Water Quality In Eutrophic Lakes Research Articles

Temporal variations in dissolved organic matter properties in a eutrophic lake under water dilution and aquatic plant litter decomposition: A simulated microcosm study revealing the environmental and microbial driving factors

Dilution by importing external clean water and restoration of aquatic vegetation are widely applied strategies for improving water quality of eutrophic lakes, while the influence of dilution or aquatic plant litter decomposition on dissolved organic matter (DOM) properties, which is closely associated with the health of aquatic ecosystems, is rarely known. In this study, the temporal variations of DOM properties in the overlying water of a eutrophic lake (Yilong lake in Yunnan, southwest China) under water dilution and aquatic plant litter decomposition were comparatively investigated via a simulated microcosm study using in situ samples. The results showed that water dilution reduced DOM concentration and bioavailability in the overlying water in a short term (about 45 d), and increased DOM humification, but such effect diminished over time. DOM concentration increased substantially during aquatic plant litter decomposition, and reed litter released much more amounts of DOM than that of cattail litter, which dominated by protein-like substances and characterized by high bioavailability and low humification degree. Nutrient (available phosphorus (AP), NH4+-N and TN) contents in the sediment indirectly affected DOM properties by remarkably influencing microbial community compositions and enzyme activities. The strong correlations between the relative abundances of dominant genera Bacillus and Clostridium and concentrations of DOM components implied the important roles of these taxa in DOM transformations. Our findings highlighted the effects and potential mechanisms of dilution and aquatic plant litter decomposition on DOM properties in eutrophic water bodies, and the necessity of proper water diversion and plant litter harvest to reduce endogenous organic pollution in lakes.

Hot summers raise public awareness of toxic cyanobacterial blooms

Water quality of eutrophic lakes is threatened by harmful cyanobacterial blooms, which are favored by summer heatwaves and expected to intensify with global warming. Societal demands on surface water for drinking, irrigation and recreation are also highest in summer, especially during dry and warm conditions. Here, we analyzed trends in online searches to investigate how public awareness of cyanobacterial blooms is impacted by temperature in nine different countries over almost twenty years. Our findings reveal large seasonal and interannual variation, with more online searches for harmful cyanobacteria in temperate regions during hot summers. Online searches and media attention increased even more steeply with temperature than the incidence of cyanobacterial blooms, presumably because lakes attract more people during warm weather. Overall, our study indicates that warmer summers not only increase cyanobacterial bloom incidence, but also lead to a pronounced increase of the public awareness of toxic cyanobacterial blooms.

Deep-reinforcement-learning-based water diversion strategy

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.

Diverse and abundant arbuscular mycorrhizal fungi in ecological floating beds used to treat eutrophic water.

An increasing number of investigations have shown the universal existence of arbuscular mycorrhizal fungi (AMF) in aquatic ecosystems. However, little is known about the accurate distribution and function of AMF inhabiting aquatic ecosystems, especially ecological floating beds (EFBs), which are constructed for the remediation of polluted water bodies. In this study, we collected root samples of Canna generalis, Cyperus alternifolius, and Eichhornia crassipes from three EFBs on two eutrophic lakes in Wuhan, China. We aimed to investigate the resources and distribution of AMF in EFBs using Illumina Mi-seq technology. A total of 229 operational taxonomic units (OTUs) and 21 taxa from 348,799 Glomeromycota sequences were detected. Glomus and Acaulospora were the most dominant and second most dominant genera of AMF in the three EFBs, respectively. Different aquatic plant species showed varying degrees of AMF colonization (3.83-71%), diversity (6-103 OTUs, 3-15 virtual taxa), and abundance (14-57,551 sequences). Low AMF abundance, but relatively high AMF diversity, was found in C. alternifolius, which is usually considered non-mycorrhizal. This finding indicated the high accuracy of Illumina sequencing. Our results also revealed a lognormal species abundance distribution that was observed across AMF taxa in the three plant species. The AMF community composition was closely related to nitrogen and phosphorus contents. Overall, our data show that EFBs harbor diverse and abundant AMF communities. Additionally, the AMF community composition is closely related to the water quality of eutrophic lakes treated by the EFBs, indicating the potential application of AMF in plant-based bioremediation of wastewater. KEYPOINTS: • Aquatic plants in EFBs harbor diverse (229 OTUs) and abundant (348,799 sequences) AMF. • Different plant species host different taxa of AMF. Cyperaceae, originally considered non-mycorrhizal, may in fact be a variable mycorrhizal plant family. • The AMF community composition in EFBs is closely related to nutrient concentrations (nitrogen and phosphorus).

