中文摘要：

运用物质流分析方法，对北京市地表饮用水源地——密云水库流域进行了磷循环特征的研究；分析了研究区域内种植业、畜牧业、人口和简单子系统内部及子系统间的磷输入输出状况，以及系统整体的代谢效率特征，讨论了流域水体磷污染负荷的影响因素．研究结果表明：①化肥、饲料添加剂和农药是流域磷输入的主要来源，占直接物质磷输入总量的52．9％；整个系统向环境输入磷2868．44t，其中的26．5％直接进入水体．②在水体磷负荷中，畜牧业系统的贡献最大，为1800．26t，达到输出总量的82％，其次为种植业系统，占9．4％．③系统整体结构不协调，呈现单向和开放状态．研究区种植业系统运行出现磷亏缺，并具有区域性和不均衡性的特点；而畜牧业系统则出现磷盈余，整体结构不协调；畜禽的排泄物未能得到有效处置和循环再生，其中进入水体的量占畜禽粪尿磷总量的40．9％，从而造成严重的资源浪费和广泛的生态环境影响．④水体污染负荷与城市化率密切相关．

英文摘要：

Based on Material Flow Analysis, the phosphorus cycle in the watershed of the primary source water area for Beijing-the watershed of the Miyun Reservoir-was studied. Phosphorus （P） input and output of four sub-systems （planting, animal husbandry, population and a simple sub-system representing all other inputs and outputs）, the metabolic efficiency of the whole system, and the factors affecting pollution load are discussed. The main conclusions are as follows： （1）Chemical products, mainly fertilizers, feed additives, and pesticides, are the main sources of P input to the watershed, accounting for 52.9% of total imported P. The P input of the system to the environment is 2868.44 t, among which 76.5% of system phosphorus enters the water body directly. （2）The animal husbandry sub-system is the largest contributor of P load in water, which exports 82% of the total P load in water. The planting sub-system contributes 9.4% of the total P load in water. （3）The overall structure of the system is open, monodirectional and unharmonious. The P cycle in the planting system is deficient, but the animal husbandry system has a P surplus with uneven regional characteristics. Excreta from livestock and humans has not been effectively reused and recycled, so 40.9% excreta went directly into the water, resulting in P accumulation in water and further serious waste of resources and extensive environmental impact. （4）The water pollution loads of different counties are related closely with urbanization rates.