[Estimation of and Control Strategies for Pollution Loads from Non-point Sources in the Chenghai Watershed].

The calculation of non-point source (NPS) pollutant loads of nitrogen and phosphorus is the key step in preparing a pollution control plan. This study modified the export coefficient model by taking into account the precipitation, slope, distance between pollution sources and water bodies, and other relevant factors. The NPS pollution load assessment method established in this study can be applied to data-scarce basins and is suitable for plateau lake regions affected by terrain and precipitation. In this study, Chenghai Lake, which belongs to one of the nine major plateau lakes in Yunnan Province, is selected for the case study. This study first verifies the rationality of the improved export coefficient model based on actual observed values, and then utilizes the improved export coefficient model to assess the loads of dissolved nitrogen (DN) and dissolved phosphorus (DP) pollution. As indicated by the results, in 2014, the loads of DN and DP into Chenghai Lake are 158.48 t·a and 24.70 t·a, respectively. The maximum contributions of DN and DP pollution load into Chenghai Lake are from agricultural cultivated land are 46.19% and 48.16%, respectively, in terms of land use. The results present a relatively consistent spatial distribution of DN and DP that indicates that the south bank is a key area for governance. Livestock and rural living are the main pollution sources influencing the load of DN and DP into Chenghai Lake and should be prioritized for control. If the pollution from rural living, livestock, fertilizer loss, and land use can be effectively controlled, the load of DN and DP into Chenghai Lake will be decreased by a maximum of 38.47% and 40.76%, respectively. The results of this study suggest that the improved export coefficient model can be applied for study of the NPS pollution assessment of plateau lake regions and can provide a theoretical basis for the NPS pollution control of the Chenghai Lake basin.