Abstract:The Tibetan Plateau is one of the most important high altitude areas on the earth, which is sensitive to global changes. As the Asia Water Tower, the land surface water resources and their changes of the Tibetan Plateau have an important impact on the economic and social development of the plateau itself and its surrounding areas. However, under the condition of climate warming, there is less recognizance of the surface water facies shifting and their transformation for components of surface water resources, such as glaciers, lakes, rivers, precipitation and other water bodies. Lakes are the key link of the surface water facies shifting and water cycling on the Tibetan Plateau. Lake areas are sensitive to precipitation changes of the westerlies and the Indian monsoon dominant areas, but the responses of lake area and lake water storage are not always consistent in different regions and period. Lake water temperature has obvious response to climate warming, and the changes of lake water temperature and thermocline depth have obvious influence on the heat exchange of water-atmosphere, thus affecting the regional water cycle processes such as evaporation and precipitation. Due to the increase of lake water storage, the salinity of lakes in the Serling Co area has generally decreased since the 1970s. Based on the remote sensing inversion model constructed by the in-situ investigation of more than 60 lakes, it is found that the lake transparency has generally increased during 2000 and 2019. In terms of water balance monitoring in the big lakes of different supply types, the meteorological and hydrological factors affecting the lake change are quite different. In the current warm and humid climate state, lakes of the Tibet Plateau will continue to expand. In order to further understand the role of lake changes in the regional water cycle and climate change of the Tibetan Plateau, it is necessary to fully understand the variation of lake water storage and their continuous time series, to deeply understand the changes of lake physical and chemical parameters and the effect on heat exchange between lakes and atmosphere, and to obtain more comprehensive and continuous observation data from the great lake basins.

Abstract:During the flood season and impoundment period, there will be a large amount of floating debris gathering in the water area near the dam of the Three Gorges Reservoir. In order to explore the influence of water surface floating debris on the water quality near the dam section of the Three Gorges Reservoir (about 12.7 km long before and after the dam), floating immersion test and water quality monitoring of floating body covered water were carried out in 2018. Correlation analysis and regression analysis were used to analyze both the drift production of 2014-2018 and the water quality monitoring data of the near dam section. The results showed that the floating debris increased the concentration of nitrogen nutrient salts and organic pollutants in front of the dam, and led to the increase of NH₃-N concentration in the bay area resulting in the change of nitrogen nutrients composition and organic pollutants pollution due to the difference of COD_Mn/TOC ratio. In addition to NH₃-N, the influence of floating debris on the water quality in front of the dam was greater than that in the bay area. For the bay area, this influence became more obvious during the impoundment period. There was no obvious stratification of water quality factors within 2 m in the vertical direction of the water body covered by floating debris. Comparing to the comprehensive floating debris, the effect of plant floating debris on water quality was more rapid and obvious. The floating debris only affected the nitrogen nutrient index within a small range of water covered by it. The increase of floating debris production led to the concentration increase of suspended matter, organic pollutants and reducing inorganic substances (COD_Mn) in the water near the dam, forming a certain influence law. Therefore, it is of great significance for water environment protection to arrange the floating debris cleaning operation points reasonably, to carry out floating debris cleaning efficiently and timely, to give priority to the salvage of plant floating debris in a short period time, to implement reservoir scheduling reasonably in order to slow down the accumulation and retention time of floating debris, to enhance the monitoring about the impact of floating debris on water quality near the dam.

Abstract:In order to make a scientific reasonable plan for the total amount control of water pollutants, taking Zhangjiagang City as an example, a single-factor environmental Gini coefficient model was constructed, which involved in the factors of population, resources, economy and water environment tolerance. The main unfair pollutant distribution units were also analyzed by selecting the contribution coefficient as a judge. According to the minimum model of Entropy-Environmental Gini coefficient, the total amount allocation of ammonia nitrogen based on multivariate fairness in the towns of Zhangjiagang was proposed. The research found that there is no consistency between the proportion of pollutant reduction and the current discharge of pollutants in the total water pollutant load allocation process, and the final allocation scheme should be determined by considering many factors. In this study, the minimum model of entropy-environmental Gini coefficient takes many objective factors such as society, economy and resources into account. As for the plain river network areas, due to its special geographical location and natural conditions, the distribution of population and resources is relatively uniform, so the allocation scheme based on the model fully embodies the principle of multivariate fairness, which is more fair and reasonable.

Abstract:Zhejiang area of Taihu Basin is affected by human factors such as industrial, urban wastewater and farmland surface runoff. Pollution problems are becoming more and more serious. Based on the data of hydrological survey and water quality monitoring in 2013, inbound and outbound water quantity and spatial-temporal distribution of water quality indexes such as permanganate index (COD_Mn), ammonia nitrogen (NH₃-N), total nitrogen (TN) and total phosphorus (TP) in Zhejiang area of Taihu Basin were analyzed. The results showed that the inbound and outbound water quantity in Zhejiang area of Taihu Basin in 2013 was mainly outbound. The primary pollutant in the entry-exit section is TN. The average concentration is in the V-inferior V level in all entry-exit sections. The average concentrations of COD_Mn, NH₃-N, and TP generally reach the Ⅱ-Ⅲ standard. The outbound and inbound fluxes of the four pollutants are mainly outbound. The northern part of the study area is the main inbound section of pollutants, and the eastern part is the main outbound section of pollutants. The net outbound water quantity is the key factor affecting the net outbound flux of pollutants, and the water quality of the entry-exit section is the main factor affecting the net outbound flux. The key to reducing water pollution in Zhejiang area of Taihu Basin is controlling agricultural non-point source pollution and discharging industrial wastewater and urban domestic sewage after reaching the standard, which is the main measure of water pollution control and treatment in Taihu Basin.

