Abstract:One hundred years ago,Prof. Chu Kochen published “On the origins of the West Lake (Hangzhou)” in the journal Kexue (Science) in 1921. In 1940, the Chinese Institute of Geography was founded in Beibei (Chongqing), then moved to Nanjing after the victory of Anti-Japanese War. In 1953, the Institute of Geography (Academia Sinica) was officially established in Nanjing, and soon after the Lake Group was set up (directed by Shi Chengxi) in 1958, which announced modern lake research in China. In 1987, the institute changed its name to Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS). Since then, NIGLAS have witnessed lake research progresses in China, from early activities such as lake survey to the comprehensive studies of lake sedimentology, physics, biological resource, eutrophication control, freshwater ecology, aquatic environment restoration and so on to meet the needs of national resource utilization, environment protection and ecological restoration in different times. Meanwhile, NIGLAS have developed novel watershed geography after integrating rural geography, regional studies and lake research.
In recent 30 years, NIGLAS have achieved a number of pioneering outputs in distinctive fields of limnology and watershed geography, and turned out to be an influential base on the geographical and limnological research both at home and abroad. It pioneered analytical study of national conditions and proposed a saving-style national economy strategy; edited important thematic maps such as “Agricultural Atlas of China” which essentially promoted the progress of regional geography; systematically studied natural resources, ecology, environment and urbanization in the lower Yangtze River area, thus developed integrated watershed study methodology; conducted comprehensive lake survey and established national lake information system and based on that created the systematic lake sciences in China; built a high efficiency utilization model for lake and wetland resources and proposed new aquaculture models for large surface waters. The institute has become an important research base for watershed geography and lake science with both domestic and international reputation.
To celebrate the 80th anniversary of NIGLAS,Journal of Lake Sciences invited some distinguished scholars who have long been engaged in relevant fields to conduct a systematic review of the progress in different sub-fields, such as shallow lake limnology and Lake Taihu eutrophication, the connotation of limnology and the challenge/reflection on the limnology development in China, lake environment and engineering, lake hydrology and water resources, lake paleo-ecology, remote sensing of water regimes. In addition, we also organized well-known experts to publish their scientific and academic views on current hot topics and focal lakes, i.e. 40-year physical changes in Lake Taihu, environmental protection for dredging decisions, evolution of Lake Baiyangdian since 1960s, Chinese sturgeon protection reflection, cyanobacteria blooms mitigation and Satellite-Aerial-Ground 3-D monitoring system for eutrophic lake/reservoirs.
We hope that the publication of this special issue will provide a systematic review of lake science development in China, andbring certain in-depth thinking for the future. With the continuous developing of earth surface system science and advancing of national integrative “Mountain-water-forest-field-lake-grass” system protection and restoration strategy in China, NIGLAS, as the only national research institute featuring lake science, aims to provide scientific and technological support for the key ecological civilization construction tasks, such as national drinking water safety, freshwater biodiversity protection, aquatic ecosystem services improving, and sustainable watershed management. NIGLAS will strive to become the main force in research on global lake change, freshwater ecosystem, and watershed environmental protection. The catastrophic floods in the Yangtze River Basin in 2020 brings new challenges to the lake science and catchment studies in China, such as the optimized regulation of the Three Gorges Reservoir, reflection on floods mitigation and river-lake relationship, regulative function change of watershed-scale lakes and reservoirs, future flood-drought alternates mechanism and disaster mitigation, interrelations of water resources protection, utilization and eutrophication.

Abstract:Unprecedented high intensity and large-scale restoration have been conducted in Lake Taihu since 2007 when the water crisis happened in Wuxi, and the cumulative investment of various governance measures has exceeded 100 billion RMB. As the long-term monitoring indicated, the nitrogen and phosphorus concentration in Lake Taihu decreased significantly and the water quality improved during the first few years. However, the water quality fluctuated and cyanobacteria bloom rebounded during the recent years. Studies implied that the external loading of nutrients did not decrease in Lake Taihu, which was largely related to the increase of urban water consumption, low sewage discharge standard and insufficient reduction of non-point source pollution. Meanwhile, the internal loading was aggravated by continuous cyanobacteria blooms. In addition, the impact of internal loading on lake eutrophication and cyanobacteria blooms was hence exacerbated in the case that the characteristics of shallow lakes as small water depth and strong disturbance are in favor of the efficiency of phosphorus cycling and uptake. The intensity and frequency of cyanobacteria blooms, of which the spatial and temporal distribution is determined by lake hydrodynamics, were aggravated by the combined effects of climate warming and nutrient enrichment, and changes in meteorological and hydrological conditions such as the decrease in wind speed over the lake catchment and the increase in the intensity and frequency of rainstorm events. In order to control the eutrophication of Lake Taihu, ensure the water environment security and maintain the sustainable development of society and economy, we should combine the lakes and basins as a whole, and should be conscious of importance to the combination of natural science and technology, the humanities and management.

