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Climate change effects on nitrogen loading from cultivated catchments in Europe: Implications for nitrogen retention, ecological state of lakes and adaptation
Abstract
Climate change might have profound effects on the nitrogen (N) dynamics in the cultivated landscape as well as on N transport
in streams and the eutrophication of lakes. N loading from land to streams is expected to increase in North European temperate
lakes due to higher winter rainfall and changes in cropping patterns. Scenario (IPCC, A2) analyses using a number of models
of various complexity for Danish streams and lakes suggest an increase in runoff and N transport on an annual basis (higher
during winter and typically lower during summer) in streams, a slight increase in N concentrations in streams despite higher
losses in riparian wetlands, higher absolute retention of N in lakes (but not as percentage of loading), but only minor changes
in lake water concentrations. However, when taking into account also a predicted higher temperature there is a risk of higher
frequency and abundance of potentially toxic cyanobacteria in lakes and they may stay longer during the season. Somewhat higher
risk of loss of submerged macrophytes at increased N and phosphorus (P) loading and a shift to dominance of small-sized fish
preying upon the key grazers on phytoplankton may also enhance the risk of lake shifts from clear to turbid in a warmer North
European temperate climate. However, it must be emphasised that the prediction of N transport and thus effects is uncertain
as the prediction of regional precipitation and changes in land-use is uncertain. By contrast, N loading is expected to decline
in warm temperate and arid climates. However, in warm arid lakes much higher N concentrations are currently observed despite
reduced external loading. This is due to increased evapotranspiration leading to higher nutrient concentrations in the remaining
water, but may also reflect a low-oxygen induced reduction of nitrification. Therefore, the critical N as well as P loading
for good ecological state in lakes likely has to be lower in a future warmer climate in both north temperate and Mediterranean
lakes. To obtain this objective, adaptation measures are required. In both climate zones the obvious methods are to change
agricultural practices for reducing the loss of nutrients to surface waters, to improve sewage treatment and to reduce the
storm-water nutrient runoff. In north temperate zones adaptations may also include re-establishment of artificial and natural
wetlands, introduction of riparian buffer zones and re-meandering of channelised streams, which may all have a large impact
on, not least, the N loading of lakes. In the arid zone, also restrictions on human use of water are urgently needed, not
least on the quantity of water used for irrigation purposes.
KeywordsClimate change–Nitrogen loading–Lakes–Ecological state–Modelling–Streams–Subtropics–Temperate–Warm arid
... Ensemble average total phosphorus concentration within the valley is also predicted to increase compared to the baseline period along the streams of the valley apart from P1 and P2 (Fig. 5). These results are in agreement with predictions of changes in instream nutrient concentrations (Whitehead et al., 2006;Jeppesen et al., 2011), particularly with studies which suggest increases in riverine phosphorus and nitrogen concentrations (Arheimer et al., 2005;Kaste et al., 2006;Atkins, 2014;Molina-Navarro et al., 2014;Charlton et al., 2018). In fact, lower river flow under climate change reduces the dilution capacity of rivers, thereby resulting in higher concentrations of nutrients (Whitehead et al., 2006;Whitehead et al., 2009;Molina-Navarro et al., 2014;Charlton et al., 2018). ...
... For sites P1, P2, P10, and P11, the ecological status will remain poor under different scenarios except for the RCP8.5 scenario projecting bad status for all sites in the Far Future. The findings of this study are consistent with previous reports on the potential effects of climate change on freshwater ecosystems (Jeppesen et al., 2011;Mantyka-Pringle et al., 2014;Kakouei et al., 2018), particularly with the study predicting that the good ecological status of several EU rivers may be downgraded in future because of climate change, with more vulnerable sites located in Mediterranean countries (Abily et al., 2021). ...
... This prediction agrees with Rocha et al. (2020), which states that climate change would negatively impact water quantity and quality in reservoirs. Other studies also reported higher concentrations of P and N in warm arid lakes during dry periods (when the water table is low) despite lower external nutrient loads due to enhanced evapotranspiration and decreased inflow (Özen et al., 2010;Jeppesen et al., 2011). Thus, the improvement of WWTPs providing high-quality effluents and the sustainable management of agriculture with less nutrient loss to surface waters should be implemented in the valley to reduce the external nutrient load. ...
Understanding the effects of environmental stressors (e.g., potential changes in climate and land use) on ecological status is essential for freshwater management. The ecological response of rivers to stressors can be evaluated by several physico-chemical, biological, and hydromorphological elements as well as computer tools. In this study, an ecohydrological model based on SWAT (Soil and Water Assessment Tool) is used to investigate climate change impact on the ecological status of Albaida Valley Rivers. The predictions of five General Circulation Models (GCMs) each with four Representative Concentration Pathways (RCPs) are employed as input to the model for simulating several chemical and biological quality indicators (nitrate, ammonium, total phosphorus, and the IBMWP (Iberian Biological Monitoring Working Party) index) in three future periods (Near Future: 2025-2049, Mid Future: 2050-2074, and Far Future: 2075-2099). Based on chemical and biological status predicted with the model, the ecological status is determined at 14 representative sites. As a result of increased temperatures and decreased precipitations from most of GCMs projections, the model predicts decreased river discharge, increased concentrations of nutrients, and decreased values of IBMWP for future compared to the baseline period (2005-2017). While most representative sites have poor ecological status (10 sites with poor ecological status and four sites with bad ecological status) in the baseline, our model projects bad ecological status for most representative sites (four sites with poor ecological status and 10 sites with bad ecological status) under most emission scenarios in the future. It should be noted that the bad ecological status is projected for all 14 sites under the most extreme scenario (i.e., RCP8.5) in the Far Future. Despite the different emission scenarios, and all possible changes in water temperature and annual precipitation, our findings emphasize the urgent need for scientifically informed decisions to manage and preserve freshwaters.
... On the other hand, studies to date suggest that climate change will likely increase the loadings of non-point source pollution such as N and P to water bodies in the Nordic countries (Jeppesen et al., 2011;Hashemi et al., 2018;Pengerud et al., 2015) while the increasing average temperature may increase the stress on freshwater ecosystems and biodiversity (ECA, 2021). The climate change scenarios in Sweden project an increasing trend in annual precipitation, including extreme rainfall events, which may add to increase in water discharge (Eckersten et al., 2008;Grusson et al., 2021). ...
... Catchment-scale studies in Denmark have shown that nation-wide implemented measures to reduce nutrient loads were ignoring the fact that the response of catchments to measures is unique and a combination of multiple drivers such as precipitation, temperature, hydrology, farm practices, etc. (Hashemi et al., 2018;Hoffmann et al., 2020) are important drivers of loads. Another Danish study investigated the future nutrient loads in view of climate change scenarios and concluded that an increase in discharge and N transport is expected on an annual basis (Jeppesen et al., 2011). A higher temperature will create a low-oxygen induced reduction of nitrification leading to higher N concentrations in streams. ...
... Similar observations on flushing of nutrients following the first heavy rain after a dry-spell have been reported by other studies (Lisboa et al., 2020;Mellander and Jordan, 2021) as well. In addition, the crop rotation considers best timing to control weeds and pests, which influences the amount and pattern of N loads to waterbodies in different seasons (Jeppesen et al., 2011). On the other hand, higher evapotranspiration will also lead to higher nutrient concentrations in the water (Jeppesen et al., 2011). ...
Water quality related to non-point source pollution continues to pose challenges in agricultural landscapes, despite two completed cycles of Water Framework Directive actions by farmers and landowners. Future climate projections will cause new challenges in landscape hydrology and subsequently, the potential responses in water quality. Investigating the nutrient trends in surface waters and studying the efficiency of mitigation measures revealed that loads and measures are highly variable both spatially and temporally in catchments with different agro-climatic and environmental conditions. In Sweden, nitrogen and phosphorus loads in eight agricultural catchments (470–3300 ha) have been intensively monitored for >20 years. This study investigated the relationship between precipitation, air temperature, and discharge patterns in relation to nitrogen (N) and phosphorus (P) loads at catchment outlets. The time series data analysis was carried out by integrating Mann-Kendall test, Pettitt break-points, and Generalized Additive Model. The results showed that the nutrient loads highly depend on water discharge, which had large variation in annual average (158–441 mm yr⁻¹). The annual average loads were also considerably different among the catchments with total N (TN) loads ranging from 6.76 to 35.73 kg ha⁻¹, and total P (TP) loads ranging from 0.11 to 1.04 kg ha⁻¹. The climatic drivers were highly significant indicators of nutrient loads but with varying degree of significance. Precipitation (28–962 mm yr⁻¹) was a significant indicator of TN loads in five catchments (loamy sand/sandy loam) while annual average temperature (6.5–8.7 °C yr⁻¹) was a significant driver of TN loads in six out of eight catchments. TP loads were associated with precipitation in two catchments and significantly correlated to water discharge in six catchments. Considering the more frequent occurrence of extreme weather events, it is necessary to tailor N and P mitigation measures to future climate-change features of precipitation, temperature, and discharge.
... Increased climate variability and higher flows in winter from precipitation, snowmelt runoff, and changes in cropping patterns are expected to increase nutrient loading in rivers in temperate climates, including North America, Europe, and Japan (Alexander et al. 2020;Jeppesen et al. 2011;Onishi et al. 2020;Wilson et al. 2019b). As previously mentioned, nutrient losses in runoff are predicted to exceed nutrient uptake rates by terrestrial plants (Luo et al. 2020;Sperotto et al. 2019;Suddick et al. 2013;Zheng et al. 2020). ...
... Arctic regions are expected to experience a greater increase in temperature than other regions, especially the poles (Alexander et al. 2020;Bartosova et al. 2019;Jeppesen et al. 2011;Wade et al. 2018;Wilson et al. 2019a) and increased winter precipitation (Alexander et al. 2020;Bartosova et al. 2019;Jeppesen et al. 2011;Wilson et al. 2019b). However, surface warming and declining snowfall in recent decades have reduced snowcover, a process that has been intensified by a reduction in the Arctic surface albedo by 70% caused by a de-cline in the snow cover fraction, known as the surface albedo feedback . ...
... Arctic regions are expected to experience a greater increase in temperature than other regions, especially the poles (Alexander et al. 2020;Bartosova et al. 2019;Jeppesen et al. 2011;Wade et al. 2018;Wilson et al. 2019a) and increased winter precipitation (Alexander et al. 2020;Bartosova et al. 2019;Jeppesen et al. 2011;Wilson et al. 2019b). However, surface warming and declining snowfall in recent decades have reduced snowcover, a process that has been intensified by a reduction in the Arctic surface albedo by 70% caused by a de-cline in the snow cover fraction, known as the surface albedo feedback . ...
This study is a meta-analysis of global articles on hydrological nutrient dynamics to determine trends and consensus on (1) the effects of climate change-induced hydrological and temperature drivers on nutrient dynamics and how these effects vary along the catchment continuum from land to river to lake; (2) the convergence of climate change impacts with other anthropogenic pressures (agriculture, urbanization) in nutrient dynamics; and (3) regional variability in the effects of climate change on nutrient dynamics and water-quality impairment across different climate zones. An innovative web crawler tool was employed to help critically synthesize the information in the literature. The literature suggests that climate change will impact nutrient dynamics around the globe and exacerbate contemporary water quality challenges. Nutrient leaching and overland flow transport are projected to increase globally, promoted by extreme precipitation. Seasonal variations in streamflow are expected to emulate changing precipitation patterns, but the specific local impacts of climate change on hydrology and nutrient dynamics will vary both seasonally and regionally. Plant activity may reduce some of this load in non-agricultural soils if the expected increase in plant uptake of nutrients prompted by increased temperatures can compensate for greater N and P mineralization, N deposition, and leaching rates. High-temperature forest and grass fires may help reduce mineralization and microbial turnover by altering N speciation via the pyrolysis of organic matter. In agricultural areas that are at higher risk of erosion, extreme precipitation will exacerbate existing water quality issues, and greater plant nutrient uptake may lead to an increase in fertilizer use. Future urban expansion will amplify these effects. Higher ambient temperatures will promote harmful cyanobacterial blooms by enhancing thermal stratification, increasing nutrient load into streams and lakes from extreme precipitation events, decreasing summer flow and thus baseflow dilution capacity, and increasing water and nutrient residence times during increasingly frequent droughts. Land management decisions must consider the nuanced regional and seasonal changes identified in this review (realized and predicted). Such knowledge is critical to increasing international cooperation and accelerating action toward the United Nations's global sustainability goals and the specific objectives of the COP26.
... Similarly, in Lake Pontchartrain (Louisiana, USA), the internal phosphorus load accounts for approximately 30-44% of the total annual phosphorus load to the waterbody (Roy et al. 2012). Consequently, tangible benefits of external nutrient load reduction to a waterbody may take too long to manifest, whilst incurring huge costs (Jeppesen et al. 2011). For instance, at Lake Taihu, US $16.25 million was spent on nutrient control in 2007, but by 2013 nutrient load reductions had not yielded positive results and a massive cyanobacteria bloom occurred in the summer of that year (Merel et al. 2013). ...
... Therefore, costs may limit the application of external nutrient restriction programs in some areas, especially in low-income countries. Furthermore, the benefits of external nutrient load reductions can also be compromised by the effects of climate change on the watershed hydrology and nutrient loading dynamics, water temperature, lake mixing regime, and internal nutrient dynamics (Jeppesen et al. 2011). ...
Eutrophication of fresh waterbodies is a global phenomenon that is exacerbated by increases in agricultural activities, industrialization, and urbanization, all driven by the global increase in human population. This paper reviews the state of inland waterbodies in South Africa, identifying the major drivers of eutrophication and discussing how different sectors of the economy are negatively impacted by eutrophication. Data indicate that up to 76% of major water impoundments and approximately 70% of major river systems are eutrophic to hypereutrophic and experience protracted periods of cyanobacterial blooms, particularly in the summer months. Negative impacts of eutrophication on the agricultural sector, potable water supply and tourism are well documented and are becoming more explicit. Evidently, nutrient loading patterns into water bodies have changed and become more complex. Although wastewater treatment plants remain the major contributors of nutrient loads to most waterbodies, non-point sources including agricultural runoff, untreated sewage from leaking and overflowing sewer systems, as well as runoff from informal settlements, also make substantial contributions. As a result, the strategies employed to prevent eutrophication, including within-waterbody remediation programs have fallen short in reducing the trophic status of water impoundments and thus ameliorating the symptoms of eutrophication. Tailor-made, integrated management initiatives that target point source, non-point source, and internal nutrient loads are, therefore, required.
... Potentially, this could be due to climate change induced increases in winter precipitation (+17 %) which have been recorded over the past two decades and which would likely have increased rates of winter nitrate leaching across the catchment in recent years. Higher winter temperatures (DJF), which have increased 0.26°C between 2000(Met Office, 2022, would also have increased rates of soil nitrogen mineralisation thus making more nitrate available for leaching (Jeppesen et al., 2011). Alternatively, it could also be due to an increase in the cultivation of spring crops leaving more bare soils exposed over winter and vulnerable to leaching. ...
... BOD and reduce dissolved oxygen concentrations, thereby offsetting some of the water quality improvement gains made during the early 2000s. Conversely, mean winter (DJFM) discharge in the River Wensum has already increased by 13 % since 2000, with increased winter rainfall likely to increase leaching of nitrogen and pesticides from agricultural soils, whilst also increasing the risk of soil erosion, urban surface runoff and the activation of sewer storm overflows (Jeppesen et al., 2011;Miller and Hutchins, 2017). Hence, increased precipitation could potentially lead to increased riverine pollution with heavy metals, petrochemicals, pharmaceuticals, and other emerging contaminants such as microplastics over the coming decades. ...
