Abstract:Algae present in aquatic ecosystems have the capacity to enter the atmosphere through the process of bubble bursting at the water-air interface. Subsequent to this primary entry, the algae can then be disseminated via the process of aerosol transmission. This process is of critical importance in facilitating algal dispersal, thereby influencing population structures in adjacent water bodies. However, it should be noted that this process also poses significant health risks due to the increased presence of harmful algal species in the atmosphere. The current state of knowledge regarding airborne algae remains limited, with the majority of extant research documented in international literature. This review systematically examines the distribution characteristics of airborne algae, encompassing dominant taxa, seasonal fluctuations, and diurnal variation patterns. Moreover, it furnishes a comprehensive overview of the environmental determinants that govern algal survival and atmospheric transport, including temperature, humidity, and wind speed. A particular emphasis is placed on the health implications that arise from the presence of aerosolized harmful algae and cyanotoxins. In order to address the existing knowledge gaps, future research should priorities three critical domains: The primary research question pertains to the dynamics ofcolonization, with the objective of investigating the viability and reproductive potential of airborne algae in atmospheric environments. The second research question pertains to the identification of source-sink dynamics, with the aim of tracing emission hotspots and deposition patterns. The third research question focuses on the development of comprehensive risk assessment frameworks, with the objective of evaluating the long-term health impacts of algal aerosols and establishing early warning systems. The proposed directions are intended to facilitate a more profound comprehension of the subject matter, thereby providing a foundation for the development of evidence-based environmental management strategies.

Abstract:Phytoplankton, as primary producers in aquatic ecosystems, reflects the ecological structure and functional status of water bodies. The water circulation structure of arid lakes is highly variable, making phytoplankton communities particularly sensitive to environmental changes. This study explored the response and successional mechanism of phytoplankton communities in Lake Ulungur to seasonal environmental changes, examining factors such as species composition, diversity, dominant species, and interspecific interactions across different seasons. The surveys were conducted in May (spring), July (summer), and October (autumn) of 2019. A total of 161 phytoplankton species from 73 genera and 7 phyla were identified across 28 sampling sites, with 85, 49, and 149 species detected in spring, summer, and autumn, respectively. Tetraëdron minimum was the dominant species in all three seasons. The absolute dominant species in spring were Oocystis lacustis and Synedra acus, while Aphanizomenon flos-aquae and O. marssonii dominated in summer, and Planktolyngbya circumcreta and Aphanizomenon flos-aquae dominated in autumn. The interspecies association characteristics showed significant positive associations among dominant species in spring and autumn, while significant negative associations were observed in summer. Phytoplankton diversity was highest in spring, followed by autumn and summer. Non-metric multidimensional scaling and permutational multivariate analysis of variance indicated significant differences in phytoplankton community composition across the three seasons. Multiple regression on distance matrices analysis revealed that water temperature, transparency, and nitrate nitrogen positively influenced community heterogeneity, while the permanganate index had a negative effect. Additionally, the community structure was closely related to the abundance of Oocystis marssonii, Tetraëdron minimum, Microcystis sp., and Staurastrum sp. Overall, the phytoplankton community in Lake Ulungur exhibited stable succession patterns under the influence of seasonal environmental changes and interspecies interactions. This study provides essential ecological insights into the response of phytoplankton in arid lakes to environmental factors and interspecies relationships.

Abstract:In situ coverage is a commonly used method for the remediation of eutrophic sediments. Carbon-based materials offer several advantages, including widespread availability, environmental friendliness, and the absence of secondary pollution, particularly when compared to other remediation options. In this study, we pre-treated and structurally characterized activated coke and assessed its potential for sediment remediation for the first time. We examined the effects of activated coke (363.9 g/m²) and the submerged aquatic plant (Hydrilla verticillata, 32.4 g/m²) both individually and in combination on nutrient release from eutrophic sediments, as well as the impact of activated coke on the growth of submerged plants. The results demonstrated that activated coke possesses a high specific surface area and a rich mesoporous structure. Compared to the control group, the concentrations of COD_Mn, Chl.a, TN, TP, NH₃-N and SRP in the overlying water, as well as the total release fluxes of TN, TP, NH₃-N and SRP from the sediments, were significantly reduced. The combination treatment of activated coke and submerged plants yielded better results for the overlying water and sediment indicators than either treatment alone. Furthermore, the activated coke treatment increased the growth rate of submerged plants by 40.32% and significantly reduced the amount of reactive phosphorus within the plants, thereby decreasing the risk of phosphorus release after their decay. These findings indicate that activated coke has strong potential for application in the ecological restoration of eutrophic water bodies and exhibits a synergistic effect when combined with submerged plants.

Abstract:Lake sediments play a crucial role in the elemental cycling of water bodies and represent one of the current challenges in managing eutrophication. To uncover the pollution characteristics and sources of total nitrogen (TN), total phosphorus (TP), and organic matter (OM) in the sediments of urban lakes and provide a new traceability perspective for assessing the environmental effects of comprehensive water environment management, this study collected and measured TN, TP, and OM contents in sediment points from 25 sites in Lake Yiai, Huanggang City. Water quality at nine lake sampling sites and at CSO (combined sewer overflow) outlet was monitored. Analyze the spatial distribution characteristics of TN, TP, and OM in lake water and sediment. The comprehensive pollution index method was employed to quantitatively assess the pollution risks of TN, TP, and OM in the sediments. Cluster analysis combined with stoichiometric characteristics was used to qualitatively identify and quantitatively analyze the sources of N, P, and OM in lake sediments. The results indicate that: There were spatial differences in the distribution of TN, TP and OM in sediments. The horizontal distribution of TN, TP and OM contents ranged from 940-3677 mg/kg, 323-1667 mg/kg and 1.03%-7.44%, the high-concentration sites of TN, TP, and OM were concentrated along the lake shores and near the discharge outlets. Vertically, the overall trend showed that the surface layer had higher concentrations than the middle and bottom layers. Specifically, the content ranges of TN, TP, and OM in the surface sediments were 920-4450 mg/kg, 208-1970 mg/kg and 2.05%-7.48%, respectively. The TP content of surface sediments was higher than the average value of shallow lakes in eastern China, and was similar to the level of lakes with serious sediment pollution in China. The comprehensive pollution index method revealed severe TP pollution in the surface sediments, with 76% of the lake area experiencing moderate to severe TP pollution, while TN pollution and overall pollution levels were relatively low. Cluster analysis combined with stoichiometric characteristics showed that the C/N ratio in sediments at locations with CSO pollution was 11, and the C/N ratio in the surface sediments of Lake Yiai was 10.67, with C/P values ranging from 20.16 to 190.97. Approximately 44% of OM originated from the decomposition of dead algae, while 20% was influenced by overflow discharges and 36% by diffuse pollution. TP primarily came from diffuse pollution, followed by overflow sewage, while the sources of TN were similar to those of OM.

