction of the dilution capacity of point source effluents.
Although microscope analysis is very useful for studying phytoplankton community composition, it does not allow for high frequency (spatial and/or temporal) data acquisition. In an attempt to overcome this issue, fluorescence-based approaches that use selective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass and composition is still debated, and only a few datasets have been tested to date. In this study, we sampled of a wide range of water bodies (n=50) in the Ile-de-France region (North Central France). We used the resulting extensive dataset to assess the ability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton community composition in lakes and reservoirs. We demonstrated that FP data yields better estimates of total phytoplankton biovolume than do spectrophotometric chlorophyll a measures and that FP data can be further corrected using the average chlorophyll a to biovolume ratio among phytoplankton groups. Overall, group-specific relationships between FP and biovolume data were consistent. However, we identified a number of cases where caution is required. We found that Euglenophytes are expected to depart from the global FP vs. biovolume relationship of the 'green' group due to varying Fv/Fm and pigment content in response to environmental conditions (photoautotrophic vs. photoheterotrophic growth). Then, it appears necessary to consider the composition of the Chromophytes community in order to obtain a good agreement between both biomass estimation methods. Finally, we confirmed the misattribution toward the 'red' group of phycoerythrin-containing cyanobacteria and the occurrence of a strong scattering in the relationship between the FP vs. biovolume of the 'blue' group that can be partly attributed to the occurrence of large colony-forming cyanobacteria (e.g., Microcystis spp, Aphanizomenon flos-aquae). We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs.
Agriculture and urban activities are major sources of phosphorus and nitrogen to aquatic ecosystems. Atmospheric deposition further contributes as a source of N. These nonpoint inputs of nutrients are difficult to measure and regulate because they derive from activities dispersed over wide areas of land and are variable in time due to effects of weather. In aquatic ecosystems, these nutrients cause diverse problems such as toxic algal blooms, loss of oxygen, fish kills, loss of biodiversity (including species important for commerce and recreation), loss of aquatic plant beds and coral reefs, and other problems. Nutrient enrichment seriously degrades aquatic ecosystems and impairs the use of water for drinking, industry, agriculture, recreation, and other purposes. Based on our review of the scientific literature, we are certain that (1) eutrophication is a widespread problem in rivers, lakes, estuaries, and coastal oceans, caused by over-enrichment with P and N; (2) nonpoint pollution, a major source of P and N to surface waters of the United States, results primarily from agriculture and urban activity, including industry; (3) inputs of P and N to agriculture in the form of fertilizers exceed outputs in produce in the United States and many other nations; (4) nutrient flows to aquatic ecosystems are directly related to animal stocking densities, and under high livestock densities, manure production exceeds the needs of crops to which the manure is applied; (5) excess fertilization and manure production cause a P surplus to accumulate in soil, some of which is transported to aquatic ecosystems; and (6) excess fertilization and manure production on agricultural lands create surplus N, which is mobile in many soils and often leaches to downstream aquatic ecosystems, and which can also volatilize to the atmosphere, redepositing elsewhere and eventually reaching aquatic ecosystems. If current practices continue, nonpoint pollution of surface waters is virtually certain to increase in the future. Such an outcome is not inevitable, however, because a number of technologies, land use practices, and conservation measures are capable of decreasing the flow of nonpoint P and N into surface waters. From our review of the available scientific information, we are confident that: (1) nonpoint pollution of surface waters with P and N could be reduced by reducing surplus nutrient flows in agricultural systems and processes, reducing agricultural and urban runoff by diverse methods, and reducing N emissions from fossil fuel burning; and (2) eutrophication can be reversed by decreasing input rates of P and N to aquatic ecosystems, but rates of recovery are highly variable among water bodies. Often, the eutrophic state is persistent, and recovery is slow.
A simplified method for the analysis of total P(TP), total dissolved P(TDP) and dissolved reactive P (DRP) in multiple water samples has been developed. The reported modification utilizes a single digestion reagent and a single "mixed reagent" to eliminate neutralization, transfer and dilution steps normally required in total P analyses. The method results in a 70 percent decrease in analysis time for multiple samples, a reduction in the glassware required, and about a 30 percent increase in sensitivity. The method can be directly applied to water samples with P levels of 2 to 1100 ug P/l. Reproducibility and precision measurements compare to or exceed commonly used P techniques.
