Simulating the land use change effects on non-point source pollution in the Duliujian River Basin.

The uncertainty in the generation and formation of non-point source pollution makes it challenging to monitor and control this type of pollution. The SWAT model is frequently used to simulate non-point source pollution in watersheds and is mainly applied to natural watersheds that are less affected by human activities. This study focuses on the Duliujian River Basin (Xiqing section), which is characterized by a dense population and rapid urbanization. Based on the calibrated SWAT model, this study analyzed the effects of land use change on non-point source pollution both temporally and spatially. It was found that nitrogen and phosphorus non-point source pollution load losses were closely related to land use type, with agricultural land and high-density urban land (including rural settlements) being the main contributors to riverine nitrogen and phosphorus pollution. This indicates the necessity of analyzing the impact of land use changes on non-point source pollution loads by identifying critical source areas and altering the land use types that contribute heavily to pollution in these areas. The simulation results of land use type changes in these critical source areas showed that the reduction effect on non-point source pollution load is in the order of forest land > grassland > low-density residential area. To effectively curb surface source pollution in the study area, strategies such as modifying urban land use types, increasing vegetation cover and ground infiltration rate, and strictly controlling the discharge of domestic waste and sewage from urban areas can be implemented.

Review: The application of source analysis methods in tracing urban non-point source pollution: categorization, hotspots, and future prospects.

The contribution of urban non-point source (NPS) pollution to surface water pollution has gradually increased, analyzing the sources of urban NPS pollution is of great significance for precisely controlling surface water pollution. A bibliometric analysis of relevant research literature from 2000 to 2021 reveals that the main methods used in the source analysis research of urban NPS pollution include the emission inventory approach, entry-exit mass balance approach, principal component analysis (PCA), positive matrix factorization (PMF) model, etc. These methods are primarily applied in three aspects: source analysis of rainfall-runoff pollution, source analysis of wet weather flow (WWF) pollution in combined sewers, and analysis of the contribution of urban NPS to the surface water pollution load. The application of source analysis methods in urban NPS pollution research has demonstrated an evolution from qualitative to quantitative, and further towards precise quantification. This progression has transitioned from predominantly relying on on-site monitoring to incorporating model simulations and employing mathematical statistical analyses for traceability. This paper reviews the principles, advantages, disadvantages, and the scope of application of these methods. It also aims to address existing problems and analyze potential future development directions, providing valuable references for subsequent related research.

[Factors Influencing Willingness of Farmers to Pay for Agricultural Non-point Source Pollution Control Based on Distributed Cognitive Theory].

The analysis of the willingness of individual farmers to cover costs is an important basis for measuring the economic value of agricultural non-point pollution management， and determining the ecological and economic value of rural surface pollution control is a necessary measure to internalize the externalities of agricultural production. Based on the analysis of the hierarchy of factors influencing the cognition of farmers， this study constructed a theoretical framework based on distributed cognition theory to analyze their willingness to pay for agricultural non-point source pollution control from the perspective of individual farmers. On the basis of this framework， we used the Double-Hurdle model to empirically test the overall process of farmers'willingness to pay and their willingness to pay the amount for agricultural non-point source pollution control by combining 531 microscopic research datapoints in Guanzhong， Shaanxi Province. The results showed that： ① the number of farmers with willingness to pay for agricultural non-point source pollution control was 267， accounting for 50.30% of the total sample， and the average value of willingness to pay was 1 469.77 yuan·hm-2； the total economic value of agricultural non-point source pollution control in Shaanxi Province in 2020 was estimated to be 5.791 billion yuan based on the expected value of the willingness to pay level of the research sample. ② Farmers'willingness to pay for agricultural non-point source pollution control was influenced by the combined effects of personal， regional， and cultural forces， and the effects of each dimension were similar； farmers' willingness to pay for agricultural non-point source pollution control was mainly influenced by the cultural force factor， and the effects of personal and regional forces were very limited. ③ The results of the regressions by income level showed that personal and cultural strengths had a significant impact on the willingness to pay among the low-income group but did not contribute to the increase in the willingness to pay.

