Mornitoring And Evaluation Of Non-point Source Pollution In Tumenxigou Small Watershed, Miyun Reservoir

Miyun Reservoir has been an important source of drinking water for Beijing. About 70% drinking water demands of the city has been provided by Miyun Reservoir. But some researches about present situation of the watershed showed that reservoir water had been seriously polluted. Tumenxigou small watershed, which is in the east of the Reservoir and about 5 km from the Reservoir, located in the secondary protection area of water resource conservation forest. Since 1996, the watershed has being managed as the demonstration project of water resource conservation forest. Water and soil loss has been controlled to some extent after returning a lot of farmlands to forests. However, studies for the loss amount and laws of the region's annual precipitation and nutrients are rarely. Therefore, the aims of the research were to master pollution features in the three small watersheds of Tumenxigou watershed and the source and contribution rate of various non-point source pollutants, and then provide a basis for the design of the watershed controlling program, through investigating,monitoring and analyzing.The methods of the research are field survey, household survey and water monitoring. According to the geography situation and present land-use, it firstly divided the studying region into various source areas of non-point source pollution, such as coniferous forests, hardwood forests, coniferous-hardwood mixed forests, fresh fruit forests and dry fruit forests. Then, the typical patches were .selected to test soil physicao and chemical properties. Investigate showed that the main reason of non-point source pollution of the watershed was that a great lot of fertilizer had been applied. A part of them, which hadn't been absorbed, would be carried into water by soil loss and runoff. Additionally, random treatment of rural life wastewater also was an important part of non-point source pollution.Precipitation-runoff, Total Nitrogen (TN), Total Phosphorus (TP), Nitrate Nitrogen (NO₃^--N), Nitrite Nitrogen (NO₂^--N), Ammonia Nitrogen (NH₃-N) and Chemical Oxygen Demand (COD) of the watershed were monitored simultaneously with the existing observation facilities and automatic hydrological recording equipments. Non-point source pollution features were obtained by analyzing the water indexes. Results showed that water quality in the watershed, which had been seriously polluted, were worse than the required water quality which is for centralized life drinking in secondary protection area of surface water source. TN and TP are the main pollutants. The descending order of contribution rate were mid watershed, south watershed and north watershed.Calculated with USLE, in 2006, TN and TP pollution load that were lost with soil loss were 438.83kg and 402.26kg; Calculated with empirical coefficients, TN and TP pollution load that were lost with runoff were 583.33kg and 184.57kg, TN and TP pollution load that caused by rural life wastewater were 386.83kg and 64.45kg。Among different land-use type, annual soil erosion modulus of fresh fruit forests and dry fruit forests are more than others, they are 7.42t/ha and 4.05t/ha. TN and TP pollution load that came from dry fruit forests are on top of the list. Their contribution rates are 49.95% and 63.48%.Finally, on the basis of above investigation and research results, several of feasibility measures about controlling non-point source pollution were discussed.