Spatiotemporal modelling of groundwater flow and nitrate contamination in an agriculture-dominated watershed

In this study, both groundwater flow and nitrate transport were simulated in the Upper White River Watershed (Indiana, US) dominated by agricultural production. MODFLOW and MT3DMS were used for groundwater flow and contaminant transport modelling of the watershed under transient conditions. The input files for MODFLOW and MT3DMS were obtained by the GMS groundwater simulator. Model simulations were performed for 25 years between 1995 similar to 2019 with one-year intervals. Groundwater observation data (hydraulic heads and nitrate concentrations) for 1995 similar to 2013 and 2014 similar to 2019 were used for the model calibration and validation, respecttively. A heuristic optimization model based on the modified Clonal Selection Algorithm (a class of Artificial Immune Systems) was improved for calibration of the groundwater contaminant transport model. MODFLOW and MT3DMS were linked with the algorithm and run in MATLAB. Based on land use/cover, recharge and recharge nitrate concentrations were calibrated while other groundwater parameters (storage, porosity, longitudinal dispersivity, and denitrification rate coefficients) were calibrated for 7 aquifers. Furthermore, the models were run for different scenarios representing possible future conditions. The results demonstrated that the models performed well in terms of the fate and transport of nitrate in the Upper White River Watershed.