A Proposed Framework for the Management of Water Quality in Arid-Region Lakes

For arid-region lakes, management conflicts are likely to occur between quantity and quality of water supplied: increasing quantity of water supply can lead to water quality deterioration. Such conflicts can best be resolved within an effective management program based on awareness and cooperation at all levels of water management from policy makers to experts. We propose a general framework for designing effective water resource management programs for lakes based on concrete definitions of management criteria such as water quality. The proposed system requires close interaction between policy makers, water resource managers, water suppliers and users, hydrological engineers and limnologists. The significance of mathematical modeling as a self-organizing tool of the management program is emphasized, especially with regards to designing limnological investigations directed toward lake management. We illustrate the application of this approach to water resource management in arid-region lakes (Lake Kinneret, Israel and Lake Sevan, Armenia), where artificial variability of lake morphometry due to water use is a forcing function affecting water quality.     

Synergistic changes in river-lake runoff systems in the Yangtze River basin and their driving force differences

Climate change and human activities simultaneously alter river–lake relationships. Determining the dynamics of river–lake runoff systems on multiple time scales and their differences in response to driving forces can provide insights into hydrological processes and water resource management. This study investigates the synergistic evolution of river–lake runoff systems in the middle and lower reaches of the Yangtze River basin (MLYR) using the cross-wavelet transform method. The effects of different driving force changes on river–lake runoff regimes are quantified based on the Budyko hypothesis, and an InVEST model is developed to assess the spatial and temporal patterns of habitat quality. The results indicate that during the variation period, the runoff distributions of the Yangtze River–Dongting Lake and Yangtze River–-Poyang Lake runoff systems are both skewed towards lower values in the flood seasons compared with those in the base period. The storage of lakes mitigates the extent of human disturbance to the mainstream hydrological regime, particularly under extremely low conditions. From 1960 to 2021, five significant resonance periods are indicated in the river–lake runoff system, and the phase–angle relationships indicate a positive phase coupling between the lake and mainstream hydrological regimes, with the lake lagging behind the mainstream; however, this interaction tends to weaken. In the mainstream and Dongting Lake basins, subsurface conditions are the dominant factor contributing to runoff variability, with contributions ranging from 50.9% to 72.6%; in the Poyang Lake basin, precipitation is the dominant factor, with a contribution of 50.6%; and in the Han River basin, changes in the potential evapotranspiration contribute to 50.6% of runoff variability. The proportion of high habitat quality in the MLYR is approximately 52%, the Dongting and Poyang Lake basins indicate a high habitat quality rating. However, frequent human activity is the main reason of conversion from higher habitats to lower ones, which may result in wetland habitat degradation.     

The impact of water quality on the Asian clam,Corbicula fluminea,distribution in Pergau Lake,Kelantan, Malaysia

In the present study described the impact of water quality on the Asian clam, Corbicula fluminea, distribution in man – made Pergau Lake was carried out. Recently, Pergau Lake was gazette as state park and any activities related to fishery and agricultural were not allowed in the park. Subsequently, the nearby lake community was affected as many of them earn a living by carrying fisheries activity in the lake especially harvesting Asian clam. 10 sampling sites were selected in the lake to monitor water quality and Asian clam distribution. Water parameters data were also subjected to cluster analysis by using Ward’s method with squared Euclidean distances as a measure of similarity and a dendrogram was successfully generated. The water quality of the lake is under good condition and suitable to carry fishery activities by referred to Malaysia National Water Quality Standards (NWQS). The dendrogram revealed that the sampling sites can be divided into 2 clusters where Location 1 alone in its own cluster. Another cluster possesses 2 sub-clusters where Location 2 and 3 shared similar sub cluster. Another sub-cluster has two groups namely Location 5, 6 and 8 in one group whereas Location 4, 7, 9 and 10 shared similar group. The findings of the present study showed most of sampled Asian clam in Pergau Lake was semi mature indicating highly exploitation of Asian clam in the Lake. Furthermore, there were no correlation was detected between the population of Asian clam and water quality of the lake. Hence, we suggest that seasonal harvesting Asian clam should be implemented in order to conserve the population of Asian clam in the lake at the mean time the community to continue earn a living through carrying fishery activities in the lake.     