Accumulation and decomposition of cyanobacteria and reed debris in eutrophic lakes and its potential co-metabolism effects

为探究富营养化浅水湖泊所富集的有机物对湖泊碳循环和水质的影响，本研究构建微宇宙系统，模拟蓝藻和芦苇碎屑单独分解及混合分解过程.通过测定各组上覆水营养盐浓度、有机质含量及结构的变化，揭示富营养化湖泊藻草残体混合分解过程中养分和有机碳的释放特征.结果表明，在实验0~88 h内，在添加相同的碳源条件下，蓝藻和芦苇混合处理组总碳（TC）释放量显著高于理论值，表明藻草碎屑混合分解存在共代谢效应.在培养初期，沉积物通过共代谢效应对水质产生了较大的影响，加速向水体中释放氮、磷物质.相较单独的植物分解，混合处理组中总氮（TN）、总磷（TP）的最大释放量分别提高了13.49%和26.84%；通过三维荧光光谱表征的类富里酸荧光强度变化也表明：较芦苇处理组，混合处理组中芦苇的分解速率更快.在培养开始后，各处理组均快速转变为厌氧状态，TC、TN、TP浓度随时间变化总体上呈先快速上升再逐渐平缓的趋势，分别在第228、108和324小时达最大值（372.4±2.98）、（138.45±2.97）和（7.95±1.11） mg/L.细菌特异性脂肪酸含量变化表明，将蓝藻碎屑添加到芦苇碎屑中，会增加芦苇碎屑中细菌的丰度，从而提高分解速率，激发共代谢效应.在全球气候变暖的背景下，随着富营养化湖泊藻类暴发频次增加，共代谢效应可能还会进一步加强，对富营养化湖泊水质将会持续产生影响.;In order to explore the effect of enriched organic matter in eutrophic shallow lakes on water quality and carbon cycle, in this study, we constructed a microcosm system to simulate the separate decomposition and mixed decomposition of cyanobacteria and reed debris. The changes of nutrient concentration, organic matter content and structure of the overlying water in each treatment were determined to reveal the release characteristics of nutrients and organic carbon during the mixed decomposition process of cyanobacteria and reed debris in eutrophic lakes. The results showed that the total carbon (TC) release of the mixed treatment was significantly higher than the theoretical value within 0-88 hours of the experiment under the same carbon source addition, indicating that there is a co-metabolism effect during the mixed decomposition of cyanobacteria and reed debris. In the initial stage of the cultivation, sediments accelerated the release of total nitrogen (TN) and total phosphorus (TP) to the overlying water and caused a significant impact on the water quality via the co-metabolism effect. Compared with the reed treatment, the maximal release of TN and TP in the mixed treatment increased by 13.49% and 26.84%, respectively. The change of fluorescence intensity of fulvic acid characterized by the three-dimensional fluorescence spectroscopy (EEMs) also showed that the decomposition rate of reed was faster in the mixed treatment group. At the beginning of cultivation, each treatment quickly turned into anaerobic state, and the concentration of TC, TN and TP displayed a trend of dramatical increase and then gradually flattened, with a maximum of (372.4±2.98), (138.45±2.97), and (7.95±1.11) mg/L at 228, 108 and 324 hours, respectively. The variations of bacterial specific fatty acid showed that the input of Microcystis detritus into Phragmites detritus increased the abundance of decomposing bacteria in Phragmites detritus, and accelerated the decomposition rates, resulting in the co-metabolism of Microcystis and Phragmites carbon. Under the background of global warming, with the increasing frequency of algae outbreaks in eutrophic lakes, the co-metabolism effect may be further strengthened, and the water quality of eutrophic lakes will be affected continuously.