Abstract:Chloroanisoles (CAs) in the environment are mainly derived from chlorophenols and other chlorinated hydrocarbons with similar structures. As molluscicide, pentachlorophenol was released to the schistosomiasis area of Lake Dongting watershed in China and caused CAs pollution. This study aims at quantifying the pollution characteristics and potential risks of chloroanisoles in surface waters and sediments of three tributaries, the Lishui River (LS), the Ouchihe River (OCH) and the Tuojiang River (TJ) of Lake Dongting. Gas chromatography-mass spectrometry was used to measure the concentration of CAs. Results show that:(1) Water is the main sink for CAs. The CAs concentrations in surface water of the three river shows significant differences with each other. The water pollution level from high to low was LS > OCH > TJ, with CAs concentration being 18.94, 8.83 and 4.14 ng/L, respectively. There is no significant difference in total CAs content in the sediments of the three tributaries, with CAs content being 2.86, 3.61 and 4.07 ng/g, respectively. (2) Trichloroanisole (TCA), tetrachloroanisole (TeCA) and pentachloroanisole (PCA) were the main pollutants of LS both in surface water and sediments (73.75% and 68.89%, respectively). The proportion of chloroanisole (CA) and dichloroanisole (DCA) in the surface water of OCH is relatively higher than other CAs (both, 48.59%), while in sediments TCA, TeCA and PCA were the main pollutants (the three, 93.38%); The CAs in the surface water and sediments of TJ were dominated by CA, accounting for 28.26% and 75.56%, respectively. (3) From upstream to downstream, the CAs in the surface water of LS showed a downward trend, while in the sediments increased slightly; the CAs in the surface water of OCH showed a downward trend, and the content of CAs in the sediments did not have significant trend; in TJ, only CA in water and sediments fluctuating rose, while other CAs had fluctuations but no significant changes. (4) PCA concentration in the water was lower than the acute 50% lethal concentration for fish and invertebrates reported in previous studies. There was no serious impact on aquatic organisms so far, however, the risks of CAs to the human health and environment could not be ignored.

Abstract:To better understand the contamination of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in sediments from Lake Baiyangdian, 20 OCPs and all 209 PCB congeners were measured in 11 surficial sediment samples collected from different locations of Lake Baiyangdian. Moreover, the risks posed by OCPs and PCBs were assessed based on sediment quality guidelines. The results show that 10 OCPs and 24 PCB congeners were detectable. The total OCPs concentrations ranged from 1.22 to 52.45 ng/g(DW) (dry weight), while the total PCBs levels were from below detection limit to 37.61 ng/g. These results indicate a moderate pollution level within China. HCHs and Dieldrin were predominant in all OCPs, which accounted for 39.9% and 31.5% of total OCPs, respectively. Seven sampling sites of Lake Baiyangdian were contaminated by Lindane (γ-HCH) and the other 4 sampling sites were mainly contaminated by industrial HCHs. Moreover, new HCHs inputs might exist in some locations. DDTs levels were relatively low, which suggests that DDTs in Lake Baiyangdian might be the historical residues. PCBs detected in these sediment samples were dominated by low chlorinated PCBs congeners. Mono-, di-and tri-chlorinated biphenyls accounted for 64.73% of the total PCBs. However, it is noted that some new organochlorine pesticide pollution of HCHs may be present in some areas. Ecological risk assessment based on sediment quality guidelines revealed that the risks posed by p,p'-DDD and ∑PCBs were relatively lower, while the risk associated with Dieldrin was of concern. Notably, γ-HCH posed apparent adverse effects on the local ecological system.

Abstract:In order to explore the spatial distribution of organic phosphorus in the sediments of the rivers entering Lake Hongze and the effects of exogenous inputs on its fraction transformation, we used the Ivanoff method to study the fraction characteristics of organic phosphorus in these sediments. The long-term effects of exogenous substances on the fraction changes of organic phosphorus in sediments were also investigated by adding organic matter and iron ions in the laboratory. The results showed that the contents of organic phosphorus in the sediments of the rivers entering Lake Hongze ranged from 34.8 mg/kg to 398.6 mg/kg, accounting for 7.7% to 36.9% of the total phosphorus, and which showed non-active organic phosphorus (NOP) > middle-active organic phosphorus (MLOP) > active organic phosphorus (LOP). The average proportion of LOP in the sediments of Suihe River was 19.4%, which was higher than that of other rivers. The average proportion of NOP in Chengzi River was 56.41%, which indicated that the spatial distribution of organic phosphorus was uneven. Overall, the contents of total nitrogen, total phosphorus and organic phosphorus in sediments of Anhe and Suihe rivers were significantly higher than those of Chengzi and Huaihe rivers, indicating that the former two rivers had a higher pollution level. Redundancy analysis showed that the fractions of organic phosphorus in river sediments were affected by their physicochemical properties, indicating the different influencing factors for different pollution levels of sediment. The addition of exogenous substances can mineralize organic phosphorus in sediments and promote their transformation from NOP to LOP and MLOP. The change range of organic phosphorus fraction caused by organic matter was greater than that caused by iron, and the transformation effect of exogenous substances on organic phosphorus in heavily polluted sediments was more significant. Therefore, it is an effective way to reduce the bioavailable phosphorus of Lake Hongze by reducing the discharge of exogenous pollutants around rivers.

