Abstract:In shallow lakes, primary producers are mainly benthic plants and phytoplankton distributed in benthic and pelagic habitats, respectively. The benthic plants include submerged vascular plants and benthic algae. Phytoplankton are mainly consisted of planktonic algae. The benthic plants usually dominate in oligotrophic lakes with low nutrient concentrations and high transparency as benthic plants can access the nutrient resources in the sediments. Due to the increase in external nutrient loading, nutrient concentrations increase and the limitation of phytoplankton by nutrients is reduced gradually. Due to their superior competitive ability in light, phytoplankton become the dominant primary producers in shallow lakes, and the ecosystems shift from a clear, benthic plants dominated state to a turbid, phytoplankton dominated one, i.e. regime shifts. During the process of regime shifts, ecosystem structures and functions of lakes change tremendously. This paper reviewed the changes in sediment properties, and community structures of phytoplankton, benthic plants, macroinvertebrates and fish. The impacts of these changes on the competitive advantage of phytoplankton and benthic plants, exchanges of phosphorus between benthic and pelagic habitats are synthesized. The impact of eutrophication on benthic-pelagic coupling process and the mechanisms of regime shifts in shallow lakes are discussed. There are some important implications for the restoration of shallow eutrophic lakes. The aims of shallow lake restorations are to re-establish the clear water states, and thus the criteria evaluating a successful restoration should include parameters determining clear water states, such as Secchi depth, phytoplankton biomass, benthic plant coverage or dominance. Studying the technology or methods of lake restorations should focus on controlling the major process of benthic-pelagic coupling, such as control of sediment phosphorus release and benthivorous fish, and restoration of benthic plants, specially submerged plants.

Abstract:The water quality of Lake Chaohu has improved significantly from the mid-1990s to 2012. But in recent years, water quality improvement has slowed down. In particular, cyanobacterial blooms area increased significantly in 2018. In order to evaluate the variation of water environment, we analysed the change characteristics of water quality and cyanobacterial blooms situation in Lake Chaohu using the investigation data covering 17 sites from 2012 to 2018. We also elaborated the progress and shortcomings of water pollution control in Lake Chaohu in the spatial scale of the basin, which will provide support to the modification and confirmation of pollution control policy. Our results showed that the mean values of total phosphorus concentration, total nitrogen concentration and bloom-forming cyanobacterial biomass (chlorophyll-a and phycocyanin concentration) increased significantly from 2012 to 2018, and the ammonia nitrogen concentration decreased significantly during this period. In spatial, the eutrophication presented slight decreasing trend in the western region, but it significantly increased in the central and eastern regions, especially for the total phosphorus concentration. Even though, the eutrophication level in the western region was still higher than those in the central and eastern regions. The relief of eutrophication was mainly attributed to the decrease in lake-inlet pollution from Nanfei River, Shiwuli-Tangxi River, and Paihe River. The increasing lake-inlet phosphorus pollution from Zhaohe River (in the central region), Shuangqiao River and Zhegao River (in the eastern region) directly contributed to the worsening trend of water quality in the two regions. In addition, with the increasing of total phosphorus level in the eastern region, the dominant bloom-forming cyanobacterial species in the region had shifted from Dolichospermum to Microcystis in summer, which might be one of the reasons why cyanobacterial blooms area in Lake Chaohu increased abnormally in 2018. Therefore, the pollution control of Lake Chaohu Basin should continue to strengthen the control in the western part of the basin, while increasing the attention and investment in the central and eastern part of the basin.

Abstract:To understand the responding mechanism of phosphorus concentration to external nutrient reduction in large shallow lakes, phosphorus concentrations, capacity in water column, and seasonal variations in Lake Taihu were calculated, based on 14 years (2005-2018) monthly monitoring data undertaken by Taihu Laboratory for Lake Ecosystem Research, Chinese Academy of Sciences. The responses of phosphorus capacity to water level, water volume and cyanobacterial bloom condition had been discussed. The result showed that total phosphorus concentration in Lake Taihu has not decreased significantly after the tremendous catchment restoration activities in the past 14 years. Fluctuations of total phosphorus concentration among seasonal timescale were spatially larger than inter-annual differences. The average total phosphorus concentration was 0.113 mg/L (n=1788), based on statistics of 32 sites in the lake and 3 layers in water column monitoring in the past 14 years. The average particulate phosphorus concentration was 0.077 mg/L, which was the main fraction of total phosphorus in the water column of Lake Taihu. Dissolved total phosphorus concentration was 0.036 mg/L in average, and the soluble reactive phosphorus concentration was 0.015 mg/L, which occupied only 13% of total phosphorus in water. The capacity of total phosphorus in Lake Taihu ranged between 410 t and 1098 t, with an average value of 688 t. The average capacities in spring, summer, autumn and winter were 604, 792, 673 and 683 t, respectively. Total phosphorus capacity in summer was much higher than that in other seasons. Conditions of algal blooms and hydrology, such as chlorophyll-a concentrations, suspended solid contents and water level, significantly influenced the spatial and temporal dynamics of phosphorus capacities in Lake Taihu. Influence of algal biomass dynamics on phosphorus capacity was even greater than hydrological conditions. The results suggested that the fluctuation of phosphorus concentrations in Lake Taihu was influenced by algal bloom and macrophyte dynamics under changing climate change scenarios. The restoration target of total phosphorus concentrations of 0.05 mg/L in the end of 2020 was difficult to achieve shortly. To further decrease the total phosphorus concentration in Lake Taihu, drastic decrease of external phosphorus loading and large-scale restoration of macrophyte vegetation are needed. For the phosphorus target management, more attention should be paid on the discharge reduction and inflow phosphorus loading, and the fluctuation of phosphorus concentration impacted by the future uncertainty of climate change favorably considered.