The EU Water Framework Directive (WFD) is widely regarded as a seminal piece of environmental legislation. However, two decades since its inception, many European waterbodies are failing to meet its ambitious goal to ensure 'good' quantitative and qualitative status. Here, we investigate the impact of the WFD upon the environmentally sensitive yet heavily impacted River Wensum, a lowland arable catchment in eastern England. Compiling a dataset of 10,950 water quality samples collected from 57 sites across the catchment at approximately monthly intervals during 2000-2022, we assess the spatio-temporal dynamics of 12 priority pollutants, identify the major drivers of water quality change, and evaluate current and future compliance with WFD goals. Our analysis reveals improvements in wastewater treatment initiated significant declines (11-50 %) in the concentration of key sewage pollution indicators (phosphorus, ammonium, biological oxygen demand (BOD)) during the early 2000s. Conversely, agricultural pollution indicators (nitrogen, suspended solids, pesticides) displayed either limited change or a deterioration in water quality, with oxidised nitrogen concentrations in particular having increased 23 % during 2015-2022. Concentration spikes of organic chemical contaminants in recent years (propyzamide, tetrachloroethylene) raise concerns about increased riverine pollution from hazardous substances. Similarly, changes in winter (+13 %) and summer (-7 %) discharge over the past two decades have increased the risk of diffuse pollution mobilisation and reduced the dilution of point source pollutants, respectively. By 2022, 'good' or 'high' water quality status for organic matter pollution indicators (dissolved oxygen, BOD, ammonium) was achieved for >98 % of samples, however WFD compliance fell to just 46 % for phosphorus and 1.8 % for nitrogen. Projections to the end of the 3rd river basin management planning cycle (2027) reveal that whilst phosphorus compliance is likely to improve, nitrogen compliance failure will persist due to the existence of catchment legacy stores and climate change induced impacts on nitrogen mobilisation.
... As a result of the human-induced climate change, alterations in the form of precipitation (rain vs. snow) and inter-annual distribution of precipitation, increases in mean temperatures, changes in the carbon, nutrient, and hydrological cycles, and their impacts on lakes have become more evident (Bates et al. 2008;Jeppesen et al. 2011Jeppesen et al. , 2014. Physical changes that include warmer surface water temperatures, altered water levels, mixing regimes, altered thermal stratification, wind patterns, longer ice-free periods, and changes in water transparency have been reported in many lakes (Adrian et al. 2009;Coats et al. 2012;Vincent et al. 2012;Woolway et al. 2017;Woolway and Merchant 2019). ...
... On the one hand, Nõges et al. (2011) have suggested that precipitation events increase nutrient levels due to external loading and support algal biomass. On the other hand, although the reduction of freshwater runoff is thought to decrease external nutrient loading due to decreased precipitation (Giorgi and Lionello 2008;Jeppesen et al. 2009Jeppesen et al. , 2011, warmer conditions and the negative effects of water deficits may enhance the internal loading and lead to eutrophication, particularly in shallow lakes (Søndergaard et al. 2003;Beklioglu et al. 2007;Ö zen et al. 2010). Therefore, higher phytoplankton biomass and altered phytoplankton biodiversity are expected (Zohary et al. 2014;Jeppesen et al. 2009). ...
Phytoplankton biomass, diversity, functional groups (FGs), and environmental parameters in three shallow lakes were evaluated to show the inter-annual fluctuations in precipitation, lake surface area, and wind speed which might affect the community structure and distribution of phytoplankton. Three lakes (Taşkısığı, Little Akgöl, and Poyrazlar) in Sakarya province (Turkey) were sampled taking into account two periods (Period A and Period B). Monthly (PRE)–daily (dPRE) total precipitation, lake surface area, and monthly (WD)–daily (dWD) average wind speed values were obtained higher in Period B. Moreover, in Period B, probably due to increased runoff, high total phosphorus values were recorded which slightly triggers the increase in biomass. Besides, higher WD and dWD values have also caused biomass increase due to the reinforcement of nutrients to the water column from the sediment in this period. It is thought that the increase in the species richness and diversity values in Period B is related to the unstable environmental conditions as well as their relationship with water temperature, total phosphorus, orthophosphate, specific conductance, soluble silica, and pH. During the studied periods, 16 phytoplankton functional groups (FGs) were prominent in the total biomass; however, FGs F, N, X1, X2, Lo, and T were abundant during Period A, while Y, E, W1, and H1 were important components of phytoplankton during Period B. Light availability was low in both periods; therefore, FGs that prefer or are tolerant to low light conditions were dominant in the lakes. However, elevated light availability in some months of Period B has selected coda W1 and H1. Higher nutrient levels in Period B have also determined the distribution of the FGs, and FGs that prefer or are tolerant to high nutrient conditions were prominent in this period.
... All biological processes are sensitive to temperature changes. The temperature rise can contribute to intensive oxygen consumption, which increases the risk of a decrease in its content in water; changes in life expectancy of aquatic organisms, phenology of communities, and trophic interactions between species; an increase in the level of water bloom with cyanobacteria, their abundance and duration of vegetation (Jeppesen et al. 2005(Jeppesen et al. , 2011Mooij et al., 2005;Winder and Hunter, 2008;Paerl and Huisman, 2009). A temperature increase changes the availability of nutrients, promotes the formation of a summer deficit of dissolved oxygen in reservoirs, and increases internal phosphorus load. ...
... Our scenario study considers the effect of changes in nutrient loading and epilimnion temperatures through SSP and RCP scenarios. However, climate change may also alter precipitation which is positively related to nutrient loading by runoff (Özen et al., 2010;Jeppesen et al., 2011;Meerhoff et al., 2022). For example, in the far future, large increases in riverine N loading are projected by precipitation increases in highlyfertilized eastern China (Sinha et al., 2017). ...
... In particular, the increase in phytoplankton concentration during the last period of the season defies current interpretation. To address this, possible explanations and model improvements are proposed in line with the existing literature (e.g., Potužák et al., 2007;Jeppesen et al., 2011): ...
Given the increasing importance of data- and model-driven design and control in food production systems, this paper addresses the need to improve the reproducibility, replicability, and reusability of datasets, models, and modeling frameworks. While sensor data and machine learning-based control and operation of agricultural and aquacultural systems face reproducibility and replicability challenges, reusability is becoming critical for computational model-based design and planning of complex processes. This study evaluates the reusability of an existing pond aquaculture model and outlines a systematic, stepwise approach for reusability enhancements. The suggested methodology starts with an established reference model of a typical production fishpond and improves its reusability through pilot-scale experiments, covering key aspects of pond farming technologies. The reference model is subjected to stepwise reusability checks using measured data from the respective pilot units, progressing from simpler (reduced) to more complex (extended) cases. Each step concludes with the necessary parameter or sub-model refinements, which remain unchanged in subsequent steps. The refined model is validated with the measured data from other pilot experiments. This process can be repeated until satisfactory results are obtained. The resulting model is then tested to scale up a production pond model using limited case-specific input data. In addition, a hypothetically modified scenario is studied to address discrepancies between measured and simulated data.
... More frequent seasonal nitrate extremes during winter post-drought can have adverse ecological effects on downstream estuaries and lakes. Nitrates can persist for extended periods in water bodies, increasing the risk of eutrophication [5, 58,59]. Moreover, the excessive transport of nitrate from diffuse sources during post-drought periods affects groundwater even for longer periods, which could jeopardize current attempts to improve groundwater quality [7,30]. ...
Hydrological extremes can affect nutrient export from catchments to streams, posing a threat to aquatic ecosystems. In this study, we investigated the effects of hydrological drought on nitrate concentrations in the streamflow of 182 German catchments from 1980 to 2020. We found that across all seasons, 40% and 25% of the catchments showed significantly lower nitrate concentrations during drought and post-droughts respectively when compared to non-drought conditions. However, we observed pronounced spatial variability in the responses, particularly during winter droughts and post-droughts, with more catchments exhibiting higher nitrate concentrations. Specifically, nitrate concentrations were significantly higher in 25% of the study catchments during winter droughts, particularly in wetter catchments with low nitrogen retention. During winter post-droughts, nitrate concentrations are significantly higher in 19% of the catchments, especially in wetter catchments with more nitrogen surplus. Moreover, the likelihood of nitrate seasonal extremes increased by 6% during winter post-drought in our study catchments. Considering the projected increase in the frequency of droughts in Germany, the increase in nitrate concentrations during the corresponding post-drought periods poses a potential threat to aquatic ecosystem health.
... 76 Furthermore, climatic changes affecting the balance of precipitation during the year can have a major impact on the transport of nitrogen and phosphorus into rivers and the subsequent eutrophication of lakes. 84,85 The rainy season can cause a rapid and significant increase in nutrient content and subsequent change in the composition and structure of the phytoplankton of the lentic ecosystem. 86,87 Local adaptation to any of the above-mentioned environmental variables may be related to mechanisms that effectively prevent immigrant genotypes from being incorporated into local populations, such as the priority effect, 88 resulting in rapid sympatric speciation. ...
... The combination of temperature increases and eutrophication has been reported to increase cyanobacterial abundances (Jeppesen et al., 2009(Jeppesen et al., , 2011. The success of nitrogen-fixing Cyanobacteria under nutrient-limited conditions is still under debate (Reynolds, 1999;Schindler et al., 2008). ...
Harmful algal blooms are important threats to reservoir condition. Over a 15-year period, we sampled fiveArgentinian reservoirs to identify the responsible species for harmful algal blooms and determine the waterquality factors driving their occurrence. These reservoirs exhibit diverse morphological and hydrological char-acteristics and are distributed across varying climatic zones. Cyanobacterial blooms included an array of species,including toxin producers such as Raphidiopsis raciborskii, Aphanizomenon gracile, and Microcystis aeruginosa. Incontrast, dinoflagellate blooms were predominantly characterized by Ceratium. The cyanobacterial blooms pri-marily occurred in the shallower reservoirs located in warmer regions, whereas dinoflagellate blooms occurredwhere temperatures were lower. The most intense blooms occurred during the summer, and although cyano-bacterial and chlorophyte blooms co-occurred, they never coexisted with dinoflagellate blooms. We identifiedcyanotoxins in the reservoirs over the past three years, a phenomenon previously unreported in the region. Giventhat these reservoirs are drinking water sources for human populations, ongoing and systematic monitoring isneeded to protect public health. Controlling the proliferation of algae and cyanobacteria in reservoirs requiresresource management at the watershed level, and in the case of the Itiyuro and El Lim�on requirea binational management with Bolivia.
... Lakes play an important role in regulating ecological balance at global and regional scales, mainly by maintaining biodiversity, purifying water bodies, and regulating local [1][2][3]. However, lakes are becoming increasingly threatened by agricultural modernization, industrialization, and urbanization [4][5][6]. ...
Since July 2022, the Yangtze River basin has experienced the most severe hydro-meteorological drought since record collection started in 1961, which has greatly affected the ecological environment of the Dongting Lake (DTL) basin. To investigate the effects of drought events on the eutrophication and phytoplankton community structure of DTL, the lake was sampled twice in August and September 2022 based on the water level fluctuations resulting in 47 samples. Furthermore, we combined the comprehensive trophic level index (TLI) and phytoplankton Shannon–Wiener diversity index (H) to characterize and evaluate the eutrophication status. The key influencing factors of the phytoplankton community were identified using redundancy analysis (RDA), hierarchical partitioning, and the Jaccard similarity index (J). Our results showed that the TLI of DTL changed from light–moderate eutrophication status (August) to mesotrophic status (September), whereas the H changed from light or no pollution to medium pollution. The phytoplankton abundance in August (122.06 × 104 cells/L) was less than that in September (351.18 × 104 cells/L) in DTL. A trend in phytoplankton community succession from Bacillariophyta to Chlorophyta and Cyanophyta was shown. The combination of physiochemical and ecological assessment more accurately characterized the true eutrophic status of the aquatic ecosystem. The RDA showed that the key influencing factors in the phytoplankton community were water temperature (WT), pH, nitrogen and phosphorus nutrients, and the permanganate index (CODMn) in August, while dissolved oxygen (DO) and redox potential (ORP) were the key factors in September. Hierarchical partitioning further indicated that temporal and spatial variations had a greater impact on the phytoplankton community. And the J of each region was slightly similar and very dissimilar, from August to September, which indicated a decreased hydrological connectivity of DTL during drought. These analyses indicated that the risk to the water ecology of DTL intensified during the summer–autumn drought in 2022. Safeguarding hydrological connectivity in the DTL region is a prerequisite for promoting energy flow, material cycle, and water ecosystem health.
... The availability of nutrients could be sustained by the changes in rainfall patterns under the changing climate. Higher rainfall could lead to more significant nutrient inputs to water bodies through surface runoff within the watershed (76,77). In addition, heavy storms can play a vital role for destratification of the water column and may enhance flushing (78). ...
Harmful cyanobacterial blooms (CyanoHABs) impact lakes, estuaries, and freshwater reservoirs worldwide. The duration, severity, and spread of CyanoHABs have markedly increased over the past decades and will likely continue to increase. This article addresses the universal phenomena of cyanobacterial blooms occurring in many freshwater ecosystems worldwide. Based on analysis of ecophysiological traits of bloom-forming cyanobacteria and their interactions with environmental processes, we summarize and decipher the driving forces leading to the initiation, outbreak, and persistence of the blooms. Due to the coupling effects of eutrophication, rising CO 2 levels and global warming, a multidisciplinary joint research approach is critical for better understanding the CyanoHAB phenomenon and its prediction, remediation, and prevention. There is an urgent need to evaluate and guide proper use of bloom control techniques at large scales, using science-based and environmentally friendly approaches.
Expected final online publication date for the Annual Review of Environment and Resources, Volume 48 is October 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... However, riverine N management is extremely challenging due to not only the large quantity of anthropogenic N that is added to the land surface (9, 10) but also the complexity of N transformation, the unknown composition of different forms of N and their transport in soils and inland water bodies. These delivery pathways are themselves impacted by changing climatic conditions, especially in the form of precipitation and temperature changes (11)(12)(13)(14)(15)(16). How these alterations will translate to changes in N loading is of great concern for water quality protection and agricultural nutrient management. ...
Climate change, especially in the form of precipitation and temperature changes, can alter the transformation and delivery of nitrogen on the land surface and to aquatic systems, impacting the trophic states of downstream water bodies. While the expected impacts of changes in precipitation have been explored, a quantitative understanding of the impact of temperature on nitrogen loading is lacking at landscape scales. Here, using several decades of nitrogen loading observations, we quantify how individual and combined future changes in precipitation and temperature will affect riverine nitrogen loading. We find that, contrary to recent decades, rising temperatures are likely to offset or even reverse previously reported impacts of future increases in total and extreme precipitation on nitrogen runoff across the majority of the contiguous United States. These findings highlight the multifaceted impacts of climate change on the global nitrogen cycle.
... High HLR and N load can result in low relative N removal in wetlands. However, absolute N removal may be of greater concern, as maximizing the amount of N removed will decrease eutrophication effects in downstream water bodies (Smith, 2003;Jeppesen et al., 2011). Thus, placing wetlands where large quantities of agricultural runoff can pass through them is paramount for high absolute N removal, and may be advisable even if resulting relative N removal is low. ...
Wetlands in agricultural areas mitigate eutrophication by intercepting nutrient transports from land to sea. The role of wetlands for nutrient removal may become even more important in the future because of the expected increase in agricultural runoff due to climate change. Because denitrification is temperature dependent, wetland nitrogen (N) removal usually peaks during the warm summer. However, climate change scenarios for the northern temperate zone predict decreased summer and increased winter flows. Future wetlands may therefore shift towards lower hydraulic loading rate and N load during summer. We hypothesised that low summer N loads would decrease annual wetland N removal and tested this by examining 1.5-3 years of continuous N removal data from created agricultural wetlands in two regions in southern Sweden (East and West) during different periods. West wetlands showed relatively stable hydraulic loads throughout the year, whereas East wetlands had pronounced no-flow periods during summer. We compared East and West wetlands and tested the effects of several variables (e.g., N concentration, N load, hydraulic load, depth, vegetation cover, hydraulic shape) on annual absolute and relative N removal. We found no difference in annual N removal between East and West wetlands, even though summer N loads were lower in East than in West wetlands. A possible explanation is that stagnant water conditions in East wetlands suppressed decomposition of organic matter during summer, making more organic matter available for denitrification during winter. Absolute N removal in all wetlands was best explained by N load and hydraulic shape, whereas relative N removal was best explained by emergent vegetation cover and hydraulic shape. This study highlights the importance of design and location of agricultural wetlands for high N removal, and we conclude that wetlands in a future climate may remove N from agricultural runoff as efficiently as today.
... northernmost lake: 57°62′21″ N, 10°34′66″ E; southernmost lake: 54°71′07″ N, 11°57′68″ E; westernmost lake: 56°55′69″ N, 8°13′82″ E; easternmost lake: 55°69′02″ N, 12°58′06″ E). MostDanish lakes are relatively small, shallow and nutrient rich due to intensive agriculture and urban expansion(Jeppesen et al., 2011;Søndergaard et al., 2020). ...
