[Spatial discharge characteristics and total load control of non-point source pollutants based on the catchment scale].

Agricultural non-point source pollution is one of the major causes of water quality deterioration. Based on the analysis of the spatial discharge characteristics and intensity of major pollutants from the agricultural pollution source, the establishment of spatial management subzones for controlling agricultural non-point pollution and a design of a plan for total load control of pollutants from each subzone is an important way to improve the efficiency of control measures. In this paper the Four Lake basin in Hubei Province is adopted as the research case region and a systematic research of the control countermeasures of agricultural non-point pollution based on the catchment scale is carried out. The results shows that in the Four Lake basin, the COD, total nitrogen, total phosphorus and ammonia nitrogen load of the water environment are mainly caused by agricultural non-point pollution. These four kinds of non-point source pollutants respectively account for 67.6%, 82.2%, 84.7% and 50.9% of the total pollutant discharge amount in the basin. The analysis of the spatial discharge characteristics of non-point source pollutants in the Four Lake basin shows that the major contributor source regions of non-point source pollutant in the basin are the four counties, including Honghu, Jianli, Qianjiang and Shayang where the aquatic and livestock production are relatively developed. According to the spatial discharge characteristics of the pollutants and the evaluation of the discharge intensity of pollutants, the Four Lake basin is divided into three agricultural non-point pollution management subzones, which including Changhu upstream aquatic and livestock production pollution control subzone, Four-lake trunk canal rural non-point source pollution control subzone and Honghu aquatic production pollution control subzone. Specific pollution control measures are put forward for each subzone. With a comprehensive consideration of the water quality amelioration and the allowable discharge of pollutants, a total load control solution is designed for the three non-point pollution management subzones, so as to fulfill the requirements of all indices of the monitoring sites and the requirements for the allowable discharge of pollutants of the water. Among the major pollutants, the major COD reduction area includes the Four-lake trunk canal subzone and the Honghu Lake subzone, which respectively account for 43% and 42% of the total COD reduction amount; the major ammonia nitrogen reduction area includes the Four-lake trunk canal subzone, accounting for 66% of the total ammonia nitrogen reduction amount; the major total nitrogen reduction area covers the Four-lake trunk canal subzone and the Honghu Lake subzone, accounting for 42% and 31% of the total nitrogen reduction amount in the basin respectively; the major total phosphorus reduction area is the Four-lake trunk canal subzone, accounting for 53% of the total phosphorus reduction amount in the basin.