Abstract:The comprehensive trophic level index (TLI) is widely used in eutrophication assessment of Chinese lakes. For each sub-indices of TLI, the chlorophyll-a is the final indication due to its direct manifestation of eutrophication-related risk, and the physiochemical indicators (total nitrogen, total phosphorus, Seccchi depth and permanganate index) are indirect indications. Thus, the significant difference between the values of TLI based on the physicochemical indicators and chlorophyll-a indicates that the results based physicochemical indicators over-or underestimate the actual eutrophication status and associated risk. Here, the TLI assessment results of lakes along the middle and lower reaches of the Yangtze River based on the four physicochemical indicators and on chlorophyll-a were compared. Our results showed that, for Yangtze-isolated shallow lakes, the assessment results of TLI based on total nitrogen, total phosphorus and permanganate index underestimated the actual eutrophication status and associated risk. For Yangtze-connected shallow lakes, the results of TLI based on total nitrogen, total phosphorus, and Secchi depth overestimated the eutrophication status and associated risk, while the results based on the permanganate index underestimated the eutrophication level and associated risk. For the deep reservoirs, the evaluation of TLI based on the total nitrogen overestimated the level of eutrophication and associated risk, while the results based on the rest three physiochemical indicators underestimated the eutrophication status. The reasons for the mismatch of assessment results between the physicochemical indicators and chlorophyll-a are ascribed to two aspects. For specific lake type, some physicochemical parameters have limited indication for eutrophication risk (chlorophyll-a). Such as total nitrogen, total phosphorus, Secchi depth and permanganate index in Yangtze-connected and the total nitrogen in deep reservoirs. Moreover, the original relationships between physicochemical indicators and chlorophyll-a is mismatched. For example, the response of TP to chlorophyll-a in deep lakes is more sensitive than the counterpart used in development of TLI (TP) formula. The following suggestions were proposed for the lake eutrophication assessment of the middle and lower reaches of the Yangtze River. 1) for the lakes with adequate historical dataset, establishing the lake-specific relationships between chlorophyll-a and the four physiochemical indicators through quantile regression model and developing the lake-specific evaluate formula for physiochemical indicators; 2) Making the lake subdivision based on the water retention time and water area/water depth and deriving the type-specific relationships between chlorophyll-a and physiochemical indicators, obtaining the type-specific evaluate formula for physiochemical indicators of lakes in the middle and lower reaches of the Yangtze river. 3) In the results of eutrophication assessment, the state indicators (e.g., total nitrogen and total phosphorus) and risk indicator (i.e., chlorophyll-a) may should be evaluated separately, and more attention should be paid into the ratio of chlorophyll-a to nutrient in the lake eutrophication assessment. Meanwhile, the final indication of biological indicators needs to be emphasized. Given the fact that a general eutrophication management framework was currently implemented for Chinese lakes, which may be difficult to meet cost-efficient management objective. Thus, the type-specific and lake-specific eutrophication assessment methods proposed and reviewed in this study may be of great significance in future lake management.

Abstract:Government has strengthened the comprehensive management and restoration of the water environment in Taihu Basin. Despite the great efforts, the total phosphorus concentration in Lake Taihu rebounded in 2015-2016. Occurrence of cyanobacterial blooms has not been effectively inhibited. Thus, this essay is going to examine the reasons behind and figure out the key direction in controlling the total phosphorus in Lake Taihu. The water quantity balance analysis and the total phosphorus mass balance analysis will be carried out through the calculation of the total phosphorous fluxes and the water flows between Lake Taihu and the surrounding rivers. Affecting factors, including rainfall, lake storage regulation and human factors, will also be considered. Based on the analysis, we will investigate the sources of total phosphorus change in Lake Taihu as well as the reasons of variations. The results showed that Taihu Basin had abundant rainfall in 2015-2016, especially in 2016, there was a severe basin flooding. The maximum water level of Lake Taihu reached 4.87 m, only 0.1 m lower than that of the historical record in 1999. Enormous total phosphorus load flowed from the surrounding rivers to Lake Taihu, which became the main external source of Lake Taihu's total phosphorus load. The load from rivers occupied 66.8% and 74.2% of the annual total phosphorus load in Lake Taihu in 2015 and 2016, respectively. On the other hand, for internal source, the massive reduction of submerged plants played an important role in affecting the total phosphorus concentration in Lake Taihu. The area of submerged aquatic plants in Lake Taihu decreased by 88.7% in 2015. The large-scale harvest of aquatic plants hindered the phosphorus absorption and transformation capacity of the lake. In 2015 and 2016, the total phosphorus load retained in Lake Taihu accounted for 21.5% and 27.5% of the total phosphorus load. The increase in total phosphorus concentration in Lake Taihu provided a strong foundation for cyanobacterial blooms. It is urgent to lower the amount of total phosphorus into Lake Taihu and tighten the control of the total phosphorus sources.

