Abstract:

Abstract:Inland aquatic systems are critical components of the global carbon cycle, as their carbon dioxide (CO₂) emission characteristics directly influence climate dynamics. However, current research on CO₂ emissions from these systems is predominantly conducted at local scales, lacking systematic integration across regions and at the global level. This gap introduces substantial uncertainties into global CO₂ flux estimates and hinders a comprehensive understanding of the spatiotemporal patterns and driving mechanisms of aquatic carbon fluxes. Through a systematic review of primary monitoring methods—including the floating chamber method, eddy covariance technique, and boundary layer method—and upscaling approaches, such as area-based extrapolation, statistical regression, and mechanistic process-based modeling, this study elucidates how methodological differences contribute to data uncertainty. First, the characteristics of the three monitoring methods and the observational biases resulting from their differing applicable scenarios are comparatively analyzed. Next, the sources of estimation bias in the upscaling methods are examined, including the neglect of environmental heterogeneity in area-based extrapolation, insufficient representativeness of driving factors in statistical regression, and oversimplification of boundary conditions in mechanistic process models. The findings underscore that enhanced data quality and precision are essential for improving estimation accuracy. Future studies should prioritize advancing automated monitoring technologies, strengthening the spatiotemporal representativeness of data, integrating interactions between abiotic and biotic factors, and refining model frameworks to improve carbon source/sink assessments and provide robust scientific support for global carbon mitigation strategies.

Abstract:Dissolved organic matter (DOM) is a substance characterized by a variety of structural compositions, complex physicochemical properties and a wide molecular weight distribution. It is composed primarily of humic acids, fulvic acids, proteins, lipids and other organic components, as well as carboxylic acids, hydroxyl, phenolic, aldehyde and other reactive groups. DOM is ubiquitous in lake ecosystems, where it participates in a variety of biogeochemical processes. These processes influence the migration, transformation and behavior of biotic elements and pollutants, and play an important role in the conversion of carbon sinks in ecosystems. DOM in lake water exhibits a variety of environmental behaviors. For instance, DOM can be adsorbed to the surface of water particles, and the distribution of DOM in the dissolved/suspended phase can be regulated; DOM in lakes will undergo photo-and microbial degradation, which will change the content and structural composition of DOM samples; the multifunctional groups in DOM in lakes can be easily complexed with metal ions, and can also undergo electron transfer to produce reactive oxygen species. Furthermore, the existence of DOM in lakes has been proven to have substantial ecological and environmental impacts. Specifically, DOM in colloidal particles significantly influences the stability of these colloids and the transparency of the surrounding water. Moreover, the binding of DOM with heavy metals can change the bioavailability of these metals, thus influencing the well-being of lake ecosystems. Additionally, DOM in lakes can either facilitate the degradation of organic pollutants via reactive oxygen species mediation or impede this process by acting as a light shield. It is crucial to emphasize that the behavior and ecological effects of lake DOM are intricately linked to its molecular weight, active groups, and molecular structure. In this paper, we conduct a comprehensive and systematic review of the behavior and ecological effects of lake DOM, as well as its correlation with molecular structure composition. The findings of this review can offer valuable theoretical guidance and technical support for understanding the processes and mechanisms of lake pollution, implementing lake restoration and regulation measures, and formulating lake management and planning strategies.

Abstract:As one of the world’s largest developing countries, China is facing an increasingly severe pollution problem caused by phthalates (PAEs). PAEs are widely used as plasticizers in various industries, including the food and pharmaceutical industries. Due to their widespread use and the lack of standardized treatment, they have accumulated in the environment over the long term and have become highly toxic. This study systematically analyzed the occurrence, spatial distribution, ecological risks and potential sources of PAEs in 30 typical lake water bodies and 20 typical lake sediment samples in China to explore the occurrence characteristics of PAEs and the effects of human activities. The results indicated that the concentration range of PAEs in the aqueous and sediment phases was 0.01-27.6 μg/L and 28.8-74935 ng/g, respectively. Di (2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) were the predominant PAEs in both phases. The spatial distribution of lake areas showed significant differences, with the most severe pollution occurring in the middle and lower reaches of the Yangtze River. DEHP and DBP were found to be the main PAEs in lake water and sediments, contributing the most. There were significant differences in the spatial distribution of lake areas, with those in the middle and lower reaches of the Yangtze River being the most severely polluted. Based on an ecological risk assessment using risk quotients, approximately 30% of lakes were found to pose a high risk to crustaceans, primarily due to the presence of DEHP and DBP. Further principal component analysis and multiple linear regression revealed that industrial wastewater discharge and agricultural production activities were the primary sources of PAE pollution. There was a significant positive correlation between the use of agricultural films and pesticides, and DEHP and DBP concentrations. The results of the study indicate that PAEs exhibit significant multi-media distribution characteristics in the lake water-sediment system and are profoundly influenced by human activities. Therefore, the management of PAE additives in agricultural production should be strengthened, and the efficiency of PAE removal in industrial wastewater treatment processes should be improved, in order to reduce the pollution load of lake water bodies. This study reveals the environmental behavior, risk characteristics and anthropogenic driving mechanisms of PAEs in typical Chinese lakes, providing a scientific basis for formulating water ecological and environmental protection strategies.

Abstract:The world is getting hotter and hotter, causing more and more heatwaves. It is very important to study how these factors affect the environment, for example the nutrients in lakes, the concentration of chlorophyll-a(Chl.a) in water, and the growth of phytoplankton. This will help us to understand how lakes respond to and recover from heatwaves, and it will provide scientific support for the management and regulation of lakes under climate change. This study used the GOTM-WET model to see what effect the 2022 summer heatwave had on the amount of Chl.a in northern Lake Taihu. It looked at how different levels of heatwave intensity affected Chl.a and what might be causing this. The results showed that the 2022 summer heatwave greatly reduced the concentration of Chl.a in water, and the effect of this was stronger with the higher heatwave intensity. Further analysis showed that the maximum water temperature during the 2022 heatwave exceeded 37 ℃, which could have been too hot for most algae to grow. The heatwave also made the water more mixed up, with less nitrogen and phosphorus in the surface layer and more in the bottom layer. This meant there was less nutrition available for surface algae growth, which also meant there was less Chl.a. This study looked at how water temperature and nutrients can affect the growth of algae in lakes when it is very hot. It helps us to understand more about how heatwaves affect the natural processes in lakes.

Abstract:There is a very high risk of odorous compounds contaminating drinking water sources in the Changjiang River catchment in spring. However, the key drivers for the occurrence of odorous compounds are still unclear. In May 2024, nine drinking water source reservoirs across the upper, middle and lower reaches of the Changjiang River were investigated. Four odorous compounds, 2-methylisoborneol (2-MIB), geosmin (GSM), β-cyclocitral (CYC) and β-ionone (ION) and their associated environmental factors were surveyed. The results showed that 2-MIB was the most common odorous compound in the research region, with an average concentration of 35.5 ng/L across the 32 samples from 9 reservoirs (59.4% exceeding the drinking water standard of 10.0 ng/L). GSM posed a lower risk, with an average concentration of 2.9 ng/L and only 12.5% exceeding the threshold value of 10 ng/L. CYC (averaged at 18.2 ng/L) and ION (averaged at 7.2 ng/L) exhibited minimal odorous concerns.Pseudanabaena sp. was identified as a likely major producer of 2-MIB, with its cell density showing a significant positive correlation with the concentration of 2-MIB. However, the presence of 2-MIB in two reservoirs without detectablePseudanabaena, indicated more complex 2-MIB sources in some reservoirs. 2-MIB levels positively correlated with the trophic state index, demonstrating that eutrophication directly promotes 2-MIB production. The 7-day accumulated rainfall amount before sampling was negatively correlated with the 2-MIB concentration, suggesting that short-term heavy rainfall processes will strongly change the odor compounds risk in reservoirs. Despite most drinking water source reservoirs in this region were under mesotrophic conditions, while it showed widespread 2-MIB exceedances. It is vital to reduce external nutrient loads and optimize aquatic food webs to prevent odorous issues and ensure drinking safety.