Algal models have been developed for the River Thames. Non-linear processes controlling algal growth are examined using a generalized sensitivity analysis technique, and the dominant parameters controlling system behaviour are identified. The extended Kalman filter is then used to estimate these important parameters. The technique of using generalized sensitivity analysis prior to EKF estimation is suggested as a pragmatic approach to the problem of identifying the subset of physically, chemically or biologically meaningful parameters controlling system behaviour in mechanistic models.-from Authors
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
A process-based phytoplankton model developed to simulate the movement and growth of phytoplankton in river systems is presented in this paper. The model is based on mass-balance, and takes into account water temperature, light, self-shading, dissolved phosphorus and silicon concentrations. It was implemented in five reaches of the River Thames (UK), and the results compared to a novel dataset of cytometric data which includes concentrations of chlorophytes, diatoms, cyanobacteria and picoalgae. A Multi-Objective General Sensitivity Analysis was carried out in order to test the model robustness and to quantify the sensitivity to its parameters. The results show a good agreement between the simulations and the measured phytoplankton abundance. The most influential parameters were phytoplankton growth and death rates, while phosphorus concentration showed little influence, due to the high concentration of phosphorus in the Thames. The model is an important step forward towards understanding and predicting algal dynamics in river systems.
There are still a number of gaps in our understanding regarding phytoplankton behaviour in rivers. Given predicted future changes in climate, which appear superficially at least, to favour larger phytoplankton blooms, this study was initiated to assess how well we can currently simulate this behaviour with a river water quality model. The river quality model (QUESTOR) was run for a 45 km stretch of the upper Thames for 2009-2011 (UK). To identify the most suitable model representation, phytoplankton was simulated and compared to actual observed data under three alternative assumptions. The first of these was of a Mixed Phytoplankton population and the other two being that there was domination by either of two groups (Green Algae, or cool water diatoms such as Stephanodiscus hantzschii) known to be abundant in the river. The factors for controlling the phytoplankton populations were found to be flow, temperature and radiation. Of these controlling factors, river flow has the larger effect on depletion or build-up of phytoplankton, based on residence time. The nutrient concentrations (phosphate and nitrate) seem to be in excess and not limiting or controlling of the phytoplankton behaviour. The data highlighted two main blooms in late spring and summer, which were successfully modelled with a Mixed Phytoplankton population (which explained 16-35% of the weekly variability throughout 2009-10). On a year-to-year time frame there is clear evidence of between-year differences in grazing loss rates. This can be accounted for by a combination of benthic filter feeders and zooplankton, both having been observed in sufficient numbers in the Thames. Crown Copyright
Observations have been made during five years on the fluctuations in the numbers of Asterionella formosa and other plankton diatoms, and in the concentrations of dissolved silica, nitrates and phosphates in four bodies of water in the English Lake District. This account refers mainly to the period from winter to summer. The close of the spring period of increase of Asterionella is not directly due to light or temperature. Loss of cells by floods is more or less compensated for by the replenishment of the lake with nutrients in the inflow water. Grazing by animals has no appreciable effect on the fluctuations in numbers. Fungal parasitism may affect the course of the spring increase in numbers, but is rarely the cause of its end. Very rarely, depression of the numbers of Asterionella by parasitism may lead to other diatoms becoming dominant and utilizing the available nutrients (e.g. silica). The close of the spring period of increasing numbers of Asterionella is frequently due to depletion of the available silica. Confirmation is deduced for Pearsall's (1932) view that diatoms cannot multiply to any marked extent when the concentration of silica is less than 0.5 mg. per litre. The supply of available silica does not provide a complete explanation of the fluctuations in diatom numbers in all the lakes considered or at all times of year. The mean silica content of the cells of Asterionella formosa is 140μg. per million. Confirmation has been obtained for the view of Einsele & Grim (1938) that the amount of silica per unit area of cell is constant under all conditions. The nitrogen content in natural and cultural populations varied from 6 to 12μg. per million cells (mean value 8μg.). The phosphorus content, by contrast with silica and nitrogen, varied widely in natural and cultural populations (0.06-4.2μg. per million cells). The cells of Asterionella can store phosphorus in excess of immediate requirements and when the concentration in the water is 1μg. per litre or less. Asterionella can utilize calcium at a concentration of 400μg. per litre, a lower concentration than occurs in any lake in the English Lake District. Reasons are given for the view that the supplies of nitrogen, phosphorus, carbon and calcium appear to be sufficient to support larger populations of Asterionella than are observed during the period under review. Little or nothing is known concerning the importance of any other substances in the lake waters. Limitation of growth due to lack of silica shows a difference from that due to lack of light. The present observations and conclusions are discussed in relation to those for other lakes made by the author and other workers. It is emphasized that every algal species and lake must be considered separately.
This study aims to elucidate the key mechanisms controlling phytoplankton growth and decay within the Thames basin through the application of a modified version of an established river-algal model and comparison with observed stream water chlorophyll-a concentrations. The River Thames showed a distinct simulated phytoplankton seasonality and behaviour having high spring, moderate summer and low autumn chlorophyll-a concentrations. Three main sections were identified along the River Thames with different phytoplankton abundance and seasonality: (i) low chlorophyll-a concentrations from source to Newbridge; (ii) steep concentration increase between Newbridge and Sutton; and (iii) high concentrations with a moderate increase in concentration from Sutton to the end of the study area (Maidenhead). However, local hydrologic (e. g. locks) and other conditions (e. g. radiation, water depth, grazer dynamics, etc.) affected the simulated growth and losses. The model achieved good simulation results during both calibration and testing through a range of hydrological and nutrient conditions. Simulated phytoplankton growth was controlled predominantly by residence time, but during medium-low flow periods available light, water temperature and herbivorous grazing defined algal community development. These results challenge the perceived importance of in-stream nutrient concentrations as the perceived primary control on phytoplankton growth and death.