Abstract:In order to better study the variation of water quality in Lake Hongfeng, the changing trend of nutrient and chlorophyll-a concentration was analyzed, and the water nutritional status was evaluated by water trophic level index (TLI) method based on monthly sampling monitoring data of 7 representative monitoring sites of Lake Hongfeng from 2009 to 2018 by environmental protection monitoring station of two lakes and one reservoir in Guiyang Province. Besides, the correlation between TLI and water chemical composition (total phosphorus, total nitrogen, etc.) and hydrometeorological conditions (water level, temperature, etc.) was statistically analyzed by Pearson. The results showed that the monthly concentration of total nitrogen in the water body fluctuated significantly (ranging from 0.56 mg/L to 2.80 mg/L), and the concentration in spring and summer was higher than that in autumn and winter. The monthly concentration of total phosphorus (from 0.016 mg/L to 0.103 mg/L) in summer was slightly higher than that in winter, and monthly ammonia nitrogen (from 0.007 mg/L to 0.710 mg/L) was spring > winter > autumn > summer, The monthly concentration of chlorophyll-a fluctuated seasonally from 0.8 mg/m³ to 38.9 mg/m³, summer > spring > autumn > winter, and the inter-annual trend was first increased and then decreased. The concentration of total phosphorus, ammonia nitrogen and chlorophyll-a decreased on the whole, which suggests the water quality is improving greatly during the past ten years. Lake Hongfeng was in the state of medium nutrition to the mild eutrophication state in the past ten years, and the TLI showed a trend of decline year by year. TLI in summer was significantly higher than that in other seasons. Statistical analysis showed that the chlorophyll-a concentration in Lake Hongfeng was significantly positively correlated with ammonia nitrogen, total phosphorus and potassium permanganate index, while negatively correlated with the nitrogen-phosphorus ratio. The chlorophyll-a concentration was also significantly positively correlated with water temperature, pH, rainfall, air temperature, and sunshine, and negatively correlated with transparency and air pressure, it was not significant correlation with water level, humidity, and wind speed. The results suggest that chlorophyll-a concentration in the reservoir ecosystem is not only controlled by nutrient concentration, but also controlled by meteorological and hydrological conditions.

Abstract:A comprehensive study of transportation features of nitrogen, phosphorous and dissolve oxygen at the sediment-water interface was carried out in near city areas of east Lake Chaohu. Based on the investigation of sediment nutrients analysis and nutrients release incubation experiments, the release potential and release rates of ammonia nitrogen (NH₃-N) and soluble reactive phosphorous (SRP) of different sediments were estimated. The distribution characteristics, diffusion fluxes, and consumption rates of dissolved oxygen (DO) at the sediment-water interface of different sediments were studied by using a non-invasive microelectrode analysis system. The results showed the surface sediments in the near city areas of east Lake Chaohu were in severe nitrogen and phosphorous pollution with high total nitrogen (TN) and total phosphorus (TP) loadings. Typical internal releases of NH₃-N and SRP were observed from all sediments with the average release rates of 32.44 mg/(m²·d) and 1.25 mg/(m²·d), respectively. The sediments play the role of pollution source rather than the sink for NH₃-N and SRP in the study area. Results also showed that all overlying water were at aerobic condition. The average oxygen penetration depth (OPD) and oxygen diffusion flux at sediment-water micro-interfaces reached 5.3 mm and 4.56 mmol/(m²·d) respectively, indicating good DO diffusion ability from the boundary layer to the sediment. The internal release intensity of NH₃-N and SRP are influenced by TN/TP contents of the surface sediment as well as the OPD at the sediment-water interface. The release of NH₃-N and SRP from sediments could be benefited from the high nitrogen and phosphorous loadings and low OPD and contribute to the eutrophication of the lake.

Abstract:The thermal stratification and its potential impacts on the phytoplankton biomass were studied through the four seasonal field investigations (October 2014-July 2016) in Lake Chenghai and Lake Yangzonghai, two mesotrophic deep lakes on the Yunnan Plateau, southwest China. The results revealed that these two lakes are both warm monomictic lakes, where the vertical stratification was occurred in spring, stabilized in summer and autumn, and disappeared in winter. The mean values of thermocline depth (the upper boundary), thickness and strength during the stratification periods (spring, summer and autumn) were 17.70±3.89 m, 5.54±4.44 m and 0.67±0.43℃/m in Lake Chenghai and were 12.53±3.35 m, 8.25±4.85 m and 0.53±0.43℃/m in Lake Yangzonghai, respectively. During the stabilized thermal stratification periods, the dissolved oxygen in the bottom of the water column reached less than 3 mg/L even 1 mg/L, and the specific conductance in the bottom was generally larger than that in the surface water column. In these two lakes, the maximum values of the seasonal-average algal biomass (represented by chlorophyll-a concentration) were both in winter, which was 19.22±11.08 μg/L in Lake Chenghai and 45.82±9.41 μg/L in Lake Yangzonghai. Moreover, the fading of thermal stratification may be an important factor that increases the inorganic nutrients in the surface of water column (from the bottom of water column). Thereafter, higher nutrients combined with suitable light conditions and water temperature could promote the occurrence of algal blooms in winter. Besides a certain similarity, the major influencing factors of seasonal phytoplankton biomass also had inter-lake and seasonal heterogeneity during the other periods of season changes.