Abstract:Lake Taihu is a large eutrophic lake. Significant variations were observed in the endogenous pollution and release characteristics of sediments between phytoplankton and macrophyte-dominated areas of the lake. The present study aimed to investigate and analyze the variations in endogenous pollution and nitrogen and phosphorus diffusion fluxes in Lake Xuhu (macrophyte-dominated area) and Zhushan Bay (phytoplankton-dominated area) with different water depths. The results demonstrated that: The total nitrogen content in the sediments of Lake Xuhu and Zhushan Bay was found to be between 2.59 and 3.33 g/kg and between 2.95 and 3.63 g/kg, respectively. The total phosphorus content was found to be between 0.462 and 0.652 g/kg and between 0.749 and 0.916 g/kg, respectively. The nutrient content of the sediments in the phytoplankton-dominated area was found to be significantly higher than that in the macrophyte-dominated area, and the content exhibited fluctuations that were irregular in nature with respect to changes in water depth. Phosphorus speciation analysis of sediments demonstrated that Ca-P constituted the predominant sediments in Lake Xuhu, and the proportion of Ca-P in total phosphorus exhibited a marked decrease with increasing water depth. The phosphorus morphology in the sediments of Zhushan Bay was dominated by Fe-P, and the proportions of Fe-P, Al-P and Ca-P in the total phosphorus gradually increased with the increase of water depth. The soluble active phosphorus (SRP) content at the sediment-water interface in the shallow water area of Lake Xuhu was significantly higher than that in the deep-water area, while the difference in Fe²⁺ and ammonia nitrogen (NH₃-N) concentrations between different water depths was relatively small. The SRP, Fe²⁺ and NH₃-N contents at the sediment-water interface in the shallow water area of Zhushan Bay were found to be higher than those in the deep-water area. The endogenous release risk of Lake Xuhu and Zhushan Bay was determined to be minimal, and the diffusion fluxes of NH₃-N in Lake Xuhu and SRP, NH₃-N in Zhushan Bay were found to be higher in shallow water areas. The results obtained are of great significance in understanding the nitrogen and phosphorus migration of water depth at the sediment-water interface in the phytoplankton and macrophyte-dominated areas of Lake Taihu.

Abstract:In recent years, the excessive input and inefficient utilization of nitrogen and phosphorus in cropping systems has led to significant losses of these elements. Lake Poyang Basin has led to significant losses of these elements, resulting in persistent nitrogen and phosphorus levels exceeding the legal limit, as well as other environmental issues. Therefore, tracing the spatiotemporal patterns of nitrogen and phosphorus metabolism in the Lake Poyang Basin cropping system is crucial for ensuring the basin’s ecosystem sustainability. This study used the material flow analysismethod to investigate the spatiotemporal variations in nitrogen and phosphorus fluxes in cropping systems across the Lake Poyang Basin from 2000 to 2022. Four scenarios were designed based on the current status of nitrogen and phosphorus pollutant emissions: a baseline scenario, a scenario with reduced fertilizer inputs for arable land, a scenario with increased straw recycling rates, and a scenario with comprehensive measures. The emission reduction potential was calculated for each scenario, and the optimal strategies for reducing and preventing nitrogen and phosphorus pollution were then proposed. The results show that nitrogen and phosphorus inputs to the basin initially increased and then fluctuated stably, peaking around 2015. In terms of spatial distribution, the total nitrogen and phosphorus inputs were highest in the coastal lake district, reaching 281000 t of nitrogen and 64000 t of phosphorus, respectively. Chemical and organic fertilizers accounted for over half of the total inputs. In terms of nutrient use efficiency, the combined use rates of nitrogen and phosphorus were 48.5% and 31.0%, respectively. Since 2010, the utilization rates of nitrogen and phosphorus for all crops have declined, as has the ratio of nutrient inputs of nitrogen and phosphorus, with an average N/P ratio of 3.9. Scenario analysis suggests that reducing chemical fertilizer use could decrease nitrogen output by 150000 t by 2050 and reduce nitrogen and phosphorus emissions by 159000 t/a, which would reduce pollutants by 53.4%. Compared with the baseline scenario, the N/P ratio discharged into the environment could rise to 6.5. Reducing fertilizer application accounts for 75.7% of the emission reduction, demonstrating its effectiveness as a mitigation strategy. This study provides a scientific basis for developing effective, integrated nitrogen and phosphorus management measures in the Lake Poyang Basin, and evaluating the potential outcomes of future scenarios.

Abstract:In agricultural watersheds across China, small waterbodies serve as important sites for the retention and storage of phosphorus, acting as protective barriers for rivers and lakes. However, under conditions of long-term phosphorus accumulation and specific environmental factors, there is a risk of phosphorus being released. Currently, research on the risk of phosphorus release from small water bodies, and on the dynamic changes in phosphorus retention and release and the influencing factors through long-term experiments, is lacking. This study focuses on a typical agricultural watershed, conducting sediment sampling from four types of pond alongside a six-month static incubation experiment. The study analyses the phosphorus forms in sediments and the phosphorus exchange dynamics at the sediment-water interface to assess the risk of phosphorus release from the ponds and its influencing factors. The results showed that: (1) The total phosphorus (TP) content of pond sediments was higher than that of other types of wetland, ranging from 0.55 to 3.02 g/kg. The highest phosphorus content was found in village ponds, while the lowest was observed in paddy ponds. (2) In the agricultural watersheds of the middle and lower reaches of the Yangtze River and in ponds that have existed for a long time, phosphorus exchange at the sediment-overlying water interface exhibits significant seasonal variation: sediments release phosphorus to the overlying water in summer and autumn, while phosphorus settles from the overlying water to the sediments in autumn and winter. For ponds of a similar age, the phosphorus sink capacity decreased in the following order: forest pond ＞ paddy pond = dryland pond ＞ village pond. This study revealed large accumulations of phosphorus in agricultural ponds in China, highlighting their long-term function as phosphorus sinks which transform into sources during summer and autumn. The findings also clarified the influence of surrounding land use types and provided scientific guidance for improving management strategies for different pond types. These insights are applicable to the control of non-point source pollution and the protection of aquatic environments in rivers and lakes.

Abstract:Frequent outbreaks ofCladophorablooms in the newly formed littoral zone of Lake Qinghai have been observed due to the warming and humidification of the Qinghai-Tibet Plateau climate. Previous studies on the extraction ofCladophorablooms mainly relied on multi-source satellite remote sensing imagery. However, the limitations of image spatial resolution and mixed-pixel effects hindered the accurate identification of the true distribution and detailed features of the blooms. This study utilized low-altitude UAV imagery combined with the Attention DeepLab V3+ deep learning model to automatically extractCladophorabloom features in Lake Qinghai. A comparative analysis was conducted with results derived from spectral indices and machine learning methods, and the differences between UAV imagery and optical satellite remote sensing imagery in extractingCladophorablooms were explored. The subsequent results are outlined below: (1) It has been demonstrated that Attention DeepLab V3+ is capable of accurately detectingCladophorablooms without the necessity of prior thresholds, achieving a kappa coefficient, precision, recall, and F1 score of 0.985, 0.969, 0.983, and 0.976, respectively. (2) In comparison with both the random forest model and the red-green-blue floating algae index, the model demonstrated a marked improvement in both the kappa coefficient and the F1 score, with increases of 4.47% and 6.35%, respectively. This is particularly noteworthy in terms of its superior adaptability to complex bloom distribution patterns, as evidenced by its ability to capture boundary details and differentiate between voids. (3) Optical satellite remote sensing imagery tends to overestimate Cladophora blooms in Lake Qinghai, with mean relative error values ranging from 5.5% to 323.47%. This study utilized the high-resolution capabilities of UAV imagery to provide technical support for accurately assessing the true distribution of Cladophora blooms in Lake Qinghai, thereby establishing a foundation for the monitoring and tracking of algal bloom features in other water bodies.