Abstract:The prevention and control of heavy metal pollution in lake sediments has always been a hot issue in the environmental field. In this study, amino modified biochar was used as the covering material and Diffusive Gradients in Thin-films (DGT) was used to monitor the characteristics of in-situ release of Cu(Ⅱ) and Pb(Ⅱ) at the sediment-water interface with different pH and water flow disturbance conditions. The in-situ remediation effect of amino modified biochar on heavy metal pollution was also analyzed. The results show that the mobile heavy metal ions have a tendency to diffuse from the sediment to other media at 0 r/min or 100 r/min hydrodynamic conditions. The cover strength of 1.86 kg/m² for amino modified biochar can reduce the release flux of Cu (Ⅱ) and Pb (Ⅱ) over 89%, which effectively reduces the potential ecological risk of heavy metals in the water environment. A large amount of H⁺ or complex in the water will weaken the adsorption of heavy metal ions by amino biochar. When the overlying water is in neutral condition with pH=7, the in-situ remediation effect is the best. The content of Cu(Ⅱ) and Pb(Ⅱ) in the overlying water under the disturbance of 100 r/min water flow is 0.036-0.096 μg/mL higher than that at 0 r/min when the equilibrium is released. The high-intensity water flow disturbance easily caused the lifting and floating of the covering material, resulting in desorption of heavy metals escaping from the covering material.

Abstract:Pond culture, as a major component of aquaculture, is one of the important sources of agricultural source pollution. Pollutions from pond culture has been a big threat in the Taihu Basin, where with dense water network and developed fisheries. Hence, to reduce the eutrophication of water bodies, and to restore water quality and health, it is important to control the discharges of nitrogen, phosphorus, chemical oxygen demand and other pollution sources during pond culture. Based on field sampling survey and remote sensing interpretation, this study combined with GIS software to estimate the pollution load of pond culture in the Taihu Basin. The results showed that discharges of total nitrogen (TN), nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), total phosphorus (TP), dissoluble phosphorus (DP) and chemical oxygen demand (COD_Cr) in the Taihu Basin during 2014-2015 were 6.1×10⁶, 1.1×10⁶, 1.7×10⁶, 1.3×10⁵, 1.1×10⁵ and 8.0×10⁷ kg, respectively. The discharge factor of the above pollutions for fish ponds were 69.5, 12.4, 20.1, 1.6, 1.3 and 919.8 kg/ha, shrimp ponds were 3.0, 0.5, 0.9, 0.07, 0.06 and 39.3 kg/ha and crab ponds were 6.4, 1.2, 1.9, 0.2, 0.1 and 84.9 kg/ha. All of the pollutions from fish pond culture were much higher than those of shrimp and crab pond culture. The distribution characteristics of various pollution sources in pond culture in this basin were similar. The pollution discharge in the northwest, south and northeast of the Lake Taihu was higher in most areas than those in the east and southwest of it. Factors such as the well-developed pond farming industry and high fertilizer input result in high pollution discharge from ponds in this basin. Therefore, we proposed some reduction measures to control pond culture pollution in this basin, these could also be referenced by other basins.

Abstract:Taking the water around the uranium tailing pond in the upper reaches of Lake Poyang Basin as the research object, the pollution characteristics of chromium (Cr) were studied, and the contents of Cr in different speciations were calculated by the hydrogeochemical simulation software PHREEQC. Then the morphological variations under different conditions were discussed, and health risk assessment was realized. The results showed that the concentrations of Cr in the uranium tailing discharge water, tailing leachate and shallow groundwater did not exceed the relevant standard values. It was found that trivalent chromium was the main form with exhibition of Cr(OH)²⁺ and Cr(OH)₂⁺ in most samples. Chromium speciation were affected by pH and electron activity (pe) together. In the condition of pH=3-5, CrF²⁺ was the dominant species. When pH>5, the effect of pe value on the chromium speciation was more obvious with the increase of pH. When the pe value increased, the concentration of hydrolysate Cr(Ⅲ) decreased gradually but the oxidation product Cr(Ⅵ) increased gradually. The health risk assessment proves that chromium in shallow groundwater did not cause carcinogenic risk and non-carcinogenic risk to human health. While the pH and pe changed, the carcinogenic risk coefficient of chromium will be higher than the maximum acceptable level recommended by ICRP and USEPA. As the toxicity of hexavalent chromium is much stronger than trivalent, it is necessary to pay close attention to the pe and pH values in the water to avoid the increase of pollution.