Abstract:Polyphosphate (poly-P), a phosphorus component that is widely present in organisms and exhibits high biological activity, plays a critical role in the phosphorus biogeochemical cycling in eutrophic water bodies. To elucidate the degradation and transformation processes of poly-P at the sediment-water interface and within the water column, as well as its response to key environmental factors in lake sediments, in situ samples were collected from the Zhushan Bay area of Lake Taihu. These samples were used to simulate near-natural conditions for studying the degradation and transformation of poly-P. The results indicated that under near-natural conditions, the short-term hydrolysis rate of dissolved poly-P showed no obvious upper limit and increased with rising concentrations. After two days, the soluble reactive phosphorus (SRP) concentration generated by the hydrolysis of high-concentration poly-P could reach (0.1±0.01) mg/(L·d). The hydrolysis of poly-P was primarily driven by biological degradation, with key factors influencing the degradation rate including dissolved oxygen (DO), carbon sources, temperature, and sediment resuspension caused by disturbances. Low DO accelerated the hydrolysis of poly-P and brought the SRP to its peak 12 hours earlier. The addition of carbon sources slightly increased the hydrolysis rate and promoted sustained SRP release throughout the incubation period, with a net increase reaching twice that of the control group. Low temperatures significantly reduced the hydrolysis rate, although the overall SRP continued to rise. Disturbances that led to sediment resuspension increased both the hydrolysis rate of poly-P and the peak of SRP. In the sediment, poly-P mainly existed in a strongly bound form within the Al-P fraction, undergoing continuous release and further hydrolysis, while only trace amounts were present as free poly-P in the sediment and pore water. Dissolved poly-P could rapidly settle and hydrolyze within 48 hours under near-natural conditions, contributing to the sustained supply of SRP to the water column. This study on the occurrence and rapid hydrolytic turnover of poly-P in the water column provides insights into tracing and clarifying the sources of active phosphorus that fuel algal cell proliferation during the summer and autumn seasons. It also sheds light on the biogeochemical processes involving polyphosphate in the phosphorus cycle of water bodies.

Abstract:A two-dimensional hydrodynamic and eutrophication model for a pumped-storage reservoir was developed based on MIKE21 ECOLab to investigate the methods of improving calibration efficiency, and to analyze the spatiotemporal pattern of residence time, nitrogen, phosphorus, and chlorophyll-a in the pumped-storage reservoir. The results indicate that the calibration sequence for 9 state variables in the ECOLab module is: five-day biochemical oxygen demand ＞ phosphates ＞ ammonia nitrogen ＞ nitrite ＞ nitrate ＞ chlorophyll-a = faecal coliform bacteria = total coliform bacteria ＞ dissolved oxygen, and 11 of the 41 parameters are primary calibration ones. The model satisfactorily represented the hydrodynamic and water quality processes of the reservoir, by validating with actual measurement data from 2022. Using this model, the simulated average water residence time in the reservoir is 9 days, given an annual water diversion volume of 490 million cubic meters. The residence time along the mainstream direction is relatively short, but it increases towards both sides, inversely proportional to the distance from the shore, indicating a high spatial variability. In reservoir bays, the residence time notably increases, reaching a peak of over 200 days. Based on observed water quality data of pumping water over the past five years, the simulation results indicate that the annual average concentrations of inorganic nitrogen, inorganic phosphorus, and chlorophyll-a are 0.75 mg/L, 1.93 μg/L, and 20.93 μg/L, respectively. Influenced by seasonal variations in non-point source pollution inputs from the Dongjiang River basin, the concentrations of nitrogen, phosphorus, and chlorophyll-a are higher during the wet season compared to the dry season. In regions with shorter residence times, nitrogen and phosphorus concentrations tend to increase, while chlorophyll-a concentrations tend to decrease. The outcomes of this study provide important information for model construction and eutrophication control in pumped-storage reservoirs.

Abstract:The land use and “source-sink” landscape (SSL) pattern of watershed have complex effects on water quality by influencing the production, transport and absorption of pollutants. Understanding the response relationship of river water quality to watershed SSL is the prerequisite and key to optimize watershed landscape allocation. Based on the Shangwuxi Basin of Lake Qiandao, this paper analyzed the temporal and spatial changes of river water quality indicators such as total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO^-₃-N), phosphate (PO^3-₄-P), and permanganate index (COD_Mn). The sub-catchment scale land use, SSL pattern and their effects on river water quality were analyzed. The results showed that water quality of main rivers in the basin gradual increased from upstream to downstream and from tributaries to main rivers. Monthly water quality monitoring on 31 points in non-flood season showed that 46% of the points had TN in Ⅴ- inferior Ⅴ standard, and the average concentration was significantly higher than that in flood season. TP and COD_Mn was mostly lower than class II standard, and was slightly lower than that in flood season. In order to further explore the causes of difference in water quality, this study introduced landscape pattern index and SSL spatial load ratio index (LWLI). Results found that LWLI was significantly positively correlated with water quality indexes such as TN, NO^-₃-N and TP in both flood and non-flood seasons. This indicated that the higher proportion of “source” landscape area in the sub-watershed, the closer to the catchment and the steeper the slope, the greater LWLI values and the higher nitrogen and phosphorus loss. For the flood season, the proportion of tea garden, paddy field and dry land, and landscape pattern indices such as dispersal and juxtaposition index (IJI) and LWLI could explain 46%, 27% and 58% of the spatial variation of TN, TP and COD_Mn concentration in rivers, respectively, while for the non-flood season, they could explain 25%, 46% and 62% of the spatial variation, respectively. From the perspective of SSL pattern, the spatial SSL imbalance existed in Shangwuxi Basin. The “source” landscape was concentrated near the middle and lower reaches of the river course, while the “sink” landscape was mostly distributed on the slopes far away from the river course, which made it difficult for the “sink” landscape to play the role of stream intercept and purification. It is suggested to adjust the land use structure and optimize the landscape configuration. For example, improve the management of “source” landscapes (such as precise fertilization and sewage treatment) and set up “sink” landscapes such as vegetation buffer zones or wetlands in key source areas to promote the interception of pollutants. By introducing the SSL spatial load ratio index, this study deepened the understanding of the relationship between SSL pattern and water quality response, and provided a scientific basis for the improvement of water environment quality in Lake Qiandao Basin.

Abstract:Lake bottoms generally experience repeated wind and wave disturbances, and the sediment-water interface process in the cycle of disturbance suspension-calm settling has an important impact on the mass cycle of lakes. For the change rule of particulate matter and phosphorus at the mud-water interface during the process of disturbance suspension-calm sedimentation, repeated experiments of disturbance-sedimentation were carried out. Using an oscillating grid as a disturbance device, we conducted 10 cycles of intermittent disturbance experiments with a 12-h cycle, and paid attention to the changes of turbidity, total phosphorus (TP), dissolved total phosphorus (DTP) and particles. Results showed that: the rise of TP and DTP in water would gradually reduce in the repeated suspension-sedimentation process. The greater intensity of the turbidity perturbation, peaks of TP and DTP declined greater after the perturbation. The cluster particle size in the substrate surface layer became larger after multiple disturbances, and the percentages of large flocs (about 200-400 μm) increased significantly, from 13% to 30%. With multiple perturbation, a phenomenon “perturbation-aggregation” occurred among particles. Closer between particles, stronger perturbation and more obvious aggregation made the van der Waals gravity increase and caused flocculation. Organic matter in the particles produced a “bridge-building effect” and encouraged the formation of larger flocs. The disturbed median particle size (D₅₀) of bottom sediment from Xuhu with 8.59% organic matter content was significantly larger than that in the bottom sediment with lower organic matter from Meilianghu and Gonghu.