Abstract:Lake and reservoir-type water sources play a vital role in ensuring regional water security and are crucial to China’s water supply. This study focused on the Panjiakou Reservoir, which is a vital water source for the Luanhe-Tianjin Water Diversion Project. A three-dimensional numerical model was used to reveal how bottom hypoxia responds to varying reservoir operations and nitrate concentrations in the inflow. Based on these findings, we have proposed comprehensive strategies for preventing and controlling bottom hypoxia. In this paper, measured reservoir data from 2017 to 2018 were used to verify the model’s reliability. The results showed that increasing the outflow from the reservoir significantly shortened the duration of bottom hypoxia and reduced its severity during the later stage of thermal stratification. Furthermore, a substantial reduction in nitrate concentration in the inflow resulted in a notable increase in the duration, severity and spatial extent of bottom hypoxia. Based on the reservoir’s actual operation and the water supply quality standards, this article makes the following suggestions: 1) Joint scheduling with the downstream Daheiting Reservoir should be implemented, with adjustments to outflow volumes made during January-April and September-December to concentrate discharge in mid-to-late October. This optimization could reduce the duration of severe hypoxia and the maximum hypoxic area by 54% and 23%, respectively. Secondly, we recommend reducing the upstream nitrate concentration to 1.5-2.0 mg/L as part of watershed pollution control efforts. This approach would ensure that the total nitrogen concentration in the discharged water meets the required standards while maximizing the nitrate’s mitigating effect on bottom hypoxia. Our study proposes a comprehensive strategy for protecting the quality of reservoir water from multiple perspectives, including ’controlling the concentration of pollution sources upstream, preventing reservoir hypoxia and ensuring compliance with downstream water quality standards, which are important for protecting and restoring aquatic environments in deep water source reservoirs.

Abstract:Water quality is a key factor in safeguarding ecosystem functions, protecting human health, and ensuring sustainable development. The characteristics of land use (including type, intensity, and landscape configuration) are important indicators of human activity and significantly impact river water quality, with these impacts varying across different spatial and temporal scales. This study focuses on the source region of the Chishui River, integrating two spatial scales: the riparian buffer and the sub-watershed. Using variation partitioning analysis and random forest modelling, we quantify the independent and combined contributions of land use type, intensity and landscape pattern to water quality. This allows us to identify the key influencing factors and their corresponding spatial scales. The results show that: Landscape pattern is the main dimension influencing water quality changes (explaining 33%-58% of the variation), followed by land use type (11%-22%) and intensity (4%-16%). Riparian landscape configuration exerts a more significant influence on water quality, while land use intensity at the sub-watershed scale provides stronger explanatory power. The proportion of built-up land and the intensities of construction and agriculture are key predictors of water quality, while forest cover and landscape connectivity play important roles in reducing total nitrogen and chemical oxygen demand concentrations. These findings suggest that water quality management in watersheds should consider land use characteristics at multiple scales in order to identify the most effective combinations of riparian and sub-watershed interventions. Specifically, we recommend prioritizing the control of industrial and domestic point-source pollution at the riparian scale and enhancing agricultural non-point source management at the sub-watershed scale to form an integrated ‘point-source and non-point source’ control system. This study provides new empirical evidence on the multidimensional interactions and scale effects of land use-water quality relationships, offering important theoretical and practical insights for the protection of watershed resources and the optimization of spatial planning.

Abstract:Rivers are links connecting the biogeochemical processes among terrestrial, atmospheric, and oceanic carbon pools, and are important participants in the global water and carbon cycles. Riverine partial pressure of carbon dioxide (pCO₂) is a key indicator reflecting the CO₂ exchange process at the riverine water-air interface, which exhibits complex spatiotemporal variations due to the co-impacts of various natural and anthropogenic factors. However, the current understanding of the main controlling factors and their effects on riverine pCO₂ is still limited. In this study, the spatiotemporal distribution characteristics of riverine pCO₂ were identified, and the relative contributions and controlling effects of potential controlling factors were quantified and revealed using an interpretable machine learning method (boost regression tree (BRT) and accumulated local effects (ALE)), based on monthly datasets with high spatial resolution in the Hanjiang River Basin (HRB). Results indicated that multi-year average riverinep CO₂ in the HRB showed an increasing trend from upstream to downstream, and was higher than the atmospheric average. The fluctuation type of multi-year monthly average riverine pCO₂ in the HRB could be classified into three types based on thek-Shape clustering algorithm, with stationary (T1), unimodal (T2), and bimodal (T3) structures, respectively. The BRT model effectively simulated the multi-year average and multi-year monthly average values of riverine pCO₂ in the HRB, showing high performance (r＞0.86,NSE＞0.75) and acceptable errors (MAE＜212.18 μatm,RMSE＜274.16 μatm) in replicate experiments. Multi-year average riverine pCO₂ was primarily influenced by temperature factors, accounting for approximately 66.1% of the total relative contribution rate. The relative contributions of the controlling factors for multi-year monthly average riverine pCO₂ exhibited significant variation among each fluctuation type, while temperature continued to play a critical role (approximately 26.6%-46.9%). The findings of the study demonstrated that vegetation and water quantity factors exerted a significant influence on types T2 and T3, respectively. Conversely, the importance of water quality factors was found to be comparatively limited, with their contribution ranging below 20.1%. The non-linear and non-monotonic relationships between riverine pCO₂ and its potential controlling factors were revealed based on ALE analysis, which showed significant differences between multi-year average and multi-year monthly average scales, as well as between different fluctuation types. The present study revealed the complex spatiotemporal variations of the main controlling factors and their effects on riverine pCO₂ in the HRB, thus improving the understanding of riverine carbon cycle processes.

Abstract:The construction of the Three Gorges Dam has had a considerable effect on the water and sediment fluxes in the Yangtze River, yet the impact on microbially mediated multifunctionality (carbon, nitrogen, and phosphorus cycling) in sediments remains to be elucidated. The present study employed 16S amplicon sequencing, co-occurrence network analysis, and structural equation modelling to investigate the effects of the dam on bacterial community composition, diversity, and multifunctionality in upstream and downstream sediments. The results of the study indicated that upstream sediments were predominantly composed ofProteobacteria(about 25.5%), while downstream sediments exhibited a preponderance ofDesulfobacterota(about 24.8%). The construction of the dam resulted in a substantial reduction in bacterial α-diversity in the downstream sediments. This reduction was closely correlated with decreases in moisture content (about 35.39%), cation exchange capacity (about 49.64%), and dissolved organic carbon (about 49.88%). The findings of structural equation modeling suggested that a decrease in α-diversity directly impaired ecological functions and indirectly reduced multifunctionality by weakening bacterial network interactions. The present study underscores the ecological ramifications of the Three Gorges Dam on downstream sediment functions and puts forward the recommendation of long-term monitoring of dissolved organic carbon and cation exchange capacity, in conjunction with optimized reservoir management, as a means of mitigating biodiversity loss.

