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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.
... 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.
... In addition to nutrients, physical parameters (light, water temperature, flow, and residence time) are assumed to promote phytoplankton blooms in fluvial systems ( Bowes et al. 2016) and to control the occurrence, intensity, and duration of phytoplankton blooms ( Chételat et al. 2006;Bowes et al. 2016;Dodds and Smith 2016). It is expected that high temperatures and low flow rates can thus increase the number of riverine phytoplankton blooms ( Mitrovic et al. 2008). ...
... In addition to nutrients, physical parameters (light, water temperature, flow, and residence time) are assumed to promote phytoplankton blooms in fluvial systems ( Bowes et al. 2016) and to control the occurrence, intensity, and duration of phytoplankton blooms ( Chételat et al. 2006;Bowes et al. 2016;Dodds and Smith 2016). It is expected that high temperatures and low flow rates can thus increase the number of riverine phytoplankton blooms ( Mitrovic et al. 2008). ...
... One data point in the long-term data set of physico-chemical parameters and phytoplankton taxonomy on 08 September 2015 matched the event of the ammonium nitrate spill and the corresponding phytoplankton bloom at the river outlet. Due to the excess input of ammonium nitrate, TN and DIN increased to 8.0 and 7.3 mg L −1 , whereas orthoP was depleted below the detection limit (Fig. 4, arrows) and thus most likely restricted bloom intensity (Davis and Koop 2006;Bowes et al. 2016). This also affected the TN:TP ratio, which increased to 81, while Chl a reached 146 μg L −1 and was comparable with maximum values during phytoplankton blooms in spring (Fig. 4, arrows). ...
Global change will increase the number and severity of extreme events resulting in strongly pulsed nutrient loading to rivers. Recent studies indicate the potential for rapid plankton shifts as short‐term response to storm events and highlight the need for high‐frequency methods to understand these complex processes. Here, we studied the effects of a strong short‐term pulse of ammonium nitrate in a eutrophic temperate river that elevated nitrate‐N concentrations from 3.1 to 10–55 mg L−1. An intense phytoplankton bloom increased chlorophyll a concentrations from below 10 μg L−1 to over 140 μg L−1 despite of high background N concentrations and followed the N‐pulse downstream. High‐throughput sequencing revealed the temporal dynamics of the bacterial (16S rRNA gene) and microeukaryotic (18S rRNA gene) community throughout the event. Bacterial and microeukaryotic community richness was reduced, and community composition changed significantly during the bloom. Few microeukaryote taxa (e.g., Cyclotella meneghiniana, Chlamydomonas) dominated the bloom and replaced the rich summer phytoplankton community. Long‐term monitoring data (2008–2016) using classical microscope analyses showed that seasonal shifts in phytoplankton community composition were linked to physical parameters and nutrient availability with P‐limitation observed in spring but not in summer. We conclude that a disturbance in abiotic and biotic control factors, such as caused by a nutrient pulse, can induce structural shifts in the microplankton community leading to a phytoplankton bloom, even in eutrophic waters.
... Moreover, in the River Thames (UK), the subject of the present study, phytoplankton biomass appears suppressed in mid-summer possibly due to short-lived nutrient limitation together with biological interactions (e.g. control by grazers at higher trophic levels) (Waylett et al., 2013;Bowes et al., 2016). Hence, an alternative hypothesis of biological response is that phytoplankton biomass is dominated by cool water diatom species which bloom in spring and early summer. ...
... The importance of abiotic-biotic feedbacks, physical factors and climatic variables, in addition to nutrient levels, in controlling phytoplankton and DO in large rivers has been widely demonstrated (e.g. Hardenbicker et al., 2014;Istvanovics et al., 2009, van Vliet andZwolsman 2008;Bowes et al., 2016;Minaudo et al., 2018). However, whilst detailed, these contrasting studies highlight that understanding arising of multi-stressor impacts cannot be comprehensive, instead being largely rudimentary typically only providing snapshots rather than response along stressor gradients of a system. ...