Knowledge about long-term dynamics of phytoplankton in river ecosystems as well as the physical and chemical drivers that potentially control the plankton is essential for predicting future developments, e.g. in response to global climate change. The present study analyzes long-term trends in phytoplankton biomass and shifts in the timing of phytoplankton spring blooms observed in the large rivers Rhine and Elbe from 1990–2009 and 1994–2009, respectively, and analyzes the factors potentially regulating phytoplankton biomass. While phytoplankton biomass in the Elbe was high (seasonal mean chlorophyll-a concentration: 62 µg/L) and showed an increasing tendency, it was much lower in the Rhine (seasonal mean chlorophylla concentration: 10 µg/L) where it decreased significantly during the study period. This decrease coincided with an earlier occurrence of the phytoplankton spring maximum. In the Elbe, the timing of low discharge conditions was crucial for the occurrence of the spring bloom, i.e. an earlier end of the discharge maximum was connected with an earlier spring bloom. In the Rhine, we found a positive correlation between the timing of the spring bloom and the end of winter flood flow. The maximum chlorophylla values during the bloom correlated with the timing of maximum light availability in the Rhine. The findings indicate that climate related factors, like discharge or light conditions, have a high potential to regulate phytoplankton spring bloom dynamics in large rivers. Such dependence could be relevant for predicting phytoplankton development under climate change.
“There is nothing so practical as a good theory” Bertrand Russell
The paper recapitulates the theory of catchment water deficits and the use of density analysis previously published in this journal. Thereafter theory and method are applied to the Thames River Basin in England where it is shown that the catchment is marginally in deficit but that future developments in population growth, output growth and climate change require the application of specific redemptive options if a serious deficit situation is to be avoided. In particular, strict house-building controls are called for as well as the universal metering of domestic water use.
Abstract Ten years ago plans were made to reduce the phosphorus load from sewage-treatment works' effluents into the River Thames. This was driven by the EC Urban Wastewater Treatment Directive in relation to sensitive areas (eutrophic). Modelling work identified the most significant loads to tackle first. Phosphorus removal had been commissioned at 36 works by 2003. The orthophosphate load to the River Thames from these works has reduced from 5755 to 688 kg P/day. The impact of the improvement programme on the quality of the river was assessed by comparing pre- and post-investment data. Orthophosphate concentrations in the river have reduced from between about 0.5 and 2 mg P/L to 0.2 and 0.4 mg P/L. These observations match the model predictions. Chlorophyll a concentrations in the river have also reduced. This was unexpected given that the orthophosphate concentrations still exceed the values thought to be limiting for algal growth.
Freshwater algal blooms have become an important water quality problem in Europe and Australia. Countries such as Belgium, Denmark, Germany, Italy and The Netherlands have experienced severe algal blooms (Anabaena,Microcystisetc.). These have caused considerable losses in recreation opportunities, expenses to provide alternative water supplies and deaths among livestock. Most of the phosphorus in European waters derives from point sources such as sewage plants, livestock industries and detergents. In Australia non-point sources from agriculture and other sources are more important. The emphasis in controlling algal blooms in Europe as well as in Australia is on phosphorus removal in wastewater by upgrading sewage plants and installing new sewage processing facilities. In Europe control of detergent phosphorus has also received emphasis but in Australia detergent problems are largely ignored. The attention to the use of economic measures to control phosphorus is inadequate in both Europe and Australia, but Europe is still ahead of Australia.
The optimum conditions for the determination of silicate in natural waters by a molybdenum blue method have been investigated p-Methylaminophenol sulphate has a number of advantages over other reducing agents for the reduction of silicomolybdic acid to molybdenum blue. Beer's law is obeyed up to concentrations of at least 3 mg/l.The interference of several inorganic ions has been investigated; none of those encountered in natural waters is likely to cause error. The method has been applied to the analysis of sea-water and the “salt error” correction evaluated.RésuméLes conditions optima de dosage de silicate dans les eaux normales par la méthode au bleu de molybdène ont été examinées. Le sulfate de p-méthylaminophénol présente un certain nombre d'avantages sur les autres réducteurs utilisés pour la réduction de l'acide silicomolybdique en bleu de molybdène. La loi de Beer est suivie pour des concentrations allant au moins jusqu'à, 3 mg/1. L'influence de divers ions inorganiques a été examinée, aucun de ceux présents dans les eaux naturelles ne gêne. Cette méthode a été appliquée a l'analyse de l'eau de mer.ZusammenfassungEs wurden die optimalen Bedingungen gesucht fur die Bestimmung von Silikat im natürlichen Wasser mit der Molybdenblaumethode. Das Sulfat von p-methylaminophenol weist eine gewisse Anzahl Vorteile auf gegenüber den andern Reduktionsmitteln, welche für die Reduktion der Silicomolybdänsäure zu Molybdänblau verwendet werden. Das Beer'sche Gesetz findet Anwendung für Konzentrationen, die mindestens bis zu 3 mg/l gehen. Der Einfluss von verschiedenen anorganischen Ionen wurde geprüft. Keines der im naturlichen Wasser vorkommenden Ionen stört die Bestimmung. Diese Methode wurde verwendet für die Analyse des Meerwassers.