Identifying critical source areas of non-point source pollution to enhance water quality: Integrated SWAT modeling and multi-variable statistical analysis to reveal key variables and thresholds.

By integrating soil and water assessment tool (SWAT) modeling and land use and land cover (LULC) based multi-variable statistical analysis, this study aimed to identify driving factors, potential thresholds, and critical source areas (CSAs) to enhance water quality in southern Alabama and northwest Florida's Choctawhatchee Watershed. The results revealed the significance of forest cover and of the lumped developed areas and cultivated crops ("Source Areas") in influencing water quality. The stepwise linear regression analysis based on self-organizing maps (SOMs) showed that a negative correlation between forest percent cover and total nitrogen (TN), organic nitrogen (ORGN), and organic phosphorus (ORGP), highlighting the importance of forests in reducing nutrient loads. Conversely, Source Area percentage was positively correlated with total phosphorus (TP) loads, indicating the influence of human activities on TP levels. The receiver operating characteristic (ROC) curve analysis determined thresholds for forest percentage and Source Area percentage as 37.47 % and 20.26 %, respectively. These thresholds serve as important reference points for identifying CSAs. The CSAs identified based on these thresholds covered a relatively small portion (28 %) but contributed 47 % of TN and 50 % of TP of the whole watershed. The study underscores the importance of considering both physical process-based modeling and multi-variable statistical analysis for a comprehensive understanding of watershed management, i.e., the identification of CSAs and the associated variables and their tipping points to maintain water quality.

Functional keystone taxa promote N and P removal of the constructed wetland to mitigate agricultural nonpoint source pollution.

Characterized by irregular spatial and temporal variations of pollutant loading and complex occurrence mechanisms, agricultural nonpoint source pollution (ANPSP) has always been a great challenge in field restoration worldwide. Returning farmlands to wetlands (RFWs) as an ecological restoration mode among various constructed wetlands was selected to manage ANPSP in this study. Triarrhena lutarioriparia, Nelumbo nucifera and Zizania latifolia monocultures were designed and the water pollutants was monitored. N. nucifera and Z. latifolia could reach the highest TN (53.28 %) and TP (53.22 %) removal efficiency, respectively. By 16s high-throughput sequencing of rhizosphere bacteria, 45 functional species were the main contributors for efficient N and P removal, and 38 functional keystone taxa (FKT) were found with significant ecological niche roles and metabolic functions. To our knowledge, this is the first study to explore the microbial driving N and P removal mechanism in response to ANPSP treated by field scale RFWs.

Facilitating mitigation of agricultural non-point source pollution and improving soil nutrient conditions: The role of low temperature co-pyrolysis biochar in nitrogen and phosphorus distribution.

The current study generated co-pyrolysis biochar by pyrolyzing rice straw and pig manure at 300 °C and subsequently applying it in a field. Co-pyrolysis biochar demonstrated superior efficiency in mitigating agricultural non-point source pollution compared to biochar derived from individual sources. Furthermore, it displayed notable capabilities in retaining and releasing nutrients, resulting in increased soil levels of total nitrogen, total phosphorus, and organic matter during the maturation stage of rice. Moreover, co-pyrolysis biochar influences soil microbial communities, potentially impacting nutrient cycling. During the rice maturation stage, the soil treated with co-pyrolysis biochar exhibited significant increases in available nutrients and rice yield compared to the control (p < 0.05). These findings emphasize the potential of co-pyrolysis biochar for in-situ nutrient retention and enhanced soil nutrient utilization. To summarize, the co-pyrolysis of agricultural waste materials presents a promising approach to waste management, contributing to controlling non-point source pollution, improving soil fertility, and promoting crop production.

Comprehensive effects of climate, land use/cover and management practices on runoff and nutrient variations in a rapidly urbanizing watershed.

