Diffuse Pollution Control and Water Soil Conservation in the Watershed of Miyun Reservoir, Beijing, China

Miyun Reservoir, the only one source of drinking surface water of Beijing, Capital of China, is situated at Miyun County where is within northern mountain area of Beijing. Nitrogen and phosphorus, coming mainly from diffuse pollution, are major nutrients to cause eutrophication to degrade water quality of Miyun Reservoir. Loss from chemical fertilizer, animal waste and soil erosion are the main patterns of diffuse pollution. It is estimated the percent diffuse pollutants as TN (75 %) and TP (94 %). As a example of Shixia water soil conservation in Miyun County, the twenty experimental units and two monitoring channels, residential area and livestock units were used to monitor the flow, runoff and erosion, nitrogen and phosphorous content associated with various land uses in the meantime. Based on the relevant data which range from meteorological and hydrological data to land use, fertilizer and pesticide usage, and even livestock raising information, a total of four land use scenarios were modeled to evaluate various land management strategies on sediment and nutrient loading from catchment. From the study, conclusions are summarized as follow: (1) Variations of TN, TP and COD in continuous rainfall processes are almost accordant with rate of flow. At the beginning of runoff, concentrations of suspended matter, TN, TP and COD are higher. (2) The pollutant content of residential area and livestock units are nearly 10—20 times of that of other land use areas. These areas should be treated as critical areas of diffuse pollution. (3) Different land use influences intensively the loss of pollutants, especially slope tilling in agricultural land. The amount of nutrient loss from the agricultural land per unit is the highest, that from forestry is the secondary and that from grassland is the lowest. (4) Nutrient is enriched in sediment. Phosphorus is migrated with sediment, while the dissoluble form in runoff is very little. Being carrier of loss nutrients, the fine particles are thought to be the controlling focus. Based on the distribution of pollutants and ecological characteristics, we divide the Control zones of diffuse pollution in Miyun Reservoir as following: (1) Water source Forest remedial zone in the northeast and west mountain area with greater density of soil erosion. (2) Eco-agricultural manage zone in the northern rim around reservoir with agricultural land use and villages. (3) Water soil erosion control zone in northern hilly areas.