密云水库土门西沟流域非点源污染负荷估算

密云水库水质影响北京市地表饮用水源质量，非点源污染成为密云水库水质下降的主要原因。为了满足水资源管理规划，在密云水库土门西沟小流域内根据不同的水土保持措施选择6个径流小区，主要有：板栗林、油松林、刺槐林、混交林、灌木林、梯田，于2007年对小区地表径流进行水质水量的监测。运用RUSLE公式和SCS法估算流域内不同水土保持措施的非点源污染负荷，利用ArcGIS工具绘制了土壤侵蚀量空间分布图。结果表明：土门西沟小流域非点源污染物主要来源于土壤侵蚀，泥沙中的吸附态是非点源污染物存在的主要形式；其次土门西沟小流域不同水土保持措施单位面积的污染负荷输出由大到小排列顺序为，经济林＞阔叶林＞灌木林＞针叶林＞混交林＞梯田。研究结果表明减少经济林来增加混交林用地面积，提高水源林的覆盖率，梯田可以维持现有的用地状况，禁止陡坡栽种农作物，坡脚和沟道农地采取梯田的耕种方式，以此来达到控制非点源污染的目的。跟以往研究得出的结论相反，梯田非点源污染负荷比林地小，主要是因为梯田相对坡耕地大大增加了地表入渗量，此外是因为梯田施用有机肥料，减少非点源污染。

Estimation of non-point source pollution load in Tumenxigou watershed of Miyun Reservoir

Water quality of Miyuan Reservoir affects water quality of the surface drinking water sources in Beijing. At present, non-point source pollution is a major contributor to water quality decline in Miyuan Reservoir with the point source pollution efficiently controlled. To meet the needs of the water resources protection, six runoff plots with different soil and water conservation measures were chosen in Tumenxigou small watershed of the reservoir basin, namely, chestnut (Castanea mollissima Bl.) economic forest, Chinese pine (Pinus tabulaeformis Carr.) plantation, Chinese pine (Pinus tabulaeformis Carr. ) and blacklocust (Robinia pseudoacacia Linn.) mixed forest, shrub (Vitex negundo Linn. var. heterophylla Rehd.), and maize agriculture land, then pollutant concentration and overland discharge under runoff generating rainfall events were monitored in 2007. Non-point source pollution load and spatial distribution of soil erosion within the watershed were estimated and mapped by using RUSLE and SCS method integrated with ArcGIS tools. The results showed that non-point source pollution was mainly generated by soil erosion with pollutant absorbed in the soil particles. Of all different soil and water conservation measures, the order pollutant load per unit area is economic forest>broadleaf forest>shrub>coniferous forest>mixed forest and farmland. Therefore, land use planning in this region to control soil erosion should be developed by reducing economic forest, increasing broadleaf and coniferous mixed forest, sustaining existing terrace field, forbidding growing crops on steep slopes, adopting terrace mode at the slope toe and channel system in order to control the non-point source pollution. In contrast with the general conclusion drawn by other similar research, the non-point source pollution of the farmland is lesser than woodland due to large infiltration capacity (small overland flow contribution) and organic fertilizer applied for growing crops.