As non-point source pollution has emerged as a significant global and regional concern, climate change (CC), land use/cover transformation (LUCT), and management practices (MP) play vital roles in addressing nutrient pollution. However, current studies lack comprehensive quantification and consistent conclusions on the response to these factors, especially for management practices. To quantify and elucidate the impact of representative environmental factors on rapidly urbanizing regions, this study focused on the Shenzhen River, which serves as the most typical urbanizing watershed. Using a process-based distributed hydrological model with a factor-controlled simulation method, we identified significant differences in nutrient concentrations and the impacts of climate variability, land use/cover changes, and anthropogenic interventions from 2003 to 2020. Moreover, effective measures greatly improved water quality in the Shenzhen River during study period, as evident from trend and cluster analysis. However, ecological water supplements implemented since 2016 have led to a slight reduction in simulated runoff performance, and CC may amplify the synergistic effects of precipitation and temperature on the river system. While the implemented practices have been effective in reducing total nitrogen (TN) and total phosphorus (TP) loads, strong TN pollution control is still needed in rapidly urbanizing areas due to the results of land use/cover type changes. Our findings emphasize the intricate interplay among CC, LUCT, and MP in shaping water quality and hydrological processes in rapidly urbanizing watersheds, and clarify the independent effects of these factors on nutrients. This study contributes to a better understanding of the complex interactions between multiple factors in watersheds and provides guidance for sustainable watershed management.

Mechanism of additional carrier with seasonal temperature changes enhanced ecological floating beds for non-point source pollution water treatment.

The continuous performance and denitrification characteristics of carriers were investigated in two modified enhanced ecological floating beds (EFBs), one with only ceramsite and the other with ceramsite and extra additional stereo-elastic packing. Over a period of more than 414 days, the extra carrier was found to improve nitrogen removal while enhancing the system's resistance to seasonal temperature variations. The denitrification of all carriers in EFBs was inhibited in practice by seasonal temperature change, especially temperature rose from below 20 °C to above 20 °C and the inhibition rate of nitrous nitrogen (NO2--N) reduction was consistently above 91%, which was higher than that of nitrate nitrogen (NO3--N). However, the denitrification process including the rate and the resistance to temperature changes of ceramsite in the same EFBs with stereo-elastic packing at different temperatures, was consistently improved. The removal rate of NO3--N and NO2--N increased by up to 23.5% and 19.5%, respectively. The potential denitrification rates of all carriers increased with time which was also evidenced by in PICRUSt results, which showed that the abundances of predicted functional genes encoding NO3--N and NO2--N reductase increased over time. The dominant denitrifier also differed over time due to seasonal temperature changes.

Ecological ditch technology and development prospect based on nature-based solutions: a review.

The core of the concept of nature-based solutions (NBS) is ecological protection, which is the same direction as China's double-carbon goal and has attracted much attention in China. Ecological ditch sewage treatment technology has been widely used in controlling agricultural non-point source pollution because of its advantages of high pollutant removal efficiency and low energy consumption. Suppose the NBS concept of sustainable management, restoration, and ecological protection is integrated into the research and development and application of ecological ditch technology. In that case, it can not only improve the effective removal of pollutants, achieve the purpose of recycling water resources and nutrient elements, but also realize economic, environmental, and social benefits. This paper describes the ecosystem service functions provided by ecological ditches in detail, evaluates their economic values through literatures review, so as to raise people's awareness of natural resource conservation and realize the sustainable management of ecological ditches.

A spatial optimal allocation method considering multi-attribute decision making and multiple BMPs random combination in sub-watersheds.