... The aim of the present study was to make an ensemble of water quality model applications to assess the sensitivity of eutrophication in the Thames to a range of stressor variables and to develop a method for representing the outputs. Five stressor variables were chosen (water temperature, phosphate concentration, river flow, urbanisation and riparian shading) to which eutrophication in the Thames is known to be especially sensitive (Waylett et al., 2013;Bowes et al., 2016;. The variables themselves reflect a range of pressure types including those related to climate, catchment management and population growth. ...
The severity of river eutrophication is influenced by multiple stressors which reflect a wide-ranging variety of drivers encompassing land management, population growth and climatic effects. Experimental studies have successfully identified response to single or paired stressors under controlled conditions in small streams but have limited capability to characterise larger systems influenced by a wider variety of stressors. Here, a physics-based water quality model of the River Thames (UK) is used to explore the impacts of water temperature, phosphate concentration, river flow, urbanisation and riparian shading on indicators of chlorophyll and dissolved oxygen concentration by way of a sensitivity analysis. To understand the impact of model structural uncertainty, results are presented from two alternative formulations of the biological response. All outputs from each unique combination of stressors are presented in one graphic comprising multiple sub-plots that display the results of thousands of model runs simultaneously. Consequently, graphical analysis allows us to pinpoint under what circumstances reductions in key variables representing management-related stressors (i.e. lowering phosphorus concentrations and establishing riparian shading) may act synergistically, antagonistically or simply in an additive manner. Furthermore, we identify how these relationships may vary under different river flow and water temperature regimes and changes in abstraction and effluent discharge rates, to indicate the likely influence of future climate and population growth. Response can vary markedly depending on the choice of biological model and also changes considerably downstream along the river system. Chlorophyll indicators consistently show antagonistic responses to reduction in stressors whereas dissolved oxygen indicators show varied and complex responses. As expected, increases in phosphorus loading are detrimental, but so too are large decreases. Whilst the analysis suggests that urbanisation impacts are in general not expected to be large, changes in water demand brought about by population growth have disproportionate effects at low flows. These may result in increased incidence of very low dissolved oxygen concentrations which damage the health of the ecosystem.
... 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.
... 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.
... House and Warwick (1998) detected a 30 h variation in TP in April in the River Swale; as levels of dissolved silica also dropped with TP, diatoms were thought to explain the TP variations. Later, Bowes et al (2016) detected daily TP variations in the river Thames during the springs of 2009-2013; they observed that most TP fluctuations went in hand with a chlorophyll-a increase and phytoplankton growth was associated with the phenomenon. In the same study, another daily TP variation event showed no increase in chlorophyll-a but a drop in dissolved silica and diatoms were believed to cause the TP fluctuations. ...
Phosphorus (P) leaching from agriculture is a major driver of water eutrophication in downstream rivers and lakes. In drained lowland areas with intensive agriculture, a reduction in the fertilizer applications may be insufficient to improve the water quality in the short term as the P accumulated in the soil during decades of high fertilization may continue leaching for many years. A complementary approach to reduce P exports from agriculture is to implement edge-of-field mitigation measures at the farm scale. The selection of effective measures requires a detailed insight into the chemical and hydrological transport mechanisms. Here, we determined the main P sources, processes, and transport routes at the farm scale to support the selection of appropriate mitigation measures. We quantified the legacy P, the different P pools stored in the upper soil, and related it to the yearly P export downstream. To do this, we combined high-resolution monitoring data from the soil, groundwater, surface water, and ditch sediments. The legacy P in the topsoil was high, about 2500 kg ha⁻¹. The predominant subsurface flow and the subsoils’ P sorption capacity retained the P mobilized from the topsoil and explained the relative moderate flux of P to surface waters (0.04 kg ha⁻¹ during the 2018–2019 drainage season). The dissolved P entering the drainage ditch via groundwater discharge was bound to iron-containing particles formed due to the oxidation of dissolved ferrous iron. Once leached from the soil to the drainage ditch, resuspension of P-rich sediment particles during flow peaks were the most important P transport mechanism (78%). Therefore, we expect that hydraulic constructions that reduce flow velocities and promote sedimentation of P-containing particles could reduce the export of P further downstream.