Abstract:The study was conducted with the objective of investigating the impact of fluoride pollution on bacterial communities in the water-soil system. Sixty-six sets of surface water, sediment, and riparian soil samples were collected from the Qingshui River Basin in Ningxia in 2022. The samples were categorized into three distinct groups based on the fluoride concentration in the surface water: low fluoride group (F- ＜ 1.0 mg/L), high fluoride Ⅰ group (1.0 ≤ F- ＜ 1.5 mg/L), and high fluoride Ⅱ group (F- ≥ 1.5 mg/L). The bacterial community responses were systematically analyzed through 16S rDNA high-throughput sequencing and polymorphic fluoride species analysis. The results indicated that fluoride pollution led to a decrease in bacterial α-diversity (low fluoride group ＞ high fluoride Ⅰ group ＞ high fluoride Ⅱ group), although the Chao1 index of sediments increased due to niche release by rare species. The phyla Campilobacterota and Desulfobacterota were identified as fluoride-tolerant bacterial phyla, with species of Desulfobacterota participating in sulfate reduction to alleviate fluoride toxicity at low abundances. Genera such asSulfurovumhave been identified as fluoride-tolerant bacterial genera within the water-soil system. The conversion of residual fixed fluoride (Res-F) in sediments and soils was facilitated by bacteria, who accomplished this by decomposing and transforming it into other forms. It was found that soil environments were more favourable for bacterial decomposition of Res-F. This study establishes the first framework linking bacterial communities to polymorphic fluoride in the Qingshui River Basin, thereby enhancing the understanding of the impact of fluoride on bacterial communities in river ecosystems. The scientific basis for the development of effective ecological and environmental protection policies is provided, thus contributing to the mitigation or reduction of the potential risks of fluoride pollution to the ecological environment.

Abstract:The Qaidam Basin is of significant importance in the context of potash salt resources, serving as the primary reservoir and the key production base for potash fertilizer in China. Recent geological explorations have identified a novel type of potassium-bearing sand and sandstone pore brine deposit in the western foreland alluvial fan of the basin. This newly discovered deposit is believed to contain significant potassium chloride resources, with the brine displaying prominent attributes of high sodium and chlorine levels, and a mineralization model resembling that of “inherited halite rock”. The Mahai Basin, a small lake basin located as a secondary basin and distinct from the Kunteyi Basin on the northern margin of Qaidam, is characterized by various types of brines (intercrystalline brines, confined brines, sand-gravel brines, anticlinal structure brines, etc.). The present study is an attempt to draw attention to the following main conclusions, which are based on a comparative analysis of the major and trace ion content, salinity, and hydrogen and oxygen isotope composition of river water and various brines in the Mahai Basin: Firstly, the average K⁺ content and TDS value of the sand-gravel brines in the Mahai Basin are 2.16 g/L and 254.5 g/L, respectively, indicating a notably high ratio of Na⁺+ Cl^-/TDS (0.94). These brines are classified as Na-Cl type according to the hydrochemical classification system. Secondly, while the potassium content and TDS value of the sand-gravel brines in the Mahai Basin are lower than those in the surface brines, intercrystalline brines, and confined brines of Mahai Salt Lake, they are close to the minimum industrial mining grade of brine, suggesting a certain potential for resource development. The spatial distribution of K+ in sand-gravel brines, intercrystalline brines, and confined brines closely aligns with potassium-containing evaporites. It is suggested that the salt solute and potassium in sand-gravel brines originate from the recharge of intercrystalline brines and confined brines; Furthermore, the utilisation of the K-B-Li equivalent map, in conjunction with the analysis of the varying B content in diverse water sources, serves to substantiate the assertion that the sand-gravel brines are formed through the combined influence of the Yuqia River water and intercrystalline brine/confined brine on the formation process of the sand-gravel brine. Finally, the δD-δ¹⁸O values of the sand-gravel brines in the Mahai Basin range from -56.9‰ to -17.6‰ and -5.70‰ to 6.00‰ for hydrogen and oxygen isotopes, respectively. These values exhibit characteristics analogous to those observed in confined and intercrystalline brines, which are distributed uniformly on both sides of the local evaporation line. Furthermore, an increase in the ²H-¹⁸O is accompanied by an increase in the concentrations of B and Li. These findings indicate that the sand-gravel brines have undergone evaporation and concentration. Consequently, the sand-gravel brines have been inheriting solutes from the intercrystalline and confined brines over a protracted period, including ions such as K⁺, Na⁺, and Cl^-, leading to their similar H-O isotopic signatures.

Abstract:Balun Mahai Basin of Qaidam is characterized by the presence of substantial brine resources; however, further research is required to ascertain the genetic mechanism and potential of these resources. The present study focuses on the intercrystalline brine in Balun Mahai Basin, conducting geochemical research on elements and hydrogen-oxygen isotopes to systematically analyze its water source, solute origins, evolution process, and genesis model. The study also explores the mining potential of potassium, boron, and lithium elements. The results indicate that the intercrystalline brine in the northern part of Balun Mahai Basin is of the magnesium sulfate subtype, while the southern part predominantly features chloride water. The solutes present in the brine are primarily derived from the dissolution of halite, potassium salts, and gypsum. The water chemistry is controlled by a combination of evaporation, water-rock reactions, and cation exchange. The chloride-type water in the southern region may be influenced by deep Ca-Cl water that is known to flow along faults. The water chemistry characteristics indicate that the intercrystalline brine is formed by halite dissolution, with low metamorphic degree and poor sealing in the salt-bearing layers. Hydrogen-oxygen isotopes indicate that the primary water source of the intercrystalline brine is atmospheric precipitation or snowmelt from the Qilian Mountains, with the predominant recharge sources being the Yuqia River and shallow groundwater that courses through the alluvial fan. The impact of strong evaporation and water-rock interactions on the formation of the brine deposits is significant. The differences in water chemistry types and spatial distribution between the northern and southern regions are fundamentally related to the recharge and mixing of these two sources. The genesis of the brine can be summarized as a dual “dissolution recharge + deep recharge” mining model. The study area has been found to have considerable potential for potassium, boron, and lithium resources. The drilling sites ZK7618, ZK8014, ZK8024, and ZK8431 are likely to be favorable targets for mineral exploration, based on the comprehensive water chemistry characteristics, salt layer thickness, and regional salt formation evolution process.

Abstract:The influx of a large amount of sulfate (SO2-4) into water bodies will inevitably deteriorate the water environment quality. Between 2019 and 2023, water samples from the Pingzhai Reservoir Basin in the southwestern karst area, precipitation samples, and sewage samples were collected. We analyzed the physical and chemical indicators of the water bodies, as well as the characteristics of sulfate sulfur and oxygen isotopes (δ34SSO4 and δ18OSO4), hydrogen and oxygen isotopes of water (δDH2O and δ18OH2O), and dissolved inorganic carbon isotopes (δ13CDIC) during the monitoring period. We conducted qualitative and quantitative studies on the sources of SO2-4 in water bodies. The hydrochemical types of the basin are mainly of the Ca-HCO3 type and Ca-HCO3-SO4 type, and the hydrochemical characteristics are influenced by the dissolution of carbonate rocks. It is clear that the biogeochemical process of SO2-4 in the Pingzhai Reservoir Basin is dominated by oxidation. On average, 61% of the oxygen comes from the surrounding water bodies when sulfides are oxidized. The monitoring period clearly showed that the main sources of SO2-4 in the basin are sulfide oxidation, soil organic sulfur, and agricultural sulfur fertilizers. Quantitative calculations definitively show that sulfide oxidation has the highest average contribution rate (72.9%), followed by soil organic sulfur (14.1%) and agricultural sulfur fertilizers (12.9%). The uncertainty analysis clearly shows that the contribution rate of agricultural sulfur fertilizers is the most stable, while that of sulfide oxidation shows relatively large uncertainty. The research results definitively provide data reference and scientific basis for protecting the water environment quality in the Pingzhai Reservoir and similar karst areas.

