基于ArcSWAT模型的老鹳河流域面源氮识别和分析

进行老鹳河流域面源氮污染负荷估算和关键源、区识别，推进流域面源污染的溯源和控制，为流域非点源氮污染控制和治理提供理论支撑。通过模型数据库构建、流域空间单元划分以及参数率定和验证建立老鹳河流域氮污染过程的ArcSWAT模型；以2017年的气象资料为背景，设置4种情景模式，模拟估算流域不同面源氮的入河量，分析和识别不同污染源的关键期以及不同土地利用类型的关键污染源。结果表明，化学氮肥施用和大气沉降是老鹳河流域面源氮的主要污染源，分别贡献了47.6%和38.6%；大气沉降、畜禽养殖和化学氮肥施用入河氮量最大值均出现在3月，农村生活入河氮量最大值出现在8月，而4类污染源入河氮量的最小值均出现在12月；雨季是老鹳河流域控制面源污染氮的关键期；减控的关键污染源旱地、园地和水田是化学氮肥施用，林地和人居地分别是大气沉降和农村生活。应分时、分区、分类制定老鹳河流域面源氮污染减控方案，对于人为氮源（化学氮肥施用、畜禽养殖和农村生活）还要关注在作物播种期和生长季节进行减控。

Identification and Analysis of Non-point Source Nitrogen in the Laoguan River Watershed Using ArcSWAT Modeling

Laoguanhe River, located in southwest Henan Province, is an important water source for the middle route of the South-North Water Diversion Project. In recent years, rapid development of agriculture, aquaculture and livestock breeding in the Laoguan River basin has resulted in large quantities of active nitrogen being discharged into Laoguanhe River. Agricultural non-point source nitrogen (N) pollution (NNPS) has become one of the primary factors affecting water quality in the Laoguanhe River watershed (LRW) and it poses a threat to water quality in the middle route of the South-to-North Water Diversion Project. In this study, an ArcSWAT model was constructed to estimate the NNPS load and identify primary sources and critical periods of NNPS for different land use types in the Laoguanhe River basin. The objective was to provide a theoretical basis for tracing, preventing and controlling NNPS in the watershed. Development of the ArcSWAT model for N pollution in the Laoguanhe River watershed included database construction, watershed spatial unit division, parameter calibration and verification. Based on meteorological data for 2017, four scenarios were set, and the inflow of N from different non-point sources was simulated and estimated. Critical periods for different pollution sources and the primary pollution sources for each land use type were then identified. Results show that chemical nitrogen fertilizer application, atmospheric nitrogen deposition, rural life discharge , and livestock and poultry operations were the four primary NNPS sources in the Laoguanhe River basin and accounted, respectively, for 47.6%, 38.6%, 7.2% and 6.6% of the total nitrogen load. Nitrogen loading from different pollution sources varied significantly by season: highest in spring, followed by summer, autumn and winter. Maximum loading from atmospheric nitrogen, livestock and poultry operations, and application of chemical nitrogen fertilizer all occurred in March, and the maximum N load by rural life discharge occurred in August. Minimum loading of these four N sources all occurred in December. The rainy season was the critical period for controlling NNPS in the Laoguanhe River basin. Chemical nitrogen fertilizer was the primary pollution source for dry land, garden land and paddy fields, while atmosphere nitrogen deposition and rural life discharge were the key pollution sources for forested and residential areas. To effectively control NNPS in Laoguan River, particular attention should be paid to the timing of crop sowing and the primary N pollution sources from different land use types. Based on the characteristics of N pollution in the watershed, we recommend that fertilization should be controlled in flood season, and technical measures should be adopted to improve the utilization rate of chemical nitrogen fertilizer. We also recommend constructing terraces, water retention ponds and vegetative buffers to improve nitrogen retention capacity in the watershed.