... Nevertheless, the environments in which T&O issues related to algae outbreaks occur in cold seasons have more extensive ranges. Long rivers such as the River Yellow in China (Li et al. 2016), River Nakdong in Korea (Kim and Treatment 2015), River Thames in the UK (Bowes et al. 2016) and River Mississippi in the USA (Roy et al. 2016) have been reported to have simultaneous occurrences of spring/winter diatom blooms and T&O issues. To summarize the issues mentioned above, non-cyanobacterial-induced T&O problems in cold waters are not limited to homogeneous T&O, algae species and outbreak environments. ...
The existence of taste and odour (T&O) in drinking water is one of the principal causes of consumer complaints and is commonly related to algae growth. Numerous studies have confirmed the existence of algal blooms emerging specifically in low-temperature periods, herein referred to as “cold algae”; these include chrysophytes, cryptophytes, dinoflagellates and diatoms. In addition, the adaption mechanisms of these “cold algae” involve high flexibility in their nutrient intake and to the hydrological characteristics of the waters and their high contents of intracellular polyunsaturated fatty acids (PUFAs). Like algae proliferating in higher temperature waters, cold algae can also produce offensive odours. The potential dominant T&O compounds of low-temperature algae probably include saturated/unsaturated aldehydes and even some terpenoids. Among these, the polyunsaturated aldehydes (PUAs), the derivatives of polyunsaturated fatty acids, are the dominant T&O compounds and are probably synthesized during cell rupture. It was found that, for cold algae, low temperature may have a favourable effect on the generation of algae-induced T&O compounds. Furthermore, to better understand the internal mechanisms of algal T&O production, the stress response theory is introduced, which provides ideas for T&O control in raw water and in water treatment. Finally, implications for T&O management are given based on this review.
Key points
• Like algae proliferating in higher temperature waters, cold algae can produce offensive odours.
• Low temperatures may have a favourable effect on the generation of algae-induced T&O compounds.
• The stress response theory can help to better understand the internal mechanisms of algal T&O production.
... However, the situation in India is improving rapidly, with a wider range of water quality parameters now been measured by the regulatory authorities, including sub-daily data from in-situ water quality probes. Such data is vitally important for increasing system understanding, knowledge of how pollution sources change under a range of flow regimes Tappin et al. 2016), and how nutrients, water quality and ecology interact (Bowes et al. 2016;Hardenbicker et al. 2014). ...
The Ganga River is facing mounting environmental pressures due to rapidly increasing human population, urbanisation, industrialisation and agricultural intensification, resulting in worsening water quality, ecological status and impacts on human health. A combined inorganic chemical, algal and bacterial survey (using flow cytometry and 16S rRNA gene sequencing) along the upper and middle Ganga (from the Himalayan foothills to Kanpur) was conducted under pre-monsoon conditions. The upper Ganga had total phosphorus (TP) and total dissolved nitrogen concentrations of less than 100 μg l−1 and 1.0 mg l−1, but water quality declined at Kannauj (TP = 420 μg l−1) due to major nutrient pollution inputs from human-impacted tributaries (principally the Ramganga and Kali Rivers). The phosphorus and nitrogen loads in these two tributaries and the Yamuna were dominated by soluble reactive phosphorus and ammonium, with high bacterial loads and large numbers of taxa indicative of pathogen and faecal organisms, strongly suggesting sewage pollution sources. The high nutrient concentrations, low flows, warm water and high solar radiation resulted in major algal blooms in the Kali and Ramganga, which greatly impacted the Ganga. Microbial communities were dominated by members of the Phylum Proteobacteria, Bacteriodetes and Cyanobacteria, with communities showing a clear upstream to downstream transition in community composition. To improve the water quality of the middle Ganga, and decrease ecological and human health risks, future mitigation must reduce urban wastewater inputs in the urbanised tributaries of the Ramganga, Kali and Yamuna Rivers.