Abstract:Demarcation of ecological protection red line is an important measure to ensure the ecological security. It is conducive to maintain the integrity of the ecosystem and achieving the sustainable development. Based on the ecosystem function and ecological sensitivity, an ecological security pattern was constructed for Qilu Lake watershed. This paper demarcates and administers the ecological protection red line. We revealed that:(1) The extremely important regions of sub-elements are superimposed to obtain the extremely important regions of ecosystem function. Zhewan River, Changsha River, Dasha River and mountainous areas have the highest ecological sensitivity, the dam area has higher ecological sensitivity. (2) The red line of first-level ecological protection covers areas of extremely important and sensitive ecology, lake shorelines and reservoirs. The red line of secondary ecological protection covers the ecological buffer zone around the lake, the ecological buffer zone in mountainous areas and the ecological corridor dominated by rivers. The three-level ecological protection red line covers the ecological coordination area, mainly farmland. (3) Ecological restoration should be adopted to protect the ecological functions of the extremely sensitive areas within the red line of first-level ecological protection. The red line for secondary ecological protection focuses on ecological protection to maintain the ecological quality of the region. Overall optimization of the three-level ecological protection red line should be carried out to improve the carrying capacity of the ecological environment.

Abstract:The speciation and ecological risk of sediment Hg and As in different water-level gradients of the Grus nigricollis habitat in Lake Caohai wetland, Guizhou Province were analyzed by modified Tessier sequential extraction. The results showed that Hg content in sediments ranged from 0.45 to 1.51 mg/kg. In terms of speciation composition, residual Hg > Organic Matter Hg > Carbonates Hg > Fe-Mn Oxides Hg > Exchangeable Hg. The content exceeds the soil environmental quality risk control standard for soil contamination of agricultural land and is related to the regional geological background and human activities. There is no regularity in the content distribution on the water level gradient. The ratio of non-residue Hg in Liujiaxiang (zone A) and Huyelin (zone C) area increased with the water level gradient, while the non-residue Hg in Zhujiawan (zone B) showed a downward trend. The As content is between 16.4 and 23.8 mg/kg, and speciation distribution residual As > Organic Matter As > Fe-Mn Oxides As > Carbonates As > Exchangeable As. The As content is equal to the land background value of Guizhou Province. With the water level gradient rises, the total content increases, the proportion of residual increases gradually, and the nature gradually stabilizes. The geo-accumulation (I_geo), the Hakanson index (E_rⁱ), and the risk assessment code (RAC) analyses of the hazard degree of Hg and As indicate that the risk of Hg pollution is high based on high Hg environment background value in Lake Caohai wetland, As is at a low level of pollution risk level and less affected to the environment. In this study, the distribution of Hg and As speciation and ecological risks on different water level gradients of Grus nigricollis habitat in Lake Caohai wetland were studied, and the effects of water-level gradient on heavy metal/semimetal distribution in sediment/soil were discussed. It provides a reference for the assessment of ecological effect of water level rise in the Lake Caohai wetland.

Abstract:As an important urban and rural development model in the three gorges reservoir area, watershed field town development model along the river has been widely popularized, and brought a series of the complex influences of the point-like aggregation pattern for human activities on the river water environment. In this study, the Heishuitan River and its main tributaries, which are featured with obviously field town development in the basin, were selected to carry out an investigation regarding carbon, nitrogen and phosphorus concentrations in surface water from September, 2014 to June, 2015, for discussing the influence of field towns distribution on the temporal and spatial patterns of water biogenic element in the basin. Results showed that, the concentrations of TOC and DOC in the water of main stream and tributaries were 4.5-39.2 and 3.2-31.4 mg/L, and TN, NO₃^--N and NH₄⁺-N were 1.12-6.96, 0.87-5.00 and 0.073-0.881 mg/L, while the ranges of TP, DTP and PO₄^3--P concentrations are of 0.078-0.454, 0.049-0.310 and 0.025-0.222 mg/L. All of the biogenic elements in the water presents a significantly spatiotemporal variability. The concentrations of carbon, nitrogen and phosphorus increased in certain extent when the water flowed through different towns, with the increasing range of the TOC, TN and TP of 4.7%-61.3%, 26.7%-144.7% and 12.8%-50.7%, respectively. Meanwhile, the water flowed through non-town reaches, the carbon concentrations of the main stream had no significant changes, and nitrogen and phosphorus concentrations were significantly reduced, indicating that the spatial variation characteristics of water biogenic elements (C, N and P) were co-regulated by the distribution pattern of the watershed towns and its self-purification capacity, and resulting that the carbon concentrations in the main stream increased "stepwise" from the upstream to the downstream. While the nitrogen and phosphorus content showed a "fluctuation" growth trend; correlation analysis shows that the concentrations of carbon, nitrogen and phosphorus were significantly related with each other, suggested that the nutrient contents had a synchronous change trend under the development mode of the towns. This study highlights that the bead-like field towns development pattern in mountain river basin would lead an obvious synchronous accumulation of pollutants from the upstream to the downstream, and then beyond the self-purification capacity of river water. In addition, the seasonal variation of carbon, nitrogen and phosphorus concentrations in rivers were mainly affected by runoff dilution, and resulting a pattern of lower concentrations in summer and autumn, and higher in spring. The eutrophication comprehensive index indicates that the monitoring sections of the Heishuitan River were above eutrophication status, and the surface water body has serious nitrogen pollution and light phosphorus pollution. Roughly estimation of the annual input flux of TOC, TN and TP from Heishuitan River to Three Gorges Reservoir amounts to 4057, 1001 and 47 t, which poses a serious threat to the water environment security. The bead-like field town development along the river, forming a specific pollution pattern with "point-surface" dual attributes and threatening the water environment safety of the Three Gorges Reservoir, should be concerned in the future.