Fish community structure is affected by a range of lake characteristics, including the cover of macrophytes that provide spawning habitats, nursery area, refuge against predators, and food.
We assessed fish–macrophyte relationships at both lake and point scale using an extensive dataset from 88 Danish shallow lakes (maximum depth ≤4.5 m). At lake scale, we used mean values from fish and macrophyte community samples for all lakes, in total 88 samples. The point scale data were derived from multiple points in each lake (in total 595 samples) where both macrophytes and fish were sampled, allowing us to assess within‐lake variations.
We found generally negative relationships between macrophyte cover and fish abundance and biomass, which was strongest at point scale. Contrary to macrophytes, chlorophyll a showed positive relationships with fish abundance—except for perch and all fish <10 cm, which did not show significant relationships. The deeper and more eutrophic the lakes, the more the fish tended to occupy points covered by macrophytes. The abundances of species such as roach and bream were negatively related to macrophyte cover, but, for perch, this relationship was not significant.
Our results suggest that fish abundance and biomass were associated with a combination of factors that are often intercorrelated and difficult to isolate. The relationship between fish abundance and biomass and macrophyte cover may depend on, among other factors, fish species, fish size, and the characteristics of the individual lakes.
... Shallow lakes are thought to be more vulnerable to climate change than deep lakes (Kundzewicz et al. 2008;Jeppesen et al. 2009Jeppesen et al. , 2011Kernan et al. 2010;Li et al. 2023;Meerhoff et al. 2022). High temperature and precipitation resulting from climate change in northern temperate region may further enhance eutrophication in shallow lakes (Jeppesen et al. , 2015Moss et al. 2012;Free et al. 2022). ...
Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community in fully mixed shallow lakes, we manipulated water depth and nutrients in a lake mesocosm experiment in north temperate Estonia and followed the microbial community dynamics over a 6-month period. The experiment was carried out in Lake Võrtsjärv-a large, shallow eutrophic lake. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on the bio-masses of bacterial and heterotrophic nanoflagellates (HNF) (RM-ANOVA, p < 0.05). Nutrients affected positively and depth negatively the mean size of individual HNF and ciliate cells (RM-ANOVA; p < 0.05). The interactions of depth and nutrients affected positively the biomass of bacterivorous and bacteri-herbivorous ciliates and negatively the biomass of predaceous ciliates (RM-ANOVA; p < 0.05). Bacterivorous ciliates had lowest biomass in shallow and nutrient-rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.
... The importance of zooplankton as an indicator of ecological conditions stems from its position in the food web, sandwiched between the top-down regulators (fish or jellyfish) and bottom-up factors (phytoplankton), thus providing information about the relative significance of top-down and bottom-up controls and their impact on water clarity (Jeppesen et al., 2011). Zoooplankton is mentioned in the WFD CIS Monitoring Guidance (2003) as a 'supportive/interpretative parameter''. ...
The main goal of gelatinous plankton monitoring is to determine species composition, patterns of its
distribution, biomass, abundance, and, using obtained data along with the other parameters, to
identify their role in trophic webs and to assess their impact on the ecosystem functioning.
The objectives of gelatinous plankton monitoring:
• Identification of species composition, their abundance, biomass and spatial distribution;
• Early registration of new non-native gelatinous macroplankton species introduction in the
region;
• Study of seasonal, , interannual and long-term variability in macrozooplankton abundance,
biomass and species composition;
• Study impact on the ecosystem state.
... Nitrogen (N) is one of the most essential nutrients in marsh ecosystem, which plays important roles in driving many ecological processes such as participating in the synthesis of N-containing compounds (protein, nucleic acids, chlorophyll and enzyme) and controlling the metabolism of plants and microorganisms (Jeppesen et al., 2011;Alldred et al., 2017;Hester et al., 2018). Generally, the distribution of mineral N in soils (Bai et al., 2012; and the transfers of N in tissues of plant (Cott et al., 2018;Tegeder and Masclaux-Daubresse, 2018) can influence the stability of marsh ecosystem. ...
To determine the potential impacts of exogenous nitrogen (N) enrichment on distribution and transfer of N in Suaeda salsa marsh in the Yellow River Estuary, the variations of N in plant-soil system during the growing season were investigated by field N addition experiment. The experiment included four treatments: NN (no N input treatment, 0 gN m−2 yr−1), LN (low N input treatment, 3.0 gN m−2 yr−1), MN (medium N input treatment, 6 gN m−2 yr−1) and HN (high N input treatment, 12 gN m−2 yr−1). Results showed that N additions generally increased the contents of total nitrogen (TN), ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) in different soil layers and the increasing trend was particularly evident in topsoil. Compared with the NN treatment, the average contents of TN in topsoil in the LN, MN and HN treatments during the growing season increased by 10.85%, 30.14% and 43.98%, the mean contents of NH4+-N increased by 8.56%, 6.96% and 14.34%, and the average contents of NO3−-N increased by 35.73%, 45.99% and 46.66%, respectively. Although exogenous N import did not alter the temporal variation patterns of TN contents in organs, the N transfer and accumulation differed among tissues in different treatments. With increasing N import, both the N stocks in soil and plant showed increasing trend and the values in N addition treatments increased by 9.43%–38.22% and 13.40%–62.20%, respectively. It was worth noting that, compared with other treatments, the S. salsa in the MN treatments was very likely to have special response to N enrichment since not only the period of peak growth was prolonged by about 20 days but also the maximum of TN content in leaves was advanced by approximately one month. This paper found that, as N loading reached MN level in future, the growth rhythm of S. salsa and the accumulation and transference of N in its tissues would be altered significantly, which might generate great impact on the stability and health of S. salsa marsh ecosystem.
... Concentrations of DOM in sediment pore water are normally orders of magnitude higher than those in overlying water, serving as an important source of DOM input into water column, especially in shallow lakes (Zhu et al., 2022). Climate change and anthropogenic water recharge have major implications for lake water balance (Jeppesen et al., 2011; Tian et al., 2020), causing uctuations in water level and salinity and increasing frequency of droughtrewetting in littoral zone, which in uences DOM migration and transformation in sediments and affects lake system DOM cycling. ...
Climate change and anthropogenic activities cause salinity fluctuations and frequent drought-rewetting process in lacustrine littoral zones. However, joint effects of these processes on quality and quantity of dissolved organic matter (DOM) in pore water and bacterial communities in sediments are not well understood. An experiment was conducted to attempt to fill the above gaps, the results showed that the joint effects of higher salinity (6,000 mg/L) and drought-rewetting process were to retain more humified, more aromatic, and less bioavailable DOM, and to maintain lower DOM concentrations in pore water. The drought-rewetting process magnified influence of salinity on bacterial communities. Before the drought-rewetting process, Hydrogenophilaceae, Oxalobacteraceae, and Flavobacteriaceae participated in the DOM transformation, while Hydrogenophilaceae, Desulfobacteraceae, Anaerolineacea, Planococcaceae, and Clostridiaceae were associated with DOM components after this process. The drought-rewetting process greatly increased significant positive correlations ( P <0.05) among bacteria, which was consistent with Stress Gradient Hypothesis and destabilized the bacterial communities. Higher (6,000 mg/L) or lower (1,200 mg/L) salinity were all not conducive to stability of bacterial communities in Shahu Lake. The results of this study may provide ideas for further investigating DOM transformation and cycling in brackish-water lakes.
... During this period, the unfavourable water balance was exacerbated by the occurrence of higher temperatures. A reduced yield is a typical response to water stress, as both the photosynthetic intensity and the plant growth processes are reduced [53][54][55][56][57]. High temperatures combined with low rainfall increase the loss of nutrients (N, P, K), particularly in poor soils [58]. Adequate weather conditions occurred in the growing seasons of 2016/2017 and 2018/2019, which resulted in higher yields (by 2.64 t and 1.72 t ha −1 , respectively) as compared to the season of 2017/2018. ...
The present state of knowledge and biotechnological advances have allowed the potential of microorganisms to be used effectively in crop cultivation. A field study on the use of commercial bacterial preparations in the cultivation of winter wheat (Triticum aestivum L.) was carried out in the years 2017–2019 at the Educational and Experimental Station in Tomaszkowo (53°71′ N, 20°43′ E), Poland. This study analysed the effect of commercial microbial preparations containing Paenibacillus azotofixans, Bacillus megaterium and Bacillus subtilis, applied during the winter wheat growing season, on the grain yield, protein content, leaf greenness index (SPAD), the course of photosynthesis and the N-NO3, N-NH4 and P contents in the soil. The highest grain yield was noted following the application of mineral fertilisation and the three microbial preparations in combination (Paenibacillus azotofixans, Bacillus megaterium and Bacillus subtilis), as well as NPK with Paenibacillus azotofixans, in relation to mineral fertilisation alone (by 19.6% and 18.4%, respectively). The microbial preparations had a significant effect on the leaf greenness index (SPAD) at both test dates. No interaction was recorded between the years of study and the preparations applied on the SPAD values. The highest leaf photosynthetic index at both observation dates was noted for the application of NPK + P. azotofixans, as well as for NPK and all the preparations combined (P. azotofixans, B. megaterium, B. subtilis). The highest N-NO3, N-NH4 and P contents in the soil were obtained using NPK and all microbial preparations combined. Strong correlations were found between the SPAD index and the photosynthetic index value and the protein content in wheat grains and between the N-NO3, N-NH4 and P contents in the soil and the wheat grain yield.
... The unidirectional impacts of greenhouse gas mitigation on climate change (Montzka et al., 2011) and, consequently, on freshwater eutrophication (Jeppesen et al., 2011) as well as the symptoms associated with it (Ficke et al., 2007;Paerl and Paul, 2012) have been well examined. However, the complex relationship between greenhouse gas emissions and the eutrophication of freshwaters needs more investigation (Beaulieu et al., 2019;Grasset et al., 2020;Sepulveda-Jauregui et al., 2018;Vachon et al., 2020). ...
Eutrophicated inland water bodies are noticed to be one of the contributing factors to greenhouse gas (GHGs) emissions. Direct discharge of untreated or partially treated water is a major concern. Microalgae-based technology and management are regarded as one of the potential nature-based approaches to combat eutrophication. In turn, the microalgae facilitate the recovery of GHGs contributing compounds in the form of organic biomass. The recovered algal biomass can be harnessed for the production of biofuels and other bio-products, like biofertilizer, using anaerobic digestion. By virtue, circular bio-economy can be achieved alongside mitigating GHGs emissions. Before implementing, it is vital to thoroughly explore the links between the process and potential alternatives for wastewater treatment, waste valorization, biofuel production, and land usage. Thus, the present review discusses the impact of eutrophication on ecology and environment, current technologies for mitigating GHGs, and energy recovery through the anaerobic digestion of algal biomass. Further, the processes at the intercept of wastewater treatment and biogas production were reviewed to leverage the potential of anaerobic digestion for making a circular bioeconomy framework.
... Additionally, while 100 Tg N per year was consumed by global agriculture, only 17% was used effectively by crops, and the rest entered the surrounding environment . This has profoundly affected lake eutrophication, the nitrogen dynamics in cultivated land, nitrogen migration, and catchment transformation (Jeppesen et al., 2011;Xin et al., 2019). ...
Nitrogen dynamics at ecosystem levels profoundly impact the Earth’s surface system due to their environmental and ecological significance. Exploring the sources and transformation of nitrogen in various Critical Zones is vital to understanding biogeochemical cycles and sustainable development. This study summarized nitrogen characteristics in soil profiles and nitrogen dynamics in diverse terrestrial ecosystems based on data from typical Critical Zones of China. The results indicated that nitrogen accumulates in the deep soils of cropland ecosystems due to intensive fertilizer applications, which potentially harms soil functions and water quality. Therefore, it is necessary and meaningful to take adequate measures to alleviate nitrogen accumulation in deep soils. Additionally, surplus nitrogen transported into groundwater and riverine systems from soil has emerged as an important issue for environmental management. There are serious nitrogen pollution issues in many river water and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. Systematic and long-term observational studies are needed to achieve the ultimate goal of ecological conservation and high-quality development. Therefore, future research should consider monitoring and evaluating ecosystems based on the long-term Critical Zone Observatories networks to advance appropriate environmental management strategies that adapt to nature’s rules and strengthen the ecosystem service function for sustainable development.
... Numerous authors have investigated the impact of climate change on hydrology, nutrient loads and ecosystem impacts at different scales (Jeppesen et al., 2009, Jeppesen et al., 2011Alcamo and Olesen, 2012;Arias et al., 2021). Land use changes both alone and combined with climate changes have also been explored in many studies in the Nordic-Baltic region, including the River Odense catchment that was appointed as one of the Danish pilot river basins for implementation of the EU WFD (Environment Centre Odense, 2007;Karlsson et al., 2016;Molina-Navarro et al., 2018;Trolle et al., 2019). ...
A societal transformation towards bio-economy will have extensive implications for land use in Nordic countries. These expected changes in land use combined with a changing climate, will have unknown consequences for water quality and quantity. To address this issue, we used the Nordic Bio-economic Pathways (NBPs), which describe five possible future scenarios (NBP1-5) for the Nordic bio-economy in 2050. The NBPs were quantified by experts using local knowledge and translated into modelling scenarios. The SWAT model was applied to simulate the effect of NBP scenarios for changes in farming intensity (varying chemical fertilizer and manure application rates), land cover change (agriculture vs forest) and nutrient loss mitigation (buffer strips and wetlands) in the River Odense catchment. Subsequently, the NBPs were combined with medium (RCP4.5) and strong (RCP8.5) climate change scenarios for the period 2041–2070 utilising the median of an ensemble of 20 and 57 climate models, respectively. Our study clearly showed that only one of the pathways, namely NBP1 (sustainability first), would enable catchment managers to fulfil the Water Framework Directive reduction target set for the total nitrogen loads in the River Odense catchment by reducing total nitrogen loads by 66%. One of the pathways (NBP5; growth first) caused an increase in the average annual total nitrogen loads by 12%, while the NBP3 scenario (self-sufficiency) reduced the total nitrogen loads with 18% compared to 2% in the case of NBP2 (business as usual) and 29 % for NBP4 (cities first). Surprisingly, climate change had only limited added impacts on the total nitrogen loads due to increased nitrogen uptake of crops. Our study provides policy makers with information on the influence of the different choices and directions taken towards transforming societies into bio-economies in the future.
... Otherwise, the increased ET was expected to decline the N loading due to a low-oxygen induced reduction of the nitrification (Jeppesen et al., 2011). On average, 54% of nitrate leaching occurred under some crop, while the highest average nitrate leaching during the cropless season occurred at L5 (60%) (Fig. S2). ...
Intensive agricultural practices increase agrochemical pollution, particularly nitrogen (N) based fertilizers, which present an environmental risk. This study aims to evaluate long-term (2009-2020) data on soil water regime and nitrate dynamics at an agricultural experimental site on fine-textured soils and to better understand the implications of N management in relation to groundwater pollution. The field site is located in the Biđ field (eastern Croatia), in the proximity of the Sava river. Zero-tension lysimeters were installed at six selected locations. Lysimeters were used to monitor the water regime, i.e., outflows in which nitrate concentration was measured, while additional soil-water samples were collected via 4 and 15-meter-deep monitoring wells. Soil hydraulic parameters were estimated by combining the laboratory measurements, and estimation in RETC software. Water regime and nitrate leaching in lysimeters were simulated using HYDRUS-1D for each year to allow crop rotation and to evaluate their effects individually. The HYDRUS-1D model successfully reproduced lysimeter outflows and nitrate dynamics, which was confirmed with high R 2 values (water: 93% above 0.7, and nitrate: 73% above 0.7) indicating the good performance of the model simulating nitrification chain reactions. Principal component analysis (PCA) was performed to identify the relationships among all soil properties and environmental characteristics. The results showed the complex interaction of soil hydraulic properties, precipitation patterns, plant uptake, and N application. All locations have a decreasing trend of nitrate leaching over the investigation period. Most of the lysimeter outflows and elevated nitrate concentrations were connected to the wet period of the year when the soil was saturated, and evapotranspiration was low. The results of this study show that it is important to optimize N fertilizer applications for each particular environmental condition to reduce nitrate loss. The study indicates the importance of long-term field studies, key for agro-hydrological modeling and the improvement of agricultural practices.