Optimization of aluminum treatment efficiency to control internal phosphorus loading in eutrophic lakes

Historical accumulation of phosphorus (P) in lake sediment often contributes to and sustains eutrophic conditions in lakes, even when external sources of P are reduced. The most cost-effective and commonly used method to restore the balance between P and P-binding metals in the sediment is aluminum (Al) treatment. The binding efficiency of Al, however, has varied greatly among treatments conducted over the past five decades, resulting in substantial differences in the amount of P bound per unit Al. We analyzed sediment from seven previously Al treated Swedish lakes to investigate factors controlling binding efficiency. In contrast to earlier work, lake morphology was negatively correlated to binding efficiency, meaning that binding efficiency was higher in lakes with steeply sloping bathymetry than in lakes with more gradually sloping bottoms. This was likely due to Al generally being added directly into the sediment, and not to the water column. Higher binding efficiencies were detected when Al was applied directly into the sediment, whereas the lowest binding efficiency was detected where Al was instead added to the water column. Al dose, mobile sediment P and lake morphology together explained 87% of the variation in binding efficiency among lakes where Al was added directly into the sediment. This led to the development of a model able to predict the optimal Al dose to maximize binding efficiency based on mobile sediment P mass and lake morphology. The predictive model can be used to evaluate cost-effectiveness and potential outcomes when planning Al-treatment using direct sediment application to restore water quality in eutrophic lakes.

Spatio-temporal Variation in Nutrient Profiles and Exchange Fluxes at the Sediment-Water Interface in Yuqiao Reservoir, China.

Nutrients released from sediments have a significant influence on the water quality in eutrophic lakes and reservoirs. To clarify the internal nutrient load and provide reference for eutrophication control in Yuqiao Reservoir, a drinking water source reservoir in China, pore water profiles and sediment core incubation experiments were conducted. The nutrients in the water (soluble reactive P (SRP), nitrate-N (NO3−-N), nitrite-N (NO2−-N), and ammonium-N (NH4+-N)) and in the sediments (total N (TN), total P (TP) and total organic carbon (TOC)) were quantified. The results show that NH4+-N was the main component of inorganic N in the pore water. NH4+-N and SRP were higher in the pore water than in the overlying water, and the concentration gradient indicated a diffusion potential from the sediment to the overlying water. The NH4+-N, NO3−-N, and SRP fluxes showed significant differences amongst the seasons. The NH4+-N and SRP fluxes were significantly higher in the summer than in other seasons, while NO3−-N was higher in the autumn. The sediment generally acted as a source of NH4+-N and SRP and as a sink for NO3−-N and NO2−-N. The sediments release 1133.15 and 92.46 tons of N and P, respectively, to the overlying water each year.

Coupled long‐term limnological data and sedimentary records reveal new control on water quality in a eutrophic lake

AbstractHuman impacts on freshwater ecosystems are pervasive, but the short and discontinuous nature of most datasets limits our ability to understand the controls on water quality and effectively manage freshwater resources. We examine change in Lake Mendota (Madison, Wisconsin) over the last two centuries by pairing analyses of a sedimentary archive with the site's > 100 yr limnological record. We show that eutrophication of the lake, evident as an abrupt shift in sediment composition, began in the late 19th century following the intensification of urban and agricultural land use in the watershed. Efforts to address deterioration of lake water quality, including the removal of point‐source pollutants and biomanipulation, have had a measurable influence on sediment composition and water clarity. Since the early 1980s, quasi‐seasonal cycles of phytoplankton blooms have induced calcite precipitation, leaving distinct laminations in the sedimentary record. These “whiting events” evidently did not accumulate in lake sediments until the late 20th century, indicating that efforts to remediate water quality have shifted the lake to a new ecosystem state. Calcite whitings can improve water quality in eutrophic lakes by coprecipitation with phosphate, increasing phosphorus (P) burial in lake sediments. Using long‐term limnological records, we report negative correlations between calcite saturation indices and P in lake surface waters and show that calcite whitings could partially explain recent P decline in Lake Mendota surface waters. Our study reveals a previously uncharacterized potential control on water quality in this eutrophic lake and demonstrates the benefit of coupling long‐term limnological data with sedimentary records.

