CO2 emissions from lakes play a crucial role in the global carbon cycle, yet their long-term dynamics remain poorly constrained. Here, leveraging a compiled lake CO2 flux dataset, machine learning model, and lake area data, we demonstrated a nationwide increase in CO2 emissions across China's lakes, from 11.25 teragrams of C per year in 2000 to 13.94 teragrams of C per year in 2021 with an abrupt shift after 2010. This transition coincided with rapid lake expansion, gaining at a pace of 71 to 462 square kilometers per year across regions. Large lakes (>50 square kilometers) dominated national emissions, accounting for ~62% of the total, despite large regional variability (33 to 79%). Lakes exhibited divergent responses to climate extremes, with CO2 flux variations of 4 to 48% across regions. The CO2 emissions in China's lakes offset ~12% of national wetland carbon sinks, revealing the critical role in terrestrial carbon budget. Our findings highlighted the urgent need for sustained and high-resolution monitoring to refine lake carbon budget and support climate mitigation policy formulation.

Fish growth is closely related to environmental variables; however, how nutrient enrichment affects fish growth conditions remains unclear in subtropical polder rivers. We investigated the growth status of six fish species and nutrient concentrations at 40 sites in the subtropical polder rivers of the Lake Chaohu Basin, with the aim of evaluating how the fish condition factor (K) responds to nutrient enrichment across different feeding groups. We observed species-specific responses of growth conditions to nutrient enrichment. The omni-zooplanktivorous Hemiculter leucisculus and zooplanktivorous Toxabramis swinhonis exhibit better growth in nutrient-enriched rivers, with their K values showing a significant positive correlation with both total nitrogen (TN) and total phosphorus concentrations. However, the K values of the omni-benthivorous Carassius gibelio and Pseudobrama simoni exhibited no significant correlation with nutrient enrichment. Interestingly, the condition factor of the piscivorous Culter species also increased with rising TN levels. The growth patterns of H. leucisculus and C. gibelio were positive allometric, where the fish body weight increased at a faster rate than length. T. swinhonis and P. simoni showed isometric growth, in which both the body weight and length of them increased at approximately the same rates. These findings highlight the importance of considering fish functional traits (e.g., feeding guilds) when assessing the ecological impacts of eutrophication and provide insights for the management of subtropical polder river ecosystems under nutrient enrichment, such as predicting changes in fish community structure and developing targeted conservation strategies.

CO 2 emissions from lakes play a crucial role in the global carbon cycle, yet their long-term dynamics remain poorly constrained. Here, leveraging a compiled lake CO 2 flux dataset, machine learning model, and lake area data, we demonstrated a nationwide increase in CO 2 emissions across China’s lakes, from 11.25 teragrams of C per year in 2000 to 13.94 teragrams of C per year in 2021 with an abrupt shift after 2010. This transition coincided with rapid lake expansion, gaining at a pace of 71 to 462 square kilometers per year across regions. Large lakes (>50 square kilometers) dominated national emissions, accounting for ~62% of the total, despite large regional variability (33 to 79%). Lakes exhibited divergent responses to climate extremes, with CO 2 flux variations of 4 to 48% across regions. The CO 2 emissions in China’s lakes offset ~12% of national wetland carbon sinks, revealing the critical role in terrestrial carbon budget. Our findings highlighted the urgent need for sustained and high-resolution monitoring to refine lake carbon budget and support climate mitigation policy formulation.

Dryland ecological restoration requires understanding how shrub communities affect plant diversity through soil-resource pathways. We investigated *Hedysarum scoparium*-dominated (HS), *Artemisia ordosica*-dominated (AO), mixed (M), and adjacent bare-land (CK) habitats in the Kubuqi Desert transition zone. Vegetation and 0–60 cm soil data were analyzed using group-specific redundancy analysis (RDA) and piecewise structural equation modelling (SEM). Shannon–Wiener diversity, Margalef richness, and Pielou evenness did not differ among shrub communities (P > 0.05). RDA was significant for AO (adjusted R² = 0.564, P = 0.001) and HS (adjusted R² = 0.612, P = 0.001), but not M (adjusted R² = 0.040, P = 0.406). Diversity was associated mainly with soil water content (SWC) in AO and with soil organic carbon (SOC) and soil N:P ratio in HS. SEM identified the strongest associations of AO with SWC (β = 0.472, P < 0.001) and HS with SOC (β = 0.551, P < 0.001); SWC and N:P were positively associated with Shannon–Wiener diversity (β = 0.384 and 0.274). Although mixed communities improved multiple resources, they conferred no diversity advantage, supporting site-specific selection of shrub species and configurations for dryland restoration.