Abstract:To assess the impacts of habitat filtering on taxonomical and functional compositions of fish communities, we conducted a fish survey in four typical microhabitats(i.e., littoral zone, open water, lake inlets and river channel) of the Lake Caizi, lower reaches of the Yangtze River Basin, in June-August, 2018. Forty-three fish species belonging to 5 orders and 31 genera were caught in total. More riverine species lived in the river channel microhabitat, while less of lacustrine biota, river-lake migratory and riverine species lived in the littoral zone microhabitat. Further analysis revealed that there exist significant differences in fish community compositions among the four microhabitats. Meanwhile, the dominant species of river channels were Sarcocheilichthys sinensis, Saurogobio gymnocheilus and Saurogobio dabryi, while Aristichthys nobilis, Ctenopharyngodon idellus, Hypophthalmichthys molitrix were dominant in the open water of the lake. In addition, Hemiculter leucisculus were found dominated in the littoral zone. By using one-way PERMANOVA analysis, we found both richness index and Shannon-Wiener index in littoral zone were significantly lower. In contrast, indices of functional diversity were stronger predictors for the impacts of habitat filtering on floodplain fishes, which showed that the RaoQ index in littoral zone was significantly lower while the FDiv index in river channel was significantly higher than those in the other three microhabitats.

Abstract:Microcystis and Anabaena are two major genera of bloom-forming cyanobacteria. The way in which the two cyanobacteria regulate their own morphology and physiological characteristics to maintain rapid growth is to explain the maintenance of two cyanobacteria blooms. In this study, the response of growth, morphological and photosynthetic characteristics of Microcystis (FACHB-905) and Anabaena (FACHB-82) to temperature changes were measured, and the trade-offs relationship between growth and these characteristics were analyzed. The results showed that the cell diameter of Microcystis decreased under high temperature, but the growth rate did not decrease under high temperature. These indicates that Microcystis could increase the growth rate by reducing the cell size under high temperature conditions. The cell diameter and the chain length of Anabaena changed significantly with the change of temperature. The chain length decreased significantly and the growth rate did not decrease under high temperature conditions, which suggests that Anabaena might regulate its morphological characteristics to maintain the high growth rate. At the same time, the specific growth rate of the two algae has a certain relationship with the photochemical activity, indicating that the two algae can adapt to the temperature change by weighing the relationship between their own morphology, photosynthetic characteristics and growth rate to obtain the best growth status. This study will be helpful to improve our understanding for the growth mechanism of cyanobacteria.

Abstract:The invasive cyanobacterial species Cylindrospermopsis raciborskii is able to produce cylindrospermopsin (CYN) that cause serious damage to human health. The published studies have showed that C. raciborskii has been widely distributed in China, and appeared to be a common species in southern China. However, its origin and toxicity potential are still unknown. In this study, ten strains of C. raciborskii isolated from Qiandenghu Lake (QDH), Guangdong Province were used to observe their growth, morphology, toxin production and phylogeography based on nifH and rpoC1 genes. Our results showed that filaments of all C. raciborskii strains were straight. Apical heterocysts were observed in all C. raciborskii strains except the strain QDH1 and akinetes were also commonly appeared. The average filament length and width of ten strains ranged from 41.0 to 77.7 μm and from 2.433 to 3.125 μm, respectively, with a significant difference between strains. The specific growth rates of the 10 strains were also significantly different, ranging from 0.075 to 0.174 d^-1. PCR analysis showed that only QDH7 gave positive amplification with six CYN synthesis genes. The strain was further analyzed by LC-MS/MS and confirmed to mainly produce deoxy-CYN isomer with the concentration of 1745.19 ng/mL. Phylogenetic analysis suggested that C. raciborskii from Qiandenghu Lake has high homology with the Australian, European and other Chinese strains, but the toxin-producing strains and non-toxin-producing strains in Qiandenghu Lake cannot be distinguished by rpoC1 and nifH genes. This study demonstrated the existence of CYN-producing C. raciborskii in water bodies of Guangdong Province, which highlights that it is necessary to prevent the ecological risks related to the newly emerging toxic cyanobacterial bloom.