Study on the Effect of Periphyton on the Water Quality of Eutrophic Lakes

In this study, we constructed aquatic microcosms, including four experimental groups, to simulate eutrophic lakes. Using polyurethane sponges as artificial substrates to support periphyton, we conducted a systematic study of the effect of periphyton on the water quality of eutrophic lakes by monitoring water-quality indexes including TN, TP, and NTU. The results show that periphyton can effectively degrade N and P in these bodies of water, reduce NTU and the concentration of Chl-a, and restore the aquatic environment. Periphyton can also promote the formation of the DO-Chl-a-NTU-TN-TP synergistic system, which can provide a basis for the comprehensive management of eutrophic lakes. Periphyton can also effectively improve the water quality of eutrophic lakes, and its positive impact on lake ecosystems cannot be ignored during the treatment of eutrophic lakes.

On the use of macrophytes to maintain functionality of overgrown lowland lakes

The presence of macrophytes is a key factor that determines good water quality in eutrophic lakes, and control of their presence is desirable to establish a clean water state. However, the subject is frequently discussed due to the intensive growth of aquatic plants that can restrict functioning of the reservoir (e.g., for swimming, fishing, etc.). Overgrowth of macrophytes also causes terrestrialisation processes of lakes, which occur very intensively in shallow and lowland artificial reservoirs. In order to analyse the contribution of macrophytes to nutrient reduction in lakes and investigate the possibility of using aquatic plants in reservoir recultivation, we investigated the nutrient budget of two artificial reservoirs located in Wielkopolska (Poland) with particular attention on macrophytes and nutrient pollution sources. To determine the loads with internal and external nutrients, we analysed the land use in the respective catchment areas, ground water quality, sewage management, quality and quantity of surface waters supplied to lakes (rivers and ditches), water, macrophytes and sediment quality in the reservoirs. Our results indicate that in both analysed catchments, the major source of nutrients is unregulated sewage systems. This demonstrates why improvement of sewage management is vital for increased water quality and more effective functioning of water reservoirs. We also propose methods to reduce the amount of nutrients directly supplied to lakes from agricultural lands. Our findings suggest that the mowing of macrophytes can reduce nutrient concentrations in the reservoirs. However, its impact is not particularly significant in comparison with the amount of nitrogen and phosphorus supplied from internal sources. Moreover, our study shows that growth limitation of particular species can stimulate growth of a desired species (e.g., charophytes). Controlled removal of macrophytes may also stimulate their intensive growth and possibly give rise to an increase in the amount of nutrients immobilised in the lake.

Aluminum application to restore water quality in eutrophic lakes: maximizing binding efficiency between aluminum and phosphorus

ABSTRACTHuser BJ. 2017. Aluminum application to restore water quality in eutrophic lakes: maximizing binding efficiency between aluminum and phosphorus. Lake Reserv Manage. 33:143–151.Aluminum (Al), typically added to lakes to reduce internal cycling of legacy phosphorus (P) in sediment, was added to the littoral zone of Lake Harriet (Minnesota) to inhibit the uptake of sediment P by buoyancy regulating species of plankton. Analytical results from sediment collected over an 11-year period showed that the added Al (32 g/m2) started to move outside the treatment zone almost immediately after treatment, with <5% remaining within the treatment area after 6 months. Although the original treatment design failed, the application method was, unexpectedly, a success with respect to binding efficiency between Al and P in the sediment. As the Al drifted to deeper areas of the lake, internal P release in non-treated, deeper areas of the lake declined and the binding ratio between Al and Al-bound P decreased, reaching 2.1 (molar) in profundal sediments 10 years after treatment. The increased contact with available (mobile) sediment P increased binding efficiency, resulting in a 163–581% increase of P bound per unit Al compared to previous whole-lake aluminum treatments. The binding efficiency exceeded expectations showing that, in addition to the amount of Al added, treatment location and subsequent translocation of the Al floc can substantially affect binding efficiency and treatment effectiveness.