China's lowland rural rivers are facing severe eutrophication problems due to excessive phosphorus (P) from anthropogenic activities. However, quantifying P dynamics in a lowland rural river is challenging due to its complex interaction with surrounding areas. A P dynamic model (River -P) was specifically designed for lowland rural rivers to address this challenge. This model was coupled with the Environmental Fluid Dynamics Code (EFDC) and the Phosphorus Dynamic Model for lowland Polder systems (PDP) to characterize P dynamics under the impact of dredging in a lowland rural river. Based on a two-year (2020-2021) dataset from a representative lowland rural river in the Lake Taihu Basin, China, the coupled model was calibrated and achieved a model performance ( R-2 > 0.59, RMSE < 0.04 mg/L) for total P (TP) concentrations. Our research in the study river revealed that (1) the time scale for the effectiveness of sediment dredging for P control was similar to 300 days, with an increase in P retention capacity by 74.8 kg/year and a decrease in TP concentrations of 23% after dredging. (2) Dredging significantly reduced P release from sediment by 98%, while increased P resuspension and settling capacities by 16% and 46%, respectively. (3) The sediment -water interface (SWI) plays a critical role in P transfer within the river, as resuspension accounts for 16% of TP imports, and settling accounts for 47% of TP exports. Given the large P retention capacity of lowland rural rivers, drainage ditches and ponds with macrophytes are promising approaches to enhance P retention capacity. Our study provides valuable insights for local environmental departments, allowing a comprehensive understanding of P dynamics in lowland rural rivers. This enable the evaluation of the efficacy of sediment dredging in P control and the implementation of corresponding P control measures. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Polder areas are typical geographic units in the middle and lower reaches of the Yangtze River and subject to intensive anthropogenic influence, resulting in complex hydrochemical processes. Current understanding of these processes remains incomplete, limiting effective water resource management. This study employs an integrated approach combining hydrochemical diagrams, isotope tracing, and multivariate statistics to elucidate the spatiotemporal patterns and controlling mechanisms of ion composition in polder waters, and to quantitatively attribute ion sources. Results show that cations are dominated by Na+ and Ca2+, with elevated concentrations during the dry season compared to the wet season, while anions are primarily HCO₃⁻, exhibiting minimal seasonal variation. Significantly higher ion concentrations were observed in ditches than in ponds, indicative of distinct hydrological connectivity and anthropogenic effects. Hydrochemical facies transitioned seasonally: HCO₃-Ca dominated the wet season, whereas Cl/SO4-(Ca·Mg), HCO3-Ca, and Cl/SO4-Na types emerged during normal and dry periods, reflecting a shift toward mixed hydrochemistry under dual natural and human influences. Although rock weathering was the predominant control, anthropogenic activities amplified spatiotemporal heterogeneity in ionic composition. Quantitative source apportionment revealed that natural processes (e.g., rock weathering) contributed 80.95% of total ions, compared to 19.05% from human activities, highlighting their considerable role. This study provides the first systematic clarification of the formation mechanisms and driving factors of hydrochemistry in polder areas, filling a critical knowledge gap in this field and offering a scientific basis for water environmental protection and sustainable development in these regions.

Submerged-macrophyte restoration has been a widely-adopted strategy to improve lake water quality. However, the restoration areas have generally been empirically determined. To achieve a cost-effective determination of the restoration areas, this study developed a grid-based framework to identify the highest-priority zones for submerged macrophyte restoration. The framework coupled hydrodynamic modeling and remote sensing data to calculate a Restorability Index (RI) in a large shallow lake (Lake Gehu) in eastern China during 1990-2024. The results showed that RI declined from 0.82 (1990s) to 0.46 (2020s), with a high-restorability area (RI > 0.8) < 1 %. The RI decline can be mainly attributed to increasing suspended matter from inflow rivers and sediment resuspension. Water velocity was the limited factor of low RI within the estuarine areas. Our grid-based investigation revealed that the highest-priority zones for submerged macrophyte restoration were mainly located at the south areas with high light availability (D-eu >= 1 m) and low water velocity (<0.13 cms(-1)). Compared to previous empirical methods in determining restoration areas, the framework provided a high-resolution approach for water managers to determine the areas to implement submerged macrophyte restoration.

