China’s Sponge City Program (SCP), the world’s largest urban green spaces (UGSs) retrofitting initiative for mitigating waterlogging and pollution, holds underappreciated potential for reconstructing plant communities. Here, we demonstrate that across 1,973 sponge city green infrastructures (SCGIs) in Wuxi, the SCP significantly enhances plant diversity (increased plant coverage, species richness, evenness, and reduced dominance), synchronizing its distribution at a high level across the catchment. We find that biodiverse designs (e.g., rain gardens [RGs], bioswales [BSs]) alongside linear project implementation are key drivers and propose a strategic network approach to maximize gains by embedding SCGIs in UGS planning, leveraging linear projects as potential corridors and employing multifunctional designs. This work reconciles stormwater management with biodiversity conservation, supporting China’s commitment to the Kunming-Montreal Global Biodiversity Framework (GBF) Target 12 through improved UGS area, quality, and connectivity. These insights offer actionable pathways for subtropical/tropical Asian cities to enhance ecological resilience amidst rapid urbanization.

Widely distributed phosphogypsum tailings ponds (PGTPs) in phosphorus (P) mining regions are important sources of by-pass riverine P. To quantify the impacts of rainfall events on by-pass riverine P concentrations and loads in surrounding well engineering-protected PGTPs-enriched area (PA), we investigated the variations of riverine P concentrations in response to 14 different rainfall events in Xiang River Watershed in the middle sections of the Yangtze River in China during Oct.2021-Oct.2022. The results showed that rainfall events with different intensities significantly enhanced ( p < 0.01) the increases of riverine total phosphorus (TP), total dissolved phosphorus (TDP) and dissolved reactive phosphorus (DRP) concentrations in the river sections by-pass PA (APA) in comparison with that of the river sections far away from PA (FPA). Such influence responses were particularly strengthened during heavier events with dominated by dissolved forms. The time period of all rainfall events was only 3.26 % of the entire year, but exported 46 %-62 % of annual P loads in both APA and FPA. The contributions of rainfall events to the annual TP, TDP and TPP loads in APA were 10.91 %, 14.96 % and 1.16 % higher than FPA, respectively. The increase of fluoride concentrations in APA indicated strong linkage of P source from PGTPs. Baseflow from subsurface runoff and groundwater seepage might be the major hydrological pathways for dissolved P transport during rainfall events in APA. Our results imply that controlling the P loss surrounding well-protected PGTPs is still the major concern during rainfall events.

Non-point source (NPS) pollution in mosaic agricultural micro-watersheds poses significant challenges for water quality management due to dynamic interactions between fragmented land uses and rainfall variability. Traditional CSA identification methods, which rely on static parameters for pollutant load estimation and simplified hydrological distance metrics, fail to capture spatiotemporal shifts in pollution hotspots, compromising management efficacy. To address this gap, we develop a dynamic EMC-MSPA-MCR framework with two key improvements: (1) quantifies event-scale pollutant loads via dynamic Event Mean Concentration (EMC) analysis, accounting for land-use-specific runoff thresholds and rainfall scenarios, and (2) refines export efficiency using Morphological Spatial Pattern Analysis (MSPA) and Minimum Cumulative Resistance (MCR) to incorporate landscape connectivity and transport resistance. Applied to the Yankou Reservoir watershed (China), the framework achieved high accuracy (Spearman's rho = 0.67-0.69), identifying CSAs that contributed 65-81 % of total phosphorus (TP) loads from only 1.54-15.85 % of the area. Key results revealed rainfall-driven CSA dynamics: transportation land dominated under light rainfall (1.4-11.4 mm; 97 % of loads), croplands under moderate rainfall (11.4-24 mm; 65 %), and mixed cropland-forest sources during heavy rainfall (>= 24 mm; 76 %). MSPA-MCR integration improved export efficiency predictions by 8-23 % compared to traditional methods, with core landscapes (45.6 % of CSAs) and branch/bridge zones (35-41 %) emerging as critical transport pathways under heavy rainfall. The framework's ability to pinpoint compact, high-impact CSAs (e.g., 63 % of annual loads from 11 % of rainfall events) supports targeted interventions, offering a scalable tool for precision NPS management in heterogeneous agricultural micro-watersheds.