... Despite improvements in the treatment of domestic and industrial wastewaters, the current levels of nutrient fluxes in sewage effluent remain substantially higher than at the beginning of the twentieth century, and are frequently far higher than would be required to elicit ecological recovery of surface waters (Sayer et al. 2010;Bowes et al. 2012Bowes et al. , 2016Naden et al. 2016;McCall et al. 2017). Small rural sewage treatment works (STWs) have been implicated in the eutrophication of surface waters in the United Kingdom (Mainstone and Parr 2002;Neal et al. 2005;Jarvie et al. 2006;Roberts and Cooper 2018). ...
Integrated Constructed Wetlands (ICWs) are potentially effective tools in the effort to restore aquatic ecosystems, and also they incorporate multiple co-benefits. An ICW was constructed in Norfolk, UK, to address the degradation of a stream and lake receiving treated effluent from a small Sewage Treatment Works (STW). Results demonstrated that: (1) nutrient concentrations significantly reduced from the ICW influent to the effluent (percentage reductions: total phosphorus [TP]: 78%, orthophosphate: 80%, total oxidised nitrogen [TON]: 65%, nitrate: 65%, nitrite: 67%, ammoniacal nitrogen: 62%), and mean dissolved oxygen concentrations increased (influent mean: 6.4 ± 1.4 mg l−1 effluent mean: 17.8 ± 3.3 mg l−1), (2) there were non-significant reductions in nutrient concentrations in the receiving stream (percentage reductions: TP: 23%, orthophosphate: 23%, TON: 26%, nitrate: 26%), with the exception of ammoniacal nitrogen (127% increase) and nitrite (76%) after ICW commissioning, and (3) mean in situ avian species richness increased from 10 to 27 species. Thus, the ICW substantially reduced nutrient concentrations, and had in situ conservation benefits. It is recommended that appropriately designed ICWs should be implemented widely and statutory authorities should ensure: 1) best-practice maintenance and 2) final effluent monitoring at both the STW and at the ICW outflows.
... Phytoplankton serves as the base of the aquatic food web in the bay ecosystem. Environmental variations (such as changes in salinity, temperature, light and nutrients) can directly affect the dynamic changes of phytoplankton communities (Muylaert et al., 2000;Bowes et al., 2016;Yang et al., 2017;Cibic et al., 2018), thus phytoplankton could be a useful indicator of ecosystem change and health. ...
... The integration and analysis of datasets from sites across the world has been facilitated by grassroots initiatives like the Global Lake Ecological Observatory Network (GLEON) (Weathers et al., 2013;Hamilton et al., 2015;. The analysis of high resolution data has advanced the understanding of various aspects of limnology such as long term (O'Reilly et al., 2015;Woolway, Weyhenmeyer, et al., 2019) and short term changes in water temperature, lake metabolism , bloom development (Pomati et al., 2011;Bowes et al., 2016) and the responses to episodic events (Jennings et al., 2012;Woolway et al., 2018;Chapter 6). A number of tools have also been developed to standardise the calculation of physical and chemical metrics using high resolution datasets such as Lake Analyser (Read et al., 2011), Lake Heat Flux Analyzer (Woolway et al., 2015) and Lake Metabolizer (Winslow et al., 2016). ...