This study leverages cyber-physical system (CPS) technology to create a digital twin model for assessing the ecological quality of ancient trees. Integrating multi-source data and machine learning, our model provides tailored conservation strategies, supports ecological restoration, and enhances disaster response capabilities. Key findings illustrate that the model is precise in monitoring tree health, managing water resources, and predicting the impacts of natural disasters. This innovative approach provides significant advantages in real-time monitoring and long-term ecological management, ensuring the sustainability of ancient tree ecosystems. Our results highlight the model's potential to transform ecological conservation practices and offer a reliable tool for researchers and practitioners in environmental science.

To overcome the challenges posed by the high parasitic resistance and poor driving performance induced by serious epitaxy defects in gate-all-around field-effect transistors (GAA FETs), a quasi-self-aligned landing pads (QSA LPs) technique is proposed, and defect-free connections among the multilayer stacked channels and single-crystal SiGe/Si superlattice source/drain (SD) structures are demonstrated in GAA FETs. When compared with devices with widely spaced LPs, reductions of 98.8% and 96.3% in the parasitic SD resistance ( R-SD) are observed for N/PFETs when using the QSA LPs technique, respectively. Therefore, the corresponding on-state current ( I-on ) values are raised to 965 mu A/ mu m and 669 mu A/ mu m for 180 nm gate length N/PFETs, respectively. In addition, no significant changes are observed in the device subthreshold characteristics, including both the subthreshold swing and the on/off current ratios. The proposed scheme offers a new and promising approach to reduce the R-SD values and enhance the performance of these advanced GAA devices.

Phosphorus (P) loss from polders is a major source of P for lowland rivers. However, quantifying this contribution is a challenge due to the complex river networks and artificial drainage in polders. To address this challenge, a Phosphorus Dynamic model for lowland Polders (PDP) was coupled with the HEC-RAS model for river network, and applied to quantify the impacts of P-controlling strategies implemented in 334 polders on 1147 river sections in the Huxi Region of Lake Taihu Basin, eastern China. The PDP and HEC-RAS models demonstrated acceptable performance in simulating water level and total phosphorus (TP) concentration, with an R-2 value range of 0.58-0.87 and 0.59-0.71, respectively. Our modelling results in 2018 indicated a TP load of 206.5 t yr(-1) (TP load intensity is 1.37 kg ha(-1) yr(-1)) from these polders to connected rivers, with the hot spot (i.e., TP load intensity >1.37 kg ha(-1) yr(-1)) located in the western/southern area, and the peak load occurring during the rice season (contributing 75.6 %). This spatial pattern of TP load was inconsistent with river TP concentration, with hot-spot occurring in the area between Lakes Gehu and Changdang (TP concentration >0.1 mg L-1). The combined P-controlling strategy of controlled-release fertilizers and no-tillage farming practices was identified as the best management practice, reducing TP load by 25.3 % in 68 polders and improving TP concentrations in 40.64 % of the river sections. This study demonstrated the high potential for controlling river TP by reducing P loss from polders.

Quantitative analysis of runoff, total suspended solids, and total nitrogen dynamics, along with the identification of key factors within catchments, is essential for accurately addressing issues related to turbid and polluted water. Nevertheless, their implementation encounters significant challenges when applied to a mixed catchment containing mountain areas and lowland polder regions, due to the highly heterogeneous hydrological behaviors and consequently the lack of an appropriate approach. Faced with this problem, this study developed a framework by coupling the Soil and Water Assessment Tool (SWAT) and improved Polder Hydrology and Nitrogen modelling System (PHNS), and Random Forest analysis method to track the spatio-temporal changes in runoff, total suspended solids, and total nitrogen loading and identify their environmental determinants in a representative mountain-lowland mixed catchment, southeastern China. The coupled model performed very well for runoff (R2≥0.90) and water quality variables (total suspended solids: R2≥0.88; total nitrogen: R2≥0.73) in both the calibration and validation periods, and showed improvements compared with standalone SWAT model. Forty years' modelling results indicated that the upstream subbasins 15 (32.86 tonnes/ha/yr), 14 (33.96 tonnes/ha/yr), and 11 (32.32 tonnes/ha/yr) were the critical source areas for total suspended solids and total nitrogen. However, the downstream polder subbasins functioned as a sink for runoff, total suspended solids, and total nitrogen, exporting lower loading intensities. Precipitation and the proportion of slope of 0 to 30° were identified as the critical factors influencing runoff, total suspended solids, and total nitrogen. The proportion of water area also significantly, negatively influenced runoff and total suspended solids. This study provided a feasible method to investigate runoff, total suspended solids, and total nitrogen processes and their environmental factors' impact, and thus identifying the critical source areas and targeted measures to control the non-point source pollution of mountain-lowland mixed catchments.