Development of a visualization platform oriented to Lake water quality targets management - A case study of Lake Taihu

Lake Taihu is well known for its severe environmental degradation. In previous studies of lake quality target management, the water quality targets were poorly correlated with watershed pollutant reduction, and most studies lacked visualized management platform that covered all elements including lakes, in-lake estuaries, rivers and watershed regions. In this study, a browser/server-based visualization platform for lake quality target management was developed. Five models that covered both the watershed and lake scales were integrated based on two critical functions. First, the proposed method can be used to determine watershed pollutant reduction amounts based on certain lake quality target parameters, such as those for TN, TP, NH₃N and COD. Second, the method can simulate the lake quality trends associated with different watershed adjustment plans. The platform was deployed by the Taihu Basin Authority (TBA) of the Ministry of Water Resources. Overall, this platform is a useful tool for watershed-lake environmental management.     

MANAGEMENT OPTIONS FOR SHALLOW HYPERTROPHIC LAKES,WITH PARTICULAR REFERENCE TO ZEEKOEVLEI,CAPE TOWN

Summary

Zeekocvlei, a freshwater coastal lake, is an important regional recreation area in the south-western Cape, South Africa. The lake is hypertrophic, experiences perenially dense populations of cyanobacteria (Microcystis), invasive bulrush and reed encroachment, and has a thick benthic layer of sediments rich in organic matter. User and scientific surveys have indicated that management problems centre around the dense phytoplankton population and the nutrient loading of the lake. Both in-lake and catchment-based management options for improving the water quality of the lake were evaluated. Given the present socio-economic constraints in South Africa, only catchment-based management can be recommended before any rehabilitation measures are undertaken in the lake itself. This would entail the investigation and implementation of measures to reduce levels of catchment-derived nutrient loading by managing the water quality of agricultural (predominantly horticulture) and urban catchment runoff.     

淀山湖富营养化控制叶绿素a 基准研究初探

水质基准是制定水质标准的重要依据, 研究以淀山湖为例, 基于淀山湖二十多年来的监测数据, 通过数据分析的方法, 探讨了淀山湖叶绿素a 基准取值方法。结合淀山湖叶绿素a 变化趋势与年内分布特征, 通过参照状态法, 将叶绿素a 分为冬春季节与夏秋季节两个时期, 建议冬春季节基准值为2.0 μg/L, 夏秋季节基准值为5.0 μg/L。并参考太湖总磷推荐基准值, 利用淀山湖总磷与叶绿素a 投入响应关系, 对获得的基准值进行了初步验证。       

洱海动态水环境容量模拟研究

基于环境流体动力学模型EFDC (Environmental Fluid Dynamic Code),建立了洱海湖泊及湖湾的三维水动力水质模型。并利用2001－2010 年的气象水文数据对洱海的水动力水质状况进行了连续10 年的数值模拟,模拟结果与实测结果吻合度较好,表明水动力水质模型计算结果较为合理。应用建立的数值模型分析了洱海的水流、水位和水质的时空变化特征,并在此基础上计算分析主要水质因子的动态水环境容量。结果表明,若以地表水二类水标准为规划目标,洱海总氮(TN)、总磷(TP)、COD_Mn和BOD₅ 的平均环境容量分别为1 150、72、12 780 和10 093 吨/年。洱海三维水动力水质模型的建立,为洱海的水环境保护工作提供了一个重要的管理和分析技术平台,对于洱海地区的污染物总量控制具有重要的意义。     

Unexpected stasis in a changing world: Lake nutrient and chlorophyll trends since 1990

The United States (U.S.) has faced major environmental changes in recent decades, including agricultural intensification and urban expansion, as well as changes in atmospheric deposition and climate—all of which may influence eutrophication of freshwaters. However, it is unclear whether or how water quality in lakes across diverse ecological settings has responded to environmental change. We quantified water quality trends in 2913 lakes using nutrient and chlorophyll (Chl) observations from the Lake Multi‐Scaled Geospatial and Temporal Database of the Northeast U.S. (LAGOS‐NE), a collection of preexisting lake data mostly from state agencies. LAGOS‐NE was used to quantify whether lake water quality has changed from 1990 to 2013, and whether lake‐specific or regional geophysical factors were related to the observed changes. We modeled change through time using hierarchical linear models for total nitrogen (TN), total phosphorus (TP), stoichiometry (TN:TP), and Chl. Both the slopes (percent change per year) and intercepts (value in 1990) were allowed to vary by lake and region. Across all lakes, TN declined at a rate of 1.1% year^?1, while TP, TN:TP, and Chl did not change. A minority (7%–16%) of individual lakes had changing nutrients, stoichiometry, or Chl. Of those lakes that changed, we found differences in the geospatial variables that were most related to the observed change in the response variables. For example, TN and TN:TP trends were related to region‐level drivers associated with atmospheric deposition of N; TP trends were related to both lake and region‐level drivers associated with climate and land use; and Chl trends were found in regions with high air temperature at the beginning of the study period. We conclude that despite large environmental change and management efforts over recent decades, water quality of lakes in the Midwest and Northeast U.S. has not overwhelmingly degraded or improved.     