The results are presented of an intensive study of phytoplankton assemblage carried out in the Berounka River above its confluence with the Vltava River (Czech Republic) in the period 2002–2007. The annual and interannual changes of phytoplankton development (based on high frequency of sampling) and their relation to hydrological conditions and concentrations of main nutrients are analysed. A marked decline of nutrient concentrations was observed during the period 1996–2007. The annual mean values of total P decreased from 0.43mgL−1 to 0.16mgL−1, those of N-NO3 from 4.6mgL−1 to 1.5mgL−1 and N-NH4 from 1.9mgL−1 to 0.04mgL−1. Despite this, the phytoplankton biomass remained at a high level. The seasonal mean values of chlorophyll-a ranged from 51.0μgL−1 to 116.8μgL−1 in the same time period. An obviously stronger relationship was found of the phytoplankton biomass and pattern of its development to the variation of flow rates than to the existing level of nutrient concentrations. A significantly decreasing relationship (R2=0.384, P
The mechanisms by which entrained planktonic organisms survive in river
systems, despite an inexorable, unidirectional downstream transport, are
revisited. The importance of channel retentivity to downstream
population recruitment is emphasized. The aggregated dead-zone (ADZ)
model is shown to be adequate to explain downstream recruitment of a
growing population. The ADZ behaviour is more prevalent in sinuous,
low-gradient reaches than in other parts of the river. Plankton
selection and dynamics relate conspicuously to flow at higher discharges
but other environmental features are important at low flows. Discharge
variability is pivotal to the opportunities for potamoplankton to
thrive.
The impact of climate change and of other anthropogenic pressures on the structure and composition of phytoplankton communities of large European rivers remains poorly documented. Here we report the findings of a study of the changes in the phytoplankton community of the middle segment of the river Loire over the past 24 years. An attempt is made to distinguish between the impact of changes acting at the local scale and that of those acting more globally. A dramatic reduction in phytoplankton abundance was observed, particularly in the mid -1990s; this was concomitant with an increase in the relative proportion of cyanobacteria. At the same time, the phytoplankton community displayed increasing richness and diversity, and little change in its size structure. All these changes seem to be related to local changes, in particular to the reduction in phosphorus concentrations, as well as to changes in climate, throughout modifications in the river discharge and water temperature. Interestingly, herbicide contamination also appeared to be of particular importance in explaining the unexpected increase in the proportion of cyanobacteria in the phytoplankton community after the 1990s. These findings suggest that combinations of numerous anthropogenic pressures acting at different spatial and temporal scales have led to a mix of predictable and unpredictable changes occurring in the phytoplankton community of the river Loire, with probable consequences for the trophic networks in this river.
Land Cover Map 2000 (LCM2000) is a thematic classification of satellite image data covering the entire United Kingdom. The map updates and substantially upgrades the Land Cover Map of Great Britain (LCMGB), made in 1990–92. This paper outlines the character of the map through a description of its specification, production and outputs. The paper is aimed at users of LCM2000 and derived data who need to understand more of the map and its characteristics. The paper also outlines plans for making data available to researchers and applied users.The most important development in LCM2000 was the spectral segmentation of images to generate vector land parcels. Land cover was then identified by the spectral classification of the image data in these parcels. Classification used specially developed procedures which exploited known spatial, spectral and contextual characteristics of land cover. The resultant GIS incorporates, within its vector structure, detailed attribute data which record parcel-based land cover, plus information on class probabilities, data on within-parcel heterogeneity, information on landscape structure and context, cover information from LCMGB, together with a record of each parcel's processing history.