The transport of excess nutrients into freshwater systems constitutes a serious risk to both water quality and aquatic health. Vegetated buffer zones (VBZs) next to waterways are increasingly used in many parts of the world to successfully intercept and eliminate pollutants and other materials in overland flow, especially in warm or temperate regions. The major processes for the retention of pollutants in VBZ are microbial degradation, infil-tration, deposition, filtration, adsorption, degradation, assimilation, etc. The effectiveness of the VBZ relies on several environmental factors, including BZ width, runoff intensity, slope, soil texture, temperature, vegetation type, etc. Among the reported factors, cold weather possesses the most detrimental impact on many of the processes that VBZ are designed to carry out. The freezing temperatures result in ice formation, interrupting biological activity, infiltration and sorption, etc. In the last twenty years, burgeoning research has been carried out on the reduction of diffuse nutrient pollution losses from agricultural lands using VBZ. Nonetheless, a dearth of studies has dealt with the problems and concerns in cold climates, representing an important knowledge gap in this area. In addition, the effectiveness of VBZ in terms of nutrient removal abilities varies from-136% to 100%, a range that reveals the incertitude surrounding the role of VBZ in cold regions. Moreover, frozen soils and plants may release nutrients after undergoing several freeze-thaw cycles followed by runoff events in spring snowmelt. This review suggests that the management and design of VBZ in cold climates needs close examination, and these systems might not frequently serve as a good management approach to decrease nutrient movement.

Base flow (BF) is harder to predict than other hydrological signatures. The lack of hydrologically relevant information or adequately broad spectrum of typically selected catchment attributes (particularly landscape and topography) hinders the explanatory power. Our goals were to identify the most influential controls on base flow spatially and temporally and to elucidate the response relationships. Base flow in 19 semi-arid sub-watersheds was separated by digital filtering. One hundred and fourteen sub-watershed attributes were related to base flow using random forest regression. The main results were as follows: (1) Annual BF significantly declined since 1999 due to decreased precipitation, increased air temperature, afforestation, urban expansion, and increasing water consumption. Annual base flow index (BFI), varying between 0.319 and 0.695, showed less noticeable temporal trends. (2) Precipitation (P) and underlying carbonate rocks primarily controlled the spatial variation of annual BF and total flow (TF), with the impacts being positive. Landscape was less influential. After the abrupt runoff decline, landscape composition rather than configuration exerted greater impacts on spatial BF and TF, and the importance of forest increased, whereas landscape configuration was decisive for BFI during the whole observation period. The absence of significant links between landscape configuration and water quantity may result from a scale issue. Concave profile curvatures were found to be topographic variables more important than slopes. The impact of soil was the least. This study would benefit the selection of catchment attributes and spatial extents to quantify these attributes in building BF predicting models in future studies.

The connectivity of large rivers is impaired by human activities, which could cause severe consequences to hydrodynamics, water quality. To clarify the changes in hydrological connectivity of large rivers and their effects on nutrients, a composite index method of river connectivity in longitudinal, lateral and vertical dimensions was developed in this study. Taking the middle reaches of the Yangtze River as an example, the hydrological connectivity of typical hydrological years and periods in the region was analyzed, and the responses of critical nutrient indexes to varied river connectivity was assessed. The results showed that significant temporal and spatial variations in river connectivity were observed, with better river connectivity in the wet year than the dry year, and worse connectivity in headwaters, tributaries, or downstream of gates and dams than other river reaches. This was mainly due to the degree of river fragmentation (DOF) and the degree of regulation (DOR) with a relative importance of 81.28% and 56.07%, respectively, implying that gate and dam interception was the main cause of impaired river connectivity in the study area. Statistical methods indicated that the impaired connectivity in the middle reaches of the Yangtze River implied a stronger retention of nutrients by dams, and that retention effect was greater during the flood period than the non-flood period. The stronger negative correlation between connectivity and TP (correlation coefficient = −0.58) than TN (correlation coefficient = −0.46) during the flood period revealed that phosphorus was more influenced by river connectivity. The results of this study provide important information on water resources and water quality for the management of large rivers.

Urban surface-deposited sediments (USDs) with different spatial positions and heights are a mixture of various pollutants with complex sources and are widely distributed in urban environments.