China, Singapore & US: Clariant – masterbatch

The presence of macrophytes is a key factor that determines good water quality in eutrophic lakes, and control of their presence is desirable to establish a clean water state. However, the subject is frequently discussed due to the intensive growth of aquatic plants that can restrict functioning of the reservoir (e.g., for swimming, fishing, etc.). Overgrowth of macrophytes also causes terrestrialisation processes of lakes, which occur very intensively in shallow and lowland artificial reservoirs. In order to analyse the contribution of macrophytes to nutrient reduction in lakes and investigate the possibility of using aquatic plants in reservoir recultivation, we investigated the nutrient budget of two artificial reservoirs located in Wielkopolska (Poland) with particular attention on macrophytes and nutrient pollution sources. To determine the loads with internal and external nutrients, we analysed the land use in the respective catchment areas, ground water quality, sewage management, quality and quantity of surface waters supplied to lakes (rivers and ditches), water, macrophytes and sediment quality in the reservoirs. Our results indicate that in both analysed catchments, the major source of nutrients is unregulated sewage systems. This demonstrates why improvement of sewage management is vital for increased water quality and more effective functioning of water reservoirs. We also propose methods to reduce the amount of nutrients directly supplied to lakes from agricultural lands. Our findings suggest that the mowing of macrophytes can reduce nutrient concentrations in the reservoirs. However, its impact is not particularly significant in comparison with the amount of nitrogen and phosphorus supplied from internal sources. Moreover, our study shows that growth limitation of particular species can stimulate growth of a desired species (e.g., charophytes). Controlled removal of macrophytes may also stimulate their intensive growth and possibly give rise to an increase in the amount of nutrients immobilised in the lake.

Biological indicators track differential responses of pelagic and littoral areas to nutrient load reductions in German lakes

External nutrient loading was reduced over the past decades as a measure for improving the water quality of eutrophic lakes in western Europe, and has since been accelerated by the adoption of the European Water Framework Directive (WFD) in 2000 (EC, 2000). A variety of eutrophication-related metrics have indicated that the response of biological communities to this decreased nutrient loading has been diverse. Phytoplankton, a major component of the pelagic community, often responded rapidly, whereas a significant delay was observed for submerged macrophytes colonizing littoral areas. In this study we tested whether assessment methods developed for phytoplankton and macrophytes in lakes during Germany's implementation of the WFD reflect this differential response. An assessment of 263 German lakes confirmed that a lower ecological state was recorded when based on the biological quality element (BQE) for macrophytes than the BQE for phytoplankton during the investigated period (2003–2012). On average, lakes had a moderate ecological status for both phytoplankton and macrophyte BQEs, but differences of up to three classes were observed in single cases. Long-term data were available for five lowland lakes subject to strong reductions in phosphorus loading. Their phytoplankton-based assessments indicated a constant improvement of the ecological status in parallel to decreasing water phosphorus concentrations. In contrast, macrophyte-based assessments indicated a 10–20 year delay in their ecological recovery following nutrient load reduction. This delay was confirmed by detailed data on the temporal development of macrophyte species diversity and maximum colonization depths of two lakes after nutrient load reduction. We conclude that the available WFD assessment methods for phytoplankton and macrophyte BQEs are suitable to track the differential response of pelagic and littoral areas to nutrient load reductions in German lakes.

What is the influence of a reduction of planktivorous and benthivorous fish on water quality in temperate eutrophic lakes? A systematic review