We measured the size structure and taxonomic composition of phytoplankton in temperate rivers during base flows of summer to investigate the influence of river size, ambient nutrient concentration, and light availability on potamoplankton community structure. Algal biomass was measured in three size classes (2–20, 20–64, and 64 m) by microscope enumeration of water samples collected in 31 rivers and by chlorophyll a in water samples collected in 46 rivers in another year across Ontario and western Quebec. Nanoplankton dominated the potamo-plankton biomass across the range of river nutrient concentrations (total phosphorus 5–280 g P L 1), water resi-dence times (1–39 d), and light regimes (euphotic zone to mixing depth ratio 0.1–33). Both nanoplankton (2–20 m) and total potamoplankton biomass were significantly correlated with water column total phosphorus concen-trations and were not related to water residence time or light availability. On average, diatoms contributed the largest percentage of the total biomass, followed by cryptophytes and an equal percentage of chlorophytes and chryso-phytes. The contribution of any one division to total biomass was not significantly correlated with nutrients, water residence time, or light regime. In contrast to temperate lake systems, both the proportion of biomass in larger size classes and the contribution of cyanobacteria did not change significantly as a function of nutrient concentrations. However, community size structure varied in relation to river size: netplankton (64 m) contributed slightly more to total biomass at sites with both shorter (2 d) and longer (10 d) water residence times. These results point to differences between the phytoplankton of lakes and rivers in response to eutrophication.
Observed concentrations of orthophosphate in the River Thames, from its source to its tidal limit, exceed 0.1 mg P/1 for most of its length; reasons for annual and seasonal variations are explained. By using data routinely collected by the Environment Agency throughout the Thames catchment, the orthophosphate load in the river, derived from agricultural sources and sewage-treatment works, is estimated.
A water quality model, TOMCAT, has been adapted to simulate observed data and used to estimate river concentrations if orthophosphate loads from sewage-treatment works are reduced.
Algae present considerable problems for river qualitymanagers and water suppliers and methods to predicttheir behaviour, growth and transport can assist inoperational management. Alternative techniques existfor predicting algal response and three approacheshave been compared and applied to data from six sitesalong the River Thames. These techniques include timeseries analysis, dynamic mass balance and growthequations and neural network approaches. It is shownthat neural network techniques offer a new approachrequiring less intuitive knowledge but predictivecapability is not improved greatly compared to otherapproaches. Neural networks enable models to bedeveloped along all six reaches of the RiverThames.
Chlorophyll-a and nutrient concentrations were monitored at weekly intervals across 21 river sites throughout the River Thames basin, southern England, between 2009 and 2011. Despite a 90% decrease in soluble reactive phosphorus (SRP) concentration of the lower River Thames since the 1990s, very large phytoplankton blooms still occur. Chlorophyll concentrations were highest in the mid and lower River Thames and the larger tributaries. Lowest chlorophyll concentrations were observed in the smaller tributaries, despite some having very high phosphorus concentrations of over 300 μg l(-1). There was a strong positive correlation between river length and mean chlorophyll concentration (R(2)=0.82), and rivers connected to canals had ca. six times greater chlorophyll concentration than 'natural' rivers with similar phosphorus concentrations, indicating the importance that residence time has on determining phytoplankton biomass. Phosphorus concentration did have some influence, with phosphorus-enriched rivers having much larger phytoplankton blooms than nutrient-poor rivers of a similar length. Water quality improvements may now be capping chlorophyll peaks in the Rivers Thames and Kennet, due to SRP depletion during the spring/early summer phytoplankton bloom period. Dissolved reactive silicon was also depleted to potentially-limiting concentrations for diatom growth in the River Thames during these phytoplankton blooms, but nitrate remained in excess for all rivers throughout the study period. Other potential mitigation measures, such as increasing riparian shading and reducing residence times by removing impoundments may be needed, alongside phosphorus mitigation, to reduce the magnitude of phytoplankton blooms in the future.
The possible effects of changing climate on a southern and a north-eastern English river (the Thames and the Yorkshire Ouse, respectively) were examined in relation to water and ecological quality throughout the food web. The CLASSIC hydrological model, driven by output from the Hadley Centre climate model (HadCM3), based on IPCC low and high CO2 emission scenarios for 2080 were used as the basis for the analysis. Compared to current conditions, the CLASSIC model predicted lower flows for both rivers, in all seasons except winter. Such an outcome would lead to longer residence times (by up to a month in the Thames), with nutrient, organic and biological contaminant concentrations elevated by 70–100% pro-rata, assuming sewage treatment effectiveness remains unchanged. Greater opportunities for phytoplankton growth will arise, and this may be significant in the Thames. Warmer winters and milder springs will favour riverine birds and increase the recruitment of many coarse fish species. However, warm, slow-flowing, shallower water would increase the incidence of fish diseases. These changing conditions would make southern UK rivers in general a less favourable habitat for some species of fish, such as the Atlantic salmon (Salmo salar). Accidental or deliberate, introductions of alien macrophytes and fish may change the range of species in the rivers. In some areas, it is possible that a concurrence of different pressures may give rise to the temporary loss of ecosystem services, such as providing acceptable quality water for humans and industry. An increasing demand for water in southern England due to an expanding population, a possibly reduced flow due to climate change, together with the Water Framework Directive obligation to maintain water quality, will put extreme pressure on river ecosystems, such as the Thames.