Abstract:Limnology is a multidisciplinary and integrative science studying inland waters, having a history of nearly 130 years since Francois Alphonse Forel defined it firstly in 1892. The main subdisciplines include geological limnology (including paleoplimnology), physical limnology, chemical (biogeochemical) limnology and biological limnology. The key feature of limnology is the interdisciplinary nature that is achieved by integrating different disciplines to synthesize the process and mechanisms at the level of the ecosystem, and to predict the ecosystem changes. Therefore, limnology is the key science supporting the protection, management and restoration of inland water ecosystems and water resources. However, the development of limnology in China is faced with the problems such as unbalanced development in subdisciplines and fragmentation in researches. The effects of increased human activities and global changes on inland waters are the challenges and opportunities for limnological researches. The main research topics in China need to focus on the effects of human activities and global changes on inland waters, including: 1) the changes in hydrodynamics and hydromorphology and their ecological and environment effects; 2) nutrient and organic matter biogeochemical cycling and the associated ecological and environment effects; 3) structures and functioning of food webs; 4) impacts of invaded species and managements; 5) the control of water associated diseases; 6) ecological quality assessments of surface waters; 7) ecosystem evolution and the mechanisms, and restoration of degraded ecosystems.

Abstract:The decision-making strategy on environmental dredging mainly involves “whether to dredge or not”, “how much to dredge”, “how to dredge” and “can we dredge”, which are related to issues such as the project approval, capital investment, process selection and dredging effect. This paper at first briefly reviews the research and development history of environmental dredging in the past 50 years, systematically summarizes the research progress on the necessity of environmental dredging in the aspects of lake eutrophication, potential ecological risk, and black bloom pollution control at home and abroad, and illustrates the differences of decision-making concepts in answering whether to dredge or not and the problems that need to be improved. Then, on the design of dredging volume, the paper analyzes the principles, methods and examples of the selection of environmental dredging zone and the determination of dredging area. Among the determination of dredging depth, eight methods are introduced and evaluated, including visual method, inflection point method, background value method, multiple standard deviation method, frequency control method, ecological risk index method, layered release method, and adsorption/desorption method. Thirdly, the research results on the reasons and influences of sediment diffusion, leakage and residue in the process of dredging with different dredging processes are summarized, and the selection requirements of dredging technology for dredging decision-making are put forward. Finally, the prospect of environmental dredging decision-making for lakes is put forward from the aspects of paying attention to the process backtracking of environmental effects after dredging, the impact of suspended particulate matter and the substantial integration of ecological risk concept. It is considered that the dredging effect of some lakes has not reached the expected level, which is mainly related to the neglect of decision-making research. The subjectivity and arbitrariness of decision-making may not only cause waste of funds, but also damage the ecological and environmental benefits. The authors point out that dredging is not a environmental protection project could be done once and for all, and not every polluted lake needs or can be dredged to improve the water environment. Even if it reaches the level of necessity research and engineering quantity design of environmental dredging, it still needs the effective control of external sources and the proper dredging technology with high precision, low diffusion and less leakage.

Abstract:Lake environment and engineering is an interdisciplinary basic research and applied research discipline, which is developed in recent 10-20 years, and studies the evolution law, interactive mechanism, protection and governance and harmonious development of lake water environment quality under changing environmental conditions. With the increasing intensity of human activities, lakes in China are faced with severe environmental problems such as eutrophication, cyanobacteria blooms and secondary disasters, and persistent and emerging pollution. It is urgent to develop regional integrated pollution prevention and control technology system for lake environment protection, to serve the national ecological civilization construction. This paper at first briefly introduces the concept and connotation of Lake Environment and Engineering; systematically describes the research on environmental behavior and reduction of major pollutants in lakes in recent 10 years around the world; analyzes the causes and control strategies of secondary disaster “black water” mainly caused by cyanobacteria bloom, and then shows the lake monitoring methods mainly based on lake sediment; summarizes the technical research development about lake pollution prevention and control. Finally, the paper looks forward to the extension of the research scale of lake environment and engineering to macro and micro dimensions, and the integration of ecological / hydraulic engineering and smart perception / big data technology.

Abstract:The natural spawning activities of the China top-level protected animal, Chinese sturgeon Acipenser sinensis, has been interrupted for three consecutive years (2017-2019) with its natural population on the verge of extinction. Based on the analysis on the life history of fish, the author pointed out that the migratory pathway blocked by the Gezhouba Hydroelectricity Dam is the root cause of the natural population decline. The operation of the Three Gorges Project (TGP), as well as the Xiangjiaba and Xiluodu hydro-dams, results in the water temperature hysteresis in the spawning ground below the Gezhouba Dam, being the fatal factor for the interruption of the natural reproduction. Additionally, river channel erosion by TGP, sand-excavating, flood control & urban landscape engineering, dredging and other human activities along the river constrains the offspring habitat and then leads to decrease in recruitment, which in turn make the spawning stock continues to decline. In the past 40 years, the restocking program, as a measure which has been given high expectations to compensate for the decline of the natural population of Chinese sturgeon, has not been scientifically and effectively implemented, resulting in the near-collapse of the hope by artificial intervention to ensure the continuation of the natural population of the fish. Under the current situation, it is urgent to take the “Chinese sturgeon rescue action plan” as a guideline, to promote the implementation of 5 key protection measures urgently: 1) implement “land-sea-land” seeding project to restore species biological trait in cultured Chinese sturgeon, 2) strengthen restocking program, 3) improve the existing spawning conditions to promote natural reproduction, 4) seek alternative natural spawning grounds, 5) restore feeding grounds and other critical habitats. Only by long-term efforts (15 years) and protect of fish from birth to individuals breeding, can it be expected to continue and restore the natural population of fish. With huge body size, long life and a wide range of migration, the Chinese sturgeon is undoubtedly the flagship species and umbrella species of the Yangtze River ecosystem. The successful protection of Chinese sturgeon is significantly important to achieve harmonious coexistence between human and nature, and promote the sustainable development of the Yangtze River Basin.