Abstract:In recent years, summer heatwaves continued to occur in summer and influenced sediment properties in shallow lakes. The sediments located at the sediment-water interface (SWI) directly impact the lakes ecological health, due to its unique structural characteristics. In order to investigate the temperature effect on sediment structural properties, this study conducted sampling in Lake Gehu before and after high temperature, complemented by indoor simulation experiments. Firstly, sampling results indicated that elevated temperatures induce a decline in the density and yield stress of lake sediments, promoting the formation of fluid sediments (density ＜ 1.25 g/cm³). Secondly, the simulation experiment also showed the same trend. As the temperature rose from 25 ℃ to 35 ℃, the density of sediments at the SWI displayed an exponentially decreasing trend from 1.244 g/cm³ to 1.229 g/cm³. Meanwhile, the increase in temperature led an increase of the sediment median size from the initial 17.22 μm to 21.16 μm, resulting in the flocculation and aggregation of sediment particles. Additionally, increasing temperatures resulted in a higher polysaccharide/protein ratio in extracellular polymeric substances (EPSs), which decreased the stability of sediments. Rheological tests and calculation of critical shear stress showed that the yield stress and critical shear stress of sediments exponentially decreased with increasing temperature. Overall, this study demonstrated that high temperatures can lead a loose and porous sediment structures with a threshold at 29 ℃, which can cause sediment particle resuspension and suspension. Overall, this study has deepened the understanding of the impact of rising temperatures on sediment properties, elucidated the response dynamics of fluid mud characteristics to its resuspension potential under elevated temperature conditions. It has provided an in-depth understanding of the characteristics of fluid sediments and their potential for resuspension.

Abstract:Lake Baiyangdian is the largest freshwater wetland in North China. Fu River is one of the main rivers that flow into Lake Baiyangdian. In recent years, increasing frequency and intensity of extreme rainfall events have introduced new challenges, driving complex spatiotemporal variations in nitrogen and phosphorus concentrations and fluxes. This study systematically investigated the Fu River-Lake Baiyangdian system through field monitoring, water sampling, laboratory measurements and statistical analysis to reveal the dynamics of total nitrogen (TN) and total phosphorus (TP) concentrations and their response to extreme rainfall. Results revealed distinct seasonal trends: TN was highest in spring and winter and lowest in summer, whereas the TP peaked in summer and declined in spring and winter. Spatially, TN and TP decreased from upstream to downstream along the Fu River. After the “7.29” extreme rainfall event, TN showed a complex increase-decrease-increase trajectory influenced by agricultural runoff, sedimentary nutrient release, and biogeochemical processes such as dilution and denitrification. TP showed a simpler increase-decrease pattern driven by sediment resuspension and subsequent attenuation. Before the extreme rainfall event, nitrogen and phosphorus loads along the river gradually decreased. After the extreme rainfall event, nitrogen and phosphorus loads along the river significantly increased due to the input of non-point source pollutants. Nutrient loads surged significantly after the extreme rainfall event, increasing by factors of 10.5 to 47.4 due to the input of non-point source pollutants. These findings underscore the vulnerability of Lake Baiyangdian to extreme hydrological events and highlight the urgent need for targeted interventions to reduce pollutant loads during such events. This research provides critical insights into nutrient cycling dynamics under changing climatic and hydrological conditions, offering a scientific basis for sustainable water quality management in lake-watershed systems.

Abstract:This study focuses on the Xibeikou Reservoir in the Huangbaihe River Basin of western Hubei, where carbonate rocks are exposed. In-situ sampling and monitoring as well as laboratory experimental analyses were conducted to obtain basic physicochemical parameters and major ions of the surface water and vertical profiles across different seasons and sections. The spatial and temporal variations, driving factors, and carbon sink capacity of the biological carbon pump (BCP) effect were analyzed from the perspective of changes in hydrochemistry. The results indicated that water in Xibeikou Reservoir was weakly alkaline with the hydrochemical type of HCO₃-Ca·Mg. The spatiotemporal variations of basic physicochemical factors were significant. Water temperature, chlorophyll-a, and pH were generally higher in summer and lower in winter, with higher values observed in the reservoir area compared to the riverine area, and electrical conductivity, total dissolved solids, and partial pressure of carbon dioxide (pCO₂) showed the opposite behavior. The ion concentrations in the inflow river were generally higher than those in the reservoir. Within the reservoir, the concentrations of HCO^-₃, Ca²⁺, Mg²⁺, and K⁺ were lower in summer while higher in winter. The BCP effect appeared to be strongest in summer, followed by spring and autumn, and weakest in winter. Spatially, BCP effect was more pronounced in the reservoir area compared to the riverine area, and stronger in the tail area of the reservoir compared to the head. The stable thermal stratification in the reservoir enhanced the BCP effect and suppressed carbon emissions. The correlations between chlorophyll-a and pCO₂, HCO^-₃ concentrations to some extent suggested significant carbon control in the Xibeikou Reservoir. Preliminary estimates of the BCP carbon sink flux of Xibeikou Reservoir ranged from 0.04 to 0.07 t/(km²·d), comparable to other karst reservoirs. Overall, the estimated BCP carbon sink flux of karst reservoirs across China accounted for approximately 4% to 26% of national reservoir carbon emission flux, highlighting its importance in carbon source-sink accounting and carbon sequestration enhancement.

Abstract:Songnen Plain is controlled by geological structure, climate and other factors, and the fluorine content of groundwater in this region is generally high. In recent years, a huge number of researches have been put in practice based on high-fluorine groundwater, however, comprehensive understanding of the geochemical background in there is scarce, evolution trend and ecological health risks of fluorine in large reservoirs in the high-fluorine area of Songnen Plain likewise. Mechanisms of action and transport of fluorine ion (F^-) in surface water of Xianghai Reservoir was analyzed using various methodologies, including mathematical statistics, the Piper three-line diagram, the Gibbs diagram, end-member analysis, PHREEQC hydrogeochemical simulations, as well as risk assessment models for ecological and health. Results revealed that the F^- concentration in the surface water of the reservoir ranged 0.69-3.68 mg/L (average 1.87 mg/L), much higher than the standard of Class V (1.50 mg/L) stipulated in China's Surface Water Quality Standard (GB 3838-2002). The surface water in this region was characterized by high fluorine content, with fluoride (F^-) concentrations in the southwest significantly exceeding those found in the northeast. The hydrochemical characteristics of the regional surface water were primarily classified as HCO₃-Na, HCO₃-Na·Ca, and HCO₃-Na·Mg types. The main factors contributing to the enrichment of fluorine in Xianghai Reservoir included evaporation and concentration processes, mineral dissolution and precipitation, as well as cation exchange. Xianghai Reservoir belongs to the risk area of fluorine ecology and brings health risks to both children and adults, with children being significantly more vulnerable to the harmful effects than adults.