The results of a nutrient stability study, pilot studies and three major 100-h monitoring campaigns measuring phosphorus (soluble reactive, total dissolved and total) and dissolved nitrogen (nitrate, nitrite and ammonium) concentrations in the R. Swale catchment in Yorkshire, UK are reported. The nutrient stability studies showed that although nitrite showed considerable stability during 24-h storage, both ammonium and phosphorus were found to be less stable. These nutrients must be analyzed as soon as possible after sampling to avoid changes caused by processes in solution and interactions of soluble compounds with colloids and suspended material during storage. The results of the intensive measurements indicate the importance of point-inputs of dissolved phosphorus to the main river and major tributaries during low-flow conditions in the autumn and spring. This was demonstrated using a simple dilution model to estimate the flux of point-inputs. However, during a storm event, diffuse inputs are also important leading to increases in soluble unreactive phosphorus and particulate phosphorus concentrations in the river. Nitrate concentrations are more influenced by diffuse inputs and previous weather conditions with the highest concentrations measured after a period of low rainfall. Nitrite and ammonium were at similar concentrations during low-flow conditions. Although nitrite concentrations generally increased with river flow, the changes were less marked when compared with nitrate. Ammonium also increased in the main river during high-flow conditions. All nutrients showed hysteresis in their concentration–discharge relationship during a major storm which indicated the importance of diffuse inputs. The effect was consistent with a depletion of nutrients during the falling limb of the hydrograph.
Phosphorus trends in the Thames Catchment have been investigated, and the relation between phosphorus, flow and phytoplankton blooms evaluated. Temporal and spatial trends in phosphorus concentrations were examined in three rivers, the Thames, Blackwater and Kennet, which have a diverse range of surrounding land use. Phosphorus levels were generally found to be high, averaging 0.99 mg/l PO4-P with a maximum of 6.70 mg/l PO4-P, particularly in relation to urban areas where effluent discharge was a significant source. A strong seasonal component relating to flow was evident. The relation between phosphorus, flow and chlorophyll-a (used as the measure of algal abundance) was analysed by regression analysis. Neither phosphorus nor flow appeared to be limiting phytoplankton growth, probably because phosphorus concentrations were much greater than levels likely to be limiting. There was a clear relation between phosphorus and phytoplankton growth, with peak values of phosphorus occurring after the phytoplankton maxima. Cycles of algal assimilation and decomposition readily explain this relationship.
Forecasting the movement and growth of algae in river systems as particularly important for operational managers responsible for the distribution and supply of potable water. Algae affect the taste and smell of water and pose considerable filtration problems at water treatment plants. In a collaborative study with the Thames Water Authority, algal models have been developed for the River Thames. The non-linear processes controlling algal growth are examined using a generalized sensitivity analysis technique and the dominant parameters controlling system behaviour are identified. The extended Kalman filter (EKF) is then used to estimate these important parameters. The technique of using generalized sensitivity analysis prior to EKF estimation is suggested as a pragmatic approach to the problem of identifying the subset of physically, chemically or biologically meaningful parameters controlling system behaviour in mechanistic models.
Assessment of phosphate species for bicarbonate-bearing lowland rivers of the Thames valley, England and acidic Welsh upland streams (the Plynlimon area, mid-Wales) reveal problems of silica interference when employing standard automated ‘phosphomolybdic acid’ colorimetric methodologies. The interference occurs under a combination of two conditions: (1) when the reagents and samples are heated to speed up the rate of formation of phosphomolybdic acid; and (2) when the strength of a sulfuric acid reagent is too low. While this paper alerts researchers to potential analytical problems with silica interference within phosphomolybdic acid methodologies to determine soluble reactive phosphorus (SRP) concentrations, it cannot detail whether or not there is a general problem. This lack of specificity occurs because there are a variety of phosphomolybdic acid methodologies available which vary in their reagent recipes and it is not clear which methods will or will not suffer from silica interference. Changing the sulfuric acid reagent strength by a factor of two overcame the problem, in this case, with regards to the determination of soluble reactive phosphorus. However, even here, the method may not be applicable to very high alkalinity waters owing to their potential for reducing the acidity of the analyte. With regard to total dissolved phosphorus (TDP) and total phosphorus (TP) measurements, the importance of undertaking the analysis under ambient conditions is clearly shown. There are many small variants on standard phosphomolybdate methods for determining SRP, TDP and TP in use and it is not always clear which methods will or will not show silica interference for particular water types. It is therefore recommended that individual laboratories check their methodologies for silica interference using phosphate-free solutions with similar silica and alkalinity ranges for the waters being assayed.
