Validation of an In-Situ Observation Method for Nonpoint Source Pollution in Paddy Fields: A Case Study of a Beijing Paddy Field

A Beijing paddy field, along with in-situ experiments, was used to validate and refine the in-situ observation (IO) method to describe nonpoint source pollution (NPS) in paddy fields. Based on synchronous observed rainfall, water depth, and water quality data at two locations (1# (near inlet) and 2# (near outlet)) with large elevation differences, the evapotranspiration and infiltration loss (ET+F), runoff depth and NPS pollution load were calculated according to IO, and a common method was used to calculate ET+F. Then, the results of the different methods and locations were compared and analyzed. The results showed that 1# observation point was located at a lower position compared with 2# observation point. According to 1# observation point, there were 5 days of dry field in the drying period, which was consistent with the actual drying period, and there was a dry period of 9 days based on 2# observation point. The ET+F estimated by IO fit well with the calculated values. In the experiment, 6 overflows and 1 drainage event were identified from the observed data at locations 1# and 2#. The relative deviation of the NPS pollution of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), nitrate-nitrogen (NO3−-N) and ammonia nitrogen (NH4+-N) was between 0.6% and 2.0%. The water level gauge location had little influence on IO but mostly affected the water depth observations during the field drying period. The mareographs should be installed in low-lying paddy field areas to monitor water depth variation throughout the whole rice-growing season.

Monitoring the Landscape Pattern and Characteristics of Non-Point Source Pollution in a Mountainous River Basin

This study aimed to assess the relationship between the landscape patterns and non-point source (NPS) pollution distribution in Qixia County, China. The sub-basin classification was conducted based on a digital elevation model and Landsat8 satellite images. Water samples were collected from each sub-basin, andtheir water quality during the wet and dry seasons was estimated. The correlation between the landscape indices and water pollution indicators was determined by Pearson analysis. The location-weighted landscape contrast index (LWLCI) was calculated based on the “source-sink” theory. Qixia was further divided into five sections based on the LWLCI score to illustrate the potential risk of NPS pollution. The results showed that the water quality in Qixia County was generally good. Cultivated land, orchards, construction areas, and unused land were positively correlated with the water pollution index and weredesignated as the “source” landscape categories, while forests, grasslands, and water bodies, which were negatively correlated with water pollution, were the “sink” landscapes; the LWCI was high in 36.94% of the study area. In these areas, measures such as increasing vegetation buffer zones are necessary to decrease the sediment and nutrient loads carried by precipitation.

Optimum Detailed Standards to Control Non-Point Source Pollution Priority Management Areas: Centered on Highland Agriculture Watershed

The Ministry of Environment in Korea aims to reduce non-point source (NPS) pollution and improve soil water management by expanding NPS priority management areas. Six NPS priority management areas to reduce suspended solids (SS) according to soil loss were chosen as they either constitute serious hazards to the natural ecosystem due to NPS pollutants or they are areas with unusual geologic structure or strata. Although more comprehensive standards are required for effective NPS management, however, no detailed consideration factors and standards are available in the legal provisions. Therefore, in this study, based on the existing six priority NPS management areas and using results from previous studies, we present detailed legal designation standards. We found that the higher the altitude, slope, and field area ratio, the higher the effect of SS on water quality during rainfall. Additionally, there is a high correlation as R2 0.9813 between SS and the habitat and riparian index. These results are useful for establishing detailed standards for areas requiring an NPS management system, future expansion of the NPS priority management area designation, and policymaking and research for reducing NPS pollution in Korea.

Can Increasing Scale Efficiency Curb Agricultural Nonpoint Source Pollution?