Abstract:The conservation protection of aquatic life in the Yangtze River is facing a great challenge, and strengthening their protection is the national strategic demand of China. The Chinese sturgeon (Acipenser sinensis) is a flagship species of the Yangtze River, and the sole one for the fish rescue program of the Gezhouba Dam in the 1980s. After a great deal of scientific research and implementing conservation measures over the past four decades, the Chinese sturgeon population has been on the verge of extinction. If lessons of Chinese sturgeon protection could not be well learned, the protection of aquatic life in the Yangtze River will be difficult to get out of the current predicament. This paper reviews the history of scientific research and protection of Chinese sturgeon since implementation of the fish rescue program. It shows that dodging or overlooking the influence of Yangtze cascade dams will be unable to reveal the quantitative mechanism of the population decline, and is impossible to take targeted measures. Therefore, to avoid repeating the same mistakes that the protection of Chinese sturgeon has arisen in the past four decades, launching introspection, reform and innovation for the lessons of the Chinese sturgeon conservation is an urgent strategic issue of conserving the aquatic life in the Yangtze River.

Abstract:Lake Baiyangdian is the largest shallow lake in the North China Plain. It enjoys the reputation of “the Kidney of North China” and “the pearl of North China”. It plays a role as an ecological security barrier to maintain the regional ecosystem balance and biodiversity of the Beijing-Tianjin-Hebei metropolitan area. For a long time, intensive human activities have led to a sharp decreasing in the amount of water into the Lake Baiyangdian, serious water pollution, and the decline of biodiversity and ecosystem functions. Therefore, the “Pearl” has lost its luster. Combined with historical documents and the long-term monitoring results on this lake, this paper systematically reviews the evolution of hydrology, water quality and water ecology in the Lake Baiyangdian since 1960s, and analyzes the possible reasons for the evolution. With the development of regional economy and the enhancement of human activities, the water quantity, water environment and ecological quality in the Lake Baiyangdian have been gradually degraded since the 1960s. In the past 20 years, with the implementation of a series of environmental control policies and ecological water replenishment projects, the deterioration trend of Lake Baiyangdian water quality has been curbed to some extent. In 2017, the CPC Central Committee and the State Council announced the establishment of the Xiong'an New Area. Its concept of “setting the city by water” highlights the importance of the Lake Baiyangdian as the center of the new area, which has a long way to go in environmental and ecological management. This paper is expected to provide a basis and support for the environmental and ecological management of the Lake Baiyangdian in the new period.

Abstract:The global environment has experienced rapid changes over the past four decades, including global climate warming, radiation dimming and brightening, wind stilling, and abnormal climate fluctuations. Meanwhile, strong human activities such as dam construction, bank hardening and water diversion and drainage have happened in Lake Taihu catchment. All these changes of natural environments and human activities have profoundly reshaped the physical environments and processes of Lake Taihu, which have further strongly driven the evolution of lake ecosystem structure and function. Based on historical literatures and documents, as well as long-term observations of meteorology, hydrology and Secchi disc depth (SDD), this study aims to systematically explore the spatial distribution and long-term change characteristics of physical environment in Lake Taihu, such as air temperature, water temperature, water level, wind speed and SDD. Meanwhile, we will elucidate the synergistic effects of air temperature and wind speed, water level and SDD and their potential ecological environmental significances for algal bloom outbreaks and aquatic macrophytes loss. Due to the global changes and rapid urbanization, the air temperature and water temperature of Lake Taihu have been increasing continuously in the past 40 years, while the wind speed near the ground has been decreasing continuously. Lake warming and decreasing wind speed facilitate the growth of algae and the floating accumulation of cyanobacteria bloom, which to some extent increases the observation frequency and area of cyanobacteria bloom. In order to control the flood and meet the increasing demand of water resources in the basin, the water level of Lake Taihu is increasing slowly due to dam control and water diversion. However, the increase of pollutants entering the lake and the development of eutrophication gradually decrease SDD. Therefore, the significant decrease of the ratio of SDD to water level (water depth) was observed in Lake Taihu, which significantly decreased the available light intensity at the bottom of the lake, and deteriorate the underwater light environment. All these changes have resulted in the loss of aquatic macrophytes and greatly driven the degradation of macrophyte-dominated ecosystem in Lake Taihu. The long-term changes of lake physical environment have gradually expanded the algae habitat space of Lake Taihu, compressed the macrophyte habitat space, accelerated the shift from a clear macrophyte-dominated state to a turbid algal-dominated state, and enhanced the long-term maintenance of algal-dominated ecosystem. Therefore, our findings highlight the importance of long-term physical environment monitoring data for deeply understanding ecosystem response to global climate change and human activities. The profound changes in physical environment has also partially offset the control of algal biomass and cyanobacteria bloom caused by the reduction of nutrients in the basin and the decrease of nutrients in the lake, which will increase the difficulty of prevention and control of cyanobacteria bloom and lake eutrophication in Lake Taihu. This means that in the future, more strict standards are needed for controlling pollution and nutrients, and the effective control of lake physical environment such as water level is the adaptive management strategy to deal with the aggravation of algal bloom and the restoration of macrophyte-dominated ecosystem.

