中文摘要：

以浙江长乐江流域为研究对象,基于2007—2009年的野外监测、调查、分析结果,构建了ArcSWAT模型所需的各类空间数据库和属性数据库,实现了基于ArcSWAT的流域径流、泥沙和氮污染过程动态模拟,定量识别了非点源氮素污染的关键时期和关键源区.结果表明,模型在校正和验证期对径流、泥沙和氮污染过程模拟的效率系数≥0.5、决定系数≥0.6、相对误差〈20%,能满足研究和管理工作需要.雨季（6—8月）的累积氮入河量约占了全年入河总量的50%,是流域氮污染的关键时期.在流域所含的7个乡镇中,崇仁镇、鹿山街道和甘霖镇单位面积的年均氮入河量最大,分别为42.8、48.5和43.7kg.hm-2.a-1,是流域氮污染的关键区域.在该关键区域中,土壤氮库、大气沉降与氮肥施用产生的氮对氮入河总量的贡献率分别为23%、29%和38%,是需要重点关注的氮源.以上关键时期和关键源区定量识别结果,为实现流域氮污染有效控制提供了重要科学依据.

英文摘要：

Based on the field monitoring,investigation,and analysis,a 3-year（2007—2009） dataset on water quality,hydrology,soil and weather condition,land use,and nitrogen sources was developed for the Changle River watershed,a typical agricultural watershed in eastern China.All types of spatial databases and attribute databases required for the ArcSWAT（Soil and Water Assessment Tool） model were established.The ArcSWAT model was efficiently calibrated and validated for modeling watershed runoff,sand and total nitrogen（TN） dynamic processes.Using the calibrated and validated ArcSWAT model,the critical periods and source areas for watershed nitrogen pollution were quantitatively identified.Results indicated that the established ArcSWAT model could be applied for practical watershed water quality management,as shown by the modeling efficiency coefficients ≥0.5,determination coefficients ≥0.6,and relative errors 20% of the three components.Rainy season（i.e.June—August） was the critical period for TN pollution,as the cumulative TN export loads to the river accounted for 50% of annual amount.Among seven towns within the watershed,Chongren Town,Lushan Town and Ganlin Town located in the southeast yielded the highest TN export rates to the river per area（i.e.,42.8~48.5 kg · hm-2 · a-1） and were the critical areas for TN pollution.For these critical areas,soil nitrogen pool,atmospheric deposition and chemical fertilizer application contributed to 23%,29% and 38% of total TN exported load to the river,respectively.Great attention should be paid onto these nitrogen sources for TN pollution.The quantified information on the critical period and source area will help local decision makers to control watershed nitrogen pollution in an effective and efficient manner.