The evaluation and prediction of agriculture-related nitrate contamination in groundwater in Chengdu Plain, southwestern China

The aquifer beneath Chengdu Plain is a main water resource for drinking and industry, which has severe groundwater nitrate contamination due to the shallow water table and intensive agricultural activities. The aim of this study is to estimate nitrogen loading to the aquifer and to predict nitrate concentration in groundwater in response to changes in land-use and agricultural practices, i.e. nitrogen fertilizer application, in Jingyang region' of the Chengdu Plain, one of the most developed agriculture areas in southwestern China. The framework utilized a geographic information system to account for the spatial and temporal distribution of on-ground nitrogen sources and corresponding loadings, and employed an export coefficient model to estimate the corresponding nitrogen loss. The simulation of nitrate fate and transport in the aquifer was conducted by developing a groundwater mass transport model using MODFLOW and MT3DMS. A number of predictive simulations for year 2026 were carried out to evaluate the impact of land-use and proposed future management options on controlling groundwater nitrate contamination. The results show that a nitrate plume would extend over most of the study area with some local areas having concentrations exceeding 20mgL(-1) under the current setting and the scenario of increasing agricultural land use. Reduction in fertilizer application rates did mitigate nitrate contamination; however, this effect diminished with the expansion of agricultural land use. Land-use planning should consider the significant effects of agriculture to improve the quality of groundwater in the Chengdu Plain.