Study On Numerical Simulation And Early Warning Of Nitrogen Pollution In Groundwater Of Guanzhong Baisen

As it is complicated and difficult to reveal and recover from groundwater pollution, the most efficacious measurement to control groundwater pollution is prevention. The Guanzhong Basin is the key developing region designated by Chinese central government and Shaanxi's crucial industrial and agricultural base. Its shortage in water resources and deteriorated groundwater pollution has posed a looming threat to rapid development in this region. In addition, due to high-dense population and significant human activity in agriculture, this region is also facing aggravating nitrogen pollution in shallow groundwater. Therefore, research on nitrogen pollution in shallow groundwater is essential and has the significance in prevention.In this dissertation, a software HYDRUS-1D is utilized to simulate and forecast transportation and transformation of nitrogen in the unsaturated zone. Early warning standard of groundwater quality is confirmed and early warning grade and threshold of nitrogen pollution in shallow groundwater of GuanZhong Basin is proposed, according to hydrogeology condition and hydrochemical characteristics. The conclusion is the following:1. The over standard rate of ammonia nitrogen,nitrite nitrogen and nitrate nitrogen in shallow groundwater of GuanZhong Basin is respectively 5.2%,0.4% and 30.0%. In this basil, the nitrogen pollution is more severe in the east than in the west, more severe in alluvial plain or billabong than in the loess altiplano and more severe in sewage irrigation than in other zones.2. The diffusion rate of ammonia nitrogen in sand is approximately 15～20cm/a. The diffusion rate of nitrite nitrogen and nitrate nitrogen is even faster. They could penetrate into water table 5m in depth in one year; within 5 years, more than 0.0007 mg/L nitrite nitrogen and 0.004 mg/L nitrate nitrogen could translocate beyond the water table.3. The diffusion rate of nitrogen with water flow in downwards varies depending on different soil. As predicted by the model, ammonia nitrogen would migrate 300cm and nitrite nitrogen and nitrate nitrogen could migrate to water table in sand in 20years later. And in loess, the translocation distance of nitrite nitrogen, ammonia nitrogen and nitrite nitrogen is approximately 25cm,80cm and 150cm, respectively.4. Most of the early warming of ammonia nitrogen pollution is reasonably satisfactory. However, ammonia nitrogen pollution is more severe in middle and lower reaches coastal of Wei River and Jiaokou and Baoji Gorge irrigation district. Early warning of nitrite nitrogen pollution is in good condition and nitrate nitrogen is in common condition. But, the early warning of nitrate nitrogen pollution is bad in Jiaokou and Baoji Gorge irrigation district, Chang'an district, north floodplain and terrace of Wei River in Chang'an and Baoji zone.5. As nitrogen fertilizer alone will not significantly influence the groundwater nitrogen pollution of GuanZhong Basin in the short term, warning state is not expected to change much, however, the range of warning state will expand and the warning grade will increase in the area where the soil is coarse and the unsaturated zone is thin.The research in this dissertation provides scientific support towards control nitrogen pollution in groundwater in Guanzhong Basin. It is important for groundwater protection and the safety of drinking water in this area.