AN IMPROVED EXPORT COEFFICIENT MODEL FOR PRIORITY AREA IDENTIFICATION AND LOAD ESTIMATION UNDER DIFFERENT HYDROLOGICAL YEAR IN MIYUN RESERVOIR WATERSHED, BEIJING, CHINA

摘要

This study examined the potential effects of precipitation change on nutrient loads in the upper watershed of Miyun Reservoir. Using historical climate dataset, stream flow, and water quality data, the improved export coefficient model (IECM) was selected to simulate changes in TN and TP loads characteristics under different hydrological year. The results demonstrate that: 1) The major source of TN and TP was livestock, which accounted for 49.4% of the total, followed by rural living (26%), land use (24.6%), while for the TP ranked differently from those of TN with rural living first (71%), followed by livestock (26.15%) and land use (2.85%); 2) The impacts of precipitation amount change on pollution load are relatively greater when compared to the impacts of rural living, livestock and poultry breeding and land use pollution load increase; the effects from rainfall increment leads to approximately 24% and 27% increases of TN and TP pollution load, respectively; 3) The high-risk areas of TN and TP load were distributed accordance to the amount of precipitation in different hydrological years and the most of the CSAs were locates beside the main stream. Total nitrogen and total phosphorous load per unit area in Miyun, Chicheng and Fengning counties were higher than others. These data will be useful and valuable in evaluating potential NPS pollution load for the control of watershed pollution in the future and understanding its migration and transformation in a large-scale watershed where meteorological and hydrological data are mutative.