Risk assessment of shallow groundwater contamination under irrigation and fertilization conditions

Due to extensive agricultural irrigation and fertilization, China now faces a severe problem of non-point source groundwater contamination. In this paper, the Daxing district of Beijing, a typical agricultural area with high fertilizer application, is chosen as the study area. With the consideration of intrinsic vulnerability and nitrate contamination load of groundwater, DRASTIC-based methodology was used to establish a GIS-based groundwater contamination risk assessment model, namely DRSIN model. The DRSIN model contains five parameters: depth to groundwater (D), net recharge (R), soil type (S), impact of the vadose zone (I) and nitrogen (N). By employing cluster analysis and fuzzy synthetic evaluation, the influence of agricultural non-point source contamination of groundwater on the formation of nitrate contamination was discussed under the existing conditions and 11 different irrigation and fertilization scenarios. The results show that the groundwater contamination risk in the north and east of Daxing District is higher than that in the south and the west, which conforms to the monitoring results of nitrate nitrogen content in groundwater. This indicates the need for reasonable groundwater utilization and protection planning to reduce agricultural non-point source contamination. Groundwater contamination risk decreases most significantly under the scenario of irrigation amount reduced by 25 %, nitrogen application reduced by 25 % and groundwater depth increased by 5 m. The findings provide data for reasonable groundwater development and utilization in this area.