Abstract Background In recent decades, many attempts have been made to restore eutrophic lakes through biomanipulation. Reducing the populations of planktivorous and benthivorous fish (either directly or through stocking of piscivorous fish) may induce ecosystem changes that increase water transparency and decrease the risk of algal blooms and fish kills, at least in the short term. However, the generality of biomanipulation effects on water quality across lake types and geographical regions is not known. Therefore, we have undertaken a systematic review of such effects in eutrophic lakes in temperate regions throughout the world. Methods Searches for literature were made using online publication databases, search engines, specialist websites and bibliographies of literature reviews. Search terms were developed in English, Danish, Dutch and Swedish. Identified articles were screened for relevance using inclusion criteria set out in an a priori protocol. To reduce the risk of bias, we then critically appraised the combined evidence found on each biomanipulation. Data were extracted on outcomes such as Secchi depth and chlorophyll a concentration before, during and/or after manipulation, and on effect modifiers such as lake properties and amounts of fish removed or stocked. Results Our searches identified more than 14,500 articles. After screening for relevance, 233 of them remained. After exclusions based on critical appraisal, our evidence base included useful data on 128 biomanipulations in 123 lakes. Of these interventions, 85% had been made in Europe and 15% in North America. Meta-analysis showed that removal of planktivores and benthivores (with or without piscivore stocking) leads to increased Secchi depth and decreased chlorophyll a concentration during intervention and the first three years afterwards. Piscivore stocking alone has no significant effect. The response of chlorophyll a levels to biomanipulation is stronger in lakes where fish removal is intense, and in lakes which are small and/or have high pre-manipulation concentrations of total phosphorus. Conclusions Our review improves on previous reviews of biomanipulation in that we identified a large number of case studies from many parts of the world and used a consistent, repeatable process to screen them for relevance and susceptibility to bias. Our results indicate that removal of planktivorous and benthivorous fish is a useful means of improving water quality in eutrophic lakes. Biomanipulation tends to be particularly successful in relatively small lakes with short retention times and high phosphorus levels. More thorough fish removal increases the efficacy of biomanipulation. Nonetheless successes and failures have occurred across a wide range of conditions.

Bottom‐up effects of lake sediment on pelagic food‐web compartments: a mesocosm study

Summary Sediment plays a key role in organic matter (OM) and internal nutrient cycling in lakes. The role of sediment as a source of OM and its potential bottom‐up effects on the pelagic food web have rarely been studied. Particularly, the influence of the biochemical composition of sediment OM on pelagic compartments remains largely unknown. During a 5‐month experiment, we studied the influence of two different sediments added at the bottom of large replicated mesocosms on the biomass of seston and zooplankton, and their elemental and lipid compositions. The influence of sediment treatments on sedimentation rates, elemental and biochemical compositions and potential biodegradability of recently sedimented OM (c. 1 week) was also examined. The two added sediments (S1 and S2) presented contrasting elemental and biochemical compositions and potential biodegradabilities. According to their contents of organic carbon, nitrogen, proteins, sugars and polyunsaturated fatty acids, S2 appeared to be much more biodegradable than S1. Therefore, the S2 sediment was expected to release more nutrients and OM to the water column than S1, leading to changes in communities, stoichiometry and lipid compositions of pelagic compartments. Probably due to its very poor content of labile compounds, the presence of S1 at the bottom of the mesocosms did not induce changes in the biomass of seston and zooplankton. Only few changes in the stoichiometry of these compartments were observed. In contrast, S2 sediment released more phosphorus and dissolved OM into the water column than S1. As a result, the S2 treatment induced an increase in seston biomass and therefore in zooplankton biomass via herbivory. None of the sediment treatments affected the lipid composition of seston and zooplankton. Moreover, neither S1 nor S2 induced changes in the sedimentation rates, elemental and lipid compositions, and potential biodegradability of recent sediments. Our mesocosm experiment suggests that differences in the quality of lake sediments lead to moderate changes in the pelagic communities in the absence of planktivorous or omnivorous fish. Our results could partly explain the efficiency of biomanipulation for improving water quality of eutrophic lakes despite potential nutrient release from sediment.

Indices of zooplankton community as valuable tools in assessing the trophic state and water quality of eutrophic lakes: long term study of Lake Võrtsjärv