为明确茅尾海中悬浮颗粒物的来源,采集了茅尾海流域红树林土壤、堤岸土、河口颗粒物、茅尾海沉积物以及湾外颗粒物等悬浮颗粒物潜在源样品.基于多元统计复合指纹图谱方法,筛选出最佳指纹因子组合,进而通过贝叶斯混合模型得出五种潜在源对茅尾海悬浮颗粒物的贡献率.结果表明:Mg、Al、Mn、Pb、Fe五种指纹元素可作为最佳指纹因子组合,累计判别正确率为78％.贝叶斯混合模型结果显示,茅尾海悬浮颗粒物主要来源于河口和湾外输送,贡献率最高达到58.9％和68.6％.其中,靠近河口区域主要受河流汇入影响,其贡献率达到42.2％～58.9％;靠近湾外区域则以湾外颗粒物贡献为主,贡献率达到44.9％～68.6％.各点位的沉积物贡献率均较低,红树林土壤和堤岸土的贡献率都在10％左右.总的来说,由河口汇入和潮汐作用带入的颗粒物是茅尾海悬浮颗粒物的主要来源.

How a series of small rubber dams distributed within urban watersheds impact nutrients transport remains less investigated. To fill this research gap, this study assesses the composition of nitrogen (N) and phosphorus (P) and their retention in five urban river segments across the Qingshui-Yanghe rivers, China from March 2019 to September 2021. The upstream and downstream of the Qingshui river (QR-up and QR-city) were enriched with dissolved N and particulate P, suggesting a greater P contribution of agricultural origin. NH4-N concentrations were lower upstream but increased downstream of the Yanghe river due to the direct discharge of sewage and other human activities. N and P concentrations varied along the urban river and were relatively low at QR-city. A total of 159.2 and 8.4 metric tons/yr, corresponding to 63% and 70% of the TN and TP loading, were trapped within QR-up and QR-city, of which the dissolved N and particulate P load retention accounted for 58% and 78%. N and P retention rates within the river segments sharply decreased from 97 to –320% and were mainly sequestered in the upstream river segments (QR-up- QR-city). The retention rate of nitrate (78%) and dissolved reactive P (67%) were higher than that of TPN (9.75%) and TPP (78%) because of biological assimilation. Further, with retention rates of −320%, the upstream river segments were a net source of dissolved organic P. These results confirm that the small dams have an important nutrient retention function that is highly variable on a spatiotemporal scale similarly to large-scale reservoirs. Due to the cumulative influence of sewage discharge downstream of the Yanghe River, the nutrient load retention is significantly higher than that in the Qingshui river segments. The variations in hydrological regimes due to seasonal events and small dam regulation have a substantial impact on nutrient retention, resulting in higher loads retention in the flood period than in other periods. Overall, the results suggest that management plans must not only focus on decreasing nutrient export from the mountainous area of the Qingshui river basin but also on sewage outfalls and enhancing the hydrodynamic status of the dammed rivers with respect to eutrophication.

深入了解不同下垫面非点源污染物的输出特征是小流域综合治理的前提之一.以红壤丘陵地区的典型小流域为例,实地对比观测了降雨条件下林地、农业种植用地(园地和耕地)和建设用地(村镇道路和屋顶)的主要下垫面非点源磷污染物输出过程后发现,典型降雨事件中5种主要下垫面总磷(TP)的场降雨平均浓度为:耕地(0.75 mg.L-1)＞园地(0.59 mg·L-1)＞村镇道路(0.38 mg.L-1)＞林地(0.25 mg·L-1)＞屋顶(0.08 mg·L-1);而 TP 输出强度依次为:村镇道路(0.07 kg.hm-2)＞耕地(0.06 kg·hm-2)＞园地(0.04 kg·hm-2)＞屋顶(0.021 kg·hm-2)＞林地(0.019 kg,hm-2).下垫面类型影响着非点源磷的输出形态,建设用地溶解态磷占比最高(51％～71％),林地溶解态磷次之(44％),而种植用地溶解态磷占比最低(25％).整个小流域土地利用面积占比和磷污染负荷贡献比分别为:林地(87％;55％)＞种植用地(9％;42％)＞建设用地(1％;3％).以上结果再结合当地降雨特征及水土流失现状,可为我国红壤丘陵地区小流域非点源污染治理提供参考.