Abstract:With the rapid development of modern molecular biology tools, especially DNA barcoding technology, a rapid, accurate and efficient identification method for species of zooplankton resting eggs is possible. In this study, zooplankton resting eggs, including copepods,cladocerans and rotifers in the surface sediments of Lake Liuye (Changde), a typical urban lake in Lake Dongting Basin, were studied. Using DNA barcode technology for species identification, 101 valid DNA sequences were successfully obtained from 191 resting eggs, and the identification success rate was 53%. According to the NCBI database comparison, 9 families, 12 genera and 11 species of resting eggs were successfully identified, and 6 samples were only identified to the genus or family level. The inter-species genetic distance of the three taxa was 68 times that of the intra-species genetic distance, indicating that the cytochrome oxidase Ⅰ (COⅠ) gene could be used for effective species identification of zooplankton resting eggs. Through the phylogenetic analysis by Neighbour-Joining tree, it was found that the identified species and their reference sequences were clustered into one branch, and all different species were clustered into independent branches respective. Therefore, different species could be effectively distinguished. The above results all indicate that the mitochondrial COⅠ gene, as a DNA barcode, can be used to identify the species of zooplankton resting eggs in sediment of lakes.

Abstract:Top soils (0-10 cm) were collected along a water gradient in three sampling belts in Caohai wetland of Guizhou Province, including agricultural areas, transition areas, shallow-water areas and deep-water areas. Soil total organic carbon (TOC), total nitrogen (TN), total phosphorous (TP) and their ecological stoichiometry in different water levels were measured to investigate their horizontal distribution patterns, as well as their influencing factors. Our results showed that the difference of TOC, TN and TP contents were significant in four water gradients. The soil TOC and TN contents gradually increased from the transition areas to the deep-water areas, while the TP content firstly decreased and then increased. The soil TN content in agricultural areas were significantly higher than that in the shallow-water areas, but TP content in the deep-water areas were significantly lower than that in the agricultural areas. The difference of soil C/N, C/P and N/P ratios were significant in four water levels. The soil C/P and N/P ratios gradually increased from the transition areas to the deep-water areas, while the C/N ratios firstly increased and then decreased. Compared with the transition areas, the soil C/N, C/P, and N/P ratios in the agricultural areas were lower. Correlation analysis showed that the spatial distribution of soil C/N, C/P and N/P ratios were related to soil physical and chemical properties such as TOC, TN and water content. In summary, the hydrology significantly affects the spatial distribution of soil TOC, TN, TP, C/N, C/P and N/P ratios in Caohai wetland, and the accumulation of soil carbon and nitrogen will be enhanced when the water level rises.

Abstract:Dissolved inorganic carbon (DIC) in river and reservoir aquatic ecosystems is an important component of global carbon cycle and the interaction among atmospheric, terrestrial and marine carbon. The hydrochemical characteristics, dissolved inorganic carbon concentration, and spatial and temporal distribution characteristics of δ¹³C_DIC in the surface water of the natural reach and cascade reservoirs in Yunnan Section of the Lancang River were analyzed. The results show that the composition of DIC and δ¹³C_DIC in the river-reservoir continuum was generally characterized by lower DIC concentration in wet season and higher in dry season, with the mean values of 2.59±0.44 and 3.30±0.37 mmol/L, respectively and negative value of δ¹³C_DIC in wet season and positive in dry season, with the mean values of -8.52‰±0.38‰ and -6.95‰±0.53‰, respectively. The changing characteristics in the Lancang River were similar with the natural rivers. The sources of DIC in water body mainly include CO₂ generated by decomposition of organic matter in soil and water body, weathering of carbonate and CO₂ exchange at water-atmosphere interface. The temporal and spatial heterogeneity of DIC concentration and the composition of δ¹³C_DIC in river-reservoir continuum is closely related to the lithology of river basin, soil biogeochemical process and microbial activity. At present, the Lancang River cascade reservoirs are short in construction age, complex in operation and changeable in hydrological conditions. The ‘hydrological effect of reservoir’ of cascade reservoirs on the accumulation of carbon, the important biogenic elements, is not obvious.

Abstract:Due to the climatic drought and a large amount of groundwater drainage, environmental geological problems such as hydrological circulation disorders, soil desertification and grassland degradation are common in open-pit coal mining areas. This study takes the Yimin open-pit coal mine area in Hulun Buir Grassland as the research object. Based on the investigation and analysis of the groundwater-lake system, this study combines hydrological, meteorological and remote sensing image data to construct the mathematics of the groundwater-lake response mechanism in the mining area. The model is used to predict and analyze the impact of mine development on lake in the area. The results show that the number of the group of lakes has changed from 5 to 2, and the total area of lakes has shrunk from 6.94 km² to 1.12 km² in the past 35 years of coal mining. The groundwater-lake interaction in the mining area has evolved from the type of natural groundwater recharge lake to the one of lake recharge groundwater. Based on the principle of water balance, the mathematical model of the groundwater-lake response mechanism in the mining area is established. Based on the analysis of the coupled mathematical model of groundwater and lake, it is found that under the condition of limited fluctuations of climatic factors and stable development of the mine, the largest chedaminor lake in the study area will shrink to 0.56 km² when the mine would be closed (in the year of 2045).