... Instantaneous nitrate concentrations have been observed to often increase with river discharge in agriculture land as rising water tables flush nitrate out of nitrogen-rich shallow soils (Ebeling et al., 2021a;Zhi and Li, 2020). Nitrate fluxes are typically lower at low flow, where high temperature and evapotranspiration reduce discharge, elongate residence times, and possibly promote nitrogen removal (Benettin et al., 2020;Jeppesen et al., 2011). ...
Nitrate is one of the most widespread and persistent pollutants in our time. Major advances have been made in the past decades, although our understanding of its predominant drivers and forecasting capabilities still lagged behind across gradients of climate, land use, and geology at the continental scale. Here we collated nitrate data from 2061 rivers along with 32 watershed characteristic indexes and developed machine learning models to reconstruct long-term mean (multi-year average) nitrate concentrations in the contiguous United States (CONUS). The trained models show similarly satisfactory model performance and can predict nitrate concentrations in chemically-ungauged places with about 70% accuracy. Further analysis of the trained models also revealed that five (out of 32) indexes (drivers) can explain about 69% of spatial variations in nitrate concentrations. The five drivers are nitrogen application rates Nrate and urban area Aurban% (human drivers), mean annual precipitation and temperature (climate drivers), and sand percent Sand% (soil property driver). Nitrate concentrations in rivers draining undeveloped sites are primarily modulated by climate and soil property; they decrease with increasing Sand% and mean discharge. Nitrate concentrations in agriculture and urban sites increase with Nrate and Aurban% until reaching their apparent maxima around 10,000 kg/km²/yr and around 25%, respectively. Results indicate that mean nitrate concentrations may remain similar or increase with growing human population. In addition, nitrate concentrations can grow even without human input, as warming escalates water demand and reduces discharge in many places. These results allude to a conceptual model that highlights distinct impacts of drivers: while human drivers predominate nitrogen input to land and rivers, climate drivers and soil properties modulate its transport and transformation, the balance of which determine long-term mean concentrations. Such mechanism-based insights and forecasting capabilities are essential for water management as we expect changing climate and growing agriculture and urbanization.
... As alterações do clima e do uso do solo na bacia hidrográfica de contribuição ao lago também podem provocar o aumento das cargas de nutrientes afluentes. Em bacias agrícolas, mudanças na precipitação e decomposição de matéria orgânica podem alterar principalmente a importação de nutrientes para corpos d'água (ADRIAN et al., 2009;JEPPESEN et al., 2011). As cargas de nutrientes são modificadas não apenas pela precipitação, mas também pelo aumento populacional, demandando maior quantidade de alimentos, que levará a modificações no uso do solo e no gerenciamento na agricultura, incluindo as mudanças nas culturas escolhidas, na rotação de culturas etc. (OLESEN et al., 2007). ...
Climate change can cause drastic changes in lake ecosystems, especially due to the increase in temperature and changes in precipitation, promoting, among other factors, an increase in the nutrients input and, therefore, eutrophication. This paper estimated the projected flow and nutrients load (NO3⁻, PO4–3) at the Mangueira lake — a large subtropical shallow lake, located in southern Brazil. The projections were based on the AR5 products for RCP 2.6, RCP 4.5, and RCP 8.5 scenarios. In each scenario, data from as many as 39 global climate models were used to estimate the projected values of flow and nutrients in two 30-year time intervals centered at 2,030 (near future) and 2,070 (long future). Results show the increase in flow is more likely, with a greater agreement between AR5 products when compared to AR4 products estimated in previous work. The pattern of increase also prevails in the projections of nutrient loads. The nutrients analyzed show an average annual load increase of 9.34% in the near future and RCP 2.6 scenario, while in the long future and RCP 8.5 scenario, this value rises to 22.48%. Mitigation measures should be studied to reduce the nutrient inputs and to preserve a good ecological status of the lake.
Keywords:
climate change; flow projections; nutrient load projections
... Other concerns regarding climate change outcomes on contaminant dynamics effects include higher sediment and nutrient load transports to water bodies [19][20][21][22][23][24][25]. For example, Ockenden et al [4] evidenced that high flow events, which are expected to increase under a climate change scenario, transported >90% of sediment loads from two rural headwater catchments in the UK. ...
Anthropogenic activities are affecting marine ecosystems, notably coastal ones, in multiple ways and at increasing rates, leading to habitat degradation, loss of biodiversity, and greater exposure of flora and fauna to chemical contaminants, with serious effects on ocean health. Chemical pollution, in particular, is a significant negative stressor for aquatic ecosystems, both oceanic and coastal, and has recently been identified as a priority for conservation efforts. Metals and metalloids, in particular, present environmental persistence, bioavailability, tendency to bioaccumulate along the trophic chain, and potential toxic effects. However, the current scenario of climate change is increasingly affecting the aquatic environment, altering water mass flows and the transport of pollutants, aggravating toxic effects and ecological risks. Moreover, although traditional sources of contamination have been studied for decades, many knowledge gaps persist, in addition to the emerging effects of climate change that are still poorly studied. In this regard, this review aims to discuss climate change implications for metal and metalloid dynamics in aquatic ecosystems and its context within the Decade of Ocean Sciences. We also discuss how an increasing interest in plastic pollution has led to
contamination by metals and metalloids being neglected, requiring mutual efforts to move forward in the understating of the negative and often lethal impacts of this type of pollutants, thus aiming at prioritizing contamination by metals and metalloids not just in the oceans, but in all water bodies.
... crop uptake, leaching from the soil, nitrification, denitrification, etc) that are temperature-and precipitation-dependent. Thus, the alteration of the hydrological cycle and thermal regimes under climate change scenarios is expected to significantly affect both the magnitude and timing of N processing and delivery to inland waters and ultimately the sea [7][8][9]. Changes in precipitation frequency, intensity, and duration alter watershed hydrological cycles by emphasizing extreme hydrologic events (floods and droughts) and, consequently, the seasonality of N load generation and transport from land to aquatic ecosystems via runoff. Reductions in precipitation and higher evaporation rates are expected to decrease discharge in summer, whereas higher winter rainfall or periods with short-term but heavy precipitation likely result in increased discharge and N leaching from agricultural areas outside the growing season [10,11]. ...
Temperature is one of the most fundamental drivers governing microbial nitrogen (N) dynamics in rivers; however, the effect of climate change-induced warming on N processing has not been sufficiently addressed. Here, annual, and seasonal (spring and summer) N loads exported from the Po River watershed (Northern Italy), a worldwide hotspot of eutrophication and nitrate pollution, are investigated in relation to water temperature trends over the last three decades (1992–2019). Despite large inter-annual variations, from the early 1990s, the Po River experienced a significant reduction in total N loads (-30%) represented mainly by nitrate, although agricultural N surplus in croplands and other watershed conditions have remained constant. In parallel, the Po River water is steadily warming (+0.11°C yr-1, for average annual temperature) and the number of warm days is increasing (+50%, in the spring-summer period). The inverse relationship between water temperature and N loads strongly indicated that the higher temperatures have boosted the denitrification capacity of river sediments along the lowland reaches. Overall, over the last three decades, annual total N loads declined by around one-third due to a near 3°C increase in temperature and this evidence was even more marked for the summer season (-45% for TN loads and +3.5°C for temperature). Based on these observations, it is suggested that near-term effects of climate change, i.e., warming and an increase in the duration of low-flow periods in rivers, may have negative feedback on eutrophication, contributing to the partially buffer the N export during the most sensitive period of eutrophication.
... However, with the rapid development of economic and industrialization, large amounts of domestic sewage, industrial, and farming wastewater are discharged into rivers. The deterioration of water quality and severe ecological issues gradually appeared, including drinking water shortage and pollution, biodiversity reduction, and eutrophication (Jeppesen et al. 2011;Hu et al. 2020). Water pollution constantly changes the physical, chemical, and biological quality of the polluted water, soil, and living species; as a consequence, the food chain can be altered and affect human health (Duan et al. 2013). ...
Assessment of river quality has been attracting a great deal of attention because of its important implications for the living environment of human beings and aquatic organisms. This study investigated the spatial and temporal variation of water quality and its possible driving factors of Guanting Reservoir Basin. For this purpose, water quality was assessed with the Canadian Council of Ministers of the Environment Water Quality Index, together with nutrient inputs and social-economic data which were collected and analyzed during the period 2009-2019. The results showed that the overall water quality in Guanting Reservoir increased over time and was rated as "good" during the studied decade. Spatially, water quality in tributary upstream of Yanghe River and Sanggan River was better than that in Guishui River, resulting in better quality in West Reservoir than in East Reservoir. Among water quality indices, total nitrogen was the main pollutant affecting the water quality of the studied area. In addition, principal component analysis and correlation analysis were applied to evaluate the relationships between the socio-economic factors and water quality variation. Urbanization and industry structure were significantly correlated with the water quality variation in upstream tributaries. The findings provide insightful understanding into the spatio-temporal variations of water quality and the associated driving factors of Guanting Reservoir basin, which would help managers in executing theoretical reference for water quality protection.
... This balance is, as in many natural systems, delicate, and subject to tipping into imbalance as a result of only small changes in any of its elements. In terms of the likely effects of climate change, loads of N (Jeppesen et al., 2011) and P (Jeppesen et al., 2009) from cultivated areas to surface waters will probably increase, rendering efficient functioning even more important. ...
This chapter gives an overview of the types of (semi-) constructed wetlands, and how these can be applied for the management and, specifically, the retention of agricultural diffuse loads so that they do not reach inland surface waters.
To achieve an effective wetland design, a multi-faceted approach is required, which accounts for the location of the wetland in the landscape (including riparian wetlands) and the compounds subjected to removal/retention, e.g., inorganic nutrients, pesticides. Agricultural diffuse loads of nonpoint source-nature will be introduced which are critical regarding (semi-)constructed wetlands, and an outlook given to related ecological issues as ecosystem services and the phenomenon of eutrophication. This chapter does not provide a detailed technical description of the processes operating in wetlands, rather an overview of their functionality and key considerations.
The chapter is primarily a review of relevant literature (seminal papers and most recent ones) focusing on the retention of inorganic nutrients from reaching surface waters.
An overview is provided on the most important characteristics of (semi-)constructed wetlands in retaining diffuse loads from entering inland surface waters. Wetlands, and their location, is among the utmost capable tools of handling these emerging problems, thus it would be strongly preferable to preserve and protect existing wetlands rather than to let them degrade and then create artificial wetlands as a subsequent mitigation strategy.
Understanding how lake ecosystems respond to anthropogenic disturbance and climate change is crucial to apply suitable adaptation and remediation measures for their sustainable management and protection. However, the risk of lake eutrophication is dependent upon inherent lake system characteristics and ecological behaviour. To be able to account for all the varying factors that drive changes in lake systems, a classification scheme that can assign levels of lake resilience (or sensitivity) to change is required. For most lakes around the world there is a lack of data to apply such an approach, with profound implications on the ability to map, monitor and understand regional and global lake behaviour in response to climate change, land use/land management and further disturbance pressures. In this study, lake eutrophication risk was assessed using a typology-based approach developed using remotely sensed, modelled and open access datasets from 738 lakes and their catchments worldwide. The new framework classifies lakes according to (i) their natural sensitivity to eutrophication and, by extension, (ii) their resilience to external pressures. Support for the approach is evidenced from independent space-based water quality assessment illustrating that lakes with higher risk of eutrophication typically exhibit higher chlorophyll-a concentrations. Whilst other classifications schemes exist, the novelty of the proposed approach is that it combines explanatory variables (ten lake and catchment metrics) to develop a framework with global applicability. Results showed that 93% of the study sites exhibited low-to-moderate risk of the catchment on the water body in terms of accelerating or slowing down nutrient loading, whereas 6% of the study sites exhibited high sensitivity to such external influence, i.e. risk potential for having high rates of eutrophication. Knowing the rate at which each water body is expected to, or could become, more eutrophic provides a frame of reference in the prediction of the effect of human pressures and climate change on lake systems, both now and in the future. Targeted monitoring of more sensitive lakes can ensure that early warning signs of potentially irreversible or damaging water body change will not be missed. This global risk eutrophication assessment framework can, therefore, help to better safeguard, manage and protect freshwater resources for future societal and ecosystem wellbeing and sustainable economic growth.
Background and aims
Agroforestry, whereby trees are associated with crops and/or livestock, is expected to mitigate nitrogen (N) losses from agriculture. However , little is known about how nitrification potential, an important process that drives N losses, is affected by agroforestry systems. This study aimed to investigate the effect of different silvopastoral agroforestry systems on soil nitrification potential.
Methods
Nitrification potential was evaluated in two agroforestry systems (hedgerow and alley cropping) associated with temporary grasslands in Brittany, France. In each system, soil was sampled along a transect spanning from the center of the tree row into the grass alley. Soil nitrification potential was determined ex situ and was explained by univariate and multivariate analysis of variables describing vegetation, physicochemical soil properties, and soil organisms.
Results
Nitrification potential differed between the two agroforestry systems and among the positions in relation to the trees. In the alley cropping system, nitrification potential was on average 1.5 times higher in the tree row than at 1.5 and 10 m into the grass alley, while in the hedgerow system, nitrification potential at 1.5 m into the grass alley was on average 40% lower than at 10 m into the grass alley. Nitrification potential was strongly correlated with soil pH, whereas no correlation was observed between nitrification potential and community size of soil nitrifiers.
Conclusion
Our results point out the diverse effects of agroforestry systems on nitrification, a key soil process that is involved in the regulation of N losses.
Purpose
Climate change and anthropogenic activities cause salinity fluctuations and frequent drought‒rewetting processes in lacustrine littoral zones. However, the joint effects of these processes on the quality and quantity of dissolved organic matter (DOM) in pore water and bacterial communities in sediments are not well understood. Therefore, an experiment was conducted to attempt to fill the above gaps.
Materials and methods
An experiment with three salinities (1200, 3600, and 6000 mg L⁻¹) and the drought‒rewetting process was conducted. DOM characteristics were monitored by a UV–Vis spectrometer and a fluorescence spectrophotometer; bacterial communities were analyzed by 16S rRNA.
Results and discussion
Higher salinity (6000 mg L⁻¹) and the drought‒rewetting process retained more humified, more aromatic, and less bioavailable DOM and maintained lower DOM concentrations in pore water. Before the drought-rewetting process, Hydrogenophilaceae, Oxalobacteraceae, and Flavobacteriaceae participated in DOM transformation, while Hydrogenophilaceae, Desulfobacteraceae, Anaerolineaceae, Planococcaceae, and Clostridiaceae were associated with DOM components after this process. The drought‒rewetting process, higher (6000 mg L⁻¹) or lower (1200 mg L⁻¹) salinity was not conducive to the stability of bacterial communities in sediments.
Conclusions
Salinity fluctuations and drought‒rewetting processes changed DOM characteristics in pore water and destabilized the bacterial communities. Therefore, it is necessary to take appropriate water recharge measures to avoid these processes.
Water diversion is a common strategy to enhance water quality in eutrophic lakes by increasing available water resources and accelerating nutrient circulation. Its effectiveness depends on changes in the source water and lake conditions. However, the challenge of optimizing water diversion remains because it is difficult to simultaneously improve lake water quality and minimize the amount of diverted water. Here, we propose a new approach called dynamic water diversion optimization (DWDO), which combines a comprehensive water quality model with a deep reinforcement learning algorithm. We applied DWDO to a region of Lake Dianchi, the largest eutrophic freshwater lake in China and validated it. Our results demonstrate that DWDO significantly reduced total nitrogen and total phosphorus concentrations in the lake by 7% and 6%, respectively, compared to previous operations. Additionally, annual water diversion decreased by an impressive 75%. Through interpretable machine learning, we identified the impact of meteorological indicators and the water quality of both the source water and the lake on optimal water diversion. We found that a single input variable could either increase or decrease water diversion, depending on its specific value, while multiple factors collectively influenced real-time adjustment of water diversion. Moreover, using well-designed hyperparameters, DWDO proved robust under different uncertainties in model parameters. The training time of the model is theoretically shorter than traditional simulation-optimization algorithms, highlighting its potential to support more effective decision-making in water quality management.
