关中盆地包气带氮迁移转化数值模拟及预测

Numerical simulation and prediction of N transportation and transformation in unsaturated zone in Guanzhong Basin

目的针对关中盆地潜水硝态氮面状污染比较突出的实际状况,研究施入氮肥后在耕作层以下的包气带中“三氮”运移转化和累积规律。方法以地貌为基本单元,结合包气带厚度和岩性,通过建立相应的数学模型进行模拟和计算。结果按照目前的农田施肥条件,在2年中,区域内沙丘和河漫滩进入地下水的氮通量可达170-300 kg/hm^2;黄土台塬洼地和河谷低阶地等地进入地下水的氮通量100-140 kg/hm^2;在包气带较厚（大于20 m）且透水性较差的河谷高阶地、黄土台塬和山前洪积平原等地区,进入地下水的氮通量一般低于50 kg/hm^2。结论区内河漫滩、沙丘、河谷低阶地和黄土台塬洼等地区,是关中地下水易产生氮污染的脆弱区,因而应是地下水重点保护地区。

Aim In view of the existing situation that the unconfined water in Guanzhong Basin has undergone heavily nitrate non-point pollution,to study on N transportation and transformation in unsaturated zone below the plough horizon.Methods Based on topographical unit,the thickness and the lithology of the unsaturated zone,established numerical models,simulate and predict the N variation and accumulation process.Results According to present fertilizer application condition in farm field,the inward flux（kg/hm^2）through unsaturated zone into unconfined aquifer in 2 years is：from 170 to 300 in river flood plain or in dune;from 100 to 140 in the lower terrace or in loess tableland depression;less than 50 in the river higher terrace,or in loess tableland,and or in the mountain front talus plain,the thickness of unsaturated zone is greater than 20meters and their permeability is poor.Conclusion These areas of river flooding plain,the dune,the lower terrace and the loess tableland depression in Guanzhong are groundwater vulnerability area of N pollution,also are areas that should be fully protected.