Study on the Contribution of Groundwater Nitrogen Pollution Sources in a Typical Section of the Wei River in China

Abstract

Aiming to assess the groundwater nitrogen pollution problem in a typical section of the Wei River in China, the contribution of groundwater nitrogen pollution sources in the region was studied. Using Hydrus-1D to implement the simulation process of substituting points for surfaces, we calculated the volume and nitrogen concentration of the water leaching out from the bottom of the encompassing aeration zone. The results of the Hydrus-1D simulation were input as initial values into the nitrogen migration and transformation numerical model constructed using Visual MODFLOW to integrate the simulation calculations between the surface, the aeration zone, and the aquifer system. In addition, the contribution rates of different groundwater nitrogen pollution sources were calculated using the equilibrium formula combined with the groundwater nitrogen test results. The simulation results showed that the groundwater nitrogen in the southern part of the Wei River comes from two main sources: vertical infiltration and river recharge. Specifically, ammonia nitrogen vertical infiltration and river recharge contribute 95.82% and 4.18%, respectively; nitrite nitrogen vertical infiltration and river recharge contribute 92.41% and 7.59%; and nitrate nitrogen vertical infiltration and river recharge contribute 94.26% and 5.74%. According to the simulation results, an increase in the intensity of surface water pollution control is required in the study area. It is also necessary to control the use of nitrogen fertiliser on farmland in the study area and improve the utilisation rate of nitrogen fertiliser to reduce the nitrogen pollution loads from these sources.