Floodplain lakes share characteristics of both deep and shallow lakes throughout any given year. Seasonal fluctuations in their water depth drive changes in nutrients and total primary productivity, which directly and indirectly affect submerged macrophyte biomass. To investigate how water depth and environmental variables affect submerged macrophytes biomass, we surveyed six sub-lakes in the Poyang Lake floodplain, China, during the flood and dry seasons of 2021. Dominant submerged macrophytes include Vallisneria spinulosa and Hydrilla verticillata. The effect of water depth on the biomass of these macrophytes varied between the flood and dry seasons. In the flood season, there was a direct effect of water depth on biomass, while in the dry season only an indirect effect was observed. During the flood season, the direct effect of water depth on the biomass of V. spinulosa was less than the indirect effect, with water depth primarily affecting the total nitrogen, total phosphorus and water column transparency. Water depth directly, positively affected H. verticillata biomass, with this effect being greater than the indirect effect by affecting the carbon, nitrogen and phosphorus content in the water column and sediment. During the dry season, water depth affected H. verticillata biomass indirectly through sediment carbon and nitrogen content, while for V. spinulosa, the effect on biomass was indirect through carbon content of the sediment and water column. The main environmental variables affecting submerged macrophytes biomass in the Poyang Lake floodplain during the flood and dry seasons, and the mechanisms through which water depth affects dominant submerged macrophytes biomass, are identified. An understanding of these variables and mechanisms will enable improved management and restoration of wetland.
Greenhouse gas (GHG) emissions from small inland waters are disproportionately large. Climate warming is expected to favour dominance of algae and free-floating plants at the expense of submerged plants. Through different routes these functional plant types may have far-reaching impacts on freshwater GHG emissions in future warmer waters, which are yet unknown. We conducted a 1,000 L mesocosm experiment testing the effects of plant type and warming on GHG emissions from temperate inland waters dominated by either algae, free-floating or submerged plants in controls and warmed (+4°C) treatments for one year each. Our results show that the effect of experimental warming on GHG fluxes differs between dominance of different functional plant types, mainly by modulating methane ebullition, an often-dominant GHG emission pathway. Specifically, we demonstrate that the response to experimental warming was strongest for free-floating and lowest for submerged plant-dominated systems. Importantly, our results suggest that anticipated shifts in plant type from submerged plants to a dominance of algae or free-floating plants with warming may increase total GHG emissions from shallow waters. This, together with a warming-induced emission response, represents a so far overlooked positive climate feedback. Management strategies aimed at favouring submerged plant dominance may thus substantially mitigate GHG emissions.
This study was aimed at evaluating composition and distribution of zooplankton fauna of River Ethiope, Delta State, Nigeria. Sampling and survey of zooplankton was carried out for 24 (twenty four) months (January, 2016 to December, 2017) across the wet and dry seasons. Five designated stations were sampled with varying anthropogenic activities along the river stretch. The five stations included station1 (Umuaja) which is the main source of the river, station 2 (Umutu), station 3 (Ubiaruku), station 4 (Abraka) and Station 5(Eku). The zooplankton species recorded in the study comprised of one thousand six hundred and sixty two individuals. A total of 47 zooplankton taxa comprising 19 Copepoda, 7 rotifers and 21 Cladocera species were encountered during the study period. The Copepoda was the most abundant constituting (45%) followed by theCladocera (40%) and Rotifera which accounted for 15%. Abundance was highest at stations 1 and 4. The dominant zooplankton was Tropocyclops prasinus, Mesocyclops bodanicola, Metacyclops minutes and Thermocyclops neglectus. The rotifers were dominated by Platyias lelupui and Lecane ungulate. The values of diversity (H), Evenness (E) and Dominance were highest at station 3, while species richness value (D) was highest at station 4. The similarity index (Bray Curtis) showed that stations 1 and 4, and stations 2 and 5 had the highest similarities. The results obtained showed variation in the composition and distribution in the stations.
NON FORMATED PUBLISHED VERSION
Feedbacks between climate change and eutrophication: revisiting the allied attack concept and how to strike back
Despite its well-established negative impacts on society and biodiversity, eutrophication continues to be one of the most pervasive anthropogenic influence along the freshwater to marine continuum. The interaction between eutrophication and climate change, particularly climate warming, was explicitly focused upon a decade ago in the paper by Moss et al. (2011), which called for an integrated response to both problems, given their apparent synergy. In this review, we summarise advances in the theoretical framework and empirical research on this issue and analyse the current understanding of the major drivers and mechanisms by which climate change can enhance eutophication, and vice versa, with a particular focus on shallow lakes. Climate change can affect nutrient loading, through changes at the catchment and landscape levels by affecting hydrological patterns and fire frequency, and through temperature effects on nutrient cycling. Biotic communities and their interactions can also be directly and indirectly affected by climate change, leading to an overall weakening of resilience to eutrophication impacts. Increasing empirical evidence now indicates several mechanisms by which eutrophying aquatic systems can increasingly act as important sources of greenhouse gases to the atmosphere, particularly methane. We also highlight potential feedbacks between eutrophication, cyanobacterial blooms, and climate change. Facing both challenges at the same time is more pressing than ever. Meaningful and strong measures at the landscape and water body levels are therefore required if we are to ensure ecosystem resilience and safe water supply, conserving biodiversity, and decreasing the carbon footprint of freshwaters.
Climate change and eutrophication are among the main stressors of shallow freshwater ecosystems, and their effects on phytoplankton community structure and primary production have been studied extensively. However, their combined effects on the algal production of polyunsaturated fatty acids (PUFA), specifically, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are currently unresolved. Moreover, the proximate reasons for changes in phytoplankton EPA and DHA concentrations are unclear, i.e., the relative importance of ecological (changes in the community composition) vs. ecophysiological (within taxa changes in EPA and DHA levels) factors.
We investigated the responses of phytoplankton EPA and DHA concentrations to warming (IPCC climate scenario) and nutrient additions in mesocosms which had been run continuously at varying temperature and nutrient levels for 15 years prior to this study. Nutrient treatment had a significant effect on phytoplankton EPA and DHA concentrations and about 59 % of the variation in EPA and DHA concentrations could be explained by changes in the phytoplankton community structure. Increased biomass of diatoms corresponded with high EPA and DHA concentrations, while cyanobacteria/chlorophyte dominated mesocosm had low EPA and DHA concentrations. Warming had only a marginal effect on the EPA and DHA concentrations in these mesocosms. However, a significant interaction was observed with warming and N:P ratio.
Our findings indicate that direct nutrient/temperature effects on algal physiology and PUFA metabolism were negligible and the changes in EPA and DHA concentrations were mostly related to the phytoplankton community structure and biomass. These results also imply that in shallow temperate lakes eutrophication, leading to increased dominance of cyanobacteria, will probably be a greater threat to phytoplankton EPA and DHA production than warming. EPA and DHA are nutritionally important for upper trophic level consumers and decreased production may impair secondary production.
Severe eutrophication threatens freshwater systems around the world. The application of aquatic buffer zones with plants, for example around agricultural lands, can increase nutrient retention and thereby reduce nutrient loading to downstream systems. However, not much is known about greenhouse gas (GHG) emissions from these buffer zones and how they are affected by nutrient loading and the dominant plant species. Here, using a full-factorial mesocosm experiment with different nutrient loadings (20–4,000 mg N and 1–200 mg P m⁻² d⁻¹) and plant types (e.g. submerged and free-floating species), we show that emissions of methane (CH4) and nitrous oxide (N2O) were strongly related to nutrient loading, leading to total greenhouse gas emissions up to 177.84 g CO2-eq m⁻² d⁻¹. Overall, total GHG emission (as the sum of CH4 ebullition and diffusive water-atmosphere emission of CH4 and N2O in CO2 equivalents) was not significantly affected by plant species. CH4 ebullition was significantly lower in experimental units with submerged plants that rooted in the sediment as compared to non-rooted plants, possibly related to rhizosphere CH4 oxidation fueled by radial oxygen loss or plant-mediated transport that limits the build-up of gaseous CH4 in the sediment. We conclude that aquatic buffer zones that experience intense nutrient loading (e.g. due to release of sewage or agricultural fertilizer) can be GHG emission hotspots and recommend careful consideration of environmental conditions (e.g. the organic carbon content), expected nutrient loadings, and alternatives, prior to their construction.
Characteristics of bottom sediments in lake mesocosms 11 years after starting the experiment were studied in order to determine the effects of nutrient loading, temperature increase and vegetation type on concentration and vertical distribution of phosphorus (P) forms. The experimental setup consisted of 24 outdoor flow-through mesocosms with two nutrient treatments – low (L) and high (H) and 3 temperature levels – ambient (T0), heated by 2–4 °C (T1) and 3–6 °C (T2) in four replicates. Thickness of the organic sediment was measured and the sediment analysed for dry weight, organic matter, and P fractions (according to a sequential extraction scheme) and organic P compounds (by ³¹P nuclear magnetic resonance spectroscopy). Higher nutrient loading led to increased sediment accumulation and higher concentration of total P and most P fractions, except P bound to aluminium and humic matter. The dominant vegetation type covaried with nutrient levels. Vertical gradients in Ca bound P and mobile P in low nutrient mesocosms was perhaps a result of P coprecipitation with calcite on macrophytes and P uptake by roots indicating that in macrophyte-rich lakes, plants can be important modifiers of early P diagenesis. Temperature alone did not significantly affect sediment accumulation rate but the interaction effect between nutrient and temperature treatments was significant. At high nutrient loading, sediment thickness decreased with increasing temperature, but at low nutrient loading, it increased with warming. The effect of warming on sediment composition became obvious only in nutrient enriched mesocosms showing that eutrophication makes shallow lake ecosystems more susceptible to climate change.
Despite its well-established negative impacts on society and biodiversity, eutrophication continues to be one of the most pervasive anthropogenic influence along the freshwater to marine continuum. The interaction between eutrophication and climate change, particularly climate warming, was explicitly focused upon a decade ago in the paper by Moss et al. (2011), which called for an integrated response to both problems, given their apparent synergy. In this review, we summarise advances in the theoretical framework and empirical research on this issue and analyse the current understanding of the major drivers and mechanisms by which climate change can enhance eutophication, and vice versa, with a particular focus on shallow lakes.
Climate change can affect nutrient loading, through changes at the catchment and landscape levels by affecting hydrological patterns and fire frequency, and through temperature effects on nutrient cycling. Biotic communities and their interactions can also be directly and indirectly affected by climate change, leading to an overall weakening of resilience to eutrophication impacts. Increasing empirical evidence now indicates several mechanisms by which eutrophying aquatic systems can increasingly act as important sources of greenhouse gases to the atmosphere, particularly methane. We also highlight potential feedbacks between eutrophication, cyanobacterial blooms, and climate change. Facing both challenges at the same time is more pressing than ever. Meaningful and strong measures at the landscape and water body levels are therefore required if we are to ensure ecosystem resilience and safe water supply, conserving biodiversity, and decreasing the carbon footprint of freshwaters.
Annual patterns in hydrology, phosphorus circulation, and sediment dynamics were studies in a southern Illinois, USA floodplain swamp dominated by bald cypress (Taxodium disyichum) and swamp tupelo (Nyssa aquatica). The study emphasized the swamp's interactions with the adjacent river. For the year, major inputs of water to the swamp were throughfall (74.3 cm) and runoff (69.4 cm) with minor contributions due to groundwater (21.6 cm). Outflows were by evapo-transpiration (72.3 cm), surface outflow (56.5 cm), and groundwater (21.0 cm), with the latter two draining primarily to the river. A flood occurred during the study period, passing 1.6 x 10^7m^3 of river water over the swamp and depositing 0.06 cm of sediments. An annual phosphorus budget was developed for the swamp from field measurements. The greatest input of phosphorus to the swamp was 3.6 g P^.m-^2^.yr-^1, due to deposition of high-phorsphorus sediments during the flood. This was 10 times greater than the outflow of phosphorus to the river, 0.34 g P^.m-^2^.yr-^1, and 26 times greater than the throughfall input of 0.14 g P^.m-^2^.yr-^1. Total tree uptake from sediments was estimated to be 0.87 g P^.m-^2^.yr-^1 of which 0.77 g P^.m-^2^.yr-^1 returns as litterfall to the swamp sediments. Duckweed productivity was estimated to take 3.3 g P^.m-^2^.yr-^1 from the water column and deposit this in the sediments during die-off. For the period 1937-1967, cypress growth, based on tree ring analyses, was closely correlated with several measurements of flooding frequencies and magnitude, all obtained from past river data. Three ring data prior to 1937 showed poor correlation with flooding, probably because of logging activity. Cypress growth has decreased dramatically in recent years, corresponding to the rise in water level caused by beaver activity.
1930 Climate change may have profound eff ects on phosphorus (P) transport in streams and on lake eutrophication. Phosphorus loading from land to streams is expected to increase in northern temperate coastal regions due to higher winter rainfall and to a decline in warm temperate and arid climates. Model results suggest a 3.3 to 16.5% increase within the next 100 yr in the P loading of Danish streams depending on soil type and region. In lakes, higher eutrophication can be expected, reinforced by temperature-mediated higher P release from the sediment. Furthermore, a shift in fi sh community structure toward small and abundant plankti-benthivorous fi sh enhances predator control of zooplankton, resulting in higher phytoplankton biomass. Data from Danish lakes indicate increased chlorophyll a and phytoplankton biomass, higher dominance of dinophytes and cyanobacteria (most notably of nitrogen fi xing forms), but lower abundance of diatoms and chrysophytes, reduced size of copepods and cladocerans, and a tendency to reduced zooplankton biomass and zooplankton:phytoplankton biomass ratio when lakes warm. Higher P concentrations are also seen in warm arid lakes despite reduced external loading due to increased evapotranspiration and reduced infl ow. Th erefore, the critical loading for good ecological state in lakes has to be lowered in a future warmer climate. Th is calls for adaptation measures, which in the northern temperate zone should include improved P cycling in agriculture, reduced loading from point sources, and (re)-establishment of wetlands and riparian buff er zones. In the arid Southern Europe, restrictions on human use of water are also needed, not least on irrigation. O n average, global surface temperatures have increased by about 0.74°C over the past 100 yr (Trenberth et al., 2007), with the majority of the increase (0.55°C) occurring over the past 30 yr. We may expect marked changes to occur in the global climate during this century (IPCC, 2007). Increasingly reliable regional climate projections are available for many regions of the world, but fewer projections are available for many developing countries than for the developed world (Christensen et al., 2007). Th e warming generally increases the spatial variability of precipitation with reduced rainfall in the subtropics and increases at higher latitudes and in parts of the tropics. Th e changes in temperature and rainfall lead to changes in agricul-tural land use and management, including changes in soil cultivation and in the rates and timing of fertilization (Howden et al., 2007). Th ese changes have cascading eff ects on the P cycling, directly and indirectly, that aff ect the aquatic environment. Th e direct eff ects are related to the increased temperatures, increased rainfall intensity, and changes in winter rainfall that are expected to enhance the P loading to freshwaters in the temperate zone (IPCC, 2007) and the Arctic (Arctic Climate Impact Assessment, 2002) and to reduce the loading, but not the concentrations, in streams and freshwater lakes in the Mediterranean region. However, a few quantitative studies are avail-able (Chang, 2004; Andersen et al., 2006). Th e indirect eff ects are related to changes in the choice of crops, crop rotations, use of catch crops, and agricultural practices, including tillage and fertilization. In northern temperate areas, new heat-demanding, warm-season crops (e.g., maize and sunfl ower) will replace many of the present grain cereals and oilseed crops (Olesen and Bindi, 2002). At the same time, changes occur in planting and harvesting times (Olesen, 2005) and in fertilization rates and strategies (Olesen et al., 2007). Crop rotation must be adapted to changes in crop choices, in crop maturing, and in the need to control weeds, pests, and diseases. Th is will aff ect the amount of P released to freshwaters and its seasonal pattern. More-Abbreviation: TP, total phosphorus.