Abstract:Suburban lakes, under the dual influence of agricultural expansion and accelerated urbanization, are facing increasingly severe heavy metal pollution, posing threats to aquatic ecosystems and surrounding human health. This study focuses on Lake Shitang, a typical suburban lake in the middle and lower reaches of the Yangtze River. Through sediment core sampling and chronological reconstruction, combined with grain size and elemental concentration analysis, the enrichment factor method and potential ecological risk index were employed to assess and reconstruct the pollution history of Cd, As, Pb, Co, Cu, Ni, Cr, and Zn over the past two centuries. Additionally, correlation analysis, cluster analysis, and positive matrix factorization were used to determine the sources of heavy metals and their relative contributions. The results show that most heavy metals (e.g., As, Pb, Co, Cu, Ni, Cr, and Zn) exhibited low pollution levels and slight ecological risks. However, Cd had significantly higher pollution levels and potential ecological risks, increasing from no pollution to moderate pollution starting in 1981, with strong ecological risk levels reached in 2004. Furthermore, since the mid-1970s, the comprehensive potential ecological risk index of the sediment has risen significantly, although the overall risk remains at a slight level. Source analysis revealed that before 1930, heavy metals in Lake Shitang sediments primarily originated from natural weathering (average contribution rate of 63.63%), while industrial and agricultural sources contributed 25.22% and 11.15%, respectively. From 1930 to 1974, the contribution of agricultural sources increased to 23.44%, while natural and industrial sources accounted for 51.72% and 24.84%, respectively. After 1975, the contributions of agricultural and industrial sources rose to 46.74% and 41.19%, becoming the main sources of pollution. This study provides a scientific basis for the prevention and control of heavy metal pollution in the Lake Shitang Basin, offers a long-term perspective for the ecological protection of lakes in the middle and lower reaches of the Yangtze River, and serves as a theoretical reference and technical support for managing suburban lake pollution in other developing countries and regions under rapid urbanization.

Abstract:It is evident that microbial activities have a considerable impact on the concentration and speciation of arsenic in groundwater, thereby playing a pivotal role in its regulation. Despite its status as a region with a notable arsenic presence, the Kuitun River Basin has received scant research attention with regard to the metabolic characteristics of arsenic-metabolising microorganisms in its groundwater. This study procured 11 groundwater samples from the Kuitun River Basin for metagenomic sequencing, and analyzed the chemical characteristics of both high- and low-arsenic groundwater, as well as the associations between the community structure and functional genes of arsenic-metabolizing microorganisms and various environmental factors. The results of the study indicated that the predominant bacterial phyla present in the study area's groundwater were Proteobacteria, Actinobacteria, and Planctomycetota. At the genus level, low-arsenic samples exhibited a notable advantage in species richness and diversity. Furthermore, the abundances of Nitrosomonas, Thiobacillus, and Sulfuritalea were found to be significantly positively correlated with total arsenic (As) concentrations. A total of 12 functional genes associated with arsenic methylation, arsenite (As(Ⅲ)) oxidation, arsenate (As(V)) reduction, and arsenic transport were annotated. That the concentrations demonstrated a substantial negative correlation with arsenate reductase gene and organic arsenic oxidase gene, while concurrently exhibiting a significant positive correlation with arsenite methyltransferase gene. The presence of arsenic in the environment had a significant impact on the proliferation and diversity of microbial communities responsible for arsenic metabolism. This impact was characterized by the exertion of inhibitory effects on the abundance and diversity of arsenic-metabolizing microbial communities and the functional genes that facilitate this process. Consequently, this resulted in the selective pressure on the microbial community, leading to the enrichment of arsenic-resistant microorganisms in environments with elevated levels of arsenic. The study area's groundwater microorganisms were observed to demonstrate a variety of arsenic metabolic pathways, encompassing arsenic methylation, arsenic redox reactions, and arsenic efflux. Among these, arsenic methylation was identified as the primary pathway of microbial arsenic metabolism in high-arsenic groundwater within this basin. The relationships between arsenic-metabolizing microbial communities and functional genes, and arsenic concentrations, were regulated and influenced by multiple environmental factors rather than a singular one. By means of screening microbial populations that are capable of arsenic metabolism, in conjunction with their key functional genes, this study has not only deepened our understanding of arsenic metabolism mechanisms, but also provided novel strategies for bioremediation technologies that are aimed at addressing arsenic pollution.

Abstract:Nitrous oxide (N₂O), a potent greenhouse gas, is a major contributor to climate warming. Urban rivers, characterized by substantial pollutant inputs, are recognized as hotspots for N₂O emissions. However, N₂O emissions in rivers with weak hydrodynamics in plain areas remain unclear. This study investigated N₂O emission patterns in rivers flowing in to Lake Gehu, a plain urban area in China, and analyzed functional microbial abundance using quantitative PCR (q-PCR) to explore the underlying mechanisms during both the dry and wet seasons. The results showed no significant seasonal variation in N₂O emissions but highlighted pronounced spatial differences. N₂O emissions decreased significantly along the flow direction and were positively correlated with the distance to the lake. For every 1 km decrease in distance from the lake, N₂O emission flux decreased by 0.05 mg/(m²·d). Furthermore, N₂O emission flux increased with the ratio of nitrifying to denitrifying bacteria, highlighting the critical roles of nitrification and its substrate, ammonium, in regulating N₂O production. The average emission factor value in the study area was approximately 5.5 times higher than the default value in the IPCC-2019 guidelines. These findings enhance the understanding of N₂O emissions from urban rivers in plain areas and provide a scientific basis for improving regional emission estimates.

Abstract:The necessity of concerted endeavors to safeguard and rejuvenate the Taihu Basin environment is of the utmost importance in the context of the integrated, high-quality development of the Yangtze River delta region. It is of great significance in enlightening the policy-making of the regional environmental cooperation and enriching the theory of collaborative environmental governance. The present study sets out to systematically study how to coordinate the interests of local main bodies to carry out cross-boundary synergistic paths of environmental governance actions. The paper employs a qualitative research method of case study, and through the long-term tracking and investigation of the Suzhou-Jiaxing transboundary water governance practices, it constructs a comprehensive pathway framework for transboundary collaborative environmental governance from the aspects of synergistic content demand and realization guarantee, based on the theory of collaborative governance. The study has identified institution, technology and action as the key synergistic contents of the transboundary environmental collaborative governance path. The synergistic implementation of these three factors is identified as an important guarantee to promote the success of transboundary collaborative environmental governance. The Suzhou-Jiaxing grassroots government's pioneering introduction of a joint river-chief system can be regarded as a governance model through institutional synergy, with a deepening and expansion of the content of action-oriented synergy in the order of institutional cost and implementation cost from low to high. This has been demonstrated to be effective in improving the quality of the transboundary river environment. However, the content of technical synergy is less substantial, which limits the improvement of transboundary collaborative environmental governance capacity. The coordination of local stakeholders' interests in transboundary environmental cooperation is identified as the key driving force for the development of its cooperative governance path. The results obtained reveal the focus of synergistic contents, the characteristics of time-sequence combination and the synergistic effect of local subjects in the process of transboundary collaborative environmental governance. The findings of this study are of good practical guiding value.

