土地利用和农业管理对丹江流域非点源氮污染的影响

为研究土地利用和农业管理对流域非点源氮污染的影响,选择南水北调中线的重要水源地丹江流域作为研究区,应用SWAT模型模拟了流域地表水硝酸盐氮和氨氮负荷,揭示了土地利用变化和不同施肥灌溉措施对氮污染负荷的贡献。结果表明:(1)流域内全年氮污染分布不均,硝酸盐氮和氨氮污染较为严重的时段集中在每年7—9月,输出量分别为734.32,735.36 t,占全年硝酸盐氮和氨氮输出量的50%以上;(2)硝酸盐氮和氨氮的输出量具有较大的空间差异,自上游至下游逐渐加重,污染较为严重的子流域主要集中在丹凤县和商南县;(3)通过设置情景模拟,当坡度大于15°和25°的耕地退耕还林时,流域硝酸盐氮负荷分别减少59.83%和45.89%,氨氮负荷分别减少48.91%和35.78%。当流域内施肥量和灌溉量分别降低20%时,流域硝酸盐氮负荷分别减少3.63%和13.26%,氨氮负荷分别减少0.12%和15.65%;(4)耕地是流域氮污染的主要来源,降低流域施肥灌溉量和陡坡地退耕还林是控制流域非点源氮污染的关键。

The Impact of Land Use and Agricultural Management on Non-point Source Nitrogen Pollution in Dan River Watershed

To study the effects of land use and agricultural management on non-point source nitrogen pollution in the watershed,Dan River watershed which is an important water source in the middle route of South-to-North Water Diversion project was selected as study area in this research, SWAT model was applied to simulate the nitrate nitrogen and ammonia nitrogen loads in the watershed, and quantify the contribution of land-use change and fertilization and irrigation measures on the nitrogen pollution loads of the river. The results indicated that:(1) The nitrogen pollution changed in different seasons, the most serious nitrogen pollution was from July to September, with the output of nitrate nitrogen and ammonia nitrogen loads of 734.32, 735.36 t, respectively (total accounting for more than 50% of the nitrate nitrogen and ammonia nitrogen load); (2) The nitrate nitrogen and ammonia nitrogen loads had large spatial difference, and the pollution increased from the upstream to the downstream. The sub-watershed with high nitrogen pollution load were mainly distributed in Danfeng and Shangnan counties; (3) The situational analysis indicated that when the farmland with slope greater than 15° and 25° in the basin was converted to forest, the nitrate nitrogen and ammonia nitrogen load in the basin decreased by 59.83% and 45.89%, respectively, and the ammonia load decreased by 48.91% and 35.78%, respectively. Both of fertilizer application and irrigation decreased by 20%, nitrate nitrogen load would decrease by 3.63% and 13.26%, and ammonia nitrogen load would decrease by 0.12% and 15.65%, respectively; (4) Cultivated land is the main source of nitrogen pollution in river basin, reducing the amount of fertilizer,irrigation and vegetation restoration in sloping cropland is the key to control non-point source nitrogen pollution in the watershed.