Abstract:Lakes are important components of the Earth's surface water bodies. They serve as irreplaceable functions in regional socio-economic development and conservation of biological diversities. Climate variations and intensive water consumption result in significant deviations in temporal change and spatial pattern in terms of physical and chemical processes. As a sub-discipline of hydrology, lake hydrology addresses the changing patterns of hydrological variables, their relationships, balancing and evolution. It addresses fundamental scientific questions and offers solutions to practical issues. Examples includes hydrological attribution and dynamic evolution, hydrological extremes and practical mitigation, lake resources assessment and sustainable utilization, which have been strongly supporting regional developments. This article reviews the progress of lake hydrology in China in the latest 50 years, with emphases on lake water balance and variation, lake hydrodynamics, lake hydrological extremes, and remote sensing of lake hydrology. Several key research areas are also identified and discussed for future research interests.

Abstract:Lake palaeoecology is an important branch of palaeolimnology, which aims to reconstruct the evolution of lake ecosystems on various spatiotemporal scales, and answer the questions of ecology, global change and environmental management through multiple subfossil biological proxies in the sedimentary records. This paper reviewed the history of palaeoecology studies at home and abroad. After introducing the fundamental principles of lake palaeoecology, this paper further elaborated the main progresses and achievements of palaeoecology research in China in the past 20 years, including (1) the transfer function models to quantitatively reconstruct past climate and environmental parameters (temperature, salinity, total phosphorus, etc.) based on a variety of biological and biomarker compound proxies were established; (2) the laws of the lake ecological environment evolution in different geological historical periods and in the past century, and its response characteristics and mechanisms to the natural and anthropogenic driving forces were revealed; (3) the palaeoecological records were used to diagnose the regime shift patterns and early signal characteristics of lake ecosystems, and the relationships between the biological structures and resilience loss of lake ecosystems were quantitatively revealed. These results provide important basis for lake environmental management and governance. In the end, the paper makes a prospect for the study of lake palaeoecology in China and puts forward the emphasis for the future studies.

Abstract:Lakes and reservoirs are the main sources of drinking water in China, but most of them are in the state of eutrophication with frequent cyanobacterial blooms. This has become major issues affecting social sustainability and restricting the local development. The overall response strategy of cyanobacterial blooms must have modern and comprehensive monitoring methods and systems, so as to timely grasp the status and trends of such blooms and their derived disasters. This article aims at the emergency monitoring of cyanobacterial blooms in eutrophic lakes and reservoirs. According to the three monitoring levels of “the entire lake, key areas, and key locations”, the current satellite, drone, and shore-based /platform video, buoy, manual inspection and other technologies or methods have proposed the construction goals, system framework, and workflow. These are also applied in the Lake Chaohu. It is believed that this framework of monitoring system proposed in this paper has important application and promotion value not only in Lake Chaohu, but also in more eutrophic lakes and reservoirs.

Abstract:As the key component of available freshwater resources, lakes play an important role in all aspects of life and human activities. Influenced by global climate change and human intervention, lakes have been undergoing rapid changes. Thus it is necessary to conduct lasting and accurate investigation of spatial and temporal variations of these lakes, serving better for water resources management and protection, and early warning of future climate change risks. The emergence and development of remote sensing technology provides great opportunity for large-scale and near real-time monitoring of lake dynamics, which overcomes the limitations of field-based investigation of lakes. In this paper, the existing remote sensing technologies and methods of lake monitoring are reviewed, and the progress of remote sensing research in the aspects of lake area extraction, lake level reconstruction, lake water volume/storage variation estimation, etc., are summarizes. This review focuses on the new methods and new technologies employed in recent years. The application prospect of multi-source remote sensing data fusion and cloud computing platform in continuous change monitoring of surface water bodies is also mentioned. Finally, in view of the promising development of remote sensing technology, the application potential and prospective of remote sensing monitoring of lake dynamics in the future are discussed briefly.

Abstract:Many important lakes and reservoirs of China, including Lake Taihu, Lake Chaohu, Lake Dianchi, Lake Erhai and Three Gorges Reservoir, were plagued with cyanobacterial blooms. However, the intensity of the blooms in these freshwaters varied significantly in different years, which exhibited significant challenges to the blooms collection organizations and drinking water plants, leading to the urgent need to cyanobacteria blooms prediction model based on annual dataset. Therefore, the long-term (15 years) observation data and meteorological and hydrological datasets of Lake Taihu were collected for the prediction of algal blooms. In current study, cyanobacterial bloom intensity index (BI) were proposed with the consideration of yearly average blooms area interpret by high frequency remote sensing images and whole lake average chlorophyll-a concentration. Furthermore, environmental factors, such as water temperature, rainfall, water level, nitrogen and phosphorus concentrations were used as the crucial factors to predict BI. Our results showed that average water temperature in winter and early spring, as well as the rainfall of the former year were significant positive factors of the yearly BI value in Lake Taihu. While the nutrient-related factors in early spring had no significant relationships with BI. In addition, a multiple (or univariate) regression analysis based on the above factors (BI was the dependent variable and the remaining environmental factors were the independent variables) were performed in this study, and the optimal model was selected. In general, the predicted results of the selected optimal model had a high consistency with the measured concentrations, thus the model obtained in this study had relatively high accuracy for predicting the interannual intensity of cyanobacteria blooms in Taihu Lake. This study may serve reliably for the medium- and long-term prediction of cyanobacteria blooms in Lake Taihu, and other eutrophic lakes.