Best management practices (BMPs) have been extensively employed in effective watershed management for non-point source pollution. The weights of objective functions and the restrictive conditions of combined BMPs are the vital requirements for BMPs allocation. Therefore, it is more beneficial to explore that a spatial optimal allocation method considering multi-attribute decision making and multiple BMPs random combination. Here is the novel framework based on Soil and Water Assessment Tool (SWAT) and the Non-dominated Sorting Genetic Algorithm II (NSGA-Ⅱ), which considers multiple objectives in deriving watershed-scale pollution control practices by considering BMPs cost and combined reduction rates of total nitrogen (TN) and total phosphorus (TP). The framework also integrates combined Entropy Weight method (EWM) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to solve the weights of TN and TP, and considers the attributes of the sub-basin itself, which is more local suitability. Four categories of BMPs, tillage management, nutrient management, vegetative filter strips, and landscape management, were evaluated in the Jing River Basin (JRB) and resulted in reduction rates of 9.77%, 10.53%, 16.40%, and 14.27% averagely, respectively. BMP allocation schemes, derived from multi-objective optimization, are stratified into three financial scenarios. Low-cost scenario, costing up to 2 billion RMB, primarily targets the grain for green program in 28.81% of sub-basins. Medium-cost scenario, between 2 and 6 billion RMB, predominantly utilizes the grain for green in areas with a slope greater than 15°, accounting for 20.00% of sub-basins. High-cost scenario exceeds 6 billion RMB, mainly due to the implementation of multiple combination measures. The three configuration scenarios can provide decision-makers with a trade-off between measure costs and reduction efficiency. Overall, the innovative framework not only facilitates cost-effective implementation but provides a beneficial methodology for selecting cost-effective conservation practices in other regions.

Long-term control of non-point source pollution by adjusting human environmental behavior in watershed-a new perspective.

The control of non-point source pollution is a major scientific and technological problem faced by mankind. We proposed a new approach to eliminate non-point source pollution, focusing on adjusting human environmental behavior. The implementation procedures are as follows: (1) Investigate the intention of pollution discharge behavior through interviews and questionnaires. (2) Carry out targeted intervention within the framework of social psychology to transform it into an environmentally friendly mode. (3) Calculate the amounts of pollutants produced and discharged before and after the intervention, and then evaluate the effect of the intervention on reducing pollution. (4) Based on successful interventions, a scheme can be developed to curb non-point source pollution. Aiming to reduce fertilizer use, a case study was conducted in Hetao Irrigation District, one of the three major Irrigation districts in China. The results showed that the interventions indirectly affected intention through attitude, subjective norm, and perceived behavioral control. The structural equation model explained 76.0% of the total variance of farmers' intention to reduce fertilizer application (SMC = 0.760), indicating effective intervention. Subsequently, a program to curb non-point source pollution was developed. This study can provide a key scientific and applied reference for the long-term control of non-point source pollution in watershed.

Differences in nonpoint source pollution load losses based on hydrological zone characteristics: a case study of the Shaying River Basin, China.

Agricultural nonpoint source (NPS) pollution loss is closely related to hydrological processes. Understanding the differences in NPS pollution load loss under hydrological processes is useful for the management and prevention of NPS pollution. In this paper, hydrological and water quality data from 2016 to 2018 and monitoring data of physical and chemical indicators in 1347 field soil samples in the Shaying River Basin (SYRB) were used to analyze spatiotemporal variations in NPS pollution using the Soil and Water Assessment Tool and multifactor analysis of variance. The intensities and differences in NPS pollution losses for different soil types and land use patterns were evaluated under different hydrological zones. The annual rainfall in the SYRB decreased gradually from 1136.50 to 404.04 mm, showing a significant zoning. Areas with high loss intensities were mainly distributed in areas with steep slopes and in the 800-1000 mm rainfall zone. Cultivated land had the largest loss of NPS pollution, followed by forest land and rural residential land. Fluvo-aquic soil had the largest loss of NPS pollution, followed by cinnamon soil and lime concretion black soil. A nonlinear regression model was established for rainfall and the NPS pollution loss intensity and had a correlation coefficient of 0.60-0.99 at a 95% confidence level. Slope and rainfall were the main factors influencing the nitrogen and phosphorus losses. In the 800-1000 mm rainfall zone, the soil background nitrogen and phosphorus load was also a major factor influencing the nitrogen and phosphorus loss intensities.

Distribution characteristics of non-point source pollution of TP and identification of key source areas in Nanyi Lake (China) Basin: based on InVEST model and source list method.

