Application of MT3DMS and Geographic Information System to Evaluation of Groundwater Contamination in the Sherwood Sandstone Aquifer, UK

摘要

Groundwater quality usually correlated with different land use types. As Britain's second largest aquifer, the Sherwood Sandstone is confronted by the threat of high nitrate concentrations caused by intensive agricultural activities. The aim of this study is to estimate nitrogen loss on the aquifer outcrop and to predict nitrate concentration in groundwater in the future appropriately. GIS was used in the study for spatial analysis of land use data, pre-processing nitrate inputs for a groundwater model. An export coefficient model was adopted to help estimation of nitrogen losses in the study area. A groundwater flow and mass transport model was constructed and calibrated to groundwater level in 45 monitoring points and nitration concentration in 22 public supply boreholes, respectively. Then, the calibrated model was used to predict nitrate concentrations in groundwater boreholes to explore nitrate trend in the future under current land use mode and agricultural practice. The simulative results show that even if some moderate mitigation methods are adopted, nitrate concentrations in boreholes would increase in the future (before eventually decreasing) and fail to meet water quality standards (50 mg NO_3/L). The nitrate concentration would reach 73 mgL~(-1) in selected borehole by December 2025 unless more radical changes in land use were adopted. It is concluded that a time scale of several decades may be considered for the sandstone aquifer in the context of nutrient management and nitrate mitigation in order to achieve improvements in water quality.