Abstract:Hydrological processes are crucial factors affecting the suitability and areas of waterbird habitats in floodplain wetlands. Currently, extreme hydrological events triggered by global warming have become more frequent. For example, Lake Poyang experienced extreme flooding in 2020 and extreme drought in 2022, and a winter flood in 2015. So far impacts of extreme hydrological events on wintering habitat area of waterbirds in Lake Poyang remain unclear. This study extracted data on the wintering waterbird habitats in Lake Poyang from satellite imagery between 2013 and 2023 for the period from September to February of the following year. By comparing the spatial and temporal changes in waterbird wintering habitats between extreme hydrological event years with normal hydrological years, the study explores the impact of extreme hydrological events on wintering waterbird habitats area at Lake Poyang. The findings are: 1) The area loss of wintering habitats for waterbirds in Lake Poyang caused by extreme flooding in summer (EFS), extreme drought in late summer and autumn (EDSA), and winter flooding (WF) reached as high as 67.62%, 29.83% and 18.18%, respectively; 2) EFS and EDSA led to a significant reduction in the area of waterbird wintering habitats from September to November, but they did not reduce the habitat area during the critical wintering period (winter). Although the intensity of WF was not as severe as that of EFS and EDSA, WF resulted in an average habitat area loss of 14.31% during the critical wintering period; 3) There were significant spatiotemporal differences in the impact of extreme hydrological events on the waterbirds' wintering habitats in Lake Poyang, which were related to the extreme hydrological process and the lake's elevation. The study is valuable for the management and waterbird conservation of Lake Poyang and similar floodplain wetlands.

Abstract:In order to understand the status of early fish resources in the river-lake corridor of Lake Poyang during the early period of fishing ban, daily surveys on juvenile fishes were carried out from 5th April to 21st August 2023 in the corridor. Results showed that a total of 142054 juveniles were collected, and 38 species of juveniles belonging to 7 orders and 9 families were identified. There were 6 dominant species, with Coilia nasus which recovered remarkably after the ban on fishing and followed by the other five Hemiculter bleekeri, Rhinogobius giurinus, Hemiculter leucisculus, Pseudolaubuca sinensis, and Xenocypris argentea. During the survey period, smolts' abundance peaked on 21st July, reaching 11476 ind./100 m³. Spatial analysis showed that larvae abundance in the south bank was significantly higher than those in both north bank and the central sampling site. Redundancy analysis showed that turbidity, flow velocity and water level were the key environmental factors affecting the juvenile fish abundance. Turbidity was significantly and positively correlated with the juvenile fish abundance. According to the migratory habits of their parents, the fish communities were dominated by freshwater sedentary fishes, accounting for 76.32% and 68.29% of the total species number and abundance, respectively. According to the spawning mode of their parents, the fishes were mainly drift-spawning ones, accounting for 47.37% and 48.94% of the total species and abundance, respectively. Our study showed high diversity in fish communities in Hukou, but mainly consisted of small fishes. Meanwhile, we found that the average abundance of juvenile fish was higher on the south bank (1743 ind./100 m³) than that on the north bank (431 ind./100 m³) and in the center of the sampling site (258 ind./100 m³). The results of this survey supplemented basic data of early fish resources in the lake mouth of Lake Poyang after the ban on fishing in the Yangtze River, and provided a scientific basis for the fish diversity protection.

Abstract:Challenges such as the “invisibility” of fishway entrances, the “inaccessibility” of chutes, and “post-passage swimming behavior” have long persisted in the restoration of fish migration routes and the comprehension of fish life history. Specifically, urgent issues such as how fish swim after passing through a dam, whether they get entrapped in reservoir “ecological traps”, and if they can traverse the reservoir to reach their habitats require immediate attention. In this study, three typical fish species in the Heishui River of the Jinsha River, namely Schizothorax prenanti, Paracobitis variegatus, and Paracobitis potanini, were chosen as research subjects. The status of these target fish resources was evaluated by means of net-capture methods, and post-passage upstream movement data were gathered using telemetry technology. Subsequently, a quantitative evaluation model of post-passage upstream movement effectiveness was developed, integrating the hydrological and hydrodynamic factors of the reservoir. The key factors influencing this effectiveness were determined, and the response relationships between upstream effectiveness and these factors were established. The results are as follows: 1) S. prenanti, P. variegatus, and P. potanini were dominant species in the area from the upper part of the dam to the fishway and then to the lower part of the dam, accounting for more than 40% of the total catch in aggregate. 2) The fishway passage rate of the three target species was 11.14%, and their success rate of upstream migration from the fishway exit to the reservoir tail was 30.87%. 3) After passing through the fishway, the target fish exhibited different habitat preferences. Seventy percent remained in the near-dam reservoir area, which was the highest proportion; 28% continued to swim upstream to the pebble riverbed area; no target fish were observed to migrate upstream from the gravel braided riverbed area to the meandering gravel-sand riverbed area. 4) The sensitive factors affecting post-passage upstream effectiveness include fish species, flow rate, rate of change in hydrological conditions, and diurnal rhythm. 5) The success rate of upstream migration after passing the dam decreased as the river flow increases; target fish tended to migrate during short periods of rising water; over 60% of target fish chose to migrate at night; the success rate of post-passage upstream migration for S. prenanti was significantly higher than that for P. variegatus and P. potanini.

Abstract:The Chinese sturgeon (Acipenser sinensis), a flagship species of the Yangtze River, has suffered a dramatic population decline after the construction of the Gezhouba Dam. Currently, its natural reproduction has been disrupted for several years, with the migratory breeding group less than 20 individuals, placing the survival of the natural population in jeopardy. The release of artificially bred individuals has become a crucial measure to sustain the Chinese sturgeon population and facilitate its sustainable population recovery in the wild. However, the current approach to selecting release candidates and locations remains somewhat arbitrary. A fundamental question remains unresolved: Can Chinese sturgeons that have not undergone the downstream migration process from spawning grounds to the ocean during their larval and juvenile stages successfully initiate reproductive migration and navigate back to the spawning grounds on reaching sexual maturity? To investigate this, the current study analyzed release experiments involving Chinese sturgeons in the Yangtze River Estuary. In these experiments, we employed satellite tagging (pop-up archival tags, PAT) to track the artificially bred adult and sub-adult Chinese sturgeons' migration patterns. The findings indicated that, from 2004 to 2021, a total of 13227 Chinese sturgeons (including natural individuals and artificially bred individuals) were released into the Yangtze River Estuary, in which there were 671 artificially bred adult and sub-adult Chinese sturgeons (aged over three years). Of these, 71 were equipped with PAT tags, and data from 42 of these tags were successfully retrieved. Crucially, among the 21 individuals older than 10 years with valid PAT monitoring data, three exhibited upstream migration behavior along the Yangtze River. These findings suggested that the downstream migration experience during early life stages may not be a prerequisite for upstream migration in sexually mature Chinese sturgeons. To further validate this conclusion and gain a deeper understanding of the breeding migration process following release, more rigorous and detailed experimental research is urgently needed.