Heavy metals (HMs) in aquatic ecosystems threaten environmental and public health, highlighting the urgent need for high-resolution, dynamic risk assessments. However, conventional methods are constrained by sparse monitoring data of HM concentrations and limited capacity to capture the cause-effect relationship between HM dynamics and environmental conditions. To address this gap, we developed a machine learning framework that integrated Shapley additive explanation (SHAP) analysis to describe daily dynamic of HM concentrations and risks, and to quantify environmental effects by incorporating dynamic coefficients. The framework was applied to a lowland agricultural pond during 2016-2019, and achieved robust performance (R²>0.69 during both training and testing periods) using random forest algorithm. Both simulated and observed data revealed an increasing trend during the study period, with seasonal peaks of arsenic (As), cadmium (Cd) and lead (Pb) in summer or autumn. Our analysis revealed diverse thresholds and interaction patterns of environmental factors governing HM enrichment, ranging from unidirectional (positive/negative) to bidirectional (U-shaped/inverted U-shaped) relationships, with artificial irrigation as the key driver. Daily risk assessments showed substantial temporal variability, with risk levels of low, moderate, considerable, and high accounting for 19 %, 50 %, 29 %, and 2 % of the study period, respectively. Notably, overall HM risk was driven predominantly by human carcinogenic risks, which remained present even at levels compliant with water quality guidelines. This study demonstrated the value of the proposed framework in enabling fine-scale risk assessment and improving mechanistic understanding, thereby offering practical benefits for HM risk control in water management.

The increasing frequency and magnitude of harmful algal blooms (HABs) threatens the integrity of aquatic ecosystem functioning and human health worldwide. Nutrient reduction strategies have been widely used to mitigate HABs, but their efficiency in light of on-going changes in climate remains unclear. Here, we assembled an 18-year (2005-2022) national water quality dataset for 97 lakes across China. We examined the dynamics of HABs and their response to nutrient reduction under historical climate change trends using a combination of statistical and process-based modeling. The results revealed an increase in HABs despite a widespread decline in ambient nutrient levels, with 80.5 % of lakes experiencing a decline in phosphorus but 61.8 % displaying an increase in Chlorophyll a concentrations. We attributed this counterintuitive trend to climatic warming, which can hinder the mitigation of HABs until the ambient nutrients reach sufficiently low levels. The extent of HAB promotion by warming varied spatially, with a distinctly greater proliferation in China's lower-latitude lakes (<35 degrees N), primarily due to the prevailing warmer temperatures. Notwithstanding the persistence of HABs in China's lakes, national-scale modeling suggests that nutrient loading control remains valuable in protecting our water resources, as the HAB risk would have been 32.6 % higher due to climate change. The anticipated future nutrient reduction efforts in China are expected to alleviate higher latitude lakes from frequent HAB occurrences, but lower latitude lakes will still face considerable HAB risks. Our national-scale assessment demonstrates a variant efficiency of nutrient reduction in offsetting HAB risks amid rapid climate change, and highlights the need of adaptively enhancing our mitigation strategies in response to the ever-changing ecological conditions.

This study assesses the ecological status of alpine lotic ecosystems in Khunjerab National Park, Pakistan, situated at approximately 4000 m in the Karakoram Range along the Pakistan–China border. An integrative approach was employed, evaluating alpine stream ecosystems through benthic macroinvertebrate indices in conjunction with physicochemical habitat parameters. Samples were gathered using kick nets and hand-picking at seventeen randomly selected sites in early spring and summer. The study recorded 710 summer taxa from 41 families and seven orders, and 1250 early spring taxa from 30 families and six orders. The abundance of macroinvertebrates increased in early spring, while taxonomic diversity increased during the summer. Statistical tests revealed a strong relationship between water quality conditions and biological features. The biotic index reached its peak in early spring, while diversity indices peaked in summer when Ephemeroptera dominated. Due to the macroinvertebrate source in early spring, the majority of EPT taxa were abundant at all alpine stream sites during early spring, except for upstream sites in summer. The indices from the biotic metric evaluation revealed low levels of natural environmental disturbance caused by humans. This research is significant in terms of natural resource conservation and health assessment based on the benthic fauna community structure in alpine streams.

