密云水库流域氮磷空间变化及污染风险

Nitrogen and phosphorus content variation and the pollution hazards present in Miyun Reservoir watershed

密云水库是北京市重要的地表饮用水源地。为了解水源保护区各区域土壤氮磷质量比空间变化规律及污染风险，采集水源保护区种植不同作物表层土壤样品，对土样氮磷质量比进行克里格空间插值，计算水源保护区不同区域面源污染风险因子。结果表明，不同区域土壤氮磷质量比存在较大差异，潮河、白马关河上游及近水库流域、水库分水岭内侧是水源保护区高和较高氮、磷质量比主要分布区域，安达木河流域氮质量比也较高，白河流域氮、磷质量比相对较低。土壤氮磷质量比高和较高区域也是面源污染风险较高区，面源污染风险因子范围为5．91-22．82，其中潮河和白马关河上游流域风险因子都大于10；白河流域风险因子最小，仅为最高风险区域的1／130。研究表明，水源保护区土壤氮磷质量比水平是密云水库流域面源污染风险的主要决定因子，潮河、白马关河流域及水库分水岭内侧是密云水库氮磷污染物主要来源区域。

The present paper is aimed at investigating the spatial variation and non-point source pollution hazards or effects likely to be caused by the nitrogen （N） and phosphorus （P） contents of the farm- ing activities to the drinking water quality in Miyun Reservoir, which serves as a chief drinking water source of Capital Beijing. For this purpose, we have collected topsoil samples covered by the different types of plants in the Drinking Water Conservation Area （DWCA） of the reservoir and analyzed their concentrations in a geo-statistieal ap- proach intensively based on the Geographic Information System （GIS）. The analysis results we have gained show that the N and P contents in the topsoil vary greatly from area to area in the sub-areas of DWCA. The highest and relatively higher soil N and P contents, relatively higher soil N have been found in the up-stream areas of the water-inlet rivers and those close to the reservoir, such as the areas of Chao River, Baimaguan River, the interior areas of the reservoir it- self, and the area of Andamu River, respectively; whereas relatively lower N and P content has been detected in the Bai River watershed. While the areas with higher N and P contents were found with higher hazards of non-point source pollution, the non-point source pollution hazardous factors were found within 5.91 - 22.82 in these areas, where they were detected both with above 10 in the upstream water- sheds of Chao River and Baimaguan River, while the least hazardous effects were found in Bai River watershed, which accounts only for 1/130 of the area with the highest hazard liabilities. In addition, these above said results also indicate that the levels of soil N and P contents should be considered as the key factors of non-point source pollution in the watershed of Miyun Reservoir, and the watersheds of Chao River, Baimaguan River and the inner side of Miyun Reservoir serve as the main origin of the non-point source of N and P pollu- tants.