... Somewhat surprising was that during the high flow periods, CD was the largest even if high among-site dispersal, denoted by the importance of spatial factors in variation partition (Table 4), should homogenize communities. It may be that high community variation stemmed from the fact that higher water discharge can drive phytoplankton communities either through settling patterns (Bowes et al., 2016;Engelhardt et al., 2004) or through the insertion of benthic species that are dislodged by the river flow and then occur as tychoplankton (Descy et al., 2017;John and Museum, 2013;Liu et al., 2013;Wang et al., 2014). Such new colonists would increase stochasticity (Abonyi et al., 2012;Devercelli et al., 2016) leading also to higher community variation. ...
... It is important to recognize that rivers are highly heterogeneous systems which respond to a wide variety of pressures and local (physical) drivers which regulate primary production (Dodds and Welch, 2000;Bowes et al., 2016). Moreover, given the added complexity of a wider range of national-scale approaches to setting thresholds, a high variability in nutrient thresholds for rivers is not surprising. ...
The aim of European water policy is to achieve good ecological status in all rivers, lakes, coastal and transitional waters by 2027. Currently, more than half of water bodies are in a degraded condition and nutrient enrichment is one of the main culprits. Therefore, there is a pressing need to establish reliable and comparable nutrient criteria that are consistent with good ecological status.
This paper highlights the wide range of nutrient criteria currently in use by Member States of the European Union to support good ecological status and goes on to suggest that inappropriate criteria may be hindering the achievement of good ecological status. Along with a comprehensive overview of nutrient criteria, we provide a critical analysis of the threshold concentrations and approaches by which these are set. We identify four essential issues: (1) Different nutrients (nitrogen and/or phosphorus) are used for different water categories in different countries. (2) The use of different nutrient fractions (total, dissolved inorganic) and statistical summary metrics (e.g., mean, percentiles, seasonal, annual) currently hampers comparability between countries, particularly for rivers, transitional and coastal waters. (3) Wide ranges in nutrient threshold values within shared water body types, in some cases showing more than a 10-fold difference in concentrations. (4) Different approaches used to set threshold nutrient concentrations to define the boundary between “good” and “moderate” ecological status. Expert judgement-based methods resulted in significantly higher (less stringent) good-moderate threshold values compared with data-driven approaches, highlighting the importance of consistent and rigorous approaches to criteria setting.
We suggest that further development of nutrient criteria should be based on relationships between ecological status and nutrient concentrations, taking into account the need for comparability between different water categories, water body types within these categories, and countries.
... Excessive nutrient input from rivers in combination with supporting climate conditions can lead to major algal blooms e.g. River Thames (Moorhouse et al., 2018, Bowes et al., 2016 and Elbe (Hardenbicker et al., 2014). This has caused severe eutrophication and hypoxia events in a number of receiving seas in the 1970s to 1990s, e.g. in the Black Sea, Baltic Sea, and Northern Adriatic Sea Rosenberg, 2008, Friedrich et al., 2014) with dramatic consequences for the functioning of coastal pelagic and benthic ecosystems (Zhang et al., 2010). ...
This deliverable summarises current research needs in European River-Sea Systems. It is a working document, which will be further developed into the Science and Innovation Agenda for DANUBIUS-RI. The Science and Innovation Agenda will be published at the conclusion of DANUBIUS-PP in 2019. The deliverable draws upon a review of the academic literature, expert consultations and discussions. It uses the Driver – Pressure – State – Impact – Response (DPSIR) conceptual framework to investigate overarching research challenges in European River-Sea Systems.
... High temporal resolution data enable the detection of both short-term events and long-term changes [9], and thus become increasingly necessary when studying the impacts of climate change on water quality due to changes in nutrient transfer dynamics [10]. Many of the existing automatic monitoring systems that provide real-time, continuous, reliable, and low-cost measurements [11], focus on the estimation of pollution pathways, assessment of the ecological status and early detection of pollution or flood/drought events [12,13]. The design of water quality monitoring programs has always been a challenge due to the many variables that need to be included [14]. ...