Abstract:In order to better understand the effect of cascade damming on river chemistry distribution in the karst region, we collected water samples from Hongjiadu Reservoir (multi-yearly regulation), Wujiangdu Reservoir (seasonal regulation) and Suofengying Reservoir (daily regulation) in January, April, July and October of 2017. We analyzed the water chemistry characteristics of the inflow, outflow and stratified water samples of these three reservoirs and investigated the cascade damming effect on water chemistry. The results show that water chemistry distribution has been highly affected by the damming effect. The HCO₃^- concentration of the hypolimnion is 12.9%, 5.5% and 8.0%, and the Ca²⁺ concentration is 15.9%, 2.4% and 8.5% higher than that of the surface water, respectively, for the Hongjiadu Reservoir, Suofengying Reservoir and Wujiangdu Reservoir. Consequently, the chemical weathering rate estimation of carbonate rock has also been affected. The annual weathering rate variation of Hongjiadu Reservoir, Suofengying Reservoir and Wujiangdu Reservoir is -1.7%-15.4%, -5.6%-1.1% and -0.3%-3.4%. The calculated weathering rate and HCO₃^- and Ca²⁺ concentrations in decreasing order is Hongjiadu Reservoir > Wujiangdu Reservoir > Suofengying Reservoir, which is consistent with the water retention time, indicating that water retention time affects the redistribution of water chemistry. At the same time, the ions concentration showed obvious seasonal variations, and the change rates in the three reservoirs were significantly greater during the flood season than that of the dry season. The above conclusions indicate that the water chemistry of rivers in karst area is highly affected by damming, which affects the estimation of chemical weathering rate. Water residence time and temperature are the main controlling factors on water chemistry redistribution. Therefore, we proposed that the damming effects should be taken into account to calculate the weathering rate accurately.

Abstract:Seasonal flooding and vegetation types are the main drivers of greenhouse gases fluxes in wetland ecosystems. In this study, undisturbed soil column simulation experiments were carried out to study the effects of hydrological regime on the emission of greenhouse gases from wetlands dominated by different types of vegetation in west Lake Dongting. Three types of vegetation were tested, i.e. Phragmites australis, Carex cinerascens and Populus deltoides. Static opaque chamber/gas chromatography method was used to measure the flux of CO₂, CH₄ and N₂O from wetlands with different vegetation types under the same dry-wet treatment. The results showed that the contributions of wetland to global warming potential were 16191.3, 3405.6 and 1883.1 kg/ha² for wetlands dominated by P. australis, P. deltoides and C. cinerascens, respectively. Specifically, CO₂ flux from P. australis wetland was significantly higher than that from C. cinerascens and P. deltoides wetlands, and flooding resulted in a significant decrease in CO₂ emission regardless of vegetation type. Flooding significantly increased methane emission from P. australis wetland but the increase was not significant for C. cinerascens and P. deltoides wetlands. For N₂O emission, the effects of both flooding and vegetation types were not significant. The results of this study indicate that the current wetland restoration program in west Lake Dongting, such as curbing the expanding of P. australis and converting P. deltoides wetland to C. cinerascens wetland, could potentially reduce its contribution to global warming.

Abstract:The Lake Taihu rim has a robust economy and a dense population. In recent years, this area is facing severe environmental problems such as eutrophication, habitat degradation and invasion of introduced aquatic species. Aimed to clarify the status quo of aquatic plant bio-diversity in riverway and littoral zone of the Lake Taihu rim, surveys on native and introduced aquatic plants were performed in this area in 2018. The results indicate that:(1) In total, 38 aquatic plants species in 22 families and 29 genera were recorded in 65 community quadrats in the Lake Taihu rim in 2018; (2) An invasive submerged plant Cabomba caroliniana has the highest relative importance value (RIV) among 31 riverway quadrats, followed by an invasive free-floating plant Eichhornia crassipes, and the latter one has the highest RIV among 34 littoral zone quadrats; (3) The aquatic plant biodiversity indices decreased with the increasing coverage of C. caroliniana and E. crassipes in riverway and littoral zone quadrats, respectively, indicating that the invasive plants had an impact on the biodiversity of aquatic plants. The expanding distribution of the free-floating plant E. crassipes, and the possible invasion of the submerged plant C. caroliniana alongside river channels should be monitored in the Lake Taihu. Facing the problems of reducing coverage of aquatic plants and the invasion of introduced plants, it is recommended to conduct a full investigation on the distribution area and bio-diversity of aquatic plants, enhance supervisory control on the spread of introduced species, and establish natural reserves on aquatic plants in the Taihu Basin.