The Nanyi Lake basin, located in the middle and lower reaches of the Yangtze River, is a crucial component of the Yangtze River ecosystem. Excessive phosphorus levels lead to eutrophication in rivers and lakes. This study aims to enhance the identification efficiency of key source areas for non-point source pollution of total phosphorus (TP) in the Nanyi Lake Basin and improve decision-making regarding the treatment of these areas. The study employs the InVEST model and utilizes GIS spatial hot spot analysis to identify key source areas of agricultural TP non-point source pollution. The accuracy of the InVEST model's simulation results was verified using the source list method. The findings indicate that paddy fields serve as the primary pollution source. TP non-point source pollution in Nanyi Lake is influenced by pollution sources, pollution load filtration rate, and potential TP runoff mass concentration. Different pollution sources correspond to distinct key source areas, and the pollution generated by these sources in different administrative regions, ultimately affecting the lake, varies as well. The InVEST model demonstrates great applicability in regions where agricultural TP is the primary pollution source. For the Nanyi Lake basin, which predominantly experiences agricultural TP non-point source pollution, a combination of the InVEST model and the source list method is recommended. The InVEST model serves as the primary tool, while the source list method supplements it. This approach not only compensates for any limitations of the InVEST model's simulation results but also avoids unnecessary economic waste. The outcomes of this study contribute to a deeper scientific understanding of TP pollution in the Nanyi Lake Basin. They also aid in effectively identifying key source areas and formulating appropriate measures based on the pollution characteristics, thereby providing guidance for non-point source pollution control in the basin.

Effects of point and nonpoint source pollution on urban rivers: From the perspective of pollutant composition and toxicity.

Wastewater discharge is considered to be one of the anthropogenic factors affecting the water quality of urban rivers. The source and composition of wastewater are complex and diverse, and it is difficult to evaluate its effect on water quality and ecological health of receiving waters. Environmental DNA method can determine all species living in waters by examining DNA sequences, reflecting the impact of water quality changes on aquatic systems. In this study, water samples from two urban rivers were collected in dry and wet seasons, and the composition of pollutants was investigated by nontarget screening. Based on the pollutant composition, compound toxicity prediction and concentration addition model were used to predict the toxicity changes of pollutants in the urban rivers. More than 1500 suspect organic pollutants were nontarget screened, and silafluofen was found to be a major toxicity contributor. Environmental DNA analysis was combined with water quality measure and pollutant toxicity prediction to reveal the effects of pollutants from different sources on aquatic ecosystems. Fish diversity was negatively correlated with the mixed toxicity of organic pollutants, suggesting potential ecological risk in these two urban rivers. Our study developed a water quality assessment method based on pollutant composition and toxicity, and the potential risk of nonpoint source pollutants on aquatic ecosystems should not be neglected.

Assessing and improving the outcomes of nonpoint source water quality trading policies in urban areas: A case study in Virginia.

Nonpoint source (NPS) water quality trading (WQT) is a market-based approach to improving water quality. Past work has shown that these programs could increase localized pollutant loadings, in part by exporting water quality controls from urban to rural areas. Virginia's NPS WQT program has enabled thousands of transactions and may provide a model for other programs, but its impacts on urban water quality have not been thoroughly assessed. We quantify the impact of NPS WQT purchases in Virginia on water quality and hydrology in an urban catchment. We go on to assess outcomes of a policy alternative where buyers and sellers are collocated in the urban catchment. Simulation results show that NPS WQT increased total phosphorus (TP) loading by an average of 0.8 lbs TP/year for each 1.0 offsite credits purchased in the analyzed catchment. The TP loading increased in years with greater rainfall, such that TP loads were increased by up to 1.2 lbs TP/year for each offsite credit purchased. These loading increases may or may not be acceptable, depending on the cumulative number of purchases within an urban catchment and existing local water quality issues. In our policy alternative with buyers and sellers collocated in the catchment, we found that the TP increase from development was completely offset at the catchment scale, with a decrease of 4.3 lbs TP/year for each 1.0 credits purchased. This suggests that credits awarded for urban mitigation practices are undervalued compared with water quality requirements for credit purchasers. This undervaluation is a result of the Virginia trading program using one approach to compute the credit value for buyers and a different approach to compute the credit value for sellers. We demonstrate how using a single model to determine both buyer and seller credit values in urban areas could provide greater transparency and mitigate the risk of urban pollution hot spots. This work demonstrates the importance of consistency in the scale of pollutant load calculations between buyers and sellers for NPS WQT, and contributes novel insight into the implications of WQT for urban NPS pollution.

