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[Display omitted] • Using soil organic matter to indicate estuarine chemical oxygen demand export risks. • Simulating coastal nonpoint source pollution based on soil erosion process. • Verifying logarithmic relations between terrestrial risks and pollutant fluxes. China has been facing severe organic pollution and the nonpoint source export from surface soil is usually overlooked in coastal areas. In this paper, from the perspective of catchment and attenuation, we have constructed a risk assessment method for coastal nonpoint source pollution (NSP) by applying the revised universal soil loss equation (RUSLE) and geostatistical analysis. Combined with the soil and water monitoring data, we have simulated regional NSP risks originating from surface soil organic matter (SOM) in the Yellow River Delta (YRD). Field surveys have verified the significant positive correlations between watershed SOM exporting risks and estuarine chemical oxygen demand (COD) fluxes during the rainy season. There present obvious logarithmic relations between the COD fluxes and the rainfall quantities, and the surface organic NSP risks. Larger NSP contributing sources are mainly located in the areas with higher soil exposure and stronger land-sea interactions. It should focus on the agricultural areas and improve relevant fertilizing and tillage methods to reduce source-exporting risks. Additionally, the summer rainfall concentrating periods need to be controlled emphatically, and vegetation-improving strategies need to be supplemented with the spatiotemporal-specific managements. This study provides a new insight for getting early terrestrial warning information for offshore organic water pollution, and presents research references for similar regional NSP issues. [ABSTRACT FROM AUTHOR]

To explore the spatial heterogeneity of nitrogen supply from human activities to soil in coastal areas, we established a soil nitrogen net replenishment index (A-SNNRI). We applied the Revised Universal Soil Loss Equation (RUSLE) model for soil loss risk calculation and geostatistical analysis for process simulation. A case study in the Yellow River Delta (YRD) showed that the A-SNNRI worked well. During the summer crop-growing season, population and land use presented significant influences on the soil total nitrogen (STN) status. Urban villages and arable land both had the largest summary STN and variety. There was a negative correlation between STN change and soil loss. The east coast held both the largest A-SNNRIs and soil loss risks. There were significant positive correlations between A-SNNRIs and population and GDP. Therefore, to control and reduce soil-source nitrogen exports in the YRD, we need to reduce nitrogen emissions from urban villages, agriculture, industry, and aquaculture and determine the main risk locations along the east coast and in the main city. [ABSTRACT FROM AUTHOR]

Soil erosion contributes greatly to nonpoint source pollution (NSP). We built a coastal NSP risk calculation method (CNSPRI) based on the Revised Universal Soil Loss Equation (RUSLE) and geospatial methods. In studies on the formation and transport of coastal NSP, we analysed the pollution impacts on the sea by dividing subbasins into the sea and monitoring the pollutant flux. In this paper, a case study in the Yellow River Delta showed that the CNSPRI could better predict the total nitrogen (TN) and total phosphorus (TP) NSP risks. The value of the soil erodibility factor (K) was 0.0377 t h·MJ−1·mm−1, indicating higher soil erodibility levels, and presented an increased trend from the west to the east coast. The NSP risk also showed an increased trend from west to east, and the worst status was found near the Guangli River of the south-eastern region. The contributions of the seven influencing factors to CNSPRI presented an order of vegetation cover > rainfall erosivity > soil content > soil erodibility > flow > flow path > slope. The different roles of source and sink landscapes influenced the pollutant outputs on a subbasin scale. Arable land and saline-alkali land were the two land-use types with the greatest NSP risks. Therefore, in coastal zones, to reduce NSP output risks, we should pay more attention to the spatial distribution of vegetation cover, increase its interception effect on soil loss, and prioritize the improvement of saline-alkali land to reduce the amount of bare land. [Display omitted] • Coastal soil erosion brought larger amounts of TN and TP nonpoint source pollutants into the sea. • Areas close to larger rivers and the sea posed higher nonpoint source pollution risks to coastal waters. • Inland waters played good sink landscape roles and consumed TN and TP nonpoint source pollutants. • Arable and saline-alkali lands contributed more to TN and TP pollution in the Yellow River Delta. [ABSTRACT FROM AUTHOR]