Abstract:The sediment seed bank of submerged macrophytes in lakes has been shown to reflect the historical species composition of aquatic vegetation. It provides germplasm resources for population maintenance and dispersal, and plays a crucial role in plant community restoration and succession. The present study focused on Lake Caohai, employing a combination of field surveys and laboratory germination experiments to elucidate the spatial distribution characteristics of submerged macrophyte seed banks in sediments. A comprehensive restoration potential assessment model was developed by integrating submerged vegetation, sediment seed banks, sediment properties, and water quality parameters. The present study investigated the status of the submerged macrophyte seed bank in Lake Caohai sediments, which was found to be relatively intact with a high storage density (average (3650±1159) seeds/m² in the 0-15 cm layer). The dominant species in this seed bank was Chara vulgaris L., a species which has been found to be pollution-tolerant and highly adaptable. The distribution of the seed bank was primarily in the surface sediment (0-15 cm), indicating an obvious “surface aggregation” phenomenon and spatial heterogeneity, with significantly higher densities in the southern and northeastern nearshore zones compared to the central lake area. Spatial aggregation analysis indicated that Chara vulgaris L.,Vallisneria natans, and Potomogeton perfoliatus L. exhibited aggregated distribution patterns. Following a thorough evaluation of the ecological restoration potential, the lake was designated as falling within one of three categories: priority restoration zones, key restoration zones and transition zones. It is imperative that, during the critical seed germination periods, low water level operations are implemented throughout the lake, with differentiated strategies. For priority restoration zones that possess abundant seed resources and high restoration potential, wave reduction measures should be adopted in order to create stable environments for seed germination and seedling establishment. This approach will promote natural recovery while enhancing species diversity and ecosystem stability through artificial regulation. The key restoration zones with the lowest restoration potential require internal pollution control and water quality purification measures to create recoverable habitats before artificial replanting of native, pollution-tolerant pioneer species. The northern shore (transition zone), characterized by relatively scarce seed bank resources and the most severe wave disturbances, can be designated as the final restoration area for submerged macrophytes across the lake. Following the completion of submerged vegetation reconstruction in the southern and central lake areas, and with wave disturbances significantly reduced, measures such as seed bank supplementation and targeted planting should be implemented to gradually restore the submerged macrophyte communities in this region. The present study provides a theoretical foundation and practical guidance for the restoration of degraded aquatic plant ecosystems in shallow lakes.

Abstract:Lake Caohai is a noteworthy example of a subtropical plateau wetland ecosystem in China. It is distinguished by its substantial aquatic flora and fauna resources and its significant ecological value. However, recent intensification of eutrophication has triggered a massive decline of submerged macrophytes, driving a gradual regime shift from a macrophyte-dominated clear-water state to an algae-dominated turbid-water state. This has had a profound impact on ecosystem functions and biodiversity. This study is based on field investigations conducted during 2022-2023. The aim of the study was to systematically examine the current status and characteristics of macroinvertebrate communities in Lake Caohai. The study also compared these communities with historical data from macrophyte-dominated periods (1983 and 2014). This approach enabled the revelation of the response mechanisms of macroinvertebrate communities during the regime shift. The results demonstrated that the current macroinvertebrate communities exhibited a mean density of (145.14±16.62) ind./m² and a biomass of (14.85±14.02) g/m², with a Shannon-Wiener diversity index (0.73±0.06), a Margalef richness index (0.36±0.03), and a Pielou evenness index (0.66±0.04). The composition of the feeding groups was as follows: 94.69% were collectors, 2.81% were predators, 1.58% were scrapers, and 0.92% were filter-feeders. The spatial distribution patterns of macroinvertebrate communities exhibited a correspondence with the distribution of submerged macrophytes. Biomass demonstrated significant seasonal variation, with higher levels observed in autumn and winter compared to spring and summer. In contrast, other community characteristics exhibited no significant seasonal differences. Redundancy analysis identified dissolved oxygen, water depth, pH, permanganate index (COD_Mn), transparency (SD), and conductivity as key environmental drivers. Over a period of more than two decades, COD_Mn demonstrated a persistent increase, while chlorophyll-a concentration rose and SD declined on an annual basis in the period following the regime shift. A comparative analysis was conducted, revealing a predominance of scrapers (Gastropoda) during the clear-water state over gather-collectors (Tubificidae and Chironomidae) in the turbid-water state. The study observed higher species richness, density, biomass, and diversity indices during the macrophyte-dominated phase. This study provides a scientific foundation that is critical for a comprehensive evaluation of the status of the aquatic ecosystem in Lake Caohai. This evaluation involves an analysis of the responses of macroinvertebrates during shifts in the regime of plateau lakes, and the implementation of targeted ecological restoration measures.

Abstract:Lake Poyang, China’s largest freshwater lake, is a crucial wintering ground for East Asian geese. This study used satellite tracking data from 2019 to 2024 to analyze the migratory phenology and spatial distribution patterns of the greater white-fronted goose (Anser albifrons), swan goose (Anser cygnoides), and bean goose (Anser fabalis). Integrating duration and home range data allowed us to quantify the importance of sub-lakes in Lake Poyang for these species. Our results demonstrate phenological differences in arrival and departure timing among the species of geese. Greater white-fronted geese arrived earliest (15th to 27th October), followed by swan geese (9th October to 30th November), with bean geese arriving latest (1st to 17th November). The average duration of overwintering in Lake Poyang was approximately (149±8) d for greater white-fronted geese, (123±5) d for bean geese, and (128±26) d for swan geese. Analysis of migratory timing dynamics revealed relative stability and low interannual variation for greater white-fronted and bean geese, while swan geese exhibited greater interannual variability. Protected areas remained the most important distribution areas for geese. However, an increasing duration and expansion of the home range outside of protected areas were observed, particularly for bean and swan geese. This study quantified the duration and spatial utilization of geese in sub-lakes, highlighting their ecological role in supporting migratory goose populations. It also identified important conservation areas for geese and determined protection gaps. We recommend expanding the boundaries of protected areas to encompass these gaps and enhancing habitat management measures within and beyond these areas to ensure the long-term sustainability of these vital wintering habitats. This research provides scientific evidence to support the identification of critical habitats and the development of targeted conservation strategies for geese and their habitats.

Abstract:The fish collection and transportation system was first implemented in China in the early 21st century at several high-head hydropower stations as an emerging solution to address fish passage challenges in high dams. Nevertheless, the extant literature on the effectiveness of this approach is inconclusive. The Wudongde Hydropower Station on the Jinsha River initiated a pioneering initiative in the form of a tailrace outlet fish collection scheme, meticulously constructing a comprehensive fish collection and transportation system to facilitate fish migration. This study utilized the diversity index, the index of relative importance, the fish autecology matrix, and Ward clustering to analyze the characteristics of fish collected from the Wudongde fish collection and transportation system from 2021 to 2023. The results were compared with environmental impact assessment and design requirements to provide a preliminary evaluation of the system’s efficacy. During the period of 2021-2023, the Wudongde fish collection and transportation system amassed a total of 95281 individuals from 52 distinct fish species. The statistical analyses yielded the following findings: (1) The collection of all 10 main and secondary fish passing objects was successful, with Percocypris pingi exhibiting the largest average size. (2) The collected specimens ofCoreius guichenoti, Rhinogobio ventralis, Jinshaia sinensis,Leptobotia elongata, and Schizothoracinae fishes were primarily 4-year-old, 3-year-old, 6-year-old, 4-year-old, and 4-year-old, respectively. (3) The indices of fish diversity indicated moderate overall diversity and a relatively simple community structure. (4) The dominant species included Hemiculter leucisculus, Botia superciliaris, and Pseudogyrinocheilus procheilus, collectively accounting for 87.3% of the total catch. At the species level, sticky and demersal eggs were predominant. (5) At the species level, sticky and demersal eggs, settlement were predominant. The lotic type species dominated, but the lentic type also comprised a notable proportion. (6) Ward’s clustering method revealed significant seasonal variations, with July and August exhibiting distinct clusters due to the high collection volumes observed during these months. Conversely, other months were grouped into a separate cluster. The Wudongde fish collection and transportation system facilitated migration for the majority of fish species in the river section, with no size-selective bias observed. Preliminary assessment suggests that the majority of the main and secondary fish passing objects collected are potential breeding populations that have reached the age of first sexual maturity. In comparison with the stipulated breeding time that was outlined during the environmental impact assessment and design stage, the collection month of certain fish specimens has been postponed or advanced. The alteration in fish composition is largely consistent with the predictions made during the design stage. A comparison of the Wudongde fish collection and transportation system with analogous fish passage facilities reveals its superior efficacy. This is attributable to the utilization of a turbine tailwater for fish attraction, which serves to effectively mitigate the barrier effects of the hydropower station. Subsequent endeavors must focus on optimizing system operations, enhancing monitoring, and conducting scientific evaluations to ascertain the effectiveness of these measures. This will facilitate the restoration of connectivity in the lower Jinsha River.