Abstract:The hydraulic engineering built at the inflow into the junction can be affected by both main and tributary floods. The control flood level has relationship not only with flood combination characteristic, but also with the coupling relation between flood and hydraulic engineering flood discharge. The existing methods of designed flood level assessment, based on the characteristic flood combination corresponding to the design flood recurrence period or the empirical combination directly, cannot accurately reflect the interaction between floods and hydraulic engineering. In this paper, the Copula-Monte Carlo simulation method is used to calculate the flood control design water level of hydraulic engineering built at the inflow into the junction. The acceptability is verified via a case study in the sluice of Guangxi Guiping Shipping Hub, Xijiang River, Pearl River Basin. The results show that, the proposed method can be used to account for the combination characteristic of main and tributary floods and coupling relationship with flood discharge of hydraulic engineering. The calculation result of the designed flood control water level meets the requirement of the flood control standard, indicating that the uncertainty of determining the designed flood control water level by using the flood return period is effectively overcame. Under the combined action of main and tributary floods, the design water level varies tremendously by using the different combinations of characteristic of the design flood recurrence period. The deviation exceeds the reasonable error range of the flood control standard, suggesting the unacceptability of the use of the design flood return period on the determination of flood control level. Otherwise, the results also indicate that it is difficult to reflect the flood and engineering characteristics of different projects reasonably by using empirical flood combination. The paper can provide a more reasonable theoretical basis and ideas for flood control design of the hydraulic engineering affecting by main and tributary floods at the inflow into the junction.

Abstract:Based on the observed daily runoff data from 7 hydrological stations covering 1960 to 2012 in the Lake Poyang Basin, this study identified and analyzed the spatiotemporal variations of the drought-flood abrupt alternation events (DFAAE) by applying the short drought-flood abrupt alternation index (SDFI), TFPW-MK trend test and Ensemble Empirical Mode Decomposition (EEMD). Further, the uncertainty of SDFI and the causes of DFAAE were also explored. The results revealed that DFAAE in Lake Poyang Basin generally occurred during March and October. Among these, the drought-to-flood events of Lake Poyang Basin mainly occurred during March and June, while the flood-to-drought events mainly occurred during July and October, with spatiotemporal difference existed between different ages. Mild DFAAE was the dominated events in the Lake Poyang Basin, while extreme DFAAE occurred less frequently. The extreme DFAAE was mainly concentrated in Fuhe River, Xinjiang River, and Raohe River sub-basins. Most of them were flood-to-drought events. The occurrence frequency of DFAAE was the highest in the 1990s and the lowest in 2000s. The TFPW-MK trend test of the minimum and maximum values of SDFI indicated there was a long-term decreasing trend in the intensity of the strongest flood-to-drought events of in the catchment except for Raohe River. Meanwhile, a decreasing trend for the occurrence intensity of the strongest drought-to-flood events was also found in Ganjiang River and the northern Xiushui River Basins. Relatively, an increasing trend occurred in Raihe River and the southern Xiushui River Basins. SDFI in the Lake Poyang Basin had two cycles which were 1 year and 21-35 years. In addition, there was a 3-year cycle in the occurrence intensity of the strongest DFAAE. The temporal and spatial variations of DFAAE were affected by spatial heterogeneity of precipitation and the strong human activities, etc. This study facilitates us to further understand the mechanism and change patterns of the extreme drought and flood events in the Lake Poyang Basin under the background of climate change. It also provides an important scientific basis for flood control, drought relief and disaster reduction in the Lake Poyang Basin.

Abstract:The Taihu Basin is located at the estuary of the Yangtze River, belonging to the intersection of China coastal economic belt and the inland economic belt along the Yangtze River. It is one of China's highly urbanized areas. Under the influence of continental polar air masses, maritime tropical air masses and tropical cyclones, the types of precipitation in the Taihu Basin are divided into plum rain and typhoon rain. Different weather systems lead to the different heterogeneous precipitation, which brings great challenges to flood management in the basin. Taking the spatial and temporal differences of flood risk caused by different weather systems into consideration, this paper analyzed the flood risk based on Copula theory. In terms of time, the probability distribution of the precipitation dominant factors was used to divide the flood period into the plum rain period and the typhoon period. In terms of space, we clustered the study areas in the plum rain period and the typhoon period respectively by the Archimedean copula function. Finally, the flood disaster risk during the plum rain period and the typhoon period was analyzed. The results indicate that the flood period of the Taihu Basin is divided into the plum rain period (June 24 to July 21) and the typhoon period (July 22 to September 22). According to the joint distribution of sub-region precipitation and the Taihu Lake water level, the Taihu Basin is divided into three sub-regions (P-Ⅰ sub-region, P-Ⅱ sub-region and P-Ⅲ sub-region) in the plum rain period, while the Taihu Basin as a whole for flood risk analysis in the typhoon period. In the future, the probability of the drainage adverse in the Taihu Basin during the plum rain periods and the typhoon period is 2.4% and 1.1%, respectively. It is of great significance for the Taihu Basin to adjust the schemes of design storm and utilize flood resource and make the decision of real-time scheduling for flood control and drainage.