The Chinese government has made great efforts to improve the scale efficiency of land through various measures during recent years, hoping to realize the coordinated developing goal of promoting agricultural benefits and protecting the environment. Statistics show that China’s land scale efficiency has steadily increased, but agricultural nonpoint source (NPS) pollution has also increased, which seems contrary to the expected outcome. Can increasing scale efficiency really curb agricultural NPS pollution? This study uses provincial-level data from China, together with a panel model and spatial econometric model, to investigate the relationship between scale efficiency and agricultural NPS pollution. It is found that the increase of scale efficiency aggravates the agricultural NPS pollution, and the conclusion still holds after considering spatial effect. The results of spatial analysis shows that the agricultural NPS pollution is spatially dependent. Further decomposition of the spatial effect shows that the scale efficiency not only intensifies the local agricultural NPS pollution, but also has a spillover effect (though not statistically significant) on agricultural NPS pollution in the surrounding areas. It is worth noting that financial policy, raising wage income and upgrading industrial structure can effectively curb agricultural NPS pollution in this region and adjacent areas, which also deserves our attention in the control of agricultural NPS pollution. In addition, it is necessary to make financial and fiscal support policies specifically for the governance of agricultural NPS pollution, adjust the distorted prices of input factors such as chemicals and pesticide, and accelerate the transformation of small-sized farmers to family farms, in order to maximize the inhibitory effect of scale efficiency on relieving agricultural NPS pollution.

Identifying critical source areas of nonpoint source pollution in a watershed with SWAT–ECM and AHP methods

Identification of critical source areas (CSAs) is pivotal for the management of nonpoint source (NPS) pollution of watersheds. Most studies focus on source (S) factors and ignore the driving (D) factors of such pollution. The Soil and Water Assessment Tool (SWAT) model and the export coefficient method (ECM) were incorporated to quantify the S factors of ammonia nitrogen (NH4–N) and total phosphorus (TP) as NPS pollution. Specifically, S factors coupled with D factors, including precipitation, slope, soil and land use, were regarded as multi–factors. Moreover, the analytical hierarchy process (AHP) method was adopted to determine the respective weights of multi–factors after overlaying the factor maps to identify the CSAs. These CSAs accounted for 23.86% of the total area, and generated 54.94% of NH4–N and 42.59% of the TP loads. In contrast with single and multi–factors, we found that using multi–factors having differing weights was more accurate for identifying CSAs. Our study results indicate this approach is reasonable for CSAs' identification in watersheds, and it can provide insights into different pollution sources and migration, thus providing a sounder basis for future decision–making.

Water Resource Risk Assessment Based on Non-Point Source Pollution

As one of the most important causes of water quality deterioration, NPS (non-point source) pollution has become an urgent environmental and livelihood issue. To date, there have been only a few studies focusing on NPS pollution conforming to the estimation, and the pollution sources are mainly concentrated in nitrogen and phosphorus nutrients. Unlike studies that only consider the intensity of nitrogen and phosphorus loads, the NPS pollution risk for the China’s Fuxian Lake Basin was evaluated in this study by using IECM (Improve Export Coefficient Model) and RUSLE (Revised Universal Soil Loss Equation) models to estimate nitrogen and phosphorus loads and soil loss and by using a multi-factor NPS pollution risk assessment index established on the basis of the data mentioned above. First, the results showed that the load intensity of nitrogen and phosphorus pollution in the Fuxian Lake Basin is low, so agricultural production and life are important sources of pollution. Second, the soil loss degree of erosion in the Fuxian Lake is mild, so topography is one of the most important factors affecting soil erosion. Third, the risk of NPS pollution in the Fuxian Lake Basin is at a medium level and its spatial distribution characteristics are similar to the intensity characteristics of nitrogen and phosphorus loss. Nitrogen, phosphorus, sediment, and mean concentrations are important factors affecting NPS pollution. These factors involve both natural and man-made environments. Therefore, it is necessary to comprehensively consider the factors affecting NPS in order to assess the NPS risk more accurately, as well as to better solve the problem of ecological pollution of water resources and to allow environmental restoration.

Evaluation of best management practices for non-point source pollution based on the SWAT model in the Hanjiang River Basin, China

Taking the Hanjiang River basin with Ankang hydrological station as the control section as the study area, the Soil and Water Assessment Tool (SWAT) model is used to identify the spatial and temporal distribution of non-point source (NPS) pollution and determine the critical source areas (CSA). Then we set up 11 best management practices (BMPs) in the CSA and evaluate their environmental and comprehensive benefits. The results show that TN and TP loads in flood season are significantly higher than that in non-flood season. The distribution of loss intensity of TN and TP load has a strong correlation with runoff and sediment erosion intensity, respectively. Among the 8 individual BMPs, the reduction rates of stubble coverage, grassed waterway and returning farmland to forest land are relatively high, and the comprehensive attribute value Z of stubble coverage is the highest. Among the 3 combined BMPs, the reduction rate of ‘stubble coverage + grassed waterway + returning farmland to forest land (>25°)’ is the highest and the Z value is the largest. Overall, the BMPs such as stubble coverage, grassed waterway, and returning farmland to forest land can be adopted alternately to control NPS pollution in the Hanjiang river basin.