Abstract:The repercussions of climate change, in conjunction with the functioning of hydraulic projects, have resulted in substantial alterations to the water cycle within the Three Gorges Reservoir area. The Three Gorges Reservoir area has experienced recurrent seasonal droughts in recent years. A comprehensive analysis of the evolution characteristics and driving mechanisms of seasonal agricultural drought in this region is imperative for formulating a systematic response to agricultural droughts. This analysis should be coupled with a quantitative determination of yield reduction thresholds under current drought defence conditions. Firstly, the spatiotemporal evolution of seasonal agricultural drought in the reservoir area from 1982 to 2022 was investigated, based on the Standardized Soil Moisture Index (SSMI). Furthermore, additional analyses were conducted using Path Analysis to explore key driving factors. Furthermore, drought return periods and representative drought years were determined using Copula theory, and historical typical drought scenarios were extracted. On this basis, effective rainfall was introduced to improve the parameters of the Jensen model, considering losses due to evaporation, interception, and runoff. A novel methodology has been proposed for the calculation of drought-induced crop yield reduction thresholds under both historical and current drought scenarios, with the improved Jensen model serving as the underlying framework. This approach is particularly pertinent in the context of the recurrence of historically typical drought conditions. The results demonstrated that agricultural droughts in the Three Gorges Reservoir area intensified between 1982 and 2022, exhibiting significant spatiotemporal variability. The tail section of the reservoir was identified as the area most susceptible to high-frequency drought, while the middle reaches were characterized by long-duration, high-intensity, and severe droughts. Similarly, the upper reaches were susceptible to extreme, protracted droughts. Subsequent analysis indicated that future agricultural droughts in the reservoir area were anticipated to diminish on a global scale. The primary factor contributing to summer-fall droughts was precipitation, while potential evapotranspiration emerged as the directly influencing factor for winter-spring consecutive droughts. Finally, within the context of the prevailing water conservancy defense conditions, drought-induced crop yield reduction thresholds for return periods of 2, 5, 10, 20, and 50 years were calculated to be 1.23%, 5.12%, 8.13%, 15.44%, and 22.32%, respectively. The findings of this study provide a robust technical foundation for the development of drought-resilient water resource planning, scheduling of drought replenishment, and scenario-based water management in the Three Gorges Reservoir area.

Abstract:The impact of “four colliding” typhoons involving a combination of heavy wind, strong storm, high tide and serious flood colliding has become the focus of attention in the disaster prevention and reduction system in the Taihu Basin. However, the impact of the wind, storm, tide and flood on the safety of flood prevention is still unclear. It is important to analyze the rainstorms, floods and their movement caused by the typical “four colliding” typhoons. This study uses the typhoons “Fitow” and “In-Fa” since 1990 as examples and other typhoons with two or three colliding events as references. Based on hydrological and engineering data, the impact of “four colliding” typhoons is compared. The results showed that: (1) All of the “four colliding” typhoons caused extreme rainfall, with a large total amount and wide range. This resulted in rainfall that was more than 70% higher than that caused by two or three colliding typhoons. This was essentially the same as the rainfall caused by typhoon “Morakot” in 2009. (2) The water levels in Lake Taihu have risen to 2nd and 3rd place respectively since 1949. In particular, typhoon “In-Fa” caused numerous floods, with the maximum water level in Lake Taihu rising by more than 1.00 m. The highest water levels recorded at 33 sites in the river network broke historical records, and the high water levels persisted for an extended period, posing a significant threat to regional flood prevention efforts. (3) Storage dominated during “Fitow”, after which the drainage capacity of the backbone projects was significantly enhanced. During “In-Fa”, the flood movement pattern changed to include both storage and drainage. The storage-to-drainage ratio changed from 1∶0.6 to 1∶1.1 and the proportion of drainage increased. (4) During the rainstorms caused by the two typhoons, drainage was obviously restricted by the astronomical spring tide. Once the rainfall had stopped and the spring tide had passed, the drainage capacity of the backbone projects increased significantly, particularly in the Yangtze River to the north and the Huangpu River to the east. (5) Although the drainage capacity of the backbone projects has been significantly strengthened, further improvement is needed in the event of a “four colliding” typhoon or the transfer of regional flood disaster risks. These research results could inform the scientific defence against the ‘four colliding’ typhoons in the Taihu Basin in future.

Abstract:Lake Dongting, located in the middle reaches of the Yangtze River, is a crucial body of water. Accurately modelling the relationships between the runoff and the various input and output stations is essential for regional ecological protection, flood control, and drought defense. In order to address the complex relationships between runoff and the various input and output stations in the Lake Dongting Basin, this study proposes a multiple-input and multiple-output runoff response model based on graph neural networks. Firstly, the model utilizes the topological spatial structure of the Yangtze River, Lake Dongting and Sishui Basins to transform the original observation sequences at each station into graph-structured data, thereby characterizing the spatial features of the basins. Secondly, the mutual correlation analysis method is used to identify the time lag relationship between the observed variables at each station, determining the input feature step of the model. Finally, graph neural networks are employed to aggregate and update the features, capturing the complex spatial and temporal dependencies among the control stations and enabling runoff simulation at multiple stations. The results show that, compared with backpropagation neural networks and long short-term memory neural networks, the graph neural network (GNN) model can achieve improvement rates of over 5% for the Nash-Sutcliffe efficiency coefficient and mean absolute error indicators. The correlation coefficient is also greater than 0.97. In dry water cutoff events, the true positive rate and precision are generally greater than 0.96. GNNs have significant advantages in simulating hydrological events such as floods and droughts, and can provide scientific support for the ecological protection of Lake Dongting and its flood control and drought resistance measures.

Abstract:The present article employs an analytical approach to quantitatively evaluate the impact of human activities on the changes of hydrologic drought characteristics in the Lake Poyang Basin. To this end, the article undertakes an inter-annual variation trend analysis of precipitation, temperature, evaporation and runoff from 1959 to 2022, according to the data of meteorological and hydrologic stations in the basin. The relationship curve between cumulative annual precipitation and runoff in the five watershed divisions of Lake Poyang is derived using the double cumulative curve method. The reference period and change period affected by human activities are then divided based on this curve, in combination with the mutation point test. The calibration of the parameters of the two-parameter monthly water balance model is achieved through the utilization of measured data on precipitation, evaporation and runoff for each period. The subsequent testing of the simulation results employs the Nash efficiency coefficient, correlation coefficient and water balance error as performance indicators. The simulation of the reduction and reconstruction of monthly runoff during the reference and change periods was undertaken in order to obtain an understanding of the impact of climate change and human activities on runoff. The severe runoff index (SRI) was used as the hydrological drought index, and drought events during the change period were identified through run length theory. The characteristics of annual average cumulative drought intensity, the maximum severity of a single drought, and drought frequency before and after parameter reduction were compared. The results show that human activities have generally reduced the runoff depth in the basin, with more significant impacts on the dry season. Spatially, the impacts on the Fuhe River and Raohe River basins are the most obvious, with the annual average runoff depth and the runoff depth during the dry season decreasing by 8.5%, 9.2%, 12.0%, and 12.3%, respectively. The frequency and severity of hydrological droughts in the Lake Poyang Basin during the change period have generally increased. The average annual number of droughts, the average annual drought severity, and the maximum severity of a single drought have increased by approximately 21.3%, 55.4%, and 24.3%, respectively compared with the reference period. The research can provide a reference for the long-term prediction of the drought trend in the Lake Poyang Basin.