Abstract:Since the operation of the Three Gorges Reservoir (TGR), algae blooms have occurred in the tributaries, for example, the eutrophication in the Xiangxi River Bay, a tributary of the TGR, has a great impact on aquatic environment and water ecological security of the overall TGR area. Sediments are an important internal source of phosphorus-induced eutrophication in lakes and reservoirs. The microbial community plays a vital role in the elemental cycling of sediments, and their activity can significantly affect phosphorus fraction changes in sediments. To investigate the characteristics of the sedimentary microbial community's structure and diversity in the Xiangxi River and its response to environmental factors, samples collected from five representative sites in the river during the four seasons from autumn 2021 to summer 2022, were conducted a 16S rRNA gene high-throughput sequencing analysis and water quality analysis. Bacterial diversity and community structures were also examined. The results revealed high microbial diversity in the sediments of Xiangxi River. The α-diversity index showed a seasonal variation pattern of autumn＞ winter＞ spring＞ summer. The β-diversity showed that the microbial communities in the bay had the greatest difference in spring and the least difference in winter. The dominant bacteria are Proteobacteria, Bacteroidota, Acidobacteriota, Nitrospirota, Desulfobacterota, Firmicutes, Chloroflexi, Verrucomicrobiota, Actinobacteriota and so on; Spearman correlation analysis and RDA redundancy analysis showed that the overlying water pH, dissolved oxygen, electrical conductivity, overlying water orthophosphate, water temperature and total phosphorus in overlying water were the most important environmental factors affecting the structure and distribution of the bacterial community, and with total phosphorus being the most critical factor. This study is helpful to better understand the effects of microbial seasonal changes on the phosphorus form and content in the sediments of the Xiangxi River Bay, and to provide reference for the improvement and management of aquatic environment in the Three Gorges Reservoir area.

Abstract:Bacterioplankton play a crucial role in mass cycling within reservoir ecosystems and drive biogeochemical cycles. Based on the vertical characteristics of water temperature and dissolved oxygen in Wan'an Reservoir, a deep-water reservoir in Southeastern China, this study utilized 16S rRNA gene amplicon sequencing technology to reveal variations in the composition, structure and assembly mechanism of bacterioplankton communities during different thermal stratification periods in the reservoir. The results indicated that the α-diversity of bacterioplankton was highest in the thermocline and lowest in the hypolimnion during the period of thermal stratification formation. During the stabilization period, α-diversity was higher in the hypolimnion and lower in both the thermocline and the mixed layer. In the recession period, α-diversity was elevated in both the thermocline and the hypolimnion, while it remained lower in the mixed layer. Molecular ecological network analysis indicated that during the recession periods of thermal stratification, bacterioplankton exhibited stronger positive correlations, lower modularity, and higher network complexity. During the period of thermal stratification formation, the proportion of key species was highest (30.00%), followed by the recession period (24.38%) and the stabilization period (21.60%). The neutral model explained 79.7%, 78.8% and 64.1% of the community variations during the formation, stabilization, and recession periods, respectively. The bacterioplankton community assembly was primarily driven by stochastic processes; however, environmental factors also significantly influenced bacterioplankton community structure. Throughout the three periods of thermal stratification, the bacterioplankton community was mainly affected by dissolved oxygen, chlorophyll-a, total nitrogen and total phosphorus. This study aids in the management of water environment and ecological status in reservoirs and the assessment of the health of aquatic ecosystems.

Abstract:To address deviations between the DEM-derived simulated river networks and actual hydrological systems that impacted sub-basin delineation, this study first extracted primary river channels from the study area using geospatial imagery. Then we adjusted elevation values in the original DEM by vertically reducing river grid elevations along the identified channels. The reduction magnitude was determined by the maximum elevation difference observed between the main river grids and the adjacent depression grids perpendicular to the fluvial pathways. The optimal watershed area threshold for the river source was determined by the river network density method. Subsequently, combined the standard range of China's first-level small watershed division (50-300 km²) and the criterion that each sub-watershed (SW) outlet was located on the mainstream of the river network, the appropriate number and SW area were determined. Finally, by comparing the daily and hourly results of the Xin'anjiang model distributed in different SW division schemes, the rationality of the SW division was verified. The application results in Taoxi watershed showed that: Lowering the elevation of the DEM grid where the actual river system's main rivers pass by 40 m and determining the optimal watershed area threshold for the river source by the river network density method, the simulated river network extracted was more consistent with the actual water system. The optimal area threshold for SWs was 108 km², and the number of SW was 7, with an average area of 213.2 km². The 7 and 11 sub-basins divided by the DEM grid elevation reduction treatment after the main river course was passed were scheme A and B, respectively, while the 7 sub-basins divided without the DEM grid elevation treatment after the main river course was passed were scheme C. The daily discharge process was simulated using the hydro-meteorological data of Taoxi watershed from 1982 to 2022 (the years from 1982 to 2012 were used as the training samples, and the rest were used as validation samples). The determination coefficients of the training samples of schemes A, B and C were 0.87, 0.87 and 0.86, and the validation coefficients were 0.90, 0.91 and 0.90, respectively. The simulation accuracy was basically consistent. A total of 20 floods were selected for secondary flood simulation, and the flood peak, flood volume and error of the time of flood peak were used as precision evaluation indexes. The qualified floods under scheme A, B and C were 19, 19 and 16, respectively. Using the certainty coefficient as the accuracy evaluation index, the average certainty coefficient of the next flood simulation in scheme A, B and C were 0.93, 0.94 and 0.93, respectively. Scheme A and scheme B had higher qualified rate of flood simulation than scheme C, and scheme A divided into 7 sub-basins had no obvious difference in accuracy compared with scheme B divided into 11 sub-basins. It can be seen that it is reasonable and feasible to reduce the elevation of the DEM grid through the main river channel and divide the SW according to the criteria that the SW outlet is located on the main river channel and the SW area is within the classification range of China's first-class small watershed (50-300 km²).

Abstract:The unit hydrograph is a simplified way to understand how a watershed responds to rainfall and offers a practical approach for flood forecasting. By approximating real-world watershed processes as a time-invariant linear hydrologic system, this paper turns the unit hydrograph to General Unit Hydrograph (GUH). The traditional runoff hydrological models for flood forecasting require a large number of parameters and datasets. In order to reduce the complexity of flood forecasting and model parameters, a simple GUH model considering rainfall loss and pre-flow is constructed in this study, combining with the Multiple Objective Particle Swarm Optimization (MOPSO) algorithm for parameters optimization. Taking Yuecheng Basin and Jiuzhou Basin as the study basins, different combinations of flood forecasting are constructed according to the improved GUH model, SCS-CN model and Nash unit hydrograph for comparison. The applicability of the model in flood forecasting in small and medium-sized basins is evaluated, and the forecasting accuracy of the improved GUH model at different lead times is discussed. The results showed that: (1) The improved GUH model's forecasting accuracy was superior to two other models. (2) The improved GUH model reached a Category II forecast level at the both basins, with mean coefficients of determination for Yuecheng and Jiuzhou Basin being 0.79 and 0.84, and pass rates of 90.91% and 83.33%, respectively. (3) The forecasting accuracy of the improved GUH model gradually decreased with increasing lead times, but it still maintained a certain level of predictive performance when the lead times ＜ 4 hours. The improved GUH model with fewer parameters and simpler structure can consider rainfall loss. It showed the potential for flood forecasting and provided new insights for flood forecasting in small and medium-sized watersheds.

