Risk Assessment And Regionalization Of Agricultural Non-point Source Pollution

Recently, rural areas of China are facing rapid development of agricultural industrialization. The intensive degree of agriculture is getting much higher. Agricultural non-point source pollution is getting more and more serious and becomes the focus of water environment pollution control. The interaction of agricultural activities with the inherent variations in climate, topography, soil type and land use gives rise to large spatial variation of agricultural non-point source pollution. Study on risk assessment, hierarchical partitioning and regionalization of agricultural non-point source pollution is helpful for putting priorities and limited resources into the areas of high pollution load and high risk to water environment, and thereby improve the efficiency of management. This paper selected a typical small watershed according to the characteristics of Yangtze River Valley foothills, and established a GIS-based model to study the spatial distribution of load losses and developed a GIS-based multi-criteria analysis model to assess the potential risk of agricultural non-point source pollution at the basin scale. Based on the results of estimation of load losses and risk assessment, hierarchical partitioning of load losses and risk levels were implemented and critical areas of high responsibility in NPS control were identified. This paper is prospected to provide valuable guidance for improving the effectiveness of agricultural non-point source pollution control.The main contents and results were showed as follows: (1) Load estimation of agricultural non-point source pollutionBased on the platform of GIS and Universal Soil Losses Equation (USLE), the soil erosion quantities and losses of TN and TP of Longdun watershed were analyzed and evaluated. Results showed that the annual average of TN loss was157.6T and TP loss was39.03T. As for the total watershed, the TN loss was strongest in southeast part and the TP loss was stronger in eastern parts than that in western parts. The intensive nutrient losses mainly happened in the parts that were farmland with intensive soil erosion and abrupt slope.(2) Risk assessment of agricultural non-point source pollutionA GIS-based multi-criteria analysis model was developed to assess the potential risk of agricultural non-point source pollution of Longdun watershed. Four criteria were developed to characterize the TN loss, TP loss, the efficiency of runoff generation and the distance of flow path to receiving water. The map of risk index highlighted the areas with high risk were mainly distributed in the southwest parts. This is mainly due to the high density of stream network and intensive agriculture landscape.(3) Identification of critical source areas and critical areas of high risksLongdun watershed was divided into12sub-basins. Critical source areas were identified according to the load of TN and TP per unit area. Results showed that critical source areas of TN were sub-basin2and4, and TP were sub-basin2,4and11, which took upl4.68%, and24.71%respectively. Critical areas of high risk were sub-basin1,2,3,4and5, which took up37.74%.(4) Strategies for controlling agricultural non-point source pollutionBased on the identification of critical source areas and critical areas of high risks, it was recommended to implement hierarchical partition management. For critical source areas (sub-basin2,4and11), it was recommended to strengthen source control to reduce the amount of potential contaminants. For the areas of high risk (sub-basin1,2,3,4and5), it was recommended to enhance transport process control to intercept and block their migration to aquatic environments in the diffusion process. Priorities should be put into the critical areas of high responsibility in NPS control (sub-basin2 and4) using the "abatement-control source-interception-transporting-repair" strategy.