Abstract:Due to the operation of the Three Gorges Dam and upstream reservoir groups, the hydrological rhythm of the middle and lower reaches of the Yangtze River has changed subsequently, which resulted in habitat changes in Lake Dongting. However, these habitat changes not only affect the distribution of wetland vegetation but also influence the soil seed bank in Lake Dongting. To explore the influence of soil moisture variation on wetland soil seed bank germination and the relationship between soil seed bank and ground vegetation, 11 typical sites were set in field investigation, which were classified into 5 kinds of floodplains (silt floodplain, silt and grass transition zone, grass floodplain, grass and reed transition zone, reed floodplain). In addition, soil seed bank germination experiment was carried out under two types of treatment (moisture and flooded conditions). The results revealed that soil moisture decreased from silt floodplain to the reed floodplain. The density of soil seed bank of 5 floodplains had no significant difference. In the germination experiment, the species richness and soil seed bank density in moisture group was significantly higher than in the water flooded group, besides, the species richness and seed bank density in soil seed bank of East Dongting Lake Nature Reserve were significantly higher. Moreover, the species richness of ground vegetation was higher than soil seed bank, and the Jaccard similarity index of soil seed bank and surface vegetation in silt floodplain was the lowest. Phalaris arundinacea, Phragmites communis and Miscanthus sacchariflorus only existed in ground vegetation, while Lindernia procumbens and Mazus japonicus only existed in soil seed bank. In conclusion, it is not possible to rely solely on the seed bank transplantation technology to restore vegetation, the seasonal water level change and the specificity of some species should also be put into consideration. Meanwhile, matching targeted hydrological regulation mechanisms and related artificial measures can help to rehabilitate successfully.

Abstract:Sediment microorganisms are the main source of sediment metabolism in urban rivers, which ultimately determine the ecological status of the rivers. In this paper, to analyze the effect of different ecological treatments on sediment microbial community, we established artificial mesocosms to mimic sediment status of the black-stinking river with different ecological treatments as calcium nitrate, bio-energizer addition, and submerged macrophytes transplantation. Illumina Miseq sequencing was applied to reveal the bacteria community variations of all treated and untreated sediments. The results showed that in the overlying water, the total nitrogen (TN) content of calcium nitrate addition group was significantly higher than that in the control group, dissolved oxygen concentration in the bio-energizer addition group was significantly higher than that in the control group. In the sediment, the oxidation reduction potential (ORP) values of all the treatment groups were significantly higher than those in the control group; TN content of calcium nitrate addition group and submerged macrophytes transplantation group were both significantly lower than those in the control group, which indicate the improvement of sediment status of treatment group. Bacterial communities were also varied in treatment group, and showed diverse variations with different treatments. The Sobs and Chao 1 microbial diversity indices in the bio-energizer addition group were both significantly higher than those in the control group and calcium nitrate addition group; the Shannon and PD diversity indices for microbes in the bio-energizer addition sediment were both significantly higher than those in calcium nitrate addition group. All sediment microbial communities were dominated by Proteobacteria (Deltaproteobacteria, Betaproteobacteria, Gammaproteobacteria), Chloroflexi, Firmicutes, Bacteroidetes and Spirochaetae phyla. Nonmetric multidimensional scaling analysis showed that the addition of calcium nitrate and bio-energizer can significantly alter the composition of bacterial community structure. Uncultured_Anaerolineaceae, Ferribacterium and uncultured_Xanthomonadales_Incertaeae_Sedis were the main genus causing variations in the bacterial community. Redundancy analysis indicated that the change of sediment ORP is a key environmental factor driving the variation of bacterial community structure.

Abstract:Zoobenthos play crucial roles in maintaining and stabilizing the structure and function of lake ecosystem. Moreover, various zoobenthic species are valuable in freshwater eco-restoration. Uncovering the succession of zoobenthic community evolution could provide important information for the application of zoobenthic species in freshwater eco-restoration. In the present study, succession of macrozoobenthic communities was examined by combing field investigation from 2007 to 2017 and various documents. It was found that the succession of zoobenthos community in Lake Wuli can be divided into four stages, including natural succession stage, rapid degradation stage, habitat restoration stage and slow recovery stage. Besides, taking the water quality, sediment characteristics, phytoplankton community, and the reported eco-restoration activities in Lake Wuli into consideration, we discussed the major impact factors in different succession stages of zoobenthos community. Summarily, based on the above results and practical application of zoobenthos in freshwater eco-restoration, the present study pointed out the research directions which should be enhanced at last.

Abstract:Phytoplankton and environmental factors were investigated at 8 sampling sites in the Lake Baiyangdian in May and August of 2018, to study their relationship which can provide theoretical basis for water resources management and aquatic ecological protection. The results of Pearson correlation analysis showed that the main environmental factors were dissolved oxygen (DO), permanganate index (COD_Mn), total nitrogen (TN) and total phosphorus (TP) in flood season while those were DO, COD_Mn, ammonia nitrogen (NH₃-N) and TP in non-flood season. Phytoplankton species were detected in 5 phyla, 38 species in flood season and 6 phyla, 43 species in non-flood season, respectively. The density of phytoplankton was 415.30×10⁵-1018.14×10⁵ cells/L and 249.62×10⁵-454.21×10⁵ cells/L, respectively. The dominant species were 6 species and 10 species and were mainly cyanobacteria and green algae. The Shannon-Wiener diversity index (H'), Margalef species richness index (dM), Pielou evenness index (J) and species diversity threshold of phytoplankton community all indicated that the diversity of phytoplankton in flood season was lower than that in non-flood season. H' and J were higher in areas with better water quality (such as the center of the Lake Baiyangdian), whereas H' and J were lower in areas with poor water quality (such as the entrance of Fuhe River and Xiaoyi River). TP and DO were the key factors affecting the characteristics of the phytoplankton community in flood season, while COD_Mn and TP were the key factors affecting the characteristics of the phytoplankton community in non-flood season. The results of water quality evaluation showed that the water quality of the Lake Baiyangdian was in eutrophication and the degree continued to deepen compared with the results of three ecological surveys of phytoplankton since 2005.