Abstract:The characteristics of wind speed and direction, and the general patterns of lake-land breezes as well as the process of typical events were analyzed, based on wind profiling radar data near the Lake Poyang from June 2021 to May 2023. Main conclusions are as follows: (1) The surface-layer wind speed was generally higher in daytime than in nighttime. The prevailing wind direction was northeast in summer and southwest in other seasons. The vertical wind profile conformed to the power law, with the wind profile index in a decreasing order as summer (0.41) ＞ spring (0.29) ＞ winter (0.26) ＞ autumn (0.23). (2) A total of 104 lake-land breezes (14.3%) occurred in the study period, among which 38 times occurred in summer and followed by autumn (24 times), spring (22 times), and winter (20 times). The lake breezes were longer-lasting and started earlier in spring and summer than in autumn and winter, while the opposite is true for the land breezes. When no land-lake breezes occurred, the southwest winds persisted throughout the day and night, and the wind profile index was 0.31. The surface-layer wind speed was generally lower when lake-land breezes occurred. The wind profile index was 0.57 with the northeast winds prevailing between 6:00 and 18:00. (3) Lake breezes in general peaked at 14:00 with a maximum height of 440 m, whereas land breezes in general peaked at midnight with a maximum height of 760 m. The seasonal patterns in lake-land breezes were related to changing water surfaces and contrasting land-water temperatures of the Lake Poyang. This paper provides preliminary conclusions for understanding the potential role of seasonal flooding lakes in local atmospheric circulation and boundary layer structure.

Abstract:Lake ice is an indicator of climate change, and global warming has a profound effect its growth and decay process. Numerous lakes on the Tibetan Plateau, where freezing phenomenon is common, is very sensitive to climate change. So far, there are few research on the thermal process of lake ice in the plateau, and the interaction mechanism between atmosphere-ice-water remains unclear. As the largest lake on the Tibet Plateau, Lake Qinghai has a particularly important impact on the plateau climate and water resource balance. Based on the in-situ observation of air-ice-water in Lake Qinghai during the ice-covered period on February 5, 2022, the variation of lake ice in Lake Qinghai under snow, dust, and bare ice conditions were analyzed. The results showed that the lake ice development was stable in February, with the maximum ice thickness and snow depth of 36.5 cm and 10.4 cm, respectively. The increase of snow depth reduced the ice thickness growth rate. The albedo of lake ice was higher in the morning and evening but lower at noon. The albedo of the snow-covered was the highest with the average value of 0.61, while the albedo under dust and bare ice conditions was 0.27 and 0.16, respectively. The net solar radiation also changed with albedo. With the increase of depth, the ice temperature increased, the daily variation decreased and the sensitivity of ice temperature to air temperature gradually decreased. The snow cover impacted the relation between air temperature and ice temperature, with the correlation coefficient decreasing from 0.93 in the bare ice stage to 0.34 if snow covers. Snow cover amplified the hysteresis effect of surface ice temperature response to air temperature, and the lag time was 73-169 min. The surface ice temperature reached its maximum 97 min earlier than the air temperature under the strong effect of solar radiation during the bare ice stage. The variation of vertical conduction heat flux in the lake ice was consistent to that of ice temperature. The heat flux decreased and the daily variation decreased with depth increased. In the bare ice stage, both the value and the daily variation amplitude of the conducted heat flux were greater than that in the snow-covered stage. The diurnal alternations of solar radiation affected the upper ice temperature, and the direction of conduction heat flux reversed accordingly. The water to ice heat flux showed an increasing trend, with the average of 8.43 W/m² in the snow cover stage and 20.14 W/m² in the bare ice stage. The latent heat flux of the ice bottom fluctuates between -10 W/m² and 10 W/m2 during the ice equilibrium period. This study has enriched the measured data of lake ice changes during the freezing period of Lake Qinghai, and provided foundation for the refinement and parameterization improvement of lake ice models applicable to high-altitude areas.

Abstract:The Three Gorges Reservoir Area (TGRA), being one of the country's typical ecologically vulnerable areas and areas prone to frequent landslide disasters, the occurrence of landslide disasters severely endangers the health and stability of the reservoir area's ecosystem. Therefore, the ecological risk assessment of landslide disasters in TGRA is crucial for the environmental management and ecological risk prevention in the reservoir area. Based on the three-dimensional model of “susceptibility-vulnerability-potential loss”, considering the impact of long-time series, the random forest model was adopted to evaluate the susceptibility of landslide disasters. Landscape pattern indices were used to represent ecological vulnerability, and the potential ecological losses caused by landslide disasters were quantitatively calculated through ecosystem services. The ecological risk assessment of landslide disasters in TGRA from 2000 to 2020 was carried out. Risk prevention zones were divided, and corresponding risk management measures were proposed. The results indicated that: Areas with relatively high and high ecological risks of landslide disasters were scattered in distribution, yet on the whole, they show a zonal distribution along both banks of the Yangtze River. Areas with moderate and relatively low risks spread from both banks of the Yangtze River and its tributaries to the periphery. Low-risk areas accounted for about 60% of the total area of the study region, mainly concentrated on the periphery of TGRA. The landslide susceptibility and ecological vulnerability in TGRA showed an increasing trend from 2000 to 2010, while the potential ecological loss was significantly reduced, resulting in a decreasing trend of landslide ecological risk; the opposite was true from 2010 to 2020, when the landslide ecological risk showed an increasing trend, and the ecological risk areas of the final high and higher-grade landslide hazard showed an expanding trend. The study area was divided into 16 risk prevention zones according to the dominant factors of the risk structure, the trend of risk change, and the potential ecological losses. By reasonably adjusting the intensity and focus of risk management, a multi-scale risk management strategy for the overall study area, different sections, and key districts and counties is formulated. This aims to achieve comprehensive disaster prevention, precise management measures, and efficient resource allocation.