Abstract:Based on the observational data and numerical simulations, the impacts of typhoon "Yagi" and "Rumbia" at Chaohu Basin were analyzed in this paper. When "Yagi" and "Rumbia" passing, they produced a large wind speed and wind wave at the surface of Lake Chaohu, inducing the greatest impact at the east part of the lake and then followed by the middle and west part of the lake. The maximum significant wave heights were 0.68, 0.67 and 0.48 m, and the maximum average wave period were 2.25, 2.33 and 1.95 s, produced by the transiting of Typhoon "Yagi" in east, mid-, and west part of Lake Chaohu, respectively. While the maximum significant wave heights could reach 1.50, 1.47 and 1.18 m, and the maximum average wave periods could reach 2.99, 3.04 and 2.74 s when typhoon "Rumbia" passed through Lake Chaohu Basin. The mid-area between the east and middle of the lake was mostly influenced by typhoon, and the impact on the east part was the most significant, followed by the middle and the west parts of the lake. Due to the large water depth and long wind fetch, the lake middle zones are often the areas with the largest wave intensity.

Abstract:The Qaidam Basin represents an important provenance for potassium salt in China and in the world. So far, studies have mostly focused on potassium salt in shallow subsurface salt lakes, whereas little has been reported about potassium salt in deep clastic pores. In the present study, the spatial-temporal evolutions involved in the metallogenesis of potassium salt in the Qaidam Basin are summarized within the context of the Kunteyi Sag as an example. A "double-layered potassium salt" model consisting of intercrystalline brine in the Q_p2-h salt-lake facies chemical salt crystal fissures underlain by the Q_p1 alluvial-proluvial gravel pore brine is established after investigating the local geology, paleo-environment, and brine reservoir distribution in the study area. The genesis of this "double-layered potassium salt" model and the internal connections between the overlying and underlying brine layers are explored by comparing the ionic contents in these layers through mathematical and geochemical approaches such as cluster analysis, characteristic coefficient, piper trilinear nomograph, and hydrogen and oxygen isotopes. The results indicate that within the Qaidam Basin, the brine in the "double-layered potassium salt" unexceptionally comprises salt rock lixiviation water from a continental sedimentary background. The overlying intercrystalline brine suggests more of salt rock dissolution, although lixiviation may have also played a role; the underlying gravel pore brine points more toward rock salt dissolution. The overlying intercrystalline brine seems to originate from the deep evolution of the underlying gravel pore brine, whereas the underlying gravel pore brine appears to be successive from the deep paleo-salt rock layers and the overlying intercrystalline layer. The oilfield water in the Neogene anticlinal structures surrounding the Kunteyi Sag also shows a close genetic connection with the "double-layered potassium salt" brine.

Abstract:The consistency of proxies at different locations in a lake is of great importance to the reliability of regional climate reconstruction. At present, a single core in the central/deep lake was usually used to reconstruct the regional climate and environment change without verification. Here we compare the same proxy among the different core sediments from different locations of Lake Toson (37°04'-37°13'N, 96°50'-97°03'E, 2808 m a.s.l), which is located in Delingha, NE Tibetan Plateau. Core TSL15S1, TSL15S3, TSL15S7 and TSLG17 were recovered at the water depth of 1, 16.5, 16.5 and 25 m in Lake Toson, respectively. Based on the dating of ²¹⁰Pb and ¹³⁷Cs analyses, the changes of grain size, carbonate content and other proxies were compared and analyzed. The results show that the mean grain size is consistent at similar locations, while the grain size are quite different at distant locations within the lake. The grain size of sediments in the shallow water vary greatly in a short time scale, while the sedimentary environment in deep water is relatively stable, and the change is not obvious in the centurial. The variations of organic matter and carbonate content are consistent with each other, which indicates that carbonate may be affected by lake productivity. The organic matter content can reflect the size of lake productivity. The variations of carbonate content are consistent with the carbonate oxygen isotope in TSLC and the pollen A/C ratio of TL06, which was regarded as the substitute index of regional effective humidity. Therefore, the grain size in Lake Toson is reflecting the local sedimentary environment, and its relationship with the regional climate is not clear. Geochemical indexes are more reliable and are recommended for environment reconstructions in a well-mixed lake.

Abstract:As one of the essential components, microorganisms are the cores of biogeochemical circulation in lakes. However, due to the complex interaction among microorganisms and the incomplete description of their habitats, less than 1% of microorganisms in lakes can be cultivated in the laboratory. In the past ten years, metagenomic methods has been widely applied to the microbial researches, which enormously contribute to the understanding of microbiomes in lake ecosystems. The obtained results not only uncovered the composition and diversity of microbial communities, but also revealed the ecological functions of microbes as well as the interactions among microorganisms. Moreover, metagenome-assembled genomes (MAGs) of uncultured microorganisms can be obtained by various contig binning strategies based on metagenomic data mining, which can be subsequently used for comparative genomics and ecological evolution studies. With the continuous development of bioinformatics discipline and the relevant sequencing technologies, metagenomics will become a more powerful tool in basic ecological principle exploration and routine environmental biomonitoring, and also become the cornerstone of understanding the ecosystem function and maintaining the ecological services of lakes.