An improved minimum cumulative resistance model for risk assessment of agricultural non-point source pollution in the...

Agricultural non-point source pollution (AGNPSP) is an important risk factor affecting the water environment. Among the areas where cropland NPSP occurs, the coastal zone should be of greater concern. Typhoons, heavy precipitation, and abundant rivers and ponds accelerate the transport process of AGNPSP to the offshore waters. It is urgent to construct a simple and accurate model to assess the risk of AGNPSP in the coastal zones. Thus, this study takes the nitrogen pollution from agricultural cultivation in the coastal zone of the Yellow River Delta as an example. A new minimum cumulative resistance (MCR) to agricultural non-point source pollution (AGNPSP-MCR) model is first proposed to simulate the transport process of cropland NPSP into the sea based on the "source-sink" theory in landscape ecology. Finally, the risk is assessed for AGNPSP transport into the sea. The results show the following. (1) The environmental factors of vegetation cover, rainfall erosivity, and soil erodibility are the three most important factors in pollution transportation, weighted 0.3433, 0.2608, and 0.2219, respectively, while the least influential factor is slope, with a weight of only 0.0053. (2) The minimum cumulative resistance of AGNPSP transportation shows a significant positive correlation with the distance to the river and sea, and is higher on the west sides away from the ocean, and smaller in the eastern coastal area near the sea. (3) Similarly, the regions facing serious AGNPSP risk are concentrated in the eastern coastal area, and the cropland area above medium risk was 252.72 km², accounting for 47.57% of the total cultivated land area. (4) Compared with the traditional MCR model, the AGNPSP-MCR model takes into account the quantitative differences of the transport process characteristics of AGNPSP, and it is constrained by the topographical parameter, so the results of AGNPSP risk are more reliable. This study provides a new reference for risk assessments of AGNPSP in the coastal zones.