Abstract:Saucer-shaped lakes (SSLs) within the Lake Poyang wetlands are regions with the largest vegetation biomass and the richest species diversity, supporting over 80% of the overwintering migratory birds of the entire wetland. These sub-lakes play a crucial role in maintaining the wetland ecosystem integrity and preserving species diversity. A comprehensive understanding of their distribution characteristics is of great significance for the optimal allocation of regional water resources and the health of the wetland ecosystem. Supported by Google Earth Engine (GEE) cloud platform, this study constructed a refined spatial catalog database of SSLs in Lake Poyang wetlands by integrating high-resolution, multi-temporal Sentinel-2A/B satellite imagery and multi-source auxiliary data to employ geospatial big data techniques. Based on this database, the study first systematically elucidated the number, size, spatial distribution patterns, cause and challenges of these sub-lakes. Results showed that Lake Poyang wetlands contained 319 SSLs larger than 0.01 km², with a total area of 557.68 km², accounting for about 28.88% of the annual average area of Lake Poyang. Among them, lakes ranging from 0.01 to 1 km² were the main type, constituting about 70.85% of the total SSLs. As the area of graded patches increased, the number of SSLs gradually decreased following a power function pattern. Regionally, the Gan-Fu estuarine delta contributed most to the total area of SSLs, with 242.82 km² (43.54%), followed by the Gan-Xiu and Raohe River deltas, with 149.67 km² (26.84%) and 138.62 km² (24.86%), respectively. The southern lake-type water body zone had the smallest share of SSLs, accounting for only 4.76%. Overall, the SSLs in the floodplain exhibited a “one main core, two secondary cores, and multi-centers” clustered spatial aggregation pattern, with spatial density evolving from high-density cores spreading outward in concentric zones. The spatial heterogeneity characteristics were marked by a “densely packed southwest, sparsely packed northeast” distribution. As the lake-bottom elevation increased, the number and area of SSLs showed a trend of initial growth followed by a sharp decline, with a significant distribution dominance in the 12-14-meter elevation range. Under the influence of seasonal flood pulses, the scale and distribution of SSLs in the Lake Poyang wetlands was the result of the combined effects of regional topography, hydrological processes, and human activities. This study will provide high-quality data support for research on hydrological process changes and their ecological impacts in Lake Poyang wetlands, and is expected to enhance the scientific basis for water resource management and drought early warning during the dry season in Lake Poyang.

Abstract:This paper analyzes the causes of siltation in the old course of the Fuhe River (OCFR) based on the sandbar evolution, water and sediment inflow conditions, and the impacts of siltation by the sandbar vegetation. It was found that from 1985 to 2022, the area of sandbars in the OCFR upstream continued to grow and the main channel silted up. The sandbar vegetation in the upstream grows luxuriantly. Under the influence of water blockage by floodplain vegetation, the flow velocity decreases, and the sediment concentration decays along the reaches, which promotes sediment deposition in the upper reaches. After the incoming water and sediment of the upper reaches enter the middle and downstream reaches, the average flow velocity decreases along the reaches due to the widening of the section width, resulting in sediment deposition. Moreover, the diversion OCFR water volume shows a decreasing trend year by year. The water and sediment conditions in OCFR are suboptimal. During periods of low flow, siltation occurs frequently, while with high-flow events, the river still lacks sufficient power to flush away the sediment. This dynamic results in a continuous accumulation of sediment within the channel. Based on a two-dimensional mathematical model, we designed multiple water-sediment control scenarios, incorporating various sandbar structures and vegetation distributions. Through detailed calculations and analyses, we proposed the following countermeasures: When the sediment concentration at the inlet of the Fuhe River exceeds 0.01 kg/m³, introducing controlled high-flow events with flow rates maintained between 85 and 125 m³/s can effectively transform the upstream section from a state of siltation to scouring. In the middle and downstream reaches, applying sandbars-cutting techniques and adjusting vegetation distribution can enhance the sediment transport capacity, thereby slowing down the rate of siltation in these areas. These countermeasures aim to provide a valuable reference for similar small and medium-sized rivers, improving their siltation conditions and restoring and maintaining the health and stability of river ecosystems.

Abstract:Since the operation of the Three Gorges Project in 2003, the hydrological regime of the Lake Dongting wetlands had undergone significant changes, subsequently affecting the distribution pattern of wetland vegetation. However, the complex relationship between the hydrological regime and vegetation distribution and the underlying mechanisms remain unclear. This study analyzed the spatial and temporal evolution of the Lake Dongting wetland vegetation pattern from 1995 to 2022 through remote sensing interpretation and field investigations. Combined with hydrological data, this paper explored the changes in inundation duration of sandbar vegetation before and after the Three Gorges Project and the driving mechanisms behind these changes. The results showed that: 1) The interannual trends of water levels in east, west, and south Lake Dongting were generally consistent. The operation of the Three Gorges Project led to a continuous decline in the annual average water level of Lake Dongting, with an average decrease of over 0.3 m and a maximum annual water level decrease exceeding 0.6 m. The duration of high water levels in west and south Lake Dongting shortened, shifting gradually toward lower water levels; 2) From 1995 to 2022, the overall trend of vegetation succession in the Lake Dongting wetlands were positive, with a continuous expansion in wetland vegetation area, specifically characterized by the encroachment of Phragmites australis communities on Carex brevicuspis, and C. brevicuspis communities on bare mudflats. 3) Changes in inundation duration before and after the operation of the Three Gorges Dam were significant in areas undergoing positive succession, from bare mudflats to C. brevicuspis and from C. brevicuspis to P. australis, whereas the changes were not significant in areas experiencing regressive succession, from C. brevicuspis to bare mudflats and from P. australis to C. brevicuspis. This suggests that reductions in inundation duration are a key driving factor promoting the positive succession of wetland vegetation in Lake Dongting.

Abstract:Studies about changes of zooplankton (e.g., Cladoceran) community and biomass, as well as the carbon sources of food web in alpine lake will deepen the understanding of lake ecosystem response to regional climatic and environmental changes. In this study, multi-index analysis of sediment core was carried out in Lake Taiji, an alpine lake in Northwest Yunnan, including the subfossil assemblage of cladoceran, the stable carbon isotope (δ¹³C) of Daphnia ephippia and chironomid headshield, and geochemical indicators (total nitrogen (TN), total phosphorus (TP), δ¹⁵N and C/N etc.), in order to understand the response pattern of cladoceran to regional environmental change and the characteristic of carbon sources change in the food web in the alpine lake during the past 200 years. Changes of TN suggested that the lake nutrient level was continue increasing in the past 200 years. Analysis suggested that exogenous inputs from the catchment and atmospheric nitrogen deposition were the main factors which driving the nutrient enrichment, regional warming and nutrient enrichment also promoted the enhancing of lake primary productivity (chlorophyll-a). Cladoceran community was dominated by littoral species Alona affinis and the facultative planktonic species Chydorus sphaericus. Before 1970s, there was no significant change of cladoceran community, after then, the relative abundance of C. sphaericus was decreased, associated with increase of A. affinis. Redundancy analysis shown that the annual average temperature and primary productivity (chlorophyll-a) were the main driving factors for the succession of cladoceran community in the past 200 years. For the stable carbon isotope values (δ¹³C), the δ¹³C of Daphnia ephippia was negative from 1860s to 1940s, probably attributed by the inputs of exogenous material, which supported by the lower lake primary productivity and higher C/N in this period. From 1940s to 2020s, the δ¹³C of Daphnia ephippia was significantly enriched, which may be affected by the enhanced primary productivity as well as the increase abundance of benthic algae. The δ¹³C value of chironomid headshell shown minimal change in the past 200 years, only had a negative trend from 1990s to 2010s, probably related to the increase inputs of terrestrial debris which driving by the increase precipitation in this period. Discrepancy in δ¹³C values between the Daphnia ephippia and chironomid headshield, indicated that there were different organic carbon composition in the planktonic and littoral zone, and affected by the changes of lake primary productivity and terrestrial inputs. Those findings reveal that regional climate change and catchment inputs changed the productivity and carbon source composition of aquatic food web in alpine lake, and ultimately affected the cladoceran community composition and stable carbon isotope values of aquatic organisms.