Market prices contain information about supply and demand, the institutions that influence both these elements, and the operation of the market. Prices also allocate scarce resources to higher-valued uses. In this paper we analyze the price history of three water markets in the arid Southwest: Arizona's Central Arizona Project, Colorado's Colorado Big Thompson Project, and New Mexico's Middle Rio Grande Conservancy District. Using water transfers over 11 years, we estimate a simultaneous system of market equations, one for price and the other for quantity demanded. Comparison of the institutional characteristics of each market reveals that Colorado's market is well developed, with many trades and rising prices that respond to market conditions, and New Mexico's market is developing well, with lower prices, but showing some response to supply and demand factors. Arizona's market is the least developed, with few trades and very low prices. Our empirical findings support our claim that markets are becoming more efficient in these regions despite the considerable institutional and historical impediments to the evolution of water markets.
A simulation model of the direct effects of climate on winter wheat production and grain yield is presented. The model was calibrated using data from field experiments in Denmark. The model was validated using data from near optimally managed experimental plots with winter wheat from The Netherlands and Denmark. The model was further evaluated using data from 1971 to 1997 for 7 sites in Denmark. The model explained from 0 to 20% of the variation in detrended observed yields, depending on soil type. A regression analysis of observed yields against monthly climate data showed a positive effect of temperature in October, November and January on grain yield, a positive effect of radiation in April and a strongly negative effect of precipitation in July. Only the positive effect of radiation in April was predicted by the simulation model, probably because the indirect effects of climate are not taken into account by the model (e.g. effects of rainfall on lodging or Septoria disease). The sensitivity of simulated grain yield to changes in mean temperature, temperature variability, precipitation, length of dry spells and CO2 concentration was analysed for 4 soil types using generated climate data from 1 site in Denmark. Yield decreased with increasing temperature. This decrease was strongly non-linear with temperature: change when using a fixed sowing date, but almost linear for the optimal sowing date. There was only a very small response to changes in temperature variability. Increasing precipitation increased yields with the largest response on the sandy soils. Large changes in grain yield were also seen on sandy soils with changes in the length of dry spells. A comparison of the simulated responses to the direct effects of temperature and rainfall with those to the indirect effects of these variables as estimated from the regression analysis showed that the indirect and the direct effects had opposite effects and that they may almost cancel each other out. The simulated increase in grain yield due to increasing CO2 concentration in most cases exceeded the simulated responses to changes in climate variables.
Denitrification rates in the range of 359 to 599 mmol N m-2 d-1 were found in the waterlogged soil of a minerotrophic fen. Three different methods were used to estimate denitrification rates. The fen revealed a zone of enhanced denitrification and within this zone the spatial variation of denitrification rates was elucidated using two different approaches: microcosms and field observations. The denitrification rates in the microcosms were measured, either by use of 15N-N2 production rates (Method 1) or by setting up a mass balance for nitrate (Method 2). Denitrification rates in the peat horizon at depths of 0 to 69 cm were in the range 182 to 243 mmol N m-2 d-1 (Method 1) and 213 to 217 mmol N m-2 d-1 (Method 2). Denitrification rates measured in the deeper sandy soil horizons at depths of 69 to 156 cm were 46 to 103 mmol N m-2 d-1 (Method 1) and 33 to 137 mmol N m-2 d-1 (Method 2). Thus, both experiments revealed a strong and comparable decrease in denitrification rate with depth, which also corresponded well to soil carbon content. Denitrification rates were calculated from field data using Darcy's law and the conservation equation for one-dimensional, steady state, advective transport of nitrate in an incompressible porous medium. The same significant decrease in denitrification rates with depth was observed as in the microcosm setup. The calculated denitrification rates were: 330 mmol N m-2 d-1 at depths of 0 to 75 cm (peat), 20 mmol N m-2 d-1 at depths of 75 to 115 cm (sandy soil), and 9 mmol N m-2 d-1 in the sandy soil horizon at depths of 155 to 205 cm. This study shows that detailed spatial information about pedological and hydrological parameters in combination with detailed spatial mapping and measurement of denitrification rates is fundamental for properly understanding nitrogen removal in waterlogged soils with ground water through-flow. Further, the results confirm that provided this information is present, it is possible to compare detailed laboratory experiments with field studies of denitrification.
Phytoplankton dominance (as biomass) by heterocystous cyanobacteria, nonheterocystous cyanobacteria, and chlorophytes was studied along a trophic gradient (0.011-2.2 mg P.L(-1)) by analyzing regularly collected semiquantitative data from 178 shallow Danish lakes (mean depth <3 m) and quantitative data from 32 lakes. Heterocystous cyanobacteria were dominant at low total P (TP) (<0.25 mg P.L(-1)) and nonheterocystous cyanobacteria at intermediate TP (0.25-0.8 mg P.L(-1)), while chlorophytes often were dominant at high TP (>1 mg P.L(-1)). In contrast with many earlier findings, heterocystous cyanobacteria were not dominant at low total N (TN):TP or low inorganic N concentrations; chlorophytes were dominant at extremely high pH, and the shift from cyanobacterial to chlorophyte dominance could not be explained by a change in the photic zone to mixing zone ratio. We suggest that chlorophyte dominance in hypertrophic shallow lakes is attributable to continuous input of nutrients and carbon from the sediment and external sources. This renders the fast-growing chlorophytes a superior competitor compared with the relatively slow-growing cyanobacteria, even when inorganic nutrient concentration is low and pH high. New predictive models relating phytoplankton dominance to TP in shallow lakes were developed, as former models failed to predict our observations satisfactorily.
With climate change northern Europe is expected to experience extreme increase in air temperatures, particularly during the winter months, influencing soil temperatures in these regions. Climate change is also projected to influence the rainfall amount, and its inter- and intra-annual variability. These changes may affect soil moisture regimes, soil water drainage, soil nitrogen (N) availability and N leaching to aquatic environment and N2O emissions to atmosphere. Thus it is important to study the effects of increased soil temperature and varying rainfall patterns on soil N cycling in arable land from temperate climates, which is a major source of N pollution. An open-field lysimeter study was carried out during 2008–2009 in Denmark on loamy sand soil (Typic Hapludult) with three factors: number of rainy days, rainfall amount and soil warming. Number of rainy days included the mean monthly rainy days for 1961–1990 as ‘normal’ and half the number of rainy days of former as ‘reduced’ treatments. Rainfall amount included mean monthly rainfall for 1961–1990 as ‘present’ and the projected change in mean monthly rainfall for 2071–2100 as ‘future’ treatments. Soil warming included increase in soil temperature by 5 °C at 0.1 m depth as ‘heated’ and non-heated as ‘control’ treatments. Automated mobile rain-out shelter and irrigation system, and insulated buried heating cables were used to impose the treatments.
Nitrate retention in riparian buffer strips is well documented in summer periods, but the potential of winter retention within these zones is poorly documented. Two sites, grass (Lolium perenne L.), and poplar (Populus italica)-vegetated riparian strips, were investigated in southern England (River Leach). Groundwater flow was via subsurface pathways within the sites, NO3/- concentration gradients and loading rates were calculated over the winter period. Nitrate retention was found to be linearly dependent on load rate. Nitrate retention occurred at the edge of the riparian zone. This was most obvious in the poplar site where all hillslope-derived NO3/- was absorbed within the first 5 m of flow within the riparian strip. When loading rates into the sites increased, NO3/- absorption migrated upslope from the riparian site. The poplar-vegetated riparian zone was found to be more resilient (99% retention of NO3/-) than the grass-vegetated riparian zone (84% retention of NO3/-) in the winter months. It is postulated that although vegetation has no active role in retaining NO3/- in the winter, above-ground vegetative biomass does contribute C to the soil microbacterial biomass that is engaged in NO3/- reduction in the winter months, this accounted for the greater efficiency of the poplar vegetated site.
The functioning of shallow lakes is supposedly very sensitive to water level fluctuations (WLF). Relationships between WLF and submerged macrophyte development were investigated in five Turkish shallow lakes located in a semi-arid to arid Mediterranean climate where the hydrological event of WLF is a common phenomenon. In all lakes, WLF emerged as a major factor determining submerged plant development. High submerged plant coverage was observed in four of the study lakes, Lake Beyşehir, Lake Uluabat, Lake Marmara and Lake Mogan when the water level was low throughout the year or during growing season, submerged plants expanded; however, in Lake Işıklı extensive submerged plant development was observed at high water levels during winter. In Lake Işıklı, an increase of 25 % in the surface area was recorded, which, in turn, might have resulted in an increased potential for expansion of submerged plants. Furthermore, in all the lakes excluding Lake Beyşehir, high sub-merged plant coverage coincided with a significant decrease in the amplitude of intra-annual water level fluctuations. The depth profile, expressed as the morphometry index (Zmean/Zmax), appeared to be critical for the development of extensive vegetation. Expansion of vegetation coincided with either an increased morphometry index or a flatter bottom profile. However, the impact of hydrology on lake morphometry differed between the lakes. In Lake Işıklı, the high water level generated a slightly flatter, albeit not significantly so, bottom; however, in the remaining lakes the same effect was observed at low water level. Differences in the morphometry index in response to WLF appeared to depend on the original bottom profile, which is either conical or ellipsoid. Therefore, the impact of hydrology on the bottom profile of a lake may profoundly affect the extent of the littoral zone. Biomass of carp (Cyprinus carpio) had a strong inverse correlation with vegetation development in Lake Marmara and Lake Uluabat, therefore, carp might also have been important in macrophyte development. It may be concluded that littoral plant communities in shallow lakes located in semi-arid to arid regions appear to be particularly susceptible to water level fluctuations.
Whether fish biomanipulation is an efficient restoration technique in eutrophic warm sub/tropical lakes has been subject to recent debate. Our investigations undertaken in warm Lake Eymir, Turkey show that fish removal increased water clarity during a five-year period. Rapid re-colonisation of submerged plants, Potamogeton pectinatus and Ceratophyllum demersum, occurred. This recovery was achieved at higher total phosphorus (TP) levels than the suggested threshold for stability, probably owing to the nitrogen-limited condition of the lake. Reestablishment of vegetation coincided with significantly reduced concentrations of TP and dissolved inorganic nitrogen (DIN). Abundance of the large-bodied Daphnia pulex was low and it later disappeared completely from the zooplankton community, probably due to increased fish predation. A severe drought, occurring two years after the fish removal, significantly lowered the water level, increased the hydraulic residence time and caused an expansion of the vegetation. The drought was also associated with a significant increase in salinity, conductivity, nutrient concentrations (TP and DIN) and in the abundance of Arctodiaptomus bacillifer. The in-lake nutrient amounts became more dependent on internal processes rather than on the external loading, which was very low during the drought period. When the water level rose to normal values, the concentrations of TP and soluble reactive phosphate (SRP) decreased. However, the DIN concentration significantly increased due to slowed denitrification processes in consequence of the low availability of dissolved oxygen. This increase in ammonium concentrations may have contributed to the instability of clear-water conditions by releasing the lake from its former nitrogen-limited state, since the TP levels in the lake had already surpassed critical levels. Along with this, tench (Tinca tinca) biomass increased to pre-biomanipulation levels and the pike (Esox lucius) to planktivorous fish ratio decreased with increased chlorophyll-a concentrations, largely by inedible cyanobacteria, which led to a decline in summer water clarity but not to disappearance of submerged plants. The early growth of plants was probably controlled by the spring water clarity, which remained high, and the lake maintained its macrophyte-dominated state, despite the relatively turbid conditions prevailing in summer. The highly positive effect of the Lake Eymir restoration effort contradicts the experiences from other subtropical lakes. This could be due to the fact that warm Lake Eymir being at high latitude with a strong presence of predatory fish and limited abundance of planktivorous fish species, as opposed to low altitude warm lakes. However, drought as an inherent feature of the arid region may be even more important in the future as drier conditions are predicted for the Mediterranean region in consequence of the global climate change.
The influence of changes in nitrogen (N) and phosphorus (P) loadings in 1983-2001 on cyanobacterial development in Lake Peipsi (3.555 km2, mean depth 7.1m) was studied. After the collapse of Soviet-type agriculture in the early 1990s, total N loadings decreased sharply while the in-lake total P concentration increased, forming favourable conditions for harmful bloom-forming N2 fixing (N2fix) cyanobacteria. The average percentage of the biomass of N2fix cyanobacteria in total phytoplankton biomass increased from 13% in 1983-1991 to 29% in 1992-2001. Gloeotrichia echinulata, a species capable of vertical migration and consequent transport of P from the lake bottom to the upper layers developed earlier in the season (June) at lower nutrient concentrations than other cyanobacteria in L. Peipsi (Anabaena, Aphanizomenon, Microcystis). The fixation of N2 by G. echinulata as well as its ability to use sediment phosphorus could bring about the enrichment of the water column with nutrients. This enables the other N2fix species Anabaena and Aphanizomenon as well as Microcystis, which is not generally N2 fixing but requires high nutrient concentrations, to flourish.
Increased nitrogen loading may lead to changes in productivity or biodiversity in freshwater systems. Field surveys have shown reduced species richness of submerged and floating-leaved plant communities in shallow lakes as winter nitrate concentrations, a surrogate for nitrate loading, have risen above 1-2 mg NO3-N L−1. Experimental tank mesocosms, containing about 3 m3 of water and sediment from Hickling Broad, Norfolk, UK were initially planted with eleven submerged plant species from the lake and its connected waterway. Constant phosphorus loadings (designed to give added concentrations of 50 μg P L−1) were given to all tanks. Four nitrate loadings were given in a randomised block design with twelve-fold replication. Loadings were designed to increase the concentration in the water by 1, 2, 5 and 10 mg NO3-N L−1 (N1, N2, N5 and N10, respectively). Nitrate loading increased phytoplankton and periphyton chlorophyll a in the N2, N5 and N10 treatments compared with the N1. It complementarily decreased total plant volume and had varied effects on different species, with most species indifferent, a few (mostly charophytes) declining above the N1 treatment, and one (Elodea canadensis) performing best in N2 and N5 compared with N1 and N10. Species richness of submerged macrophytes declined with time in all treatments and with increasing nitrogen load in the first year. In the second year, species richness did not further decline in the N1 treatment but declined at increasing rates with increasing nitrogen load in the others. The rate of decline in the second year, plotted against nitrate load, fitted an exponential relationship, allowing calculation of a critical load associated with a stable species richness of 0.61-0.64 mg NO3-NL−1 expressed as concentration in inflow water, or of an empirically determined equivalent TN concentration in the lake water of about 1.50 mg N L−1. This value broadly corresponds with estimates from field data for concentrations associated with declining species richness and is much lower than values currently often found in lowland agricultural areas in Europe.
There is a very significant, cost effective greenhouse gas (GHG) mitigation potential in agriculture. The annual mitigation potential in agriculture is estimated to be 4200, 2600 and 1600 Mt CO 2 equiv/yr at C prices of 100, 50 and 20 US$/t CO 2 equiv, respectively. The value of GHG mitigated each year is equivalent to 420 000, 130 000 and 32 000 million US$/yr for C prices of 100, 50 and 20 US$/t CO 2 equiv, respectively. From both the mitigation and economic perspectives, we cannot afford to miss out on this mitigation potential.
The challenge of agriculture within the climate change context is two-fold, both to reduce emissions and to adapt to a changing and more variable climate. The primary aim of the mitigation options is to reduce emissions of methane or nitrous oxide or to increase soil carbon storage. All the mitigation options, therefore, affect the carbon and/or nitrogen cycle of the agroecosystem in some way. This often not only affects the GHG emissions but also the soil properties and nutrient cycling. Adaptation to increased variability of temperature and rainfall involves increasing the resilience of the production systems. This may be done by improving soil water holding capacities through adding crop residues and manure to arable soils or by adding diversity to the crop rotations.
Though some mitigation measures may have negative impacts on the adaptive capacity of farming systems, most categories of adaptation options for climate change have positive impacts on mitigation. These include: (1) measures that reduce soil erosion, (2) measures that reduce leaching of nitrogen and phosphorus, (3) measures for conserving soil moisture, (4) increasing the diversity of crop rotations by choices of species or varieties, (5) modification of microclimate to reduce temperature extremes and provide shelter, (6) land use change involving abandonment or extensification of existing agricultural land, or avoidance of the cultivation of new land. These adaptation measures will in general, if properly applied, reduce GHG emissions, by improving nitrogen use efficiencies and improving soil carbon storage.