Abstract:Scientific research on hydrological drought in lake-floodplains and its impact on hydrological connectivity is of great significance for the management of local water resources and the protection of wetland ecosystems. This study utilized the ESTARFM model (enhanced spatial and temporal adaptive reflectance fusion model) to reconstruct high spatiotemporal resolution inundation datasets from 2000 to 2023. The resulting datasets were then employed to quantitatively characterize hydrological drought and hydrological connectivity in Lake Poyang. To this end, the standardized inundation area index and the geostatistical hydrological connectivity function were utilized to analyze the evolution characteristics of the aforementioned phenomena. On this basis, the response of hydrological connectivity to hydrological drought was further clarified by employing the methods of STL (seasonal and trend decomposition using Loess) time series decomposition and multivariate linear fitting function. The findings indicated that the hydrological drought in Lake Poyang exhibited both annual and interannual variations, characterized by a high frequency of occurrence and an escalating drought trend. The hydrological connectivity in the north-south direction of the Lake Poyang is stronger than that in the east-west direction. In recent years, the hydrological connectivity of Lake Poyang has exhibited a fluctuating downward trend, which is associated with variations in the intensity of hydrological drought. Subsequent quantitative analysis revealed that with an increase in the degree of hydrological drought, hydrological connectivity in Lake Poyang demonstrated a downward trend. In the east-west direction, the annual average hydrological connectivity of light drought, medium drought, severe drought and extreme drought in the Lake Poyang can decrease by 45.2%, 50.0%, 54.6% and 70.7%, respectively, compared to a no drought scenario. In a similar fashion, in the north-south direction, the annual average hydrological connectivity can decrease by 32.1%, 35.6%, 39.0% and 50.7%, respectively. The alterations to hydrological connectivity occasioned by hydrological drought in the Lake Poyang area will have further consequences for the growth and distribution of wetland vegetation. The results of this study provide a scientific basis for the management of lake ecosystems under extreme water conditions.

Abstract:Sediment peak regulation (SPR) in the Three Gorges Reservoir (TGR) during the flood season can significantly enhance the discharge of sediment. Studying the control indicators of SPR is important for ensuring the safety of the reservoir’s storage capacity and improving its overall benefits. Based on data recorded at hydrological stations in the TGR between 2003 and 2023, the characteristics of sediment transport in the reservoir during the flood season were identified. Following the impoundment of cascade reservoirs in the lower reaches of the Jinsha River, the start-up control and process regulation indicators of the SPR in the TGR were examined. The results indicated that the amount of sediment entering the TGR decreased considerably since the cascade reservoirs were impounded. Sediment transport in the TGR mainly occured during flood events. The main consideration is to activate the SPR when the forecasted peak discharge at the Cuntan Station is not less than 50000 m³/s, or the forecasted peak sediment concentration at the Cuntan Station is not less than 1.5 kg/m³, and the forecasted 7-day average sediment concentration at the Cuntan Station is not less than 0.5 kg/m³. Considering flood control safety and the multi-objective benefits of the reservoir, as well as the measured flow and sediment conditions during the SPR, dynamic scheduling can be implemented according to dispatching strategies for three periods: water discharge peak blocking, sediment transport in the reservoir and sediment discharge in front of the dam. In addition, real-time monitoring and forecasting of sediment during the flood season form the basis of the SPR. It is necessary to continuously optimize sediment monitoring and forecasting technologies to accurately control the start time and regulation process of the SPR and improve its overall benefits. This study could provide technical support for optimizing and refining the TGR’s SPR during the flood season.

Abstract:The Songzi River is one of the main channels through which the Jingjiang River diverts water into Lake Dongting. Changes in the diversion of water through the Songzi River have significant implications for flood control in the river-lake system, as well as for the utilization and ecology of water resources. This study uses an analysis of measured data and physical model experiments to investigate the relationships between water-sediment evolution, riverbed scouring, and changes in diversion in the Yangtze main channel and the Songzi outlet reach following the operation of the Three Gorges Project. Results show that, compared to the 1990-2002 period, annual average sediment transport at Zhicheng Station decreased by around 90.6% between 2003 and 2022, with a corresponding reduction of approximately 87.1% in sediment diversion at Songzi outlet. During this period, the bankfull channel between Zhicheng and Yangjiaonao underwent a total scouring of 239 million m³, with an average depth of 2.3 m, resulting in substantial riverbed coarsening. By contrast, the bankfull channel at the Songzi outlet reach was scoured by 43.25 million m³, with an average scouring depth of 3.0 m. This formed a differential scouring rate compared to the pebble-sand mixed bed in the main channel. Physical model predictions suggest that the continuous downcutting of the sandy riverbed downstream of Yangjiaonao in the Yangtze main channel caused by long-term action of sub-saturated flow will lead to progressive declines in water levels at Yangjiaonao and corresponding reductions in diversion at Songzi outlet. At a discharge of 7000 m³/s at Zhicheng Station, the water level at Yangjiaonao is projected to decrease by 1.58 m and 2.57 m in 2035 and 2050, respectively, resulting in a reduction in diversion of 8.3% and 16.7% respectively. However, asymmetric scouring between the inner and outer parts of the mouth (with higher scouring rates in the sandy reach of the mouth, which expands the cross-sectional flow area) will lead to increased diversion at Songzi outlet by the end of 2035, despite the decline in water levels at Yangjiaonao. With a discharge of 7000 m³/s at Zhicheng Station, diversion actually increases by 20.8%. Contribution rates are -33% from the drop in the Yangjiaonao water level and 133% from asymmetric mouth scouring. As discharge increases, the absolute values of both contribution rates rise significantly; however, their combined effect results in minimal net change in diversion volume. This suggests that these influences are primarily concentrated during medium-to low-flow periods. The differential riverbed composition regulates the scouring process, maintaining stable diversion at Songzi outlet. While increased low-flow diversion is beneficial for water resource allocation in Lake Dongting, it may also lead to a moderate decrease in main channel water levels and affect navigation during medium-to low-flow periods.

Abstract:The operation of the Three Gorges Project resulted in substantial channel adjustments in the downstream reaches, thereby altering the diversion patterns of flow and sediment in bifurcated reaches. This had a considerable impact on flood control, navigation, water diversion, and ecology. The present study investigated the variation characteristics of four distinct bifurcated reaches in the reach between Jianli and Shijitou of the middle Yangtze River. Utilizing a two-dimensional flow-sediment transport model, this study compared the flow and sediment diversion ratios prior to and following reservoir operation under various flow regimes, thereby identifying the drivers behind the variation in diversion patterns. The results demonstrate that during the post-operation period, the straight bifurcated reach underwent erosion and deposition, while both the main and second branches of the curved bifurcated reach underwent erosion, primarily occurring in the low-water channels. The implementation of river regulation projects has been demonstrated to impede the retreat of the high floodplain of the mid-channel bar (MCB) and to induce the deposition of the low floodplain of the MCB. The channels exhibiting higher levels of erosion intensity underwent evolution, subsequently assuming the role of the primary branches. This phenomenon induced a shift in the main and secondary branches of select bifurcated reaches. The low-discharge diversion ratios in the right branch of the bifurcated reaches of Nanmenzhou and Luxikou increased from 0.42 and 0.40 to 0.95 and 0.81, respectively, with both showing an increase of over 100%. The imbalance in erosion across the bifurcated reaches is the primary cause of variation in flow and sediment diversion patterns, with the impact decreasing for higher discharge. For every 1.0 m increase in the relative scour depth between the main and secondary branch, the flow diversion ratio of the main branch is shown to increase by approximately 7.6%-15.8%, and the sediment diversion ratio increases by approximately 8.2%-11.8%. It is evident that alterations to the mid-channel bar planform would have a consequential impact on flow diversion patterns. Sediment deposition on the low floodplain was detrimental to the inflow entering the left branch of the Nanyangzhou reach, while the retreat of the high floodplain in the left branch further decreased the flow diversion ratio under medium to high discharge conditions.

