嘉陵江流域非点源溶解态氮污染负荷模拟研究

Simulation of Dissolved Nitrogen Load in Jialing River Basin

嘉陵江流域是三峡水库最大的支流,为研究嘉陵江流域非点源溶解态氮污染负荷的年际变化规律及其来源的空间分布情况,以流域土地利用类型为研究单元,通过引入具有物理机制的半分布式水文模型——SLURP水文模型,并推导溶解态氮的流域输移损失系数,建立了流域非点源溶解态氮污染年负荷模型。借助GIS技术,应用所建模型,对嘉陵江流域各土地利用类型上的年地表径流量和溶解态氮污染负荷进行了模拟。模拟结果表明,以旱地和水田为主的涪江流域的溶解态氮流失情况最为严重,其次是渠江下游流域和西汉水流域,1990—2005年嘉陵江流域各土地利用类型上产生的非点源溶解态氮年均负荷为35726t·a-1,约占流域出口总氮负荷的32%。

Dissolved nitrogen（ DN ）on land is washed away into waters by runoff, forming the pollution load of non-point source. Therefore, simulation of runoff from each land use or land cover type plays a very important part in estimated pollution load of dissolved nitrogen. Soil conservation service（SCS ）runoff curve method was widely used for simulation of land runoff in popular non-point source pollution model, such as SWAT and AGNPS, etc. However, SCS model had a major limitation, that is, it was a statistical model for America, so there were some problems applying to Chinese basin directly. In this study, a physically-based and hydrological watershed model called Semi-Distributed Land Use-based Runoff Processes（ SLURP ）hydrological model, was used to simulate runoff from each land use or land cover type in order to estimate the DN load. Taking the Jialing River Basin as a research case, the DN model was fomled. Considering the DN loss during the transport process from land to waters, a coefficient of transport loss was introduced in the DN model, and its statistical equation was educed by the monitoring data. Consequently, by using DN model and SLURP model, the spatial distribution of output capacity of the basin DN pollution was simulated, and the DN pollution load at the watershed outlet from 1990 to 2005 was estimated by means of GIS. The results indicated that pollution in Fujiang River sub-basin which mainly consisted of dry farmland and paddy field was the most serious, and the followings were the subbasin of downstream watershed of Qujiang River and Xihanshui River sub-basin. The annual average DN load in the basin was so high that it reached 35 726 t·a^-1 from 1990 to 2005 and accounted for about 32% of the total nitrogen load at the watershed outlet.