Determining water level management strategies for lake protection at the ecosystem level

To prevent lake degradation, water level management has been a major focus of research in the past several decades. There are, however, some shortcomings in the traditional studies, and the protection of entire ecosystems is difficult to achieve in practice. In this paper, the framework of a new method for determining ecosystem-based water level regimes (WLRs) for lake protection is proposed. First, historical WLRs are divided into several sub-stages. Then, ecosystem statuses corresponding to different WLRs are quantified and compared. Finally, parameters of optimal and acceptable WLRs are used to determine water level management goals. The proposed method was applied to Baiyangdian Lake, the largest shallow lake in the North China Plain, to test its effectiveness. Results showed that to protect the ecosystem at the optimal status, 50% of the parameter values should fall within the range of the 25th and 75th percentiles of Stage I; and to protect the ecosystem from reverse succession, 50% of the water level parameter values should fall within the range of the 25th and 75th percentiles of Stage II. This method takes ecosystem status into account, and has high practicability in water resources management.     

基于管理目标的湖泊生态系统动力学

基于生态系统管理的目标,在对相关研究分析的基础上,依据生态系统生态学、淡水生态学的理论,提出了湖泊生态系统动力学研究的2个理论基础：生态系统管理和生态系统特征.在此基础上,分析得到湖泊生态系统动力学的研究方法体系,主要包括研究内容与技术路线、关键问题识别和动力学模拟、湖泊生态系统的适应性管理决策等部分.其中,湖泊生态系统结构和过程、湖泊中食物网营养动力学研究、生源要素循环、湖泊中关键过程的生态作用以及湖泊生态系统动力学模拟是研究的核心问题.此后,以P为主要的生源要素,将生态系统分为3个子过程：入流、出流和内部反馈,并以此建立了湖泊生态系统动力学的模型框架,以辅助于湖泊的生态系统管理.     

Combining multivariate statistical techniques and random forests model to assess and diagnose the trophic status of Poyang Lake in China

Floodplain lakes are valuable to humans because of their various functions. An emerging public concern on lake eutrophication has heightened the need to assess and predict the trophic status in floodplain lakes, particularly for those with high spatial heterogeneity. In this study, combined multivariate statistical techniques and random forests model were used to characterize the water quality and trophic status of Poyang Lake. By classifying and characterizing seasonal water samples comprising 11 water quality parameters collected from 13 sampling sites in Poyang Lake between 2008 and 2014, the dataset was divided into the central and northern lake groups, which corresponded to lentic and lotic regions in Poyang Lake, respectively. The spatial water quality variations and underlying patterns were investigated by performing discriminant analysis and principal component analysis (PCA). Lastly, random forests (RF) were used to predict the chlorophyll a (Chl-a) variations of the central and northern lakes. The PCA results indicated that the water quality of the central and northern areas of the lake was controlled by different environmental variables and underlying pollutant sources. The RF model outperformed the artificial neural network and linear regression and was robust with strong predictive capabilities. It was determined that the most important predictors of the Chl-a variations in the northern lake were water temperature (T) and water level, whereas transparency, T, and water level were the most efficient predictors in the central lake. The RF model can also be applied to trophic prediction in other large lakes with considerable spatial variations. This study will have implications on water quality management and eutrophication prevention in floodplain lakes with high spatial heterogeneity.     