Abstract:In order to figure out the influence of the water diversion from the Yangtze River Project (WDP) on the rebound of total phosphorus (TP) concentration in Lake Taihu after 2016,this study analyzed the water quantity, phosphorus flux and phosphorus form of Yangtze River and other inflowing rivers including Lake Taihu and Gonghu Bay around 2016 based on the data of water quantity, phosphorus flux transfer from Yangtze River and the phosphorus stock in the lake. The result shows that the average annual phosphorus flux into the lake was 97.56 t and the average annual water inflow volume was 816 million m³ around 2016. From the perspective of water volume, phosphorus flux into the lake, short-term phosphorus response after water diversion and phosphorus increment in each lake area, the correlation between the WDP and the TP rebound in the lake after 2016 is not strong. The cumulative phosphorus flux from the WDP was 877.97 t, accounting for 4.58% of the total TP flux into the lake, and the accumulative amount of lake water accounted for 7.36% of the accumulative amount of lake water in Lake Taihu, the phosphorus flux per unit of water is only about half of that of other water, which accounts for a relatively limited proportion. Compared with the main inflow rivers of Lake Taihu, the water quality from Yangtze River is good. The TP concentration in the inflow rivers is generally higher than the TP concentration of the lake itself. At present, in addition to ensuring the safety of water supply and alleviating the water bloom crisis, the incoming water from the WDP has certain improvement effect when the lake is serious eutrophic. In the next step, we must pay attention to the relationship between the phosphorus flux brought by water diversion and the phosphorus circulation system in Lake Taihu, so as to ensure the ongoing WDP continue to have a positive impact.

Abstract:Cyanobacterial biomass in water column and sediment were investigated from October 2018 to October 2019 in the center of western Lake Chaohu. Phytoplankton were mainly composed of Microcystis, Crucigenia, Phormidioideae, Cryptomonas and Anabaena. The dominate cyanobacterial genus were Microcystis between May and November, Anabaena between November and December, and Phormidioideae between January and April. Cyanobacterial biomass in water column peaked in September and January, and settled down afterwards, resulting in the two peaks of cyanobacterial biomass in sediment. In comparison with that in water column, cyanobacteria biomass was relatively low in sediment. The proportion of cyanobacterial biomass per unit surface between water column and sediment was more than 100 in June and was relatively low from November to March, with the lowest level being less than 2. Benthic cyanobacteria were mainly distributed on the surface sediment (0-2 cm). The monthly vertical flux of cyanobacterial biomass was monitored by using an in situ trap. Our results showed that cyanobacterial biomass settled massively from water column to sediment in November and February. Cyanobacteria tended to have upward migration from sediment to water column in November and June, caused by large cyanobacterial biomass in sediment and high turbulence. However, the active recruitment of benthic cyanobacteria was low throughout the whole year. The best period to reduce the cyanobacterial seed from sediment is from October to February. However, this might not function well to mitigate cyanobacterial bloom in summer, since cyanobacteria biomass is lower in sediment than in water column and the contribution of recruitment is small.

Abstract:Based on pollutant fluxes of the rivers surrounding Lake Taihu in Jiangsu Province and water quality in Lake Taihu, the response relationship between pollutant fluxes of the rivers and water quality in lake was studied from two aspects of temporal and spatial variation and correlation, main factors that affected water quality were analysed after pollutants discharged into lake. The results showed that the temporal distribution of total nitrogen (TN) and ammonia nitrogen (NH₃-N) concentrations in Lake Taihu were in good accordance with distribution of TN and NH₃-N fluxes in river channels. TN and NH₃-N concentrations in the lake declined since 2008, with the decrease rate per year of 2.1% and 2.3%, respectively. The year descending rates of annual influxes of NH₃-N, TN, COD_Mn and COD_Cr were 8.0%, 2.0%, 1.6% and 2.2%, respectively. TN and NH₃-N concentrations in Lake Taihu and their fluxes in river channels were positively significantly correlated. NH₃-N, TN, TP, COD_Mn and COD_Cr in the western and northwest areas were better than that in the centre, southern and eastern areas, corresponding to pollutant fluxes of the rivers. Analysis of collinearity diagnosis and multiple stepwise regression indicated that TN, NH₃-N concentrations in river channels,and difference values of TN, NH₃-N concentrations between river and lake were significantly related with water quality in the Lake Taihu. It's desiderated to strengthen the control of river water quality.

Abstract:To understand seasonal and spatial wet deposition characteristics of nutrients input to the Tangpu Reservior Basin, precipitation samples at four sites and stream water samples at three sites were collected from the basin during 2014-2015. The mass concentration of total nitrogen(TN), nitrate nitrogen (NO₃^--N), ammonia nitrogen and total phosphorus(TP) in the wet deposition were measured, and the precipitation characteristics of nitrogen and phosphorus nutrients, the deposition rates and their contributions compared with their counterparts from external loading of streams to the reservoir were studied. The results showed that the annual wet deposition concentration of TN was 1.02±0.58 mg/L, and the percentages of ammonium, nitrate and organic nitrogen contributed 60.65%, 34.07% and 5.28% of TN, respectively. The annual wet deposition concentration of TP was 0.033±0.028 mg/L. Seasonally, the concentrations of TN and TP in wet deposition were higher in winter and spring than in summer and autumn. Spatially, the concentrations of TN and TP were the highest at Wanghua site. The annual wet deposition rates of TN and TP were about 18.151 and 0.62 kg/(ha·a), and their average annual budgets reached 834.94 and 28.39 t, respectively. The wet depositions of water surface into Tangpu Reservoir were 24.14 and 0.82 t, and the direct contributions as 1.77% and 3.07% of the stream input. The indirect contributions of nitrogen and phosphorus from wet deposition sources accounted for 8.3% and 4.6% of the stream input. In summary, the nutrient load from the wet deposition plays a crucial role in the nutrient input of reservoirs. Understanding the nutrient load from the wet deposition will help us to better manage the reservoir basin and reduce the external nutrient loads to the basin.