Water quality indices that describe the status of water are commonly used in freshwater vulnerability assessment. The design of river water quality monitoring programs has always been a complex process and despite the numerous methodologies employed by experts, there is still no generally accepted, holistic and practical approach to support all the phases and elements related. Here, a Geographical Information System (GIS)-based multicriteria decision analysis approach was adopted so as to contribute to the design of the national network for monitoring of water quality parameters in Greece that will additionally fulfill the urgent needs for an operational, real-time monitoring of the water resources. During this cost-effective and easily applied procedure the high priority areas were defined by taking into consideration the most important conditioning factors that impose pressures on rivers and the special conditions that increase the need for monitoring locally. The areas of increased need for automatic monitoring of water quality parameters are highlighted and the output map is validated. The sites in high priority areas are proposed for the installation of automatic monitoring stations and the installation and maintenance budget is presented. Finally, the proposed network is contrasted with the current automatic monitoring network in Greece.
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.
River eutrophication and CyanoHABs are severe problems that are often ignored because of high current speed and strong self‐purification. In this paper, Liangxi River, Taihu Basin, was selected as the research area. Combined with field investigation, a 2‐D water environment mathematical model was developed to simulate the chl‐a distribution in Liangxi River. An indicator (Transverse Distribution Center, TDC) and its normalized form (NTDC) to quantitatively represent material transverse distribution in rivers is proposed and coupled in the model. The calculation showed that TDC and NTDC had the property of random fluctuation, seasonal consistency, and water transfer dependence. The multiple regression equation with normalized data indicated that the maximum offset, average variation rate and average reverting rate of Liangxi River chl‐a NTDC were most affected by the chl‐a dry matter flux ratio between tributaries and the mainstream, followed by flow and chl‐a concentration ratio. From the perspective of river morphology, for different river width change modes and river bending directions, when water flows into and out of these river sections, the chl‐a transverse distribution is subject to different specific effects. In addition, the position of nutrients and dissolved oxygen significantly affected the position of chl‐a growth when the N/P ratio was not very high. Conversely a high N/P ratio may contribute to decrease of the chl‐a concentration. Proliferation with abundant nutrients may cause the settlement of chl‐a resulting in a decrease of chl‐a in the water column.
Riparian zones of rivers are transitional environments between land and water ecosystems with distinct hydrological gradients, soils and habitats strongly related to their functioning. When these functions are intact, they integrate multi-directional processes across the land-river channel (e.g. canopy shade effects on the stream, flood inundation effects on the land) with mutual beneficial effects. In many managed landscapes these functions have been degraded. To restore them, considerable efforts have been directed over the last 20 years to understand and place effective riparian ‘buffer’ zones, particularly to enhance water quality and biodiversity. Since water quality targets are not easily met by current practices in many managed landscapes (as additive pressures increase), catchment managers will have to increasingly restore riparian functions to enhance aquatic ecosystem resilience to land and climate change. Targeting effective restoration within site-specific contexts requires availability of spatial data, in combinations that inform on individual and multiple functions. There are accelerating developments with spatial data, arising from increased spatial resolution of key underlying datasets, availability of soil and landcover data and increasing secondary derived attributes. Hence, a review is timely into the best practices in the use of these data for delineating riparian functions and management zones for rivers.
Our review evaluates the application of spatial data and is structured around three conceptual methods of riparian delineation; fixed width, variable width by river corridor features and variable width by context of local pressures or required outcomes. We explore process representation and incorporation into management across main riparian functions (hydrological connectivity, water quality, shading, resource transfers and habitat provision). Translating spatial data into functions informs the ability to go beyond contemporary, generally fixed width approaches using basic structural components towards planning to better target functional attributes to optimise ecosystem protection.