Eco-Compensation Schemes for Controlling Agricultural Non-Point Source Pollution in Maoli Lake Watershed

Maoli Lake is the water source for local residents and a national nature protected area. However, due to intensive agriculture development, the water quality has deteriorated over the past decades. An effective measure to improve water quality is to control the agricultural non-point source (NPS) pollution through elaborate schemes based on eco-compensation. In order to develop such eco-compensation schemes, three scenarios of agricultural activity adjustment were designed: S1 (halving fertilization every year), S2 (fallow every other year), and S3 (returning agricultural land to forest). A Soil and Water Assessment Tool (SWAT) model was adopted to simulate runoff, total nitrogen, and total phosphorus. Based on SWAT results, a multi-criteria spatial evaluation model considering the environmental, economic, and social effects of eco-compensation was created for best scenario decision. The results reveal the following: (1) the total nutrients loss of agricultural land reduces in all scenarios, but S2 has more reduction compared to S1 and S3; (2) from the comprehensive perspective of environment–economy–society effects, S2 is the best scenario for rice land and dry land; (3) the comprehensive effect of eco-compensation at the grid scale has a significant spatial difference, and therefore, we highlight the necessity and significance of controlling agricultural NPS pollution by eco-compensation on a precise spatial scale. This study can broaden the application field of the SWAT model and provide a scientific basis and experience for the evaluation and spatial design of agriculture eco-compensation.

Quantifying the Contribution of Agricultural and Urban Non-Point Source Pollutant Loads in Watershed with Urban Agglomeration

Urban agglomeration is a new characteristic of the Chinese urbanization process, and most of the urban agglomeration is located in the same watershed. Thus, urban non-point source (NPS) pollution, especially the characteristic pollutants in urban areas, aggravates NPS pollution at the watershed scale. Many agricultural studies have been performed at the watershed scale; however, few studies have provided a study framework for estimating the urban NPS pollution in an urban catchment. In this study, an integrated approach for estimating agricultural and urban NPS pollution in an urban agglomeration watershed was proposed by coupling the Soil and Water Assessment Tool (SWAT), the event mean concentration (EMC) method and the Storm Water Management Model (SWMM). The Hun-Taizi River watershed, which contains a typical urban agglomeration and is located in northeastern China, was chosen as the study case. The results indicated that the per unit areas of total nitrogen (TN) and total phosphorus (TP) in the built-up area simulated by the EMC method were 11.9% and 23 times higher than the values simulated by the SWAT. The SWAT greatly underestimated the nutrient yield in the built-up area. This integrated method could provide guidance for water environment management plans considering agricultural and urban NPS pollution in an urban catchment.

Present and potential future critical source areas of nonpoint source pollution: a case of the Nakdong River watershed, South Korea

Identifying critical source areas (CSAs) is the first step to effectively managing nonpoint source (NPS) pollution. Increasing variability in climate can affect identification of CSAs. In this study, we identified present and future CSAs of NPS pollution in the Nakdong River watershed and examined how climate change will influence the identification of CSAs. Nine NPS pollution-related factors affecting the watershed environment and water quality were considered. These factors were rescaled through a min-max normalization to propose an index system that ranks basins based on the sensitivity of basins to climate change on identifying CSAs. For analyses, past rainfall was replaced with future rainfall under two RCP scenarios, RCP 2.6 and RCP 8.5. Results showed insignificant differences in the spatial distribution of CSAs between the present and the future and between the future scenarios. Basins that are on or adjacent to the Nakdong River mainstream were mainly identified as CSAs, in addition to many basins of the Geumho and Nam rivers. Highly ranked CSAs including the level 1 CSAs, were mainly distributed in the mid- and downstream areas of the Nakdong River, indicating high need of NPS pollution management. This study can provide a foundation for the effective management of NPS pollution in the present and the future.