Abstract:As a widely used evaluation method, index of biotic integrity (IBI) has been used in various water bodies to evaluate the state of aquatic organisms. However, some defects and limitations in the IBI method need to be studied and solved, such as the generation and interference of deviation in IBI assessment (based on the reference site method) for time-scale trend evaluation. In this study, Songhua River Basin was used to quantitatively analyze the deviation of IBI (based on reference site method) for time-scale trend evaluation, with the survey data of macrobenthos and evaluation results of IBI during 2012-2015. In addition, the method to correct the IBI results using correction coefficients r (r: during the course of metrics scoring, the multiples of metrics base value in comparative years to initial year) and data of initial year was proposed in this work. The results showed that the value of the positive metrics (decreasing response to increasing disturbance) of reference group from 2013 to 2015 were higher than those in the initial year (2012), while the reverse metrics (increasing response to increasing disturbance) of damaged group were lower. Meanwhile, r of positive metrics was mainly ranged from 1.1 to 4.9, while 0.7 to 0.8 for the reverse metrics. The metrics 95^th of the reference group and the damaged group significantly changed in these years, with significant score deviation during the course of metrics scoring. Furthermore, during the course of evaluation criteria classification, the difference of the proportion of the worst and the best regions was 10.0%-13.4%, the disturbance from deviation was also significant on trend analysis. The comparative analysis of IBI results showed that after calibration in each year from 2012 to 2015, the proportion of excellent and good areas was higher (4.3%-13.3%) than that before calibration, while the proportion of poor areas was lower (6.7%-30.0%) than that before calibration. The results after calibration were consistent with the changes of characteristic parameters of aquatic organisms; however, the non-calibration results showed some contradiction. In summary, the deviations from the key parts during IBI assessment can significantly affect the trend analysis and determination, the deviation interference in temporal trend analysis can be preliminarily solved by the correction method.

Abstract:In order to study the effect of Potamogeton crispus decomposition on the dissolved concentrations of greenhouse gases (GHGs) and their diffusion fluxes at the sediment-surface water-air interface in the Lake Dongping, surface water and sediment core samples were collected in situ seven times from May to July in 2016, and the decomposition experiment was also carried out by using the litterbag method to explore the dynamic of the dry mass loss of P. crispus. Dissolved concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the surface water and pore water were concurrently measured, and the diffusion fluxes at the sediment-surface water interface and the surface water-air interface were calculated by using the Fick's first law and the two-layered model respectively. In addition, the physicochemical properties of surface water and sediment were also measured to explore the main factors that might affect the concentrations and diffusion fluxes of GHGs as well as their sources during the decomposition of P. crispus. The results showed that the dry mass loss of P. crispus could be described accurately by the double exponential model which suggested two stages (rapid and slow) of P. crispus decomposition. The pH and nitrite concentrations in the surface water decreased first and then increased, while the change of the dissolved oxygen, ammonia, nitrate and dissolved inorganic phosphorus concentrations was reversed. In sediment, the ammonium content first increased and then decreased, while the nitrate content first decreased and then significantly increased, the organic matter content and pH of the sediment fluctuated. Both the concentrations and diffusion fluxes of GHGs at the water-air interface were in the order of CO₂> CH₄> N₂O, and the average fluxes were 5862.9±5441.4, 31.15±41.3 and 0.15±0.57 μmol/(m²·h), respectively. Generally, the waterbody acted as the source of the GHGs to the air, dominated by the carbon emission. The concentrations of N₂O in surface water and its diffusion fluxes at the surface water-air interface first decreased and then increased, and N₂O concentrations in pore water presented maximum values of 22.7 and 55.6 nmol/L in the rapid and slow decomposition stage respectively, while its fluxes at the sediment-water interface increased slowly in the early stage and then decreased rapidly at the end of the decomposition. For CH₄, its concentrations in the surface water and pore water and interface diffusion fluxes all dropped slightly in the initial stage and then continued to rise. The concentrations of CO₂ in surface water and its diffusion fluxes at the surface water-air interface increased continually and then decreased significantly to lower levels at the end of the rapid decomposition and then remain stable; while the concentrations of CO₂ in pore water showed large fluctuations, which diffused to pore water at the initial stage of the decomposition and to surface water at the later stage. The correlation analysis between the concentrations and diffusion fluxes of GHGs as well as the physicochemical properties of surface water and sediment suggested that water temperature was the main factor that influenced the concentrations of GHGs in surface water and their fluxes at the water-air interface. N₂O and CH₄ in the water body mainly originated from sediment, and their concentrations in the pore water was the important factor that could control the sediment-water interface diffusion; while CO₂ in the surface water had multi sources, which were dominated by the mineralization of the organic matter in surface water.