There appears to be a large potential for synergies between mitigation and adaptation within agriculture. This needs to be incorporated into economic analyses of the mitigation costs. The inter-linkages between mitigation and adaptation are, however, not very well explored and further studies are warranted to better quantify short- and long-term effects on suitability for mitigation and adaptation to climate change. In order to realize the full potential for agriculture in a climate change context, new agricultural production systems need to be developed that integrate bioenergy and food and feed production systems. This may possibly be obtained with perennial crops having low-environmental impacts, and deliver feedstocks for biorefineries for the production of biofuels, biomaterials and feed for livestock.
1. In view of the paucity of data on the response of warm shallow lakes to reductions in nutrient loading, this paper presents a long-term limnological data set to document changes in the food-web of a shallow Mediterranean lake (Lake Albufera, Valencia, Spain) that has experienced reductions in phosphorus (P) (77%) and nitrogen (N) (24%) loading following sewage diversion.
2. Nine years after sewage diversion, P concentration in the lake was reduced by 30% but remained high (TP = 0.34 mg L−1), although the mean water retention time in the lake was only 0.1 years. Nitrate concentrations did not significantly change, probably because the lake continued to receive untreated effluents from ricefields.
3. Chlorophyll a concentration was reduced by half (annual mean of 180 μg L−1). Cyanobacteria abundance remained high but its composition changed towards smaller species, both filamentous and chroococcal forms.
4. Cladocera abundance increased and reached peaks twice a year (December to March and July to September). After nutrient reduction, short-term clear-water phases (up to 5 weeks) occurred during February to March in several years, concomitant with annual flushing of the lake and lower fish densities. The abundance of Cladocera in winter contrasted with the spring peaks observed in northern restored shallow lakes. The zooplankton to phytoplankton biomass ratio remained lower than in northern temperate shallow lakes, probably because of fish predation on zooplankton.
5. Improvement of the water quality of Lake Albufera remained insufficient to counteract littoral reed regression or improve underwater light allowing submerged plants re-colonise the lake.
6. Sewage diversion from Lake Albufera impacted the food web through the plankton, but higher trophic levels, such as fish and waterfowl, were affected to a lesser degree. Although the fish species present in the lake are mainly omnivorous, long-term data on commercial fish captures indicated that fish communities changed in response to nutrient level and trophic structure as has been observed in restored shallow lakes at northern latitudes.
7. Phosphorus concentrations produced similar phytoplankton biomass in Lake Albufera as in more northern shallow lakes with abundant planktivorous fish and small zooplankton. However, in Lake Albufera, high average concentrations were maintained throughout the year. Overall, results suggest that nutrient control may be a greater priority in eutrophicated warm shallow lakes than in similar lakes at higher latitudes.
The alternative stable states hypothesis for the behaviour of shallow lake communities requires switches to transform clear‐water macrophyte‐dominated communities to turbid algal‐dominated ones. Such switches have rarely been demonstrated experimentally. This study shows the role of rising salinity as such a switch while contributing a solution to the conservation problems of an important nature reserve.
Hickling Broad changed from a clear‐water, charophyte‐dominated lake to a turbid, phytoplankton‐dominated lake in the early 1970s, probably owing to guanotrophication by gulls and to increased salinity from more intensive pumping of the agricultural land that separates its main inflow from the nearby North Sea. Following a decline in nutrient loading as the gull flock moved away, the plants began to return during the 1980s and 1990s. In 1998/99, the water cleared and charophytes, including some very rare species, were abundant.
This was welcome to conservation bodies, but the vigorous growth precluded competitive sailing and there were conflicts with the local sailing club. The plants, however, began an irregular decline in 2000, though nutrient loadings and other conventional chemical drivers have remained steady.
Our hypothesis was that the unstable nature of the plant community was linked to high salinity, and that if salinity were lowered there would be vigorous and reliable growth, enabling annual cutting of plants to allow sailing races. In an experiment using mesocosms, salinities straddling the current values in the Broad led to declines in plant biomass, macrophyte species richness and macrophyte Shannon–Weaver diversity through increased release of phosphorus from the sediments, increased algal turbidity and reduction of zooplankton grazer activity.
Stabilization of the plant community of Hickling Broad would be achieved by a reduction of present salinities by about 20%. This would be possible by use of existing Environmentally Sensitive Area (High Level Environmental Stewardship) arrangements or diversion of some pumped drainage water to the sea. There remain some uncertainties about the future of the area because of rising sea levels.
Copyright © 2007 John Wiley & Sons, Ltd.
Shallow lakes respond to nutrient loading reductions. Major findings in a recent multi-lake comparison of data from lakes with long time series revealed: that a new state of equilibrium was typically reached for phosphorus (P) after 10–15 years and for nitrogen (N) after
<5–10 years; that the in-lake Total N:Total P and inorganic N:P ratios increased; that the phytoplankton and fish biomass often decreased; that the percentage of piscivores often increased as did the zooplankton:phytoplankton biomass ratio, the contribution of Daphnia to zooplankto biomass, and cladoceran size. This indicates that
enhanced resource and predator control often interact during recovery from eutrophication. So far, focus has been directed at reducing external loading of P. However, one experimental study and cross-system analyses of data from many lakes in north temperate lakes indicate that nitrogen may play a more significant role for
abundance and species richness of submerged plants than usually anticipated when total phosphorus is moderate high. According to the alternative states hypothesis we should expect ecological resistance to nutrient loading reduction and P hysteresis. We present results suggesting that the two alternative states are less stable than
originally anticipated. How global warming affects the water clarity of shallow lakes is debatable. We suggest that water clarity often will
decrease due to either enhanced growth of phytoplankton or, if submerged macrophytes are stimulated, by reduced capacity of these plants to maintain clear-water conditions. The latter is supported by a cross-system comparison of lakes in Florida and Denmark. The proportion of small fish might increase and we might see higher
aggregation of fish within the vegetation (leading to loss of zooplankton refuges), more annual fish cohorts, more omnivorous feeding by fish and less specialist piscivory. Moreover, lakes may have
prolonged growth seasons with a higher risk of long-lasting algal blooms and at places dense floating plant communities. The effects of global warming need to be taken into consideration by lake managers when setting future targets for critical loading, as these may well have to be adjusted in the future. Finally, we highlight some
of the future challenges we see in lake restoration research.
The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P 1−1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5‰ and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. 1−1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2‰ and N. integer in lakes with a salinity above 0.5‰. Above 2‰ the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwatex state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5‰.
To study how changes in biomass of cyprinids (mainly roach, Rutilus rutilus L., and bream, Abramis brama L.) affect nitrogen retention in shallow lakes, we conducted mass balances of total nitrogen for 6-11 years in four eutrophic lakes in which the fish biomass changed markedly, either from natural causes or due to manipulation. The decline in cyprinids led to a shift from a turbid to a clearwater state in three of the four lakes. In these lakes total nitrogen (N) concentrations decreased and the percentage of N retained in the sediment, or lost by denitrification (N(ret)%) increased substantially. In Lake Vaeng, summer N(ret)% increased from 22-39% before to 60-72% after the biomass of cyprinids had been reduced by 50%. N(ret)% temporarily decreased to 42% during a short-term return to the turbid state. In Lake Engelsholm, a 90% reduction in cyprinids resulted in an increase in summer mean N(ret)% from 13-50% to 58-60%, and in Lake Arreskov the annual mean N(ret)% increased from -4-34% before a major fish kill to 54-59% after. A comparison with data from 16 non-manipulated lakes revealed that these changes could not be ascribed to natural interannual variations. No significant changes in N concentrations or N(ret)% were found in Lake Sobygard, which remained turbid and maintained a relatively high biomass of cyprinids. In the three lakes that shifted to a clearwater state, N(ret)% was significantly inversely related to chlorophyll-a, but independent of the abundance of submerged macrophytes and biomass of N-fixing cyanobacteria. The increase in N(ret)% might have resulted from 1) a decrease in organic N in the lake and the outlet due to the decrease in phytoplankton biomass and thus phytoplankton-N, which was not compensated by an increase in inorganic N, 2) reduced resuspension, probably reflecting both a decrease in the number of fish foraging in the sediment and a suggested increase in benthic algal growth, 3) higher denitrification in the sediment, reflecting less competition between denitrifiers and phytoplankton for nitrate, enhanced N retention by phyto- and zoobenthos and enhanced sediment nitrification due to higher oxygen concentrations, the latter reflecting lower sedimentation, higher density of zoobenthos and higher oxygen production by benthic algae. More research is needed to elucidate the relative importance of these mechanisms. It may, however, be concluded that fish manipulation or phosphorus-loading reduction leading to a shift from a turbid to a clearwater state in eutrophic lakes may markedly enhance lake N(ret)% and consequently reduce the transfer of nitrogen to coastal waters.
Lake Taihu (Taihu) is the third largest freshwater lake in China and an important drinking water, fishing, and tourism resource for Jiangsu Province. Recent toxic cyanobacterial blooms caused by excessive human nutrient loading have focused attention on arresting blooms and restoring the lake to acceptable water quality conditions by reducing nutrient inputs. Field sampling and in situ nutrient enrichment bioassays were conducted to determine seasonal patterns of nutrient limitation and nutrient thresholds for phytoplankton growth. The TN : TP and TDN : TDP mass ratios in the ambient water showed high seasonal variation and changed from 33-80 : 1 and 52-212:1, respectively, in winter and spring, and both declined to below 20:1 in summer. In spring and winter, total phytoplankton biomass and growth rates increased significantly with additions of P, with no primary effects from N, suggesting P limitation of phytoplankton growth. During the summer and fall bloom periods, however, N additions alone revealed a significant positive effect on phytoplankton growth, and P additions only stimulated phytoplankton growth once N had been added, suggesting that N was the primary limiting nutrient, with P being a secondarily limiting nutrient. When P enrichment was ≥ 0.20 mg P L-1 and N enrichment ≥ 0.80 mg N L-1, growth of the toxin-producing, dominant bloom-forming cyanobacteria Microcystis spp. was not nutrient limited. This study suggests that availability of N during the summer is a key growth-limiting factor for the proliferation and maintenance of toxic Microcystis spp. blooms. Therefore, although P load reduction is important, N load reduction is essential for controlling the magnitude and duration of algal booms in Taihu. © 2010, by the American Society of Limnology and Oceanography, Inc.
Based on monthly mass balances on 7-8 yr of data from 16 shallow (mean depth: 1-10 m), eutrophic, unstratified, or only temporarily stratified Danish lakes, we developed a simple empirical model relating the seasonal variation in lake total phosphorus (TP) concentrations to external loading, accumulated phosphorus in the sediment, hydraulic retention time, and water temperature. The aim was to describe the early recovery phase following an external loading reduction, i.e., when internal phosphorus loading is high, and to include seasonal dynamics. We calibrated a common set of model parameters for all 16 lakes and lake-specific estimates of the exchangeable phosphorus pool in the sediment (Ps). Estimated annual mean TP deviated on average 12% from observed values in the 16 lakes. Moreover, the estimated seasonal dynamics and trend following the external loading reduction closely mimicked the observed pattern. The model was successfully tested on nine of the lakes for which data were available for an additional 7-yr period. The results suggest that TP in the sediment does not provide an adequate description of the exchangeable P pool. In Lake Arreskov, which has shifted from a turbid to a clear-water state following fish kill and biomanipulation, the model significantly overestimated TP, indicating that the model is inadequate for describing seasonal dynamics during the shift from a turbid to a clear-water state. Although simple, the empirical model predicts reasonably well the seasonal dynamics of TP following a P-loading reduction in a variety of shallow turbid lakes.
Denitrification as a sink of dissolved nitrous oxide (N[sub 2]O) was investigated in a freshwater riparian fen. In a 15-m transect extending from the hillslope and into the fen the groundwater concentrations of nitrate (NO[sub 3][sup [minus]]) declined from 1.8 mM NO[sub 3][sup [minus]] to less than 0.01 mM NO[sub 3][sup [minus]], dissolved oxygen (O[sub 2]) and nitrous oxide (N[sub 2]O) declined from approximately 110 [micro]M O[sub 2] (3.5 mg O[sub 2] LO[sup [minus]1]) and 4.0 [micro]M N[sub 2]O-N, respectively, to zero and the dissolved N[sub 2] concentration increased by 589 [micro]M N[sub 2]-N. The NO[sub 3][sup [minus]] reduction was 0.42 [micro]M cm[sup [minus]3] d[sup [minus]1] or 7.71 [micro]M cm[sup [minus]2]d[sup [minus]1] in sediment columns with continuous upward groundwater flow through the sediment. Concomitant with NO[sub 3][sup [minus]] reduction, N[sub 2]O was produced at a rate of 54.4 nM N[sub 2]O-N cm[sup [minus]2] d[sup [minus]1] in this same 18-cm narrow sediment zone. However, the N[sub 2]O produced was subsequently reduced at the same rate closer to the sediment surface. In [sup 15]NO[sub 3][sup [minus]] experiments on chloramphenicol-treated anaerobic sediment slurries, the denitrifying enzyme activity (DEA) was estimated to be 118 [+-] 16.7 nmol N (N[sub 2]-N + N[sub 2]O-N)g fresh weight[sup [minus]1] d[sup [minus]1], of which 36% accumulated as N[sub 2]O. Thus, in this permanently water-covered riparian fen, denitrification served as a sink for both the dissolved N[sub 2]O in groundwater charging the fen and the N[sub 2]O produced within the riparian sediment.
The rise in mean annual temperatures under the projected climate change will affect both soil organic matter turnover and cropping patterns in agriculture. Nitrogen (N) mineralization may be higher during autumn and winter and may increase the risk of nitrate leaching. Our study tested whether a soil cover of winter wheat or a ryegrass catch crop would be able to take up the extra N mineralized during autumn and winter under the low light conditions in Northern Europe, both at current average temperatures (T0) and at 4°C (T+4) and 8°C (T+8) above average. The crops were grown in pots in growth chambers from mid-September to February. Two sowing times were included for winter wheat, with an early sowing in September representing current practice and a late sowing in October to reflect possible future cropping conditions. Biomass yield and soil inorganic N were determined from replicate pots in November, December and February. Reference pots with bare soil were included. N mineralization clearly increased with higher temperatures with, respectively, 22% and 80% more N mineralized in bare soil at T+4 and T+8 than at T0 after 136 days. The ryegrass catch crop emptied the soil of inorganic N very efficiently during both autumn and winter months at all temperatures. The early-sown wheat crop left negligible amounts of inorganic N in the soil at the last harvest in February at T+4 and T+8, whereas it was unable to take up all mineralized N at T0. The prolonged period without a crop before the late sowing of wheat caused generally higher levels of inorganic N to accumulate in soil. Despite the higher mineralization under the raised temperatures, at T+8 the late-sown winter wheat was able to reduce soil inorganic N to a lower level than late-sown wheat at the two lower temperatures. The results indicate that even at the low light intensity during autumn and winter, accelerated N mineralization caused by raised temperatures can potentially be offset by crop N uptake. However, sowing should take place sufficiently early in the autumn to give the crop time to capture the additional N mineralized during autumn, and this may collide with the projected need for later sowing of winter cereals under a warmer climate.
The effects of elevated CO2 concentration upon rhizodeposition of nitrogen were investigated on field-grown Lolium perenne planted in soil cores set into the resident soil of a intensively managed ryegrass sward treated with elevated CO2 for nine consecutive years, under two contrasted N fertilisation regimes (Swiss FACE Experiment). The planted cores were excavated from the ambiant (35Pa pCO2) and enriched (60Pa pCO2) rings at two dates during the growing season (spring and early autumn). The cores were brought back to the laboratory for a pulse-labelling of ryegrass shoots with 15NH3, in order to quantify 15N-rhizodeposition.A recovery of 10–16% of the total 15N administred to the plant was recovered in the plant–soil system 48h after the pulse-labelling; significant amounts of 15N were released into the soil adhering (adhering soil: AS) to the roots (0.44μg15NgAS−1 and 0.60μggAS−1 in the spring and the autumn samplings, respectively).In the spring sampling, there was no effect of atmospheric CO2 concentration on N rhizodeposition. In the autumn sampling, elevated CO2 stimulated N rhizodeposition that amounted to 7.2 and 5.2mg15Nm−2, under elevated and ambient CO2, respectively. Nitrogen rhizodeposition was higher at high N (56gNm−2) than at low N fertilisation (14gNm−2), whatever the sampling date investigated.The mechanisms by which elevated atmospheric CO2 leads to a stimulation of the net root-released N flux remains to be investigated: was it caused by a higher nitrogen immobilisation by the microbial biomass and a reduced re-assimilation of mineralized N and/or by a stimulation of N efflux from roots? Concomitant to the observed reduction of C rhizodeposition, the stimulation of net N efflux suggests that the quality of root released compounds was modified under elevated CO2 concentration.