On the basis of long-term (1964-2011) research, we tested the hypothesis that the zooplankton community has a highly indicative value in assessing the ecosystem and trophic state of water bodies. Basing on the results of our study and taking into account relevant data from numerous zooplankton studies, we can conclude that the zooplankton measures deserving to be used as indicators in the monitoring of Lake Vortsjarv (and other similar eutrophic water bodies) could be the following: i) indicatory species of eutrophic waters [ Anuraeopsis fissa (Gosse), Keratella tecta (Gosse), Trichocerca rousseleti (Voigt), Chydorus sphaericus (O. F. Muller), Bosmina longirostris (O. F. Muller)]; ii) indicatory species of oligo-mesotrophic waters [ Conochilus unicornis Rousselet, Kellicottia longispina (Kellicott), Ploesoma hudsoni (Imhof), Bosmina berolinensis Imhof, Eudiaptomus gracilis (Sars)]; iii) number and diversity of species; iv) mean zooplankter weight, mean cladoceran weight, mean rotifer weight and mean copepod weight; v) rotifer abundance; vi) the share (%) of rotifers in total zooplankton abundance; vii) the ratio of abundance of large cladocerans to abundance of all cladocerans (N LargeClad /N Clad ); viii) the ratio of calanoid copepod abundance to cyclopoid copepod abundance (N Cal /N Cycl ); ix) the ratio of crustacean abundance to rotifer abundance (N Crust /N Rot ). The results of our study show that several zooplankton parameters are among the biological quality elements (BQE) deserving to be included in the Water Frame Directive system.

Restoration of aquatic vegetation and its ecological effects in the enclosure of an eutrophic lake

水体富营养化导致水生植被衰退、蓝藻水华暴发、水质恶化和水生生态系统崩溃.恢复水生植被被认为是改善受损水体水质和提高其生态系统稳定性的重要手段.本研究通过构建大型围隔,根据水生植物的耐污程度及其对水质和底质等条件的需求,选取几种适宜的水生植物在围隔内进行移栽与群落构建,并以不移栽水生植物的围隔和围隔外水体作为对照.实验期间(2011年4月至2012年6月),围隔内移栽的几种水生植物全部存活,并建立了相对稳定的群落.同时还跟踪监测了3个处理组的水质情况,结果显示,移栽水生植物的围隔内水质明显优于围隔外,与未移栽水生植物围隔相比,也有很大程度的改善,其中移栽水生植物围隔内水体的总氮、铵态氮、总磷、水下消光系数相比于围隔外水体分别低30.55%、44.09%、36.04%和42.13%,相比于未移栽水生植物围隔内水体分别低5.96%、13.40%、6.70%和7.60%,透明度分别比围隔外水体和未移栽水生植物围隔水体高74.59%和8.70%,浮游植物生物量也大大低于围隔外,而浮游动物生物量却明显高于后者.此外,实验后移栽水生植物围隔内沉积物氮、磷含量及其间隙水总氮、总磷、铵态氮浓度明显低于围隔外和未移栽水生植物围隔.研究表明,在富营养化浅水湖泊中通过建立围隔进行合理的群落配置,进而逐步恢复水生植物是完全可行的,而水生植物恢复后加强对其管理和维护至关重要.;Eutrophication induces aquatic vegetation decline, cyanobacterial bloom, deterioration of water quality, and regime shifts in shallow lakes. Restoration of aquatic vegetation is considered as an important approach to improve water quality and enhance ecosystem stability. In this study, we transplanted aquatic macrophytes in large enclosures with temporal aids of water treatments and selecting aquatic macrophyte species according to their habitat preferences. Ecological effects of the transplantation were examined by comparing water chemicals and biological indices in the enclosures with and without aquatic macrophytes, and in the open water in the lake out of the enclosures. During the experimental period (from April 2011 to June 2012), all macrophytes in the enclosure survived and built relatively stable communities. The water quality was better in the enclosure with aquatic vegetation than in area without vegetation, concentrations of total nitrogen, ammonium nitrogen, total phosphorus and light extinction in water in the vegetated enclosure decreased by 30.55%, 44.09%, 36.04% and 42.13%, respectively. In comparison, in the open water, they decreased by 5.96%, 13.40%, 6.70% and 7.60%, respectively. Secchi depth increased by 74.59% and 8.70% as compared to the open water and the enclosure without aquatic vegetation, respectively, phytoplankton biomass was lower and zooplankton biomass was higher in the vegetated enclosure than in the one without aquatic vegetation and in the open water. In addition, aquatic vegetation tended to decrease the contents of total nitrogen and phosphorus in sediments and porewater of sediments and ammonium nitrogen concentrations in the porewater of sediments, but did not affect phosphate and nitrate in porewater of sediments. The study implied that selection of eutrophication tolerant aquatic macrophytes species facilitated restoration of aquatic vegetation and thus improve water quality in eutrophic lakes.