The water quality of the River Frome, Dorset, southern England, was monitored at weekly intervals from 1965 until 2009. Determinands included phosphorus, nitrogen, silicon, potassium, calcium, sodium, magnesium, pH, alkalinity and temperature. Nitrate-N concentrations increased from an annual average of 2.4 mg l⁻¹ in the mid to late 1960s to 6.0 mg l⁻¹ in 2008-2009, but the rate of increase was beginning to slow. Annual soluble reactive phosphorus (SRP) concentrations increased from 101 μg l⁻¹ in the mid 1960s to a maximum of 190 μg l⁻¹ in 1989. In 2002, there was a step reduction in SRP concentration (average=88 μg l⁻¹ in 2002-2005), with further improvement in 2007-2009 (average=49 μg l⁻¹), due to the introduction of phosphorus stripping at sewage treatment works. Phosphorus and nitrate concentrations showed clear annual cycles, related to the timing of inputs from the catchment, and within-stream bioaccumulation and release. Annual depressions in silicon concentration each spring (due to diatom proliferation) reached a maximum between 1980 and 1991, (the period of maximum SRP concentration) indicating that algal biomass had increased within the river. The timing of these silicon depressions was closely related to temperature. Excess carbon dioxide partial pressures (EpCO₂) of 60 times atmospheric CO₂ were also observed through the winter periods from 1980 to 1992, when phosphorus concentration was greatest, indicating very high respiration rates due to microbial decomposition of this enhanced biomass. Declining phosphorus concentrations since 2002 reduced productivity and algal biomass in the summer, and EpCO₂ through the winter, indicating that sewage treatment improvements had improved riverine ecology. Algal blooms were limited by phosphorus, rather than silicon concentration. The value of long-term water quality data sets is discussed. The data from this monitoring programme are made freely available to the wider science community through the CEH data portal (http://gateway.ceh.ac.uk/).
River flow and quality data, including chlorophyll-a as a surrogate for river phytoplankton biomass, were collated for the River Ouse catchment in NE England, which according to established criteria is a largely unpolluted network. Against these data, a daily river quality model (QUESTOR) was setup and successfully tested. Following a review, a river quality classification scheme based on phytoplankton biomass was proposed. Based on climate change predictions the model indicated that a shift from present day oligotrophic/mesotrophic conditions to a mesotrophic/eutrophic system could occur by 2080. Management options were evaluated to mitigate against this predicted decline in quality. Reducing nutrient pollution was found to be less effective at suppressing phytoplankton growth than the less costly option of establishing riparian shading. In the Swale tributary, ongoing efforts to reduce phosphorus loads in sewage treatment works will only reduce peak (95th percentile) phytoplankton by 11%, whereas a reduction of 44% is possible if riparian tree cover is also implemented. Likewise, in the Ure, whilst reducing nitrate loads by curtailing agriculture in the headwaters may bring about a 10% reduction, riparian shading would instead reduce levels by 47%. Such modelling studies are somewhat limited by insufficient field data but offer a potentially very valuable tool to assess the most cost-effective methods of tackling effects of eutrophication.
Human-induced eutrophication degrades freshwater systems worldwide by reducing water quality and altering ecosystem structure and function. We compared current total nitrogen (TN) and phosphorus (TP) concentrations for the U.S. Environmental Protection Agency nutrient ecoregions with estimated reference conditions. In all nutrient ecoregions, current median TN and TP values for rivers and lakes exceeded reference median values. In 12 of 14 ecoregions, over 90% of rivers currently exceed reference median values. We calculated potential annual value losses in recreational water usage, waterfront real estate, spending on recovery of threatened and endangered species, and drinking water. The combined costs were approximately 0.3-2.8 billion per year, although this number was poorly constrained) and recreational use ($0.37-1.16 billion per year). Our evaluation likely underestimates economic losses incurred from freshwater eutrophication. We document potential costs to identify where restoring natural nutrient regimes can have the greatest economic benefits. Our research exposes gaps in current records (e.g., accounting for frequency of algal blooms and fish kills) and suggests further research is necessary to refine cost estimates.
The distribution of suspended algae was investigated in a 69-km length of a small lowland river in the UK, the Nene, using chlorophyll as a measure of biomass. Variations in chlorophyll data collected between 1975 and 1996 by water management organisations at a downstream site (km 91.7) were evaluated against a range of physical and chemical variables. Interpretation was aided by additional sampling at eight sites on the main river (including km 91.7) and three tributaries between 1994 and 1996. Significant inter-year variation was evident in all data and was most pronounced in discharge. The latter half of the 22-year period had significantly higher temperature and light and significantly lower ammonia concentrations. Discharge, temperature and light were significant predictors of chlorophyll concentration, particularly between January and June, and spring chlorophyll maxima ranged from 106 to 276 microg l(-1). Summer chlorophyll concentrations were generally low relative to spring peaks. Some summers, however, had very low chlorophyll concentrations (average < 10 microg l(-1)) which were independent of the controlling factors at other times and inter-year variation in submerged macrophyte abundance is proposed as a causal factor for their occurrence. Spring chlorophyll peaks occurred earlier and had smaller amplitude at downstream sites compared to those further upstream. Average spring chlorophyll concentration (April-June) increased significantly between km 22.4 and 43.9, thereafter remaining high to km 91.7. Spatial trends were attributed to changes in channel morphology, retention time and longitudinal variations in velocity and temperature.