In recent years, with the rapid development of satellite technology, remote sensing inversion has been used as an important part of environmental monitoring. Remote sensing inversion has been prepared for large-scale water environment monitoring in the watershed that is difficult for the traditional water environment monitoring methods. This paper will discuss some shortcomings of traditional remote sensing inversion methods, and proposes a remote sensing inversion method based on convolutional neural network, which realizes large-scale remote sensing smart and automatic inversion monitoring of the water environment. The results show that the method is practical and effective, and can achieve high recognition accuracy for water blooms.
Worldwide, many aquatic systems are under anthropogenic induced pressure by elevated nutrient inputs. In particular, increased nitrogen and phosphorus usage have led to human-induced eutrophication (including cyanobacterial blooms and hypoxia) of all kinds of water bodies. Associated pressures need to be described, and diminished, in order to reach a sustainable human usage of ecosystems. The Baltic Sea is a model system, as it is prone to Global Change, and is strongly influenced by human actions and shows recurrent cyanobacterial blooms and hypoxia. There have already been several actions to ameliorate these problems, e.g. by reducing the inflow of phosphorus. However, even the strongest possible reductions are currently not enough to restore the Baltic Sea. Coastal water bodies are still highly eutrophic, and the catchment area is affected by permanent runoff-events from adjacent land. Furthermore, new approaches are needed to improve the efficiency of water treatment plants. On the other side, legislation is sometimes inefficient on a local scale. Such problems can only be solved in multi-disciplinary approaches that include environmental, engineering and social sciences. Here, we present an overview of recent research with emphasis on phosphorus and its flows and controls into the Baltic Sea from the German catchment area.
This Science and Innovation Agenda summarises the scientific and technical framework for the development of DANUBIUS-RI. The International Centre for advanced Studies on River-Sea Systems is a distributed environmental research infrastructure dedicated to River-Sea Systems on the Roadmap of the European Strategy Forum on Research Infrastructures (ESFRI). The agenda highlights the research priorities for the first five years of the infrastructure’s operation.
DANUBIUS-RI’s Vision is to achieve healthy River-Sea Systems and advance their sustainable use, in order to live within the planet’s ecological limits by 2050. DANUBIUS-RI’s Mission is to facilitate excellent science on the continuum from river source to sea; to offer state-of-the art research infrastructure; and to provide the integrated knowledge required to sustainably manage and protect River-Sea Systems.
DANUBIUS-RI’s goal is to overcome the current fragmentation of science, knowledge, data and management in rivers and seas by integrating spatial, temporal, disciplinary and sectorial thinking. We will provide science-based solutions to environmental and societal risks arising from global and climate change. We will offer a source to sea perspective to resolve problems arising from human impacts on River-Sea Systems.
Rivers, estuaries, deltas and coastal seas connect more than three quarters of the Earth’s land surface with the ocean. The natural connection between land and ocean is essential for humankind in providing key ecosystem services including food, water and transport. However, these connections are increasingly impacted by global change, affecting entire River-Sea Systems worldwide. Urgent action is needed to harmonise future human use and the protection of River-Sea Systems to counter the effects of climate change and unsustainable use, such as landscape fragmentation, river regulation and damming, water and sediment abstraction, eutrophication and pollution, the loss of biodiversity and the spread of invasive species.
DANUBIUS-RI has identified challenges and gaps in knowledge that must be addressed if we are to achieve healthy River-Sea Systems. These include ensuring sufficient flows of water and sediment, maintaining structural integrity and continuity, facilitating processes of natural self-organisation over time and promoting resilience to extreme events. We will facilitate a source-to-sea perspective to understand the evolution and functioning of River-Sea Systems considering: the effects of Climate Change and Extreme Events; Water and Sediment Quantity and Quality; Hydromorphology; Biodiversity; Ecosystem Functioning and Services; and multiple impacts on River- Sea Systems, taking into account the need to respond to complexity.
DANUBIUS-RI has distilled its research priorities for the first five years to guide the starting activities as it proceeds to operation. These research priorities are socially relevant; they are in line with forthcoming mission areas of Horizon Europe, applied to River-Sea Systems, and will be regularly updated:
Mission Area 1: Achieving healthy inland, transitional and coastal waters.