Abstract:In recent years,dinoflagellate blooms had occurred frequently, and most of them were caused by the species of genus Peridinium and Peridiniopsis, and caused by the species of genus Ceratium were rare. Recently, however, the genus Ceratium species had been found throughout the world in the water bodies such as eutrophic reservoirs and fish ponds. In June 2019, some samples of the genus Ceratium were collected at various sites in Xiashan Reservoir of Shandong Province and found that it formed obvious light brown water blooms at local sites. Phylogenetic analyses showed that this species had the closest relationship with the common species C. hirundinella of the genus Ceratium, but the morphologically, the former had one intercalary plate and three apical plates, which were different from the C. hirundinella with four apical plates. By contrast, it is a newly recorded species of dinoflagellates-C. furcoides, which do not have been described in China. It has been reported as an invasive and water blooming species, which is often found in eutrophic water bodies during high-temperature seasons. In the Xiashan Reservoir, the chlorophyll-a concentration at the bloomed site is as high as 125.77 μg/L, and the density of the C. furcoides is 1.23×10⁶ cells/L, accounting for 1.21% of the total algal cell density. The number of cells is dominated by some filamentous cyanobacteria such as Merismopedia spp. and Planktothrix spp.; however, due to the very large individual cell size of the C. furcoides, its fresh weight is as high as 86.31 mg/L, accounting for 49.34% of the total algae fresh weight, which is the absolute dominant species in biomass. In addition, by examining multiple specimens collected from northeast China, central China, and southwest China in different periods during high-temperature seasons, based on its own and distribution characteristics, we held that C. furcoides preferred the high temperature and the eutrophic waters, and it has the potential ability to expand and form water bloom in different areas of China.

Abstract:As the second deepest lake in China, Lake Fuxian is one of the most important storages of the national strategic freshwater resources. With the intensification of climate change and catchment development, biological communities in Lake Fuxian had changed obviously in recent years with the deterioration of water quality and lake ecosystem health. We conducted a monthly survey of three sampling sites covering the south, central and north parts of the Lake Fuxian Basin in 2015 to identify the spatiotemporal pattern of phytoplankton communities and their environmental drivers. Our results showed that the phytoplankton community was composed of Chlorophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Cyanophyta and Cryptophyta, and there were strong seasonal fluctuations in biomass and community structure but no significant spatial variation was observed. The dominant taxa were Aphanocapsa sp., Ulothrix sp. and Mougeotia sp. (January), Fragilaria crotonensis, Ceratium hirundinella and Mougeotia sp. (February), Cyclotella spp. and Mougeotia sp. (March), Dinobryon spp., C. hirundinella and Mougeotia sp. (April-July), C. hirundinella and Mougeotia sp. (August), C. hirundinella, Dinobryon spp. and Mougeotia sp. (September), C. hirundinella (October), C. hirundinella, Peridinium sp. and Mougeotia sp. (November), Mougeotia sp. (December), respectively. Multivariate analyses showed that temperature and total phosphorus were significant factors in driving phytoplankton community structure, in accounting for 26.0% and 2.6% of the total variance independently with a shared portion of 3.0%. When compared to the predominance of Mougeotia sp. as surveyed in 2002-2003, there exists a significant change in phytoplankton communities with an obvious increase in algal biomass in 2015, which was likely linked to the long-term increase of lake nutrient levels.

Abstract:Juveniles of grass carp (Ctenopharyngodon idellus) and silver carp (Hypophthalmichthys molitrix) were collected in Three Gorges Reservoir (TGR), Lake Dongting and Lake Poyang from July to August 2017. Lapillar otoliths were extracted from the juveniles and were used to determine their hatch date and growth rates. The results indicated that the hatch dates of grass carp and silver carp were later in Lake Dongting than in TGR and Lake Poyang. Growth rates and otolith deposition rates of grass carp (Lake Dongting:P<0.05, Lake Poyang:P>0.05) and silver carp (P<0.05) were higher in Lake Dongting and Lake Poyang than in TGR. However, the rates of the tow fishes had no significant differences between the two lakes (P>0.05). We conclude that the impoundment of TGR has delayed the spawning time of grass carp and silver carp in the middle reaches of the Yangtze River. The juveniles grew faster in the two lakes. However, the intensive fishing in the two lakes reduced the population abundance of grass carp and silver carp significantly. At present, the complete fishing ban is being implemented in the Yangtze Basin. This measure will play a key role in restoring fish resources. Besides fishing ban, it is also suggested to protect the habitat and spawning grounds of fishes, to increase river-lake connectivity, to release more adult fishes, and to carry out ecological regulation.