Eutrophication has many known consequences, but there are few data on the environmental and health costs. We developed a new framework of cost categories that assess both social and ecological damage costs and policy response costs. These findings indicate the severe effects of nutrient enrichment and eutrophication on many sectors of the economy. We estimate the damage costs of freshwater eutrophication in England and Wales to be 77 million yr(-1) pound 54.8 m). The damage costs are dominated by seven items each with costs of $15 million yr(-1) or more: reduced value of waterfront dwellings, drinking water treatment costs for nitrogen removal, reduced recreational and amenity value of water bodies, drinking water treatment costs for removal of algal toxins and decomposition products, reduced value of nonpolluted atmosphere, negative ecological effects on biota, and net economic losses from the tourist industry. In common with other environmental problems, it would represent net value (or cost reduction) if damage was prevented at source. A variety of effective economic, regulatory, and administrative policy instruments are available for internalizing these costs.
Standard ISO method for chlorophyll a quantification (extraction into ethanol, spectrophotometrical quantification at 665 and 750 nm), spectrofluorometry (reader for 96 wells, excitation 410 nm, emission 670 nm), and a submersible fluorescence probe for in situ phytoplankton quantification (excitation 410, 525, 570, 590, and 610 nm, emission 685 nm) were compared in different freshwater environments-reservoirs and rivers. The ISO method is accepted as a standard method but requires sample handling and transport to the laboratory. Spectrofluorometry is a sensitive method, even for natural phytoplankton populations. Nevertheless, it cannot be recommended for the quantification of cyanobacterial water blooms because colonial and filamentous species such as Microcystis, Anabaena, or Aphanizomenon display unacceptable variability (18-33%). The submersible probe featured high correlation with a standard ISO method (r=0.97, P<0.05). This probe can provide the selective measurement of technologically important phytoplankton groups like cyanobacteria, diatoms, green algae, and cryptophytes in lake vertical profiles of up to 100 m. The limitation of this instrument is the possible reabsorption of the light signal, e.g. in the presence of humic substances, or dense algal blooms. The use of submersible probes for in situ phytoplankton quantification can be recommended as a sensitive tool for water management, especially in the case of drinking water resources.
Chlorophyll-a concentration variations are described for two major river basins in England, the Humber and the Thames and related to catchment characteristics and nutrient concentrations across a range of rural, agricultural and urban/industrial settings. For all the rivers there are strong seasonal variations, with concentrations peaking in the spring and summer time when biological activity is at its highest. However, there are large variations in the magnitude of the seasonal effects across the rivers. For the spring-summer low-flow periods, average concentrations of chlorophyll-a correlate with soluble reactive phosphorus (SRP). Chlorophyll-a is also correlated with particulate nitrogen (PN), organic carbon (POC) and suspended sediments. However, the strongest relationships are with catchment area and flow, where two straight line relationships are observed. The results indicate the importance of residence times for determining planktonic growth within the rivers. This is also indicated by the lack of chlorophyll-a response to lowering of SRP concentrations in several of the rivers in the area due to phosphorus stripping of effluents at major sewage treatment works. A key control on chlorophyll-a concentration may be the input of canal and reservoir waters during the growing period: this too relates to issues of residence times. However, there may well be a complex series of factors influencing residence time across the catchments due to features such as inhomogeneous flow within the catchments, a fractal distribution of stream channels that leads to a distribution of residence times and differences in planktonic inoculation sources. Industrial pollution on the Aire and Calder seems to have affected the relationship of chlorophyll-a with PN and POC. The results are discussed in relation to the Water Framework Directive.
Although the process of eutrophication is reasonably well understood in lakes, there is currently no conceptual understanding of how eutrophication develops in rivers. This issue is addressed here. A review of the main processes controlling the development of eutrophication in lakes has been carried out as a precursor to considering the effect in rivers. The importance of hydraulic flushing in controlling algal growth suggests that short-retention-time rivers will show different effects compared to long retention-time, impounded rivers. The latter are likely to operate like lakes, moving from macrophyte domination to phytoplankton domination whereas the former move to benthic and filamentous algal domination. Subsequently, a conceptual model of the development of eutrophic conditions in short-retention-time rivers is developed. Although there is general agreement in the literature that an increase in nutrients, particularly phosphorus, is a pre-requisite for the eutrophic conditions to develop, there is little evidence in short-retention-time rivers that the plant (macro and micro) biomass is limited by nutrients and a good case can be made that the interaction of hydraulic drag with light limitation is the main controlling factor. The light limitation is brought about by the development of epiphytic algal films on the macrophyte leaves. The implications of this conceptual model are discussed and a series of observable effects are predicted, which should result if the model is correct.
UK hydrometric register. Hydrological Data UK Series
- T J Marsh
- J Hannaford
Marsh, T.J., Hannaford, J., 2008. UK hydrometric register. Hydrological Data UK Series.
Centre for Ecology and Hydrology.