Abstract:The cause of dissolved oxygen (DO) evolution in deep reservoirs still remains unclarified. However, it is important to explore the evolutionary mechanism for water quality protection and management. This paper systematically analyzed the spatiotemporal variations of water temperature and DO, as well as the water quality response to these factors, in the Panjiakou Reservoir, a large deep reservoir in Beijing-Tianjin-Hebei region. Results show that the reservoir has a significant seasonal thermal stratification during mid-April to the end of November, which creates a vertically specific environment for the DO stratification. Similar to the thermal stratification, the DO stratification also shows a three-layer structure from top to down, namely, the mixed layer, the oxycline and the oxygen-deficient layer. Different biochemical processes in each layer determinate the spatial variability DO evolution. Due to excessive planktonic algae, DO is supersaturated in the mixed layer. While in the oxycline layer, DO concentration declines sharply as a result of respiration and organic matter decomposition, becoming hypoxic (i.e., DO<2 mg/L) in July and August. Due to the oxygen consumption of severely contaminated sediments in the oxygen-deficient layer, DO concentration declines continuously, potentially leading to hypolimnion at the bottom of the reservoir at the end of thermal stratification. Meanwhile, in this area, Mn reduction reaction occurs and the Mn-P is released to the hypolimnion. However, there is no Fe reduction reaction or Fe-P released. In summary, the Panjiakou Reservoir is approaching a critical point of hypoxia and massive release of endogenous pollutants. Special attentions should be paid on its water environment treatment.

Abstract:Cell size is an important element determining phytoplankton physiological and ecological processes, including nutrient uptake, sinking and grazing; thus, phytoplankton size-structure plays an important role in the structure and function of lake ecosystem. To understand the succession patterns and driving factors of total chlorophyll-a and size structure of phytoplankton, field in-situ investigation was conducted from September 2018 to September 2019 in the east Lake Dongting, a Yangtze River- connected lake. The total phytoplankton chlorophyll-a biomass showed significant seasonality and spatiality. The highest concentration of total chlorophyll-a was observed in summer (22.43 μg/L), followed by autumn (16.95 μg/L), spring (11.69 μg/L) and winter (3.28 μg/L). Spatially, the total phytoplankton chlorophyll-a was highest in the north (26.12 μg/L) and lowest in the east (5.88 μg/L) of the lake. Phytoplankton was overwhelmingly dominated by nanophytoplankton (3-20 μm). The proportion of nanophytoplankton to total phytoplankton chlorophyll-a biomass was highest in winter (68.0%), whereas the proportion of picophytoplankton (0-3 μm) increased gradually in spring and peaked in summer (42.1%). The contribution of microplankton (>20 μm) to total phytoplankton chlorophyll-a biomass was lowest with a mean of 16.2% all year round. The results of redundancy analysis indicated that phytoplankton with different cell sizes showed similar responsive trends to environmental changes, while their adaptabilities were different. Temperature, water levels, nutrients and pH were the key factors explaining size-structure of phytoplankton in east Lake Dongting.

Abstract:After the operation of the reservoirs in the upper basins of the Yangtze River and Lake Poyang, the hydrological rhythm in dry seasons of the Lake Poyang has changed. In order to ease the pressure from low water level in dry seasons, a hydraulic construction locking the outlet of Lake Poyang was suggested. The key point of this project is to determine the suitable control schemes on water level which could maintain a healthy wetland ecosystem. Cranes, Cygnets and Swan Geese feeding with winter buds of Vallisneria natans were selected as the indicator of Lake Poyang ecosystem, a numerical habitat model for wintering waterfowls was developed by integrating an EFDC hydrodynamic model and habitat suitability curves. The water depth was adopted as the key habitat factor, the habitats for the wintering waterfowls feeding in dry seasons and V. natans in wet seasons have been continuously simulated since September in 2008. The variation laws between water level at Xingzi Station and the potential habitat area of V. natans and waterfowls feeding in Lake Poyang were revealed and the quantitative response functions were developed. The potential habitat area of V. natans gets the peak (around 1703 km²) when the water level reaches 14.8 m. The three-stage quantitative response functions between potential habitat area and water level have been developed for wintering waterfowls feeding, the maximum and minimum areas are about 564 and 476 km², respectively, and the corresponding water levels at Xingzi Station are 11.73 and 9.56 m, respectively. For the proposed Lake Poyang hydraulic construction, a dynamic ecological water level control scheme as following is proposed: the water level should be controlled under 16 m during the refill period of Lake Poyang; then the water level would gradually decrease to increase the waterfowls feeding habitat areas; the maximum water level should be controlled below 12.5 m during December and January for the peak visiting of wintering waterfowls, and then gradually transits to natural state according to the inflow. The results could propose the ecological water control level for Lake Poyang hydraulic construction to protect the food resources and feeding accessibility of wintering waterfowls, and a quantitative basis for the conservation of Lake Poyang wetland ecosystem under new water-sand regime was provided.

