太湖上游地区面源污染氮素入湖量模拟研究

以太湖上游地区为研究对象,通过TM/ETM解译获取土地利用信息,应用IDRISI软件的水文分析模块,对太湖上游地区进行流域划分,选择代表性小流域进行野外监测,分析流域土地利用与河流水质的联系,估算林地、耕地产出径流的面源污染总氮浓度特征;在此基础上采用代表性流域实测参数与分布式水文模型相结合的思路,开发基于单元格网的面源污染模拟模型,应用1980~2000年水文站实测序列对模型进行率定和校验,模拟太湖上游地区面源污染总氮的空间分布及入湖量。研究结果显示,太湖上游地区林地产出径流的总氮浓度参数为0.778 mg L-1,耕地产出径流的总氮浓度参数为2.518 mg L-1。模型及参数在太湖上游地区具有较好的应用效果,验证区径流模拟的平均误差为13%,总氮输出量模拟的平均误差为11.6%。应用模型估算太湖上游面源污染总氮入湖量为7 632 t a-1,约占总入湖量的40.8%。研究区内不同土地利用类型的面源污染总氮输出差异较大,其中耕地面源污染总氮输出量为4 289 t a-1,占面源污染输出总量的56.20%;林地和城镇用地面源污染总氮输出量分别为1 849 t a-1和1 270 t a-1,占面源污染输出总量的24.22%和16.64%。

SIMULATING FLUXES OF NON-POINT SOURCE NITROGEN FROM UPRIVER REGION OF TAIHU BASIN

A study was carried out with the upriver region of the Taihu Basin as a subject.Land use information about the area was acquired by means of TM/ETM image interpretation,and the upriver region was divided into small catchments with the aid of the IDRISI software.Field monitoring was performed in some selected catchments for analysis of relationships between the land use and river water quality in the catchments,and estimation of total concentration of the non-point source nitrogen in runoff from forest land and farmland.Based on the analysis and estimation,a cell-based model for simulating non-point source pollution is developed by combining the distributed hydrological model with measured values of the typical catchments.The model is well calibrated and validated with the monthly runoff data in the period from 1980 to 2000 and then used to simulate spatial distribution and flux of non-point source nitrogen to the Taihu Lake.Results show that the mean concentration of total nitrogen is 0.778 mg L-1 in runoff from forest land,and 2.518 mg L-1 from farm land.The modeled runoff volume and total nitrogen fluxes match well the observed ones,respectively,in the validation area.The average error value is 13% for the former,and 11.6% for the latter.The non-point source total nitrogen flux from the upriver region to Taihu Lake is 7 632 t a-1,contributing about 40.8% to the total nitrogen flux of the entire basin.The flux varies with the type of land use.For farm land,the total nitrogen flux is4 289 t a-1,accounting for about 24.22% of the total non-point source nitrogen output,and for forest land and built-up land,the total nitrogen flux is 1 849 t a-1 and 1 270 t a-1,for about 24.22% and 16.64%,respectively.