A multiscale analysis of the spatially heterogeneous relationships between non-point source pollution-related processes and their main drivers in Chaohu Lake watershed, China.

A better understanding of the relationships between non-point source (NPS) pollution-related processes and their drivers will help to develop scientific watershed management measures. Although various studies have explored the drivers' impact on NPS pollution-related processes, quantitative knowledge of the properties within these relationships is still needed. This study uses the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model to produce three related processes of NPS pollution, quick flow (QF), nitrogen export (NE), and sediment export (SE), in the upstream watershed of Chaohu Lake, China. The spatial distributions of QF, NE, and SE and their responses to multiple natural-socioeconomic drivers at nine spatial scales (1 km2, 10 km2, 20 km2, 30 km2, 50 km2, 75 km2, 100 km2, 200 km2, and town) were compared. The results showed that the spatial scale has little impact on the spatial distributions of NPS pollution-related processes. Across the nine scales, the socioeconomic drivers related to agricultural activities, area proportions of cultivated land (cultivated) and paddy field (paddy), have dominant impacts on NE, while the topographical drivers, the connectivity index (IC) and slope, have dominant impacts on both SE and QF. The magnitudes of single and paired natural-socioeconomic drivers' impacts on NPS pollution-related processes increase logarithmically or linearly with increasing spatial scale, but they tend to reach a stable threshold at a certain coarse scale. Our results emphasized the necessity and importance of embracing spatial scale effects in watershed water environmental management.

E-commerce development and its contribution to agricultural non-point source pollution control: Evidence from 283 cities in China.

Agricultural non-point source (ANPS) pollution is a pressing environmental issue in developing countries that poses a substantial threat to sustainable development. With the rapid growth of e-commerce and its great penetration and transformation in many socioeconomic sectors, e-commerce plus agriculture is widely regarded as the solution to sustainable agricultural development. However, the environmental impacts of e-commerce on agriculture, as well as the underlying mechanisms have yet to be fully explored and verified. Based on China's practices of e-commerce development and its integration with agriculture, a panel dataset of 283 prefecture-level cities from 2009 to 2019 was collected, and a spatial difference in difference (SDID) model combined with a Durbin model was constructed to examine the local and spatial spillover effects of e-commerce development on ANPS pollution. It is found out that e-commerce development has significant positive environmental impacts achieved by stimulating industrial structure upgrading and promoting green technology innovation, while the mechanism of cultivation scaling up tends to aggravate the ANPS pollution. Spatial analysis demonstrates that e-commerce development also helps alleviate the ANPS pollution of neighboring regions with a decayed effect over a distance. Meanwhile, the impact of e-commerce on mitigating ANPS pollution shows regional heterogeneity. Those developed regions present significant positive effects, while those regions dominated by agriculture economy and without sufficient supporting facilities for e-commerce development, show significant negative effects. Therefore, we argue that the positive environmental contribution of e-commerce is not bound to happen but instead is contingent, while policies should be adapted to local conditions and enhanced to encourage the integration of e-commerce and other socioeconomic sectors, in order to develop beyond the immature pioneering stage.

Agricultural non-point source pollution and rural transformation in a plain river network: Insights from Jiaxing city, China.