Scientific identification of runoff output characteristics of different land use patterns is the premise of controlling non-point source pollution in watersheds. The hydrology and output process of non-point source pollutants of forest, planting, and construction land with different rainfall characteristics were observed using a micro-watershed in a low mountain and hilly region of Southern China. The results showed that land use affected the hydrological characteristics and water quality processes of runoff. The characteristics of runoff generation time and cumulative rainfall under typical rainfall conditions were as follows:construction land(9 min, 2.0 mm), planting land(35 min, 11.4 mm), and forest land(108 min, 24 mm). There were significant differences in the three land use types in the pollution output process characteristics, such as pollutant concentration of total suspended matter(TSS), total nitrogen(TN) and phosphorus(TP), their components, N/P ratio change, and output intensity. Under typical rainfall, different land use types had similar pollution output stages, the mass concentrations of TSS, TN, and TP in the initial runoff were high, and then gradually stabilized. In addition, the first 30 min of the flow generation process contributed to the TSS, TN, and TP loads within the 23%-43% range. At the annual scale, there were significant differences between the contribution rate of each land use type to TN and TP load and ratio per unit area; the highest contribution to total pollution load was planting land(57% and 45%), while the highest in pollution load per unit area was construction land(9.50-12.50). The results also showed that the distribution of key non-point source areas had different spatial and temporal dynamics, which was comprehensively determined by the land use types in catchment units, the characteristics of annual rainfall, among other factors. With the increase in rainfall, the main contribution non-point source pollution in the micro-watershed changed from construction land to planting land. Targeted ecological interception strategies should be implemented based on the distribution characteristics of key source areas and characteristics of underlying surface runoff production process.

At present, there are few reports about how impervious surface microstructure characteristics affect the runoff output process of street dust. Based on field observations of 12 rainfall events, this study quantified the microstructure characteristics of impervious surfaces by structural depth (roughness) and analyzed the correlation between roughness and accumulation characteristics of street dust on sunny days as well as scouring characteristics in rainy days. The results show that the roughness of the underlying surface notably affects dust accumulation on sunny days and scouring in rainy days. The correlation between roughness and street dust accumulation (r=0.664, P<0.01) was enhanced on sunny days, and the correlation between roughness and street dust erosion (r=0.527, P<0.01) was enhanced by rainfall. The correlation of street dust accumulation and roughness of each particle size segment increased as particle size increased (0.529 ≤ r<0.757), and the correlation between street dust scouring amount and roughness decreased as particle size increased (0.603 > R > 0.209). By establishing the linear regression model of roughness and rainfall, the cumulative pollution load of TSS in rainfall runoff can be well predicted. The effects of roughness and rainfall on the cumulative load of grain sizes<20 μm and >250 μm are significant. These results elucidate the role of roughness and rainfall analysis in predicting surface runoff pollution load characteristics, which can provide new information for predicting and evaluating urban non-point source pollution.

Discharge of phosphorus (e.g., PO4-P) and nitrogen (NO3-N) from the wastewater treatment facility (WWTF) effluent even at low occurrence (e.g., μg PO4-P L−1) could lead to eutrophication of receiving environments. Zhangjiakou city will host the international winter multi-sport event in 2022, which would probably yield a large amount of domestic WW and their associated contaminants in the water systems. To reveal the feasibility of an integrated surface flow constructed wetland (ISFCW) system for the purification of WWTF effluent, a field-scale ISFCW system was applied and operated in Zhangjiakou city. The ISFCW system consisted of a vegetated sedimentation pond (VSP) section followed by a biogeochemical barrier (BGB), and an SFCW. The purification performance of each purification component was monitored weekly over twelve months in terms of nutrient (N and P) removal. With the application of the ISFCW system, a total of 48.7, 59.4, 50.0, 54.9, and 60.2 % removal of TN, NH4-N, NO3-N, TP, and PO4-P was achieved in the summer period. Further analysis demonstrated that the contributions of VSP, BGB and FTW to all analyzed nutrient removal were 3–78 %. The key removal processes appeared to be biological and physicochemical pathways, and the integration of the VSP, BGB and SFCW enhanced the purification capacity of the system. Overall, the ISFCW system was effective at reducing nutrients from WWTF effluent and could consequently be used locally and in other similar mountain-river systems. Additional optimization of operating conditions could result in an enhanced reduction of nutrients.