Abstract:Based on the Landsat series of remote sensing data of Lake Shengjin wetland in 1989, 1996, 2003, 2010 and 2017, the ecological risk assessment model was built, the ecological risk index of different seasons was calculated, and the spatial distribution of ecological risk and its variation characteristics were analyzed. Meanwhile, the Pearson correlation coefficient was used to analyze the ecological risk correlation between seasons, seasons and years. The results showed that:(1) there were significant differences in ecological risk index in different seasons. The ecological risk from high to low was summer, winter, autumn and spring. The summer and winter risk index was 37.03% higher than that in spring and autumn. (2) In 1989-2017, the ecological risk index of Lake Shengjin wetland increased significantly. The important landscape types such as mudflats and grasslands in the lake area were highly susceptible to human activities and climate change, and gradually changed from medium-risk and high-risk areas to high risk, high-risk area. And the artificial surface and grassland area and the area of higher risk and high area show characteristics of certain synergistic change. In general, the Lake Shengjin Reserve is dominated by lower landscape ecological risks and medium landscape ecological risks. Partly higher landscape ecological risks and high landscape ecological risks are mainly located in the upper and lower lake areas. (3) The high correlation of ecological risks occurred between autumn and winter; the annual ecological risk is highly correlated with winter ecological risk. Therefore, the spatial-temporal evolution trend of the ecological risk in different seasons during the last 30 years reflects the response of the landscape pattern change to the landscape ecosystem disturbance, and the autumn and winter lakes wetlands need to be highly valued.

Abstract:Due to the spatial topographic heterogeneity in semi-humid and semi-arid regions, hydrological simulation is always a difficult problem as saturation-excess runoff and infiltration-excess runoff is coexisting during a storm. Most existing hydrological models cannot be customized to simulate flood processes of different areas because of their fixed structures and modes. This study developed a spatial combination model (SCMs) by combining the Xin'anjiang model (XAJ), Xin'anjiang-Green-Ampt model (XAJG) and Green-Ampt model (GA) for simulating runoff in the sub-watersheds where either saturation-excess or infiltration-excess runoff mechanism dominates. Curve number-topographic index method was used for dividing a watershed into infiltration-excess dominated and saturation-excess dominated sub-watersheds. The proposed models were tested for two selected watersheds:Dongwan watershed in semi-humid area and Zhidan watershed in semi-arid area. The results showed that the parameters of the Dongwan watershed are dominated by hydrological models, while the parameters of the Zhidan watershed are greatly influenced by the dominant runoff mechanism. The simulation results of the partial saturation-excess models are better than those of partial infiltration-excess models in Dongwan watershed. SCM2 model (combination model of XAJ and XAJG) simulated has the best performance (runoff depth error Re=75% and flood peak error Qe=75%), just as the SCM5 model (combination model of GA and XAJG) in Zhidan watershed (Re=53.3% and Qe =53.3%). In semi-arid and semi-humid watersheds, driven by topography and soil data, the SCMs have a more realistic model structure and parameterization with higher simulation accuracy and stability.

Abstract:Complex changes in flow division ratio can be aroused by channel morphological adjustments in anabranching reaches. Establishing a precise calculation formula of flow division ratio lays a foundation for investigating the changes in flow division ratio under different flow-sediment and channel boundary conditions. Taking the typical anabranching reach, namely the Shashi anabranching reach in the upper Jingjiang River as the case study, this paper compares the applicability in natural reaches of different flow division calculation formulas based on data observed after impoundment of the Three Gorges Reservoir (TGR) in 2003, and proposes an improved flow division formula with higher accuracy by introducing a comprehensive factor which can reflect the differences in roughness and water surface gradient between the primary and secondary branching channel. Based on this formula, the variation characteristics of flow division ratio at the study reach are further analyzed. The results reveal the following points:(1) Without accurately reflecting the differences in roughness and water surface gradient between the primary and secondary branching channels, the calculation error in low flow division ratio result is large and the maximum absolute difference (MAD) can reach 15%. (2) The average water depth ratio of the primary to secondary branching channel is highly related to their roughness-gradient comprehensive influence coefficient ratio and by introducing the average water depth ratio, a flow division calculation formula with a significantly improved accuracy of less than 5% MAD is established. (3) After impoundment of the TGR, the channel scouring and silting adjustments exert greater impacts on the low flow than high flow division ratio and led to a more significant variation of flow division ratio in the slightly curved branching reach than that in the straight branching reach.

Abstract:The WRF-Hydro modeling system (WRF-Hydro model) was used for flood forecast in semi-humid small and medium catchment in China, proposed by the National Center for Atmospheric Research Center (NCAR) in 2013. The Global Land Data Assimilated System (GLDAS) and observed rainfall data are adopted to drive WRF-Hydro model in Chenhe Basin located in the south-central Shanxi Province. This study examine the practical features and applicability of the model, and also compare with Xin'anjiang (XAJ) model in structure, parameters, inputs & outputs and simulation results. Given the excessive time consume in model running, the stepwise approach for calibration is used for five main parameters in this study. The multiplier for subsurface layer thickness (ZSOILFAC) is introduced to modify this thickness to establish contact between subsurface layer and aeration zone to meet the actual situation of the basin, and the good agreement between subsurface layer modified by ZSOILFAC and the aeration thickness evaluated by XAJ model is achieved. The results show that the time step is supposed to be reduced from 6 s recommended by User's Guidance to 1 s when spatial resolution of routing grid is 100 m in Chenhe Basin. WRF-Hydro model is good at simulating the details of flood, while XAJ model performs well and stably. The qualified rates of runoff depth and flood peak for the former are equal or slightly inferior to those for the latter. The mean root mean square Error (RMSE) of the former is 21.5% less than that of the latter for the flood events with qualified runoff depth and flood peak; while mean RMSE of the former is 56.2% greater than that of the latter for others. WRF-Hydro model has good skills in simulating the start time of observed hydrograph and has promising potential for hydrological simulation, flood forecasting and water resources evaluation for small- and medium-sized catchments.

