中文摘要：

人类活动引起的生态系统的氮输入和累积对区域环境特别是水环境有着潜在的重要影响.引入人类活动净氮累积的概念（net anthropogenic nitrogen accumulation,NANA）,将NANA定义为人类活动氮的输入和输出之差,它是通过大气沉降、肥料应用、人类食物和动物饲料、氮固定和河流的累积这五项来计算的.研究发现,北京市NANA值从2003年的12 557kg.（km2.a）-1下降到2007年的11 606 kg.（km2.a）-1,其年累积量是其他国家有关研究区域的2～6倍左右,且NANA的分布情况与人口分布及土地利用类型分布密切相关,NANA的变化主要与人口密度和肥料施用量相关.对整个北京地区而言,大气沉降氮是NANA最主要的来源,占总NANA的51%,其次为氮肥的施用37.4%和净人类食物和动物饲料的氮累积16.6%.人口密度和肥料应用量是影响NANA变化的主要因素,累积下来的氮元素主要分布在土壤、河流水系、动植物体内和大气中,通过对氮元素的来源和扩散途径的控制可以有效抑制氮元素对环境的影响.

英文摘要：

Nitrogen input and accumulation caused by human activities potentially influences the regional environment,especially the water environment.This paper introduces the concept of ＂net anthropogenic nitrogen accumulation＂,NANA and defines it as the difference between N input and N output caused by human activities,which are estimated from the accumulation in atmospheric N deposition,N fertilizer use,N accumulation of human food and animal feed,N fixation and riverine N accumulation.It is found in the study that NANA in Beijing has a downward trend from 12 557 kg·（km2·a）-1 in 2003 to 11 606 kg·（km2·a）-1 in 2007,but still 2-5 times that of other countries.The distribution of NANA is closely associated with the population distribution and land use type.The change of NANA is mainly related to the population density and the amount of applied fertilizer.As to the whole Beijing area,atmospheric N deposition is the largest source of N,accounting for 51% of NANA,which is followed by fertilizer use of 37.4% and human food and animal feed of 16.6%.The population density and the amount of applied fertilizer are main factors affecting NANA.The accumulated N is mainly distributed in soil,water system,body of animal and plant as well as the atmosphere.The effect of N on the environment can be effectively prevented by controlling the sources and proliferation of N.