Numerical Analysis Of Nitrate Groundwater Contaminatiom By Fertilization In The Laixi Region

The Laixi region is one of the important water supply regions of Jiaodong Peninsula, which supplies water to the cities of Qingdao and Laixi. Recently the nitrate concentrations in groundwater of the Laixi region are seriously exceeding the groundwater quality levels. The contamination area is over 200 square kilometers and continuously trends to expand.According to the actual situations in the Laixi region and recent water quality monitoring data and field investigations, it is believed that the main reason, which causes the nitrate groundwater contamination in the Laixi region, is the overuse of nitrate fertilizers. Hence,' based on the regulations of nitrogen transport and transformation in the vadose zone, it was chosen three typical soil profiles vertical to the Dagu river flow direction. Through lots of indoors and outdoors experiments, it was measured the parameters of hydrogeology in the vadose zone and parameters of dynamics and reaction dynamics in the water-soil system. Finally, it was established the coupling numerical model of water quantity-quality (VS2D/T). According to the parameters and VS2D/T model, it was simulated the soil moisture flow and nitrogen transport of different soil profiles at different hydrodynamic parameters, initial and boundary conditions, and types of irrigation and fertilization. It was analyzed the influences of different factors on the nitrogen contamination in the water-soil system. Based on the simulation results, it was raised the different controlling schemes. The study results show that the main factors, which control the leaching quantities of nitrate into the groundwater, are that types and quantities of irrigation, kinds and intensities of fertilization, the depth of groundwater levels, the accumulative quantities of nitrate in the soil profiles, and the characteristics of the soil profiles. Through simulating the nitrate recharge into the groundwater at different conditions of irrigation and fertilization, it was raised four different controlling schemes. At these schemes, to change the types and quantities of irrigation is the most effective way to reduce the nitrate fluxes into the groundwater. The study results provide the scientific data for the water management in the Laixi region, which can insure the sustainable development of the ecological environment.