Priority (1) Water Quantity: Understand and quantify water stores and flows across River-Sea continua to enable sustainable water resource management and mitigate against extreme events.
Priority (2) Sediment Balance: Understand and quantify sediment dynamics in a source to sink system, and manage sediments sustainably across River-Sea continua.
Priority (3) Nutrients and Pollutants: Understand and quantify singular and combined effects of nutrients and pollutants in water and sediments to establish critical thresholds as a means to support the achievement of good status at the scale of the River-Sea System.
Priority (4) Biodiversity: Understand the relationship between biodiversity and connectivity across River-Sea Systems and its response to multiple stressors.
Priority (5) Ecosystem Services: Understand and quantify how changing River-Sea Systems will affect future provision of ecosystem services and how these can be sustained.
Mission Area 2: Adapting to Climate Change: Enhancing Resilience of River-Sea Systems.
Priority (6) Climate Change: Support collection of data and the development of innovative methods and tools to assess the effects of climate change and to improve adaptation measures within and across River-Sea Systems.
Priority (7) Extreme Events: Understand and quantify the occurrence and severity of extreme events such as floods and droughts, impacting River-Sea Systems and find cost effective nature-based solutions to support disaster mitigation and management.
The DANUBIUS-RI Components comprise the Hub, Data Centre, Nodes, Supersites, e-Learning Office and Technology Transfer Office, distributed across Europe. DANUBIUSERIC, as the legal entity, provides the effective governance framework. DANUBIUS-RI will provide users from science, environmental agencies, river basin and regional seas commissions and business access to a range of River-Sea Systems, facilities, data and expertise, and enable interdisciplinary research, innovation opportunities, knowledge exchange, education and training. Cooperation is key for DANUBIUS-RI. We will cooperate closely with other research infrastructures, including ICOS-ERIC, EMSOERIC, EURO-ARGO ERIC, LifeWatch ERIC and eLTER; with research infrastructure networks such as HYDRALAB and JERICO; with River Basin and Regional Seas Commissions; with data programmes and initiatives such as the European Copernicus programme, EUMETSAT and SeaDataNet; and with research programmes and initiatives such as JPI Water and JPI Oceans.
The underlying physical and biogeochemical mechanisms associated with low dissolved oxygen (DO) levels below 5 mg L-1 were examined through field data analyses and water quality modeling of the lower 40 miles of the Minnesota River. Insights into flow and water quality data of nineteen years (1999-2017) at five sites demonstrate that low DO levels parallel the obvious longitudinal (upstream-to-downstream) decline in phytoplankton biomass and increase in ammonium nitrogen (NH4) and dissolved orthophosphate (PO4) in the last 22-mile river reach (i.e., navigation channel) during late summer low flow conditions. River discharge is inversely related to the magnitude of the longitudinal change in DO, phytoplankton biomass, NH4 and PO4, indicating that the late summer low flow hydrodynamics in the navigation channel with a longer residence time, deeper water and slower velocity provide an extended opportunity for the biogeochemical reactions involving phytoplankton, DO and nutrients. Moreover, the ratio of the longitudinal decline in DO versus the longitudinal increase in NH4 is particularly close to the Redfield O:N ratio, suggesting that the decline in DO and increase in nutrients most likely result from the decomposition of phytoplankton detritus under aerobic conditions. This is further proved by the water quality modeling of the lower Minnesota River. The primary reasons for impaired water quality are substantially elevated sediment oxygen consumption and nutrient release derived from the decomposition of settled phytoplankton detritus in the navigation channel. Therefore, we recommend that active prevention of abrupt phytoplankton blooms and collapses through regulation of river discharge and local hydrodynamics may assist in maintaining acceptable water quality in eutrophic rivers with a high level of phytoplankton biomass.
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.