Recently, agricultural non-point source pollution (ANPSP) has gained increasing attention in China. However, using a uniform paradigm to analyze ANPSP in all regions is difficult, considering their geographical, economic, and policy differences. In this study, we adopted the inventory analysis method to estimate the ANPSP of Jiaxing City, Zhejiang Province as a representative region of the plain river network area from 2001 to 2020 and analyzed it in the framework of policies and rural transformation development (RTD). The ANPSP showed an overall decreasing trend over 20 years. Compared to 2001, total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) decreased by 33.93%, 25.77%, and 43.94%, respectively, in 2020. COD accounted for the largest annual average (67.02%), whereas TP contributed the most to the equivalent emissions (50.9%). The highest contribution of TN, TP, and COD, which fluctuated and decreased over the past 20 years, originated from livestock and poultry farming. However, the contribution of TN and TP from aquaculture increased. The overall trend of RTD and ANPSP showed an inverted "U" shape with time, and the evolution of both showed similar stage characteristics. With the gradual stabilization of RTD, ANPSP successively went through three stages: high-level stabilization (2001-2009), rapid-decreasing (2010-2014), and low-level stabilization (2015-2020). Additionally, the relationships between pollution loads from different agricultural sources and indicators of different dimensions of RTD varied. These findings provide a reference for the governance and planning of ANPSP in the plain river network area and a new perspective for investigating the relationship between rural development and the environment.

Nonpoint source pollution measures in the Clean Water Act have no detectable impact on decadal trends in nutrient concentrations in U.S. inland waters.

The Clean Water Act (CWA) of 1972 regulates water quality in U.S. inland waters under a system of cooperative federalism in which states are delegated implementation and enforcement authority of CWA provisions by the U.S. Environmental Protection Agency. We leveraged heterogeneity in state implementation of the CWA to evaluate the efficacy of its nonpoint source provisions in reducing nutrient pollution, the leading cause of water quality impairment in U.S. inland waters. We used national survey data to estimate changes in nutrient concentrations over a decade and evaluated the effect of state-level policy implementation. We found no evidence to support an effect of (i) grant spending on nonpoint source pollution remediation, (ii) nutrient criteria development, or (iii) water quality monitoring intensity on 10-year trends in nutrient concentrations. These results suggest that the current federal policy paradigm for improving water quality is not creating desired outcomes.

Strategy for cost-effective BMPs of non-point source pollution in the small agricultural watershed of Poyang Lake: A case study of the Zhuxi River.

In recent years, Poyang Lake has been affected by severe agricultural non-point source (NPS) pollution, a global water pollution problem. The most recognized and effective control measure for agricultural NPS pollution is the strategic selection and placement of best management practices (BMPs) for critical source areas (CSAs). The present study employed the Soil and Water Assessment Tool (SWAT) model to identify CSAs and evaluate the effectiveness of different BMPs in reducing agricultural NPS pollutants in the typical sub-watersheds of the Poyang Lake watershed. The model performed well and satisfactorily in simulating the streamflow and sediment yield at the outlet of the Zhuxi River watershed. The results indicated that urbanization-oriented development strategies and the Grain for Green program (returning the grain plots to forestry) had certain effects on the land-use structure. The proportion of cropland in the study area decreased from 61.45% (2010) to 7.48% (2018) in response to the Grain for Green program, which was mainly converted to forest land (58.7%) and settlements (36.8%). Land-use type changes alter the occurrence of runoff and sediment, which further affect the nitrogen (N) and phosphorus (P) loads since sediment load intensity is a key factor affecting the P load intensity. Vegetation buffer strips (VBSs) proved the most effective BMPs for NPS pollutant reduction, and the cost of 5-m VBSs proved the lowest. The effectiveness of each BMP in reducing N/P load ranked as follows: VBS > grassed river channels (GRC) > 20% fertilizer reduction (FR20) > no-tillage (NT) > 10% fertilizer reduction (FR10). All combined BMPs had higher N and P removal efficiencies than the individual measures. We recommend combining FR20 and VBS-5m or NT and VBS-5m, which could achieve nearly 60% pollutant removal. Depending on the site conditions, the choice between FR20+VBS and NT + VBS is flexible for targeted implementation. Our findings may contribute to the effective implementation of BMPs in the Poyang Lake watershed and provide theoretical support and practical guidance for agricultural authorities to perform and direct agricultural NPS pollution prevention and control.