乌梁素海保护的生态需水量评估

结合乌梁素海湿地生态系统特征 ,基于保证水量、保证水质和改善水质 (对于污染湖泊 ) 3个层次的湖泊湿地保护目标 ,给出了不同环境保护目标下湖泊湿地的生态需水量估算方法 ,并在系统分析乌梁素海水文水循环特征的基础上 ,选择适合的计算方法 ,对乌梁素海不同保护目标下的生态需水量进行了估算。结果表明 ,从保证水量平衡角度看 ,乌梁素海排干系统排入湖泊水量为 6 .18× 10 8m3/ a,可以保证乌梁素海的水量平衡 ;从保证水质角度看 ,由于作为生态用水的黄河水总 N浓度超过国家地表水水质标准中湖泊水质 V类水标准限值的 1.6倍 ,比乌梁素海湖水总 N含量还要高 ,因此 ,完全达标的生态需水量是不存在的 ,但如果只考虑盐分和总 P,在现有排干水量为 6 .18× 10 8m3/ a条件下 ,则维持乌梁素海的盐分和 P浓度不变的生态需水量分别为 1.82× 10 8m3/ a和 12 .3× 10 8m3/ a;从保证湖水水质达标角度看 ,现有污染物排放情况下 ,1a盐分和总 P达标的生态需水量分别为 4 .91× 10 8m3/ a和 16 .3× 10 8m3/ a,10 a盐分和总 P达标的生态需水量应分别为 4 .2 8× 10 8m3/ a和 14 .3× 10 8m3/ a     

Quantifying Relationships Among Phosphorus, Agriculture, and Lake Depth at an Inter-Regional Scale

To date, studies examining the impact of agriculture on freshwater systems have been spatially confined (that is, single drainage basin or regional level). Across regions, there are considerable differences in a number of factors, including geology, catchment morphometry, and hydrology that affect water quality. Given this heterogeneity, it is unknown whether agricultural activities have a pervasive impact on lake trophic state across large spatial scales. To address this issue, we tested whether the proportion of agricultural land in a catchment (% Agr) could explain a significant portion of the variation in lake water quality at a broad inter-regional scale. As shallow, productive systems have been shown to be particularly susceptible to eutrophication, we further investigated how lake mean depth modulates the relationship between % Agr and lake total phosphorus (TP) concentration. We applied both traditional meta-analytic techniques and more sophisticated linear mixed-effects models to a dataset of 358 temperate lakes that spanned an extensive spatial gradient (5°E to 73°W) to address these issues. With meta-analytical techniques we detected an across-study correlation between TP and % Agr of 0.53 (one-tailed P-value = 0.021). The across-study correlation coefficient between TP and mean depth was substantially lower (r = −0.38; P = 0.057). With linear mixed-effects modeling, we detected among-study variability, which arises from differences in pre-impact (background) lake trophic state and in the relationship between lake mean depth and lake TP. To our knowledge, this is the first quantitative synthesis that defines the influence of agriculture on lake water quality at such a broad spatial scale. Syntheses such as these are required to define the global relationship between agricultural land-use and water quality.     

Effects of hypolimnetic oxygenation on water quality: results from five Danish lakes

Stratified eutrophic lakes often suffer from hypolimnetic oxygen depletion during summer. This may lead to low redox conditions and accumulation of phosphate and ammonia in the hypolimnion. Hypolimnetic oxygenation has been used as a lake management strategy to improve the water quality in five eutrophic dimictic Danish lakes where oxygenation was conducted for 4–20 years. In one lake, the hypolimnetic oxygen concentration clearly improved by oxygenation, whereas the other four lakes still exhibited low mean summer levels (<2.2 mg O₂ l⁻¹). Oxygenation generally increased the hypolimnetic water temperature by 0.5–2°C, but in one lake it increased by 4–6°C. In all lakes, oxygenation significantly reduced the hypolimnetic concentrations of phosphorus and ammonia during stratification. The accumulation of phosphorus and ammonia typically decreased by 40–88%. In two lakes oxygenation was stopped for 1–2 years and here hypolimnion concentrations of both phosphorus and ammonia increased again. Surface water quality only improved in one lake, but was likely also influenced by simultaneously occurring changes in external nutrient loading. Overall, it is concluded that hypolimnetic oxygenation reduces the hypolimnetic accumulation of phosphorus and ammonia and may prevent anoxia in the deeper parts of the lake. However, long-term oxygenation is required and it is uncertain whether the overall lake water quality can be improved by oxygenation. Reduction of the external nutrient loading is still essential to improve lake water quality. Handling editor: Luigi Naselli-Flores     