Abstract:Lake ecological water level (EWL) is an important factor to maintain the health of lake ecosystem. Based on the analysis of the daily average water level series of Chenglingji, Yangliutan and Nanzui hydrological stations in Lake Dongting from 1959 to 2016, the hydrological variation characters of Lake Dongting were determined by Mann-Kendall method, cumulative anomaly method and sliding T test method. Based on the method of annual EWL distribution and the improved method of IHA-RVA, the minimum and optimal EWLs were calculated, and the Tennant method was used for the reasonability verification. Finally, the guaranteed rates before and after the abrupt point were analyzed. The results show that: (1) The average annual water level of Chenglingji and Yangliutan hydrology stations were both on the rise, with much significant trend for the former one. While the average annual water level of Nanzui station exhibited significant decline trend. (2) The time of abrupt changes in water levels of the three stations was 2003, which was basically consistent with the beginning operation time of the Three Gorges Dam. (3) The annual minimum EWLs of Chenglingji, Nanzui and Yangliutan stations were 21.41, 28.95 and 27.84 m, respectively, accounting for 86.3%, 95.9% and 95.7% of the multi-year average level. The optimal EWLs were 23.29, 29.51 and 28.36 m, respectively, accounting for 93.9%, 97.8% and 97.5% of the multi-year average level. Such defined EWLs could meet the requirements of lake ecosystem goals with the consideration on the annual changes in natural lakes. (4) the safeguarding on the minimum ecological water level in Lake Dongting is relatively high, basically reaching more than 80%, but the guarantee degree of the appropriate EWLs is relatively low. After 2003, the guarantee degree of Lake Dongting decreased significantly in October and November, which is related to water storage and conservancy projects in the upstream. The EWL guarantee measures in Lake Dongting were suggested to maintain the health and biodiversity of the lake ecosystem based on the low guarantee degree and the difference of annual EWL distribution.

Abstract:Construction of casade dams in Heihe River had a certain influence on the river water quality. We divided the water into upstream and downstream reaches of dam and natural reaches. To explore the impact of casade dams on the water quality, multivariate statistical methods were used to analyze the spatio-temporal characteristics of water quality based on 24 different sampling sites from december 2017 to august 2018. The results showed that the main impact factors on water quality in Heihe River were water temperature (WT), pH, dissolved oxygen (DO), electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP) and biochemical oxygen demand (BOD₅). WT, EC, BOD₅, chemical oxygen demand (COD_Mn) and TN varied signnificantly on the spatial scales. The water quality of the upstream reaches of dam were greatly affected by BOD₅ and COD_Mn, while WT, EC and TN were the key drivers for the natural reaches and less environmental influence on the downstream water quality. In temporal terms, WT, EC, BOD₅ and ammonia nitrogen excerted the greatest effects on the water quality, with most of the water quality factors changed obviously in non flood seasons. Factors such as temperature, rainfall, hydrological conditions and the joint operation mode of cascade reservoirs were the main factors affecting the seasonality of water quality in the region. The spatial differences were mainly influenced by the exogenous pollutants discharging in Qilian and Zhangye areas, and the influence of sediment retention and accumulation on the environment of dam construction due to the change of hydrodynamic conditions. The results show that exogenous pollution sources were still the main factors, followed by the cascade dam construction as the indirect factors, for the water quality deterioration. Therefore, controlling the exogenous pollution sources caused by human activities in the region, and implementing a reasonable reservoir operation mode according to the seasonal variation of pollutants were the key to improve the river water quality along with the cascade hydropower development.

Abstract:This paper explored the feasibility of using water level data from a single short-time satellite source to estimate long-term changes in lake water volumes. Combined with Sentinel-3A synthetic aperture radar altimeter (SRAL) in 2016-2018 and lake water areas extracted from Landsat satellites during 1988-2018, the relationship between water level change and water area change in non-glacial period of 2016-2018 and the water volume estimation formula were used to analysis the inter-annual changes of water level and water volume from 1988 to 2018, the intra-annual change from 2001 to 2018 and the main causes of such changes. Results show that lake area, water level and water volume of Tangra Yumco rose significantly in the past three decades, increased respectively by 21.1 km², 5.29 m and 4.47 billion m³ from 1988 to 2018. Although declines in the lake area and water level and water volume decreased during 1988-1998, the lake expanded during 2000-2018, exhibiting the characteristics of the dry and wet seasons during the period of 2001-2018. From 1996 to 2014/2015, the lake water volume change was from 3.83 billion to 3.55 billion m³. Such water volume changes are in good agreement with previous research. Lake expansion occurs in the southeastern and mid-western regions where the underground-water terrain is gentle. Based on the data from global land surface data assimilation system (GLDAS) and glacier snow lines, both the changes in precipitation and air temperature exhibited strong correlations (with R² of 0.613 and 0.845, respectively) with the changes of water volume over the period 2008-2018. The wet season of lakes was significantly affected by precipitation and air temperature. This study shows the potential of sentinel-3A SYNTHETIC aperture radar data in the estimation of lake water quantity change, and provides a basis for the estimation of lake water quantity change in a long time series by using a single satellite radar data with only short-term data.

Abstract:Accurate and quantitative analysis of phytoplankton communities in lakes and rivers is very important to evaluate the health of lakes and rivers and ensure the safety of human drinking water. Microscopic examination is the only method for quantitative analysis of phytoplankton community structure, but it can not meet the requirement of phytoplankton count analysis. Based on the vision field method with an Utermöhl inverted counter, the method of using photograph taken by inverted microscope is put forward. This approach was used to count the three kinds of pure algae samples and Lake Poyang field samples and we found that: 1) The count is not accurate with the magnification of 5 or 10 times because the phytoplankton is too small, but accurate for 20 or 40 times. The number of photos is the main factor affecting the counting and analysis of the photo method, with higher accuracy for large numbers of photo-taken times. 2) For all the samples, the counting results are stable when taking 5 or 10 photos with magnifications of 20 or 40 times. 3) The method of inverted microscope photograph is more stable than that of counting frame, eyepiece field of view, and Utermöhl inverted counter field of view, with a minimum variation coefficient of 0.812.