Abstract:Lake water level is the basis for maintaining the structure, function, and integrity of its ecosystem. The water level change of Lake Poyang is complicated as it was affected by five rivers within the basin and the Yangtze River. To accurately predict the water level change of Lake Poyang, the long short-term memory (LSTM) is used to construct the water level prediction model of Lake Poyang. The model uses the flows of the Ganjiang River, Fuhe River, Xinjiang River, Raohe River, Xiushui River and the mainstream of the Yangtze River as input conditions to predict the water level process of different representative stations in the Lake Poyang area (Hukou, Xingzi, Duchang, Wucheng and Kangshan). The hydrological time series data from 1956 to 1980 is used as the training set, and data from 1981 to 2000 was used as the verification set. The influence of model parameters such as input time window, hidden neuron nodes and initial learning rate on prediction accuracy is discussed. The optimal parameters of the Lake Poyang water level prediction model are determined. The results show that the LSTM can accurately predict the water level at different parts of Lake Poyang based on the water flow from the five rivers and the Yangtze River. The RMSE value of the five stations is 0.41-0.50 m, and the NSE and R² are 0.96-0.98. In order to investigate the impact of the model training set on the water level prediction results of Lake Poyang, the study further selects data from 5 random years (1956-1960) and 5 typical hydrological years (1954, 1973, 1974, 1977 and 1978) daily average flow data to train the model. The results show that the prediction accuracy of random 5 years data as training set is worse than that of typical annual hydrological data training, especially the prediction of flood and dry water level; since the typical hydrological data volume is still much lower than 20 years of data, the overall prediction accuracy is slightly lower than the model with 20 years of data training. Therefore, representative data should be selected as much as possible for training, when applying such a data-driven LSTM neural network model.

Abstract:Source area partition and quality filtering can improve the dependability of eddy covariance (EC) flux data while reducing its temporal consistency. Here, we constructed an ultra-wide artificial neural network (ANN) structure based on the TensorFlow framework. For the ANN inputting feature information selection, we attempted to establish feature vectors utilizing adequate thermodynamic forcing information of micro-meteorological background. The temporal consistency of EC data was optimized by interpolating with the ANN modeled fluxes, raising the temporal coverage rates from under 0.40 to over 0.98 for the flux data at the lake surface of Yamzhog Yumco. The evaluation of flux simulation performance via 10-fold cross-validation indicates that the bias level exhibits minuscule perturbation over different subsamples, disclosing preferable robustness for the ANNs model. Comparing for the approximately 18.8 W/m²/81.5 W/m² of average value for the observed sensible/latent heat flux, 1.84 mmol/(s·m²) for water vapor flux, the mean absolute errors is 5.4 W/m² for the simulated sensible heat flux, 15.7 W/m² for the simulated latent heat flux, and 0.35 mmol/(s·m²) for the water vapor flux. The results suggest that the combination of ANN structure with variable selecting principle can utilize the micro-meteorological information of field observation more sufficiently to estimate the flux intensity. Consequently, the temporal consistency is efficiently optimized with the analysability of EC flux data enhanced. The optimization method we proposed makes the interpolation of EC flux observation data no longer depend on the calculation of specific micro-meteorological elements such as turbulence transport coefficient. The paper provides a reference idea for improving the data quality of EC flux observation experiments for alpine lakes and other harsh environments.

Abstract:Surface coat is a functional structure surrounding cells of cyanobacteria, and the extraction method is still not well compared and consistently reported. Previous work suggested that the main factors affecting the extraction of cyanobacterial surface coat were temperature, extractant concentration, extraction time, etc. To develop the optimal extraction methods for surface coat of cyanobacteria, Anabaena sp. and Nostoc sp. with different morphotypes of surface coat were selected. We performed a series of factors based on two-factor and orthogonal experimental design. Through comparison of cell morphology, spontaneous fluorescence and cell density after surface coat extraction, the results showed that slime can be separated from cyanobacterial cells by centrifugal method. Both sulfuric acid and sodium hydroxide water-bath methods can extract capsule, and the optimal conditions were 1 mol/L, 60℃, 30 min for sulfuric acid extraction and 0.01 mol/L, 50℃, 20 min for sodium hydroxide, respectively. The optimal method of sheath extraction was 0.01 mol/L sodium hydroxide water-bath method, 80℃, 40 min and 20 kHz, 30 W, on:3 s, off:3 s, 2 min by ultrasonic method. In addition, the polysaccharide components of extracted surface coat examination by high-performance liquid chromatography (HPLC) indicated that the sheath is highly hydrophobic and is not hydrated to slime or RPS in the culture medium. The glucosamine (1.261±0.02 mg/g) contained in capsule makes the capsule more adhesion than the sheath. Additionally, the optimal extraction methods obtained from this study can be effectively applied to other cyanobacterial and green algal species whose surface coats are mainly capsule and sheath. This study may provide technical support for further revealing the biological function of cyanobacterial and algal surface coat.