Total P (TP), total particulate P (TPP), dissolved reactive P (DRP), and dissolved organic P (DOP) were determined in waters from pipe- drains (at 65-cm depth) from the Broadbalk Experiment at Roth- amsted. Soils that have received either no P, P in farmyard manure (about 40 kg P ha- a) or superphosphate (up to 35 kg P ha - ~) annually for >150 yr, now contain 0.5 M NaHCO3-extractable P concentrations (Oisen-P) in the plow layer (0- to 23-cm depth) between 5 and 100 mg kg- ~ soil. Our aim was to determine if significant quantities of P could be detected in the drainage water and their relationship to soil P concentrations. On five occasions between October 1992 and January 1994, both TP and DRP from plots receiving superphosphate frequently exceeded 1 mg L-~ and were high compared with literature data. Ranging between 66 and 86% of TP, DRP was the largest fraction in drainage water. It remained low (
This study investigates potential changes in nitrogen and phosphorus loads under a warmer and wetter climate, urban growth, and combined changes in the Conestoga River Basin and its five subbasins in southeastern Pennsylvania. A GIS-based hydrochemical model was employed for assessing the sensitivity of the basins to the projected changes in 2030. Under the HadCM2 climate change scenario, mean annual nitrogen and phosphorus loads are expected to increase, with great increases in spring but slight decreases in fall primarily because of changes in monthly precipitation. When climate change and urbanization occur concurrently, mean annual nitrogen loads further increase by 50% in the most urbanizing subbasin. Point source nitrogen control could mitigate negative effects of climate and land use changes, reducing mean annual nitrogen loads to the contemporary baseline level.
Phosphorus released from aerobic sediment surfaces made up the major fraction of the total P-load to the trophogenic zone in four shallow Danish lakes in 1987. Gross release rates were 15, 21, 33, and 100 mg P m-2 d- l (average summer values). In three of the lakes, water temperature alone explained -70% of the seasonal variation in sediment P release. Long-term experiments with undisturbed sediment cores revealed that the P release was significantly influenced by tem- perature and NO,- in all four lakes, but by pH only in one lake when these three parameters varied within the normal seasonal range (temperature: O"-21°C; NO,-: O-200 PM; pH: 7.5-10.5). Q10 values for the temperature effect were between 4.1 and 6.8 in the three lakes with large proportions of Fe-bound P in the sediment, but only 3.5 in the lake in which the P pool was relatively small. The thickness of the oxidized layer at the sediment surface varied from 3 to 15 mm and decreased when temperature increased. High N03- concentrations increased the thickness throughout the season and accordingly sediment P release was reduced in winter and early summer. Meanwhile, in late summer when inorganic N was depleted in lake water, N03- additions increased the P release from sediment, probably by stimulating the mineralization process.
An analysis of mean growing season concentrations of chlorophyll, total phosphorus (TP), and total nitrogen (TN) in 228 north latitude lakes confirms previous observations that chlo- rophyll yield is dependent both on the phosphorus concentration and on the TN:TP ratio. Of two modified chlorophyll models which depend explicitly on both nitrogen and phosphorus developed and tested, one, a multiple regression model, appears to greatly reduce the error of chlorophyll prediction in lakes. A theoretical framework is presented which provides an explanation for the observed effects of N:P ratios.
Scenarios of climate change for Denmark suggest increases in annual mean temperature of 1 to 4°C by the end of the 21st century with an associated increase in rainfall of approximately 10%. The climatic warming and the associated increase in atmospheric CO2 concentration will increase the productivity of agricultural crops. The increase may be slightly higher for indeterminate species, such as grass and other fodder crops, compared with cereals and other determinate species, where the duration of growth depends on temperature and daylength. The full benefits of the climatic warming requires adaptation in crop management, which at the individual crop level means changes in sowing dates, i.e., later sowings for winter cereals and earlier sowings for spring cereals. Some crop substitution will probably occur. On dairy farms more cereals will be grown due to higher productivity of the grasslands, which frees up some land for grain production. On sandy loam and loam soils spring cereals may become slightly more favorable and winter cereals slightly less favorable.
Soil temperature affects both the rate and thoroughness with which a plant root system permeates soil. Root system expansion is a function of two temperature-dependent processes, growth and development. Growth processes, like cell elongation, increase root length and diameter. Development controls duration of growth and initiation of new roots and reproductive organs. Interpreting root temperature responses requires an understanding of how development and growth interact. Soil temperature affects growth of root system components, initiation and branching, orientation and direction of growth, and root turnover. Genotypic differences in root response to soil temperature exist between and within plant species. In natural soil profiles, root system expansion is affected by seasonal patterns of soil temperature. As soil warming advances downward, progressively deeper soil layers become suitable for root growth. In temperate regions, soil temperature often limits the rate of rooting-depth increase and the maximum depth attainable. A simple temperature-based model to predict rooting depth with time indicates that rooting depth may follow the downward progression of a particular isotherm, which has sometimes been observed in the field.
(C) Williams & Wilkins 1992. All Rights Reserved.
Statistical analysis of a North American Wetland Database (NAWDB) allowed us to develop a mass loading model that was used to separate P assimilative capacity (defined as P absorption with no significant ecosystem change and no elevated P output) from storage capacity (maximum storage) in wetlands. Our analysis indicates that, given ample supplies of other nutrients, average P assimilative capacity (PAC) in North American wetlands is near 1 g m-2 yr-1. From this analysis, we proposed a “One Gram Assimilative Capacity Rule” for P loadings within natural freshwater wetlands if long-term storage of P, maintenance of community structure and function, and low P effluent concentrations are required. An Everglades test site supports our hypothesis that natural wetlands will lose native species, become P saturated in a few years, and export unacceptable amounts of phosphate when phosphorus loading exceeds PAC. Moreover, our findings clearly demonstrate that even P-limited wetlands have the capacity to assimilate low levels of P loadings without significant changes in ecosystem structure and function.
1. While phosphorus (P) is often considered the most important growth limiting factor for plants in lakes, recent studies of shallow lakes indicate that nitrogen (N) may be of greater importance than realized hitherto and that submerged macrophytes may be lost when the N concentration exceeds a certain threshold, as long as the concentration of P is sufficiently high.
2. We studied the effects of different loadings of NH4-N and NO3-N on chlorophyll a and on a macrophyte tolerant of eutrophication, Vallisneria spinulosa (Hydrocharitaceae). In outdoor mesocosms we used water from a pond as control and created four levels of NH4-N and NO3-N (approximately 2.5, 5, 7.5 and 10 mg L−1) by dosing with NH4Cl and NaNO3, respectively. After the experiment, the plants were transferred back to a holding pond to study their recovery. In contrast to previous research, we used a low background concentration of phosphorus (TP 0.024 ± 0.003 mg L−1) so we could judge whether any effects of N were apparent when P is in short supply.
3. Chlorophyll a increased significantly with N dosing for both forms of N, but the increase was highest in the NH4-N dosed mesocosms (maximum 58 μg L−1 versus 42 μg L−1 in the NO3-N mesocosms), probably due to a higher total inorganic N concentration (part of the added ammonia was converted to nitrate during the experiment).
4. Although the number of ramets of V. spinulosa was not affected by the N treatment, the biomass increased up to concentrations of 7.5 mg L−1, while biomass at 10 mg L−1 remained at the control level for both N ions treatments. A similar pattern was apparent for the content of N and soluble sugar of the plant, while there were no differences in the plant P content among treatments. Five months after transplantation back to the pond no difference was found in the number of ramets or in biomass, except that the biomass of plants grown at 10 mg N L−1 during the experiment was greater than that in the control, while the N and P contents of plants were similar to those of the controls.
5. Nitrogen concentration had little influence on the growth of the eutrophication tolerant submerged macrophyte at moderately low concentrations of phosphorus. Moreover, the two N ions showed no toxic effects, suggesting that loss of macrophytes observed in other studies, run at higher phosphorus concentrations, was probably related to enhanced shading by periphyton and/or phytoplankton rather than to any toxic effects of N.
1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1 ⁺ fish ( Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m ⁻² .
2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls.
3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L ⁻¹ and TP >0.13–0.2 mg P L ⁻¹ . These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L ⁻¹ , irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L ⁻¹ .
4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor.
5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re‐establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes.
Aims To test the magnitude and direction of the effects of large‐scale environmental factors (latitude and habitat type: lotic or lentic) on the intraspecific variations in multiple life‐history traits, across multiple European freshwater fish species. To test the relevance of defining species traits by quantifying the magnitude of interspecific vs. intraspecific variability in traits.
Location Europe.
Methods We obtained estimates of 11 fish traits from published sources for 1089 populations of 25 European freshwater fish species. Traits were: longevity, maximal length, growth rate, asymptotic length, mortality rate, age and length at maturation, fecundity, egg size, gonadosomatic index, and length of breeding season. We described population habitats by latitude and habitat type (lotic or lentic), when available. For each species we tested the combined effect of latitude and habitat type on the intraspecific variation of each trait using analysis of covariance ( ancova ). We compared the intraspecific variation in traits with the variation between species using an analysis of variance ( anova ) for each trait, all species pooled.
Results We found a consistent effect in direction of latitude on six traits, but we showed that this effect is not always significant across species. Higher‐latitude populations often grew more slowly, matured later, had a longer life span and a higher maximal and asymptotic length, and allocated more energy to reproduction than populations at lower latitudes. By contrast, we noted only a slight effect of habitat type on the intraspecific variation in traits, except for Salmo trutta . All traits varied significantly between species. However, traits such as growth rate, mortality rate and length of breeding season varied more between populations than between species, whereas fecundity and traits associated with body length varied more between species.
Main conclusions Latitude, in contrast to habitat type, is an important factor influencing several traits of geographically widely dispersed populations of multiple European freshwater fish species. Species traits that vary more between species than between populations are attractive variables for understanding and predicting the responses of stream fish communities to their environment.
Physically, lakes have traditionally been viewed as individual systems forced by statistically stationary local weather. This view implies that the physical response of a lake to external physical forcing is unique and stationary. Recent recognition of the importance of large-scale climatic forcing in driving physical lake processes, combined with the realisation that this forcing is undergoing a long-term trend as a result of climate change, has led to a shift in this paradigm. The new physical paradigm views lakes more in terms of a local response to large-scale climatic forcing modulated by the addition of local noise. A strong climate signal leads to large-scale spatial coherence in the physical lake response, while the existence of trends in large-scale climatic forcing associated with climate change means that both the forcing and the physical lake response are statistically non-stationary. Thus increasing realisation of the importance of climate and climate change is invalidating the tacit assumptions of individuality and stationarity that underlie the old conceptual framework, resulting in its gradual abandonment in favour of a new paradigm based on the concepts of spatial coherence and temporal non-stationarity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Abstract Global warming is expected to result in considerable changes in northern European freshwater fish populations, fisheries and aquaculture. Shifts towards cyprinid and percid dominance in fish assemblages are expected, together with a decrease and collapse of salmonid and other coldwater fish populations. Most of the evident changes will occur in shallow lakes, where no thermal stratification occurs. The potential ranges of some fish species will shift northwards but pronounced changes will occur in the relative abundance of individual fish species. Total fish production will increase but because of changed composition of fish communities the commercial and recreational value of catches will decrease. Salmonid aquaculture productivity will increase provided that fish farmers adapt to new circumstances and cold, oxygenated water is available in larger quantities during summer.
The nitrogen (N) conserving effects of Italian ryegrass ( Lolium multiflorum L.) undersown as a nitrate catch crop in spring barley ( Hordeum vulgare L.) were evaluated over a ten‐year period in outdoor lysimeters (1.5 m deep, diam. 1 m) with sandy loam soil. Spring barley grown every year received 11.0 or 16.5 g N m ⁻² before planting or was kept unfertilized. The N was given either as calcium ammonium nitrate or as ammoniacal N in pig slurry. From 1985 to 1989, ryegrass was undersown in the barley in half of the lysimeters while barley was grown alone in the remaining lysimeters. The grass sward was left uncut after barley harvest and incorporated in late winter/early spring. From 1990 to 1994 all lysimeters were in barley only.
Barley dry matter yields and crop N offtakes were not affected by the presence of undersown ryegrass, although grain yields appeared to be slightly reduced. After termination of ryegrass growing, N offtake in barley (grain+straw) was higher in lysimeters in which catch crops had been grown previously.
The loss of nitrate by leaching increased with N addition rate. Regardless of N dressing, ryegrass catch crops halved the total nitrate loss during 1985–1989, corresponding to a mean annual reduction in nitrate leaching of 2.0–3.5 g N m ⁻² . From 1990 to 1994, lysimeters previously undersown with ryegrass lost more nitrate than lysimeters with no history of ryegrass. The extra loss of nitrate accounted for 30% of the N retained by ryegrass catch crops during 1985–1989.
It is concluded that a substantial proportion of the N saved from leaching by ryegrass catch crops is readily mineralized and available for crop offtake as well as leaching as nitrate. To maximize benefits from ryegrass catch crops, the cropping system must be adjusted to exploit the extra N mineralization derived from the turnover of N incorporated in ryegrass biomass.
1. The impact of long thermal stratification events on some key properties in a polymictic lake was studied by determining the mixing regime of Müggelsee, Germany, using water temperature profiles taken hourly over 4 years. The period included two exceptional summer heatwaves.
2. Long thermal stratification events lasted from about 1 week to 2 months, and exhibited a high variability in thermocline depth and stratification intensity within and between events.
3. During stratification events, hypolimnetic oxygen concentrations strongly decreased while hypolimnetic SRP accumulation increased, depending on the duration and intensity of stratification and on hypolimnetic water temperature.
4. The impact of stratification on the functional phytoplankton composition increased with increasing stratification duration, but was rather different for the heatwaves.
5. Stratification events were followed by strong nutrient pulses into the euphotic zone and intense phytoplankton growth, particularly after the heatwaves. Hence, the influence of the climate extremes counteracted effects of reduced external nutrient loading.
As concentrations of atmospheric CO2 increase, it is important to know whether this may result in feedbacks that could modify the rate of increase of CO2 in the atmosphere. Soil organic matter (SOM) represents one of the largest pools of C and mineralization rates are known to be temperature dependent. In this study, we investigated whether different OM fractions present in a forest soil (F/A1 horizon) would respond in a similar manner to elevated temperatures. We examined the trends in isotopic content (12C, 13C, and 14C) of soil respired CO 2 at various temperatures (10, 20, and 35°C) over a two year period in the laboratory. We also examined the total C, total N, and C : N ratio in the remaining soil and isolated humic fractions, and the distribution of the individual amino acids in the soil after 5 years of laboratory incubation at the various temperatures. We found that the rate at which C mineralization increases with temperature was occasionally greater than predicted by most models, more C from recalcitrant OM pools being mineralized at the higher temperature. This confirmed that the relationship between soil organic matter decomposition and temperature was complex and that the different pools of organic matter did respond in differing ways to elevated temperatures.
This paper analyses historic records of agricultural land use and management for England and Wales from 1931 and 1991 and uses export coefficient modelling to hindcast the impact of these practices on the rates of diffuse nitrogen (N) and phosphorus (P) export to water bodies for each of the major geoclimatic regions of England and Wales. Key trends indicate the importance of animal agriculture as a contributor to the total diffuse agricultural nutrient loading on waters, and the need to bring these sources under control if conditions suitable for sustaining ‘Good Ecological Status’ under the Water Framework Directive are to be generated. The analysis highlights the importance of measuring changes in nutrient loading in relation to the catchment-specific baseline state for different water bodies. The approach is also used to forecast the likely impact of broad regional scale scenarios on nutrient export to waters and highlights the need to take sensitive land out of production, introduce ceilings on fertilizer use and stocking densities, and controls on agricultural practice in higher risk areas where intensive agriculture is combined with a low intrinsic nutrient retention capacity, although the uncertainties associated with the modelling applied at this scale should be taken into account in the interpretation of model output. The paper advocates the need for a two-tiered approach to nutrient management, combining broad regional policies with targeted management in high risk areas at the catchment and farm scale.