Inter- and intra-specific differences in filtering activities between two unionids, Anodonta woodiana and Unio douglasiae, in ambient eutrophic lake waters

Inter-specific and intra-specific differences in the filtering activities of two unionid bivalves, Unio douglasiae and Anodonta woodiana, which thrive in small agricultural canals, were compared using a flow-through chamber system of ambient eutrophic lake water. The mean filtration rates (FRs) of these two species, size-matched for similar shell length, were not significantly different ( t-test, t = 0.024, P = 0.981), whereas there were significant differences in the FRs between mussels of different ages ( t-test, t = 5.137, P = 0.001), different densities ( t-test, t = 8.297, P < 0.0001), and different currents ( t-test, t = 3.898, P = 0.005). The FRs of A. woodiana increased significantly more with higher temperatures in younger mussels ( P < 0.01, maximum FR = 0.352 ± 0.157 L/h at 13.5–20.4 °C) than in adults. However, the mortality of the mussels was comparatively higher in younger mussels due to a low tolerance to ammonia. Correlation coefficients and PCA results collectively indicate that the two dominant unionid mussels in the canal had a strong relationship with the seston level in the lake (turbidity, suspended solids and chlorophyll- a), resulting in a higher FR, pseudo-faeces production, and ammonia tolerance and a lower mortality. In addition, the validation of the biomanipulation used in the mussel-controlled system is discussed in an effort to improve the water quality of eutrophic lakes and streams and the conservation of the benthic mussel community.

Fundamental Structure in Simultaneous Removal for Phytoplankton and Nutrient Salt in Lakes

The water quality in eutrophic lakes is affected by serious problems, such as abnormal increasing of Cyanobacteria. The purpose of this study was to investigate the possibility of a modified flotation system using a hybrid technique formed by chemical compounds and an electrostatic bridge. Therefore, experiments using the hybrid technique were performed to measure the zeta potential value on the phytoplankton surface and the removal efficiencies of phytoplankton, ammonia nitrogen, nitrate nitrogen and phosphoric acid. The results were as follows: Firstly, the zeta potential of M.aeruginosa was observed to approach charge neutralization due to adhesion of magnesium hydroxide precipitate on the phytoplankton surface in the pH range 10.5 to 11. Secondly, the concentration of chlorophyll-a decreased from about 150 to 20μg/L, with a maximum removal efficiency of 84% due to coagulation with pH values higher than 10. Thirdly, the NH4-N concentration was observed to decrease from 0.62 to 0.54mg-N/L (13%), and the PO4-P concentration, which is a limiting factor to the formation of algae blooms, decreased from 0.27 to 0.02mg-P/L (92%). These findings suggest that the modified flotation system can be applied for the purification of the raw water of numerous lakes containing high phytoplankton populations and elevated pH.

Ammonium release characteristics of the sediments from the shallow lakes in the middle and lower reaches of Yangtze River region, China

Ammonium release from sediments has significant effects on the water quality in eutrophic lakes. In this study, the ammonium release kinetics and adsorption–desorption processes were investigated in 13 sediments of 6 shallow lakes from the middle and lower reaches of Yangtze River region, China. The results show that First Order Model best described the ammonium release process, the maximal release capacity had a strong correlation with organic matter (OM), cationic exchange capacity (CEC), total nitrogen (TN) and total phosphorus (TP). But it only had a weak correlation with Fe, Ca and Al. The ammonium release capacity in more polluted sediments was higher than that in less polluted sediments. The average release rate within 0–5 min was the highest among the experimental period, the amount released within 0–5 min accounted for approximately 50–70% of the total release capacity. The ammonium release rate had a significant and positive correlation with OM. But it did not have a strong correlation with TN, TP, Fe, Ca and Al. The ammonium potential release capacity (obtained when the water/sediment ratio was about 2,500) had strong and positive relation with OM and maximal release capacity, and it may provide useful information for the sediment release risk assessment. Henry Model best described the ammonium sorption isotherms, and ammonium adsorption–desorption equilibrium concentration can be considered as the ammonium release threshold to assess the release risk in the sediments.