Clarifying carbon (C) cycling in small ponds is vital for understanding C transport in lowland agricultural landscape. Quantifying C flux is crucial for learning C cycling, but is challenging due to its complex cycling and significant impacts from intensive human activities. Here, we developed a process‐based model (CDP) to achieve a daily estimation of C dynamics in agricultural ponds within lowland artificial watersheds (polders), and proposed a dual evaluation approach (concentration and flux) to assess the model's performance using two data sets obtained from eight typical polders in the Lake Taihu Basin. The developed model captured pond C dynamics, achieving a Nash‐Sutcliffe efficiency of 0.44 ± 0.27. Our C flux estimations based on the newly‐developed model showed large C emissions, primarily through carbon dioxide (CO 2 ) (497.5 g C m −2 yr −1 ), along with significant C burial (27.8 g C m −2 yr −1 ) with a hot moment in summer. Scenario simulations revealed the distinct impacts of pond C emissions and burial associated with the growth and death of phytoplankton and macrophytes. A 10% increase in macrophyte growth rates associated with a 1.8 g C m −2 yr −1 increase in CO 2 emission, while a similar increase in phytoplankton growth rates related to a 12.2–16.2% increase in C burial. This study revealed a quick response of C flux to phytoplankton‐macrophyte dominance, and highlighted the high potential of the process‐based model for high‐resolution (daily) quantification of C fluxes, thereby enhancing our understanding of C cycling in lowland agricultural ponds.

Nitrogen and phosphorus (N & P) reduction has been widely adopted to fight against eutrophication in management practices. Most existing N & P reduction strategies were designed by reducing N & P use or ecological restoration with high costs. To introduce low-cost strategies for N & P reduction, this study proposed enhancing N & P retention by altering water flow pathways within the artificial watersheds (polders) via hydraulic regulation in the western region of Lake Taihu Basin, China. Soil and Water Assessment Tool, Phosphorus and Nitrogen Dynamic Model for Lowland Polders, and Hydrologic Engineering Center-River Analysis System were coupled together to quantify N & P flow and retention under diverse flow pathways. Our results revealed that streams and creeks have a larger total nitrogen and phosphorus (TN & TP) retention capacity compared to rivers. Polder hydraulic regulation reduced TN & TP into lakes by >8%, with larger retention capacities for Lakes Changdang and Gehu (15.1% and 11.2%, respectively) than those for Lake Taihu (3.3% and 2.5%). Notably, N & P retention correlated positively with polder density but negatively with polder-river distance particularly during summer rainfall events. The case study demonstrated a low-cost strategy for N & P retention via polder hydraulic regulation, offering a transferable solution to other lowland regions with artificial drainage.

Seasonal abandonment in the previously rice-based rotation system is increasingly prevalent worldwide particularly in southern China. Assessing the effect of this abandonment on evapotranspiration (ET) and water resources is of major importance for regional water cycle change and agricultural water management. This paper analyzed the ET characterization of rice‐winter rape and rice‐winter fallow rotation systems and its relation to weather factors in a humid lowland region, southern China based on a half-hourly ET measurement with Bowen ratio energy balance system from 2017 to 2020. Then the strategic modelling experiment combining ET and rainfall‐runoff models was used to explore the land abandoning effect on ET and water resources.

In order to investigate the effect of Potamogeton crispus on the ecological environment during the growth and decomposition period, this paper took Lake Gaoyou, the source storage lake of the South-to-North Water Diversion East Route, as the study area. By analyzing the changes of lake water quality and phytoplankton community with the growth and decomposition process of Potamogeton crispus, we revealed the changes of water environment condition under Potamogeton crispus outbreak in Lake Gaoyou. The results showed that water transparency increased significantly while total nitrogen concentration decreased to a greater extent during the growth period of Potamogeton crispus. Water quality was poorer during the Potamogeton crispus decomposition period in areas with higher Potamogeton crispus biomass. The growth and development of Potamogeton crispus had a purifying effect on the water quality, while the degradation of Potamogeton crispus by their demise can led to deterioration of water quality. Phytoplankton density and biomass were significantly lower in the growing phase of Potamogeton crispus than in the decomposition phase, and were lower in the high and medium biomass zones of Potamogeton crispus than in the low biomass zone during the growing phase. Howeverm in the decomposition phase of Potamogeton crispus, the high and medium biomass zones of Potamogeton crispus were higher in phytoplankton density and biomass than in the low biomass zone. The results of redundancy analysis showed that pH, dissolved oxygen, ammonia nitrogen, nitrate nitrogen, total phosphorus and CODMn were the main environmental factors that influenced the structure of phytoplankton community during the growth and decline of Potamogeton crispus. Piecewise structural equation modeling results indicated that Potamogeton crispus biomass can have a direct effect on phytoplankton biomass or an indirect effect by changing environmental factor.