Abstract:Surface water, heat and carbon fluxes are critical indicators of the water and carbon cycles in lake ecosystems in a changing climate. However, the impact of extreme environmental conditions, such as drought, on these processes is not fully understood. Lake Poyang, the largest freshwater lake in China, is also an internationally important wetland. It is not only a key node for regulating water resources in the Yangtze River Basin, but also plays an important role in the global carbon and water cycles. In 2022, consecutive meteorological drought events occurred in the Lake Poyang Basin during the summer and autumn, and the lake area experienced its most severe drought since 1949. This study adopted multi-year monitoring data from the eddy covariance instrument at the Lake Poyang Wetland Observation and Research Station. Located on the beach of Lake Poyang (29°27′N, 116°03′E), the station has continuously monitored the variation processes of water, heat and carbon fluxes in the lake since 2015. This study analyzed the variation patterns of the water, heat and carbon fluxes, and how they responded to the extreme drought event in Lake Poyang in 2022. The results showed that: (1) On an annual scale, the latent heat flux was relatively high from July to September, peaking in August, with an annual average of 49.5 W/m². The sensible heat flux was relatively high from September to November, peaking in October, with an annual average value of 10.6 W/m². The CO₂ flux exhibited obvious seasonal variations, with the carbon source and carbon sink shifting in response to hydrometeorological factors such as the water level and net radiation. The annual average value of the CO₂ flux was 15.0 μmol/(m²·s). (2) On a daily scale, the sensible and latent heat fluxes were essentially synchronous, exhibiting a single peak at noon, whereas the CO₂ flux exhibited a single peak at night. (3) The extreme drought event significantly intensified the carbon source effect of the wetland ecosystem by altering the pattern of energy allocation. During the drought period, the latent heat flux, sensible heat flux and CO₂ flux increased to 1.23, 1.78 and 5.44 times the average values for the same historical period, respectively. (4) Correlation analysis revealed that air temperature, wind speed, net radiation, precipitation, relative humidity, normalized difference vegetation index (NDVI) and water level were the main factors influencing the water-heat-carbon fluxes. Stepwise regression analysis further revealed the mechanisms by which various factors influenced the fluxes under different periods and underlying surface conditions. During the extreme drought period when the underlying surface was a body of water, the ranking of importance of the influencing factors for latent heat flux, sensible heat flux and CO₂ flux was as follows: wind speed ＞ air temperature ＞ relative humidity ＞ net radiation ＞ water level. When the underlying surface was a beach, the ranking of importance of the influencing factors for latent heat flux, sensible heat flux and CO₂ flux was as follows: air temperature ＞ wind speed ＞ NDVI ＞ vapor pressure deficit ＞ precipitation. The extreme drought event primarily promoted energy allocation to sensible heat flux by increasing air temperature, wind speed and net radiation, and significantly stimulated CO₂ release. This study revealed the response mechanisms of water-heat-carbon fluxes in lakes to extreme climate events, providing a scientific basis for predicting the responses of lake ecosystems to future climate change.

Abstract:This study aims to quantify the spatiotemporal dynamics of blue and green water resources in the Minjiang-Tuojiang River Basin. In addition, the study has sought to disentangle the differential sensitivities of these water resources to climate and land-use changes. The study has thereby proposed context-specific management strategies and adaptive pathways for sustainable water governance. The utilization of the Soil and Water Assessment Tool (SWAT) model and the Future Land-Use Simulation (FLUS) model, in conjunction with climate projections derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6), was employed for the analysis of historical changes (1981-2021) and the projection of future dynamics of blue and green water up to the year 2100. The following key findings were identified: (1) From 1981 to 2021, the Minjiang-Tuojiang River Basin was dominated by blue water, accounting for 63.2% of the total water resources. Climate change was identified as the primary driving factor for variations in blue and green water, with contribution rates of 79.12% and 63.18%, respectively. (2) Between 1990 and 2020, there was a decrease in cultivated land and grassland of 4.0% and 2.1%, respectively, while urban land expanded by 138%. This has resulted in a significant reduction in agricultural and grassland areas and has exacerbated spatial imbalances in water resources. Projections indicate that by 2040, urban land is expected to further expand by 135%, further compressing the spatial extent of grassland and cultivated land. The expansion will be centered in the Chengdu Plain, located in the eastern part of the basin, thereby exacerbating water scarcity risks in densely populated areas. (3) Future climate trends indicate a precipitation increase of 1.43-1.80 mm/a and a temperature rise of 0.025-0.042 ℃/a. Green water will increase significantly by 0.35-1.02 mm/a, while blue water will decrease until 2050 before rebounding. In the context of the four Shared Socioeconomic Pathways (SSPs), the fossil fuel-dominated pathway (SSP5-8.5) demonstrates the most significant alterations in blue and green water. Conversely, the strategies of curbing urban expansion and prioritizing sustainable development (SSP1-2.6) have the potential to effectively alleviate water resource pressures. (4) The concentration of blue water is observed in the southwestern basin, while the shift of green water hotspots towards the southeast is evident. The Chengdu Plain is susceptible to water scarcity and extreme events, a phenomenon attributable to population density and elevated temperatures. This study provides a scientific basis for adaptive water management strategies in the Minjiang-Tuojiang River Basin in the context of climate and land-use pressures.

Abstract:Taxonomic names constitute the foundation of biological taxonomy and are crucial for documenting and communicating biodiversity. Scientific names provide standardization and linguistic independence, whereas vernacular names are frequently inconsistent, misapplied, or nonexistent. Among fish species, about 20% of valid taxa still lack standardized Chinese taxonomic names. This study aims to establish a complete Chinese taxonomic naming system for all global fish species and to develop a scalable methodology for multilingual translation of vernacular taxonomic names. We compiled a bilingual parallel corpus of 60564 Latin-Chinese fish taxonomic name pairs by integrating multiple authoritative sources, including the Latin-Chinese Dictionary of Fish Names by Classification System. Using this dataset, we fine-tuned the mT5 model family (including small, base, and large variants) under a dual-learning framework that incorporated formal taxonomic naming rules as constraints. Model performance was assessed on an independent test set, and all translated names were manually verified by taxonomic experts to ensure scientific accuracy and nomenclatural consistency. The fine-tuned mT5-large model achieved a BLEURT score of 0.90 and a COMET score of 0.93. Compared to general-purpose large language models such as DeepSeek-R1, these results reflect an improvement of 38% to 159%. The translation error rate for taxonomic names pertaining to long-tail genera and newly described species was reduced by 25% to 80%, depending on the category. All generated Chinese taxonomic names were reviewed and approved by domain experts. This research provides the first systematic solution for completing Chinese taxonomic names for all currently valid global fish species, thereby bridging a long-standing gap between scientific nomenclature and vernacular usage. By combining a dual-learning framework with formal naming rules, our method offers a reproducible and scalable solution for multilingual translation of taxonomic names across the tree of life. To improve accessibility and practical utility, we have also developed an accompanying WeChat mini-program that delivers periodically updated taxonomic names, supporting both scientific communication and the integration of biodiversity knowledge with cultural heritage.