African manatee (Trichechus senegalensis) habitat suitability at Lake Ossa,Cameroon, using trophic state models and predictions of submerged aquatic vegetation

The present study aims at investigating the past and current trophic status of Lake Ossa and evaluating its potential impact on African manatee health. Lake Ossa is known as a refuge for the threatened African manatees in Cameroon. Little information exists on the water quality and health of the ecosystem as reflected by its chemical and biological characteristics. Aquatic biotic and abiotic parameters including water clarity, nitrogen, phosphorous, and chlorophyll concentrations were measured monthly during four months at each of 18 water sampling stations evenly distributed across the lake. These parameters were then compared with historical values obtained from the literature to examine the dynamic trophic state of Lake Ossa. Results indicate that Lake Ossa''s trophic state parameters doubled in only three decades (from 1985 to 2016), moving from a mesotrophic to a eutrophic state. The decreasing nutrient gradient moving from the mouth of the lake (in the south) to the north indicates that the flow of the adjacent Sanaga River is the primary source of nutrient input. Further analysis suggests that the poor transparency of the lake is not associated with chlorophyll concentrations but rather with the suspended sediments brought‐in by the Sanaga River. Consequently, our model demonstrated that despite nutrient enrichment, less than 5% of the lake bottom surface sustained submerged aquatic vegetation. Thus, shoreline emergent vegetation is the primary food available for the local manatee population. During the dry season, water recedes drastically and disconnects from the dominant shoreline emergent vegetation, decreasing accessibility for manatees. The current study revealed major environmental concerns (eutrophication and sedimentation) that may negatively impact habitat quality for manatees. The information from the results will be key for the development of the management plan of the lake and its manatee population. Efficient land use and water management across the entire watershed may be necessary to mitigate such issues.     

Biomanipulation of lake ecosystems: an introduction

SUMMARY 1. This paper is an introduction to a special issue of Freshwater Biology containing selected papers from an international symposium on Food Web Effects of Fish in Lake Ecosystems: Research Progress, Water Quality and Fisheries Management held from 31 May to 3 June 2000 in Rheinsberg, Germany. The primary goal of the workshop was to enlarge the current view of fish-induced effects on lake ecosystems. An additional goal was to promote biomanipulation as a multiple-use tool for managing freshwater ecosystems.
2. The three main topics addressed at the workshop were: (i) mechanisms involved in biomanipulation, (ii) whole-lake case studies and (iii) management aspects in water quality and fisheries.
3. Mortality of Daphnia , nutrient recycling, habitat selection and fish predation are reported as important mechanisms governing food-web effects as a result of biomanipulation.
4. Whole-lake case studies indicate that repeated fish removal can help improve water quality of shallow lakes, but successful biomanipulation of deep, thermally stratifying lakes remains difficult.
5. In many cases, biomanipulation of lakes has proved to provide benefits in addition to improving water quality. As all lake users are potentially affected when biomanipulation is used as a lake management tool, their concerns need to be clearly recognised if biomanipulation is to be successful in practice.     

基于生态系统敏感性与生态功能重要性的高原湖泊分区保护研究——以达里湖流域为例

内蒙古高原湖泊流域是我国北方地区重要的涵养水源区域,发挥着防汛抗旱、气候调节、生物多样性维持等多种生态系统功能。近几十年来,全球气候变化加之人类活动加剧,导致内蒙古高原湖泊的数量和面积大幅减少,流域生态系统的损害日益明显,严重威胁到了周边地区的生态安全,保护与治理内蒙古高原湖泊流域已逐渐成为社会各界关注及迫切需要解决的问题。面向内蒙古高原湖泊流域保护和管理需求,以改善和提升流域生态环境质量和生态系统功能为目的,以内蒙古高原湖泊达里湖流域为研究对象,基于流域生态特性和主要生态环境问题,选取水土流失、土壤侵蚀及土地沙化敏感性3个指标评价了流域生态系统敏感性,从水源涵养、土壤保持和生境质量重要性3个方面评价了流域生态系统功能重要性,并在此基础上,通过GIS空间分析技术将流域分为极重要敏感区,一般重要敏感区和低重要敏感区。结合流域内达里诺尔国家级自然保护区的生态重要性与3个区域评价结果,从生态保护角度将流域分为禁止开发区、重点保护区、质量提升区与潜在威胁区4个区域,同时提出针对每个区域特点的保护与管理对策。研究结果对提高高原地区湖泊流域生态环境质量以及对流域实施科学有效的管理提供了科学依据,同时在促进区域乃至全球生态建设和可持续发展方面具有重要的理论与现实意义。     