Hybrid accidental urban wetlands (HAUWs) are expected to be a potential low-cost and highly efficient alternative means of minimizing pollutant loads from municipal areas as compared to the single-stage system being used. These unexpected HAUWs are created not through deliberate restoration, but as a result of water infrastructure decisions by local government. However, information on the long-term purification efficiency of large-scale HAUW improving eutrophic urban rivers is largely unexplored. An in-situ HAUW system consisting of a rubber dam, detention pond, accidental urban wetland, and overflow weir was evaluated at the field-scale for the purification of a eutrophic urban river in Zhangjiakou City, Hebei Province. The results for seven months of operation demonstrated that the effluent TP and NH4-N in the HAUW system could comply with the Grade III of Chinese National Surface Water Quality Standards. Average removal efficiencies for TN, NH4-N, NO3-N, TP, and PO4-P in the summer–autumn period of 52.6, 65,8, 56.6, 51.4, 58.2 and 88.3%, respectively, were recorded. These removal efficiencies were 59.4, 61.5, 65.6, 57.1, 59.4 and 65.7% higher than the respective values in the spring period. Furthermore, removal rates of nutrients were highly sensitive to temperature and showed seasonal trends. Further analysis showed that, with the application of the HAUW system, a total of 92.1, 69.5, 57.3, 37.8, 33.2, 12.4, 14.5, 7.3, 3.4% removal of Al, Mn, Cd, Pb, Zn, Ni, Fe, Ni, and As was achieved. Mean removal rates of TN, NH4-N, NO3-N, TP, TDP, PO4-P in the summer–autumn period were 2- 5 times higher than in those recorded in the early spring period. These results suggest that a variety of contaminant elimination mechanisms were offered by the HAUW, including enhanced hydraulic resistance, sedimentation, plant assimilation, microbial biofilm growth on roots’ surface and the HAUW design. Overall, this study demonstrated that the monitored HAUW could be another feature of the urban landscape that could help minimize pollutant loading to surface urban water bodies. This function is especially true in warm periods, in a similar way as natural wetlands or purposely built constructed wetlands. Nonetheless, managing these accidental treatment systems to maximize pollutant dissipation in the long-term would necessitate appropriate management strategies.

The coupling of a geographic information system (GIS) and nonpoint source (NPS) models has significantly promoted NPS modeling and output visualization. This study reported an approach using R to fully integrate the GIS and a NPS Phosphorus indicator model, as well as to build an interactive web interface for the model". A case study in a semiarid northern China subwatershed showed that the proposed method was feasible, flexible and effective. Our experiences demonstrated that developing a fully-coupled GIS-NPS model system in R could simplify NPS modeling across computation platforms, promote modeling efficiency, implement dynamic simulations, enhance model inputs/outputs display and provide readily interactivity. We envision that the experiences could provide a promising option for NPS modeling.

Rubber dams are widely used for landscaping in urban rivers and they retain large amounts of sediments. The sediments are rich in phosphorus (P) which can cause river eutrophication. Little is known about P release in rubber dams. We investigated the potential of sediment P release by isotherm experiment in an urban river with 30 rubber dams of northern China. We found that the potential of sediment P release (percentage saturation of zero equilibrium P concentration, EPC sat ) was 76% at natural river part above dams, and then decreased to 67% at the 4 th dam because of high deposition of fine sediments within the upper 4 dams. Between the 5 th and the 30 th dams, EPC sat increased to 90% because of the decrease of fine sediments and water soluble reactive P. EPC sat was also significantly higher ( p < 0.05) in April and August than in November. The results suggest that the potential of sediment P release in this dammed river was mainly controlled by sediment grain size and biological effects. Therefore, management strategies for dammed rivers should focus on reducing P inputs and improving the hydraulic conditions.