洱海蓝藻爆发的时空特征及影响因子

湖泊生态环境对区域气候变化和流域人类活动十分敏感。随着流域的持续开发,洱海作为云贵高原第二大淡水湖泊面临着严重的生态与环境问题,主要包括水质恶化和生态功能的衰退,其中蓝藻水华问题尤为突出。针对湖泊现代监测数据存在时间序列较短、连续监测记录缺乏、监测位点不完全一致等问题,应用沉积物记录开展色素等多指标分析和环境变化重建研究,并对洱海湖区南、中、北3个湖盆的沉积物记录进行对比分析,从而探讨洱海富营养化与蓝藻爆发的历史与变化特征,并识别藻类响应模式的空间异同。沉积物色素记录结果表明,洱海蓝藻生物量变化具有明显的时空差异性,呈现由南至北,先后增加、最后呈现蓝藻水华全湖性持续爆发的模式。进一步的简约模型方差分解结果表明气候变暖和营养盐富集是洱海蓝藻生物量变化的主要驱动因子,此外相对较浅的南部湖盆还受到水位波动、水动力减弱、水生植物演化的综合影响。因此,在气候变暖的背景下,控制水体营养盐输入、合理调控湖泊水位、提高水体透明度并恢复水生植物是控制洱海蓝藻水华爆发和进行生态恢复的重要措施。     

Drainage ditching at the catchment scale affects water quality and macrophyte occurrence in Swedish lakes

1. We have limited knowledge of the effects of land use in general and of drainage ditching in particular on macrophyte communities in lakes. I quantified catchment land use, including drainage ditching, as well as water quality and the number of macrophyte species in 17 Swedish lakes in summer 2005. 2. Land use within 1 km of the studied lakes was analysed in a geographic information system. The following variables were included: areas of forests, mires, agricultural land and urbanization, length of drainage ditches (classified according to the use of the land they drained), and shortest distance from lake to an urban area. To extract and analyse general trends in the data sets, redundancy analysis was used. 3. Water quality was explained mainly by three land‐use related variables: the lengths of agricultural, forest and mire ditches. The length of agricultural ditches was positively correlated with lake water conductivity, total dissolved solids, Ca, N and total organic carbon (TOC). The lengths of forest and mire ditches were positively correlated with lake water characteristics, especially TOC. 4. The number of species representing different macrophyte life forms was explained by three environmental variables: conductivity, and lengths of forest and agricultural ditches. The numbers of isoetids, nymphaeids, elodeids and total obligate hydrophytes were negatively correlated with length of forest ditches. In contrast, the number of lemnids and helophytes was positively correlated with conductivity and length of agricultural ditches. Furthermore, the number of isoetids was exponentially related (negatively) to lengths of agricultural and forest ditches, indicating a threshold response to drainage ditch length. 5. The results suggest that effects on water quality and macrophyte communities result from drainage ditching in the lake catchments rather than from land use itself. Given the total area of drainage‐ditched land worldwide (millions of ha in Scandinavia alone), drainage ditching should be considered when evaluating environmental impacts on lake water quality and macrophyte occurrence and when determining reference conditions for catchment land use.     

Limnological research can improve and reduce the cost of monitoring and control of water quality

An evaluation of the programmes for control and monitoring of water quality in Sweden has demonstrated many short-comings. This paper discusses how improvements can be achieved by using new limnological knowledge.High-frequency sampling and analysis of mixed samples gives reliable average values with reduced costs. Strong correlations between, for instance, summer average values and summer maximum values, can be used for predicting the worst possible situation, which would be difficult to analyse by low-frequency sampling. Phosphorus load and lake response relationships are valuable tools for lake management and for establishing water quality criteria in physical planning. Future control may be further improved if limnological research gives better information on relationships between structure and function of aquatic ecosystems in relation to the form and size of the water body, water flushing rate, inputs from watershed and air space, etc.