Uncertainty analysis is an important prerequisite for model application. However, the existing phosphorus (P) loss indexes or indicators were rarely evaluated. This study applied generalized likelihood uncertainty estimation (GLUE) method to assess the uncertainty of parameters and modeling outputs of a non-point source (NPS) P indicator constructed in R language. And the influences of subjective choices of likelihood formulation and acceptability threshold of GLUE on model outputs were also detected. The results indicated the following. (1) Parameters RegR (2), RegSDR (2), PlossDP (fer) , PlossDP (man) , DPDR, and DPR were highly sensitive to overall TP simulation and their value ranges could be reduced by GLUE. (2) Nash efficiency likelihood (L (1)) seemed to present better ability in accentuating high likelihood value simulations than the exponential function (L (2)) did. (3) The combined likelihood integrating the criteria of multiple outputs acted better than single likelihood in model uncertainty assessment in terms of reducing the uncertainty band widths and assuring the fitting goodness of whole model outputs. (4) A value of 0.55 appeared to be a modest choice of threshold value to balance the interests between high modeling efficiency and high bracketing efficiency. Results of this study could provide (1) an option to conduct NPS modeling under one single computer platform, (2) important references to the parameter setting for NPS model development in similar regions, (3) useful suggestions for the application of GLUE method in studies with different emphases according to research interests, and (4) important insights into the watershed P management in similar regions.

Identification of the interactive responses of water quantity and quality to changes in nature and human stressors is important for the effective management of water resources. Many studies have been conducted to determine the influence of these stressors on river discharge and water quality. However, there is little information about whether sewage treatment plants can improve water quality in a region where river streamflow has decreased sharply. In this study, a seasonal trend decomposition method was used to analyze long-term (1996-2015) and seasonal trends in the streamflow and water quality of the Guanting Reservoir Basin, which is located in a semi-arid region of China. The results showed that the streamflow in the Guanting Reservoir Basin decreased sharply from 1996-2000 due to precipitation change and human activities (human use and reservoir regulation), while the streamflow decline over the longer period of time (1996-2015) could be attributed to human activities. During the same time, the river water quality improved significantly, having a positive relationship with the capacity of wastewater treatment facilities. The water quality in the Guanting Reservoir showed a deferred response to the reduced external loading, due to internal loading from sediments. These results implied that for rivers in which streamflow has declined sharply, the water quality could be improved significantly by actions to control water pollution control. This study not only provides useful information for water resource management in the Guanting Reservoir Basin, but also supports the implementation of water pollution control measures in other rivers with a sharp decline in streamflow.

The anthropogenic input of nutrients to rivers is the main cause of eutrophication,and both the excessive control and engineering of river channels further complicate the issue.To meet the demand for energy and water resources,thousands of dams,weirs,and sluices have been constructed and affected almost every river,which deeply interferes with the biogeochemistry cycles of nutrients and the ecological function of river systems.Previous research has investigated the ecological effects of eutrophication caused by phosphorus in dammed rivers,since phosphorus limitation of primary production is more predominant in river systems.Dammed rivers can reduce outflow and,hence,sequester a significant amount of phosphorus within the impoundments.As a consequence,river water becomes eutrophic,and the ratios of main nutrients change drastically,owing to the different responses of the nutrients to retention by dams.In addition,sediments in the dammed rivers,which containing high contents of phosphorus,can easily become a potential pollution source,especially under intensive scouring events.At the same time,the abundance of algae communities increases,as certain species bloom in the water column,which aggravates the ecologic effects of river eutrophication and threatens the biodiversity of river systems.Therefore,researchers have found that an efficient management strategy based on annual rainfall storage and dam discharge control can be used to improve the ecological effects of eutrophication in dammed rivers.However,as anthropogenic impacts continue to increase,further studies of dammed rivers are needed to clarify the relationship between artificial control in rivers and river eutrophication,in order to reduce the ecological effects of eutrophication,as well as to quantify the threshold of phosphorus,in order to further understand the eutrophication mechanisms of dammed rivers and the combined effects of nitrogen and carbon,to manage phosphorus within sediments,in order to prevent its release and resuspension,and to address concerns regarding the construction and restoration of landscape rivers with dams throughout China.

By comparing the performance of averaging method,Beale ratio method and regression method,a framework focusing on estimating annual sedimentloads based on concentrated sampling during high flow period,was proposed.The main results were:1) the Beale ratio method and flow-weighted concentration method could provide more robust and accurate estimation results regardless of the sampling frequency.The Beale ratio method performed better when samples were sparse rather than when samples were sufficient.2) The application of regression method was conditional,heavily depending on the significance of flow-sediment correlations.Increasing storm samples in the entire calculation dataset could improve the estimation accuracy.This study could provide a useful option in designing water sampling procedures and estimating pollutant loadings in watersheds characterized by pulsed runoffs.