Simplified Lumped Groundwater Model to Simulate Nitrate Concentration Dynamics

Abstract

Modeling of the nitrate concentration in groundwater can help ensure proper groundwater management and utilization, especially as a drinking water supply. Here, a groundwater nitrate tank model (GNTM) is proposed to simulate nitrate concentrations in groundwater. The variables used to calibrate and validate the model were daily rainfall and weekly nitrate concentration data recorded from June 2012 to February 2016 at two representative observation wells (W1 and W2) in Kumamoto, Japan. The observed nitrate concentrations range from 4.46 to 6.02 mg-N/L, and 8.60 to 24.56 mg-N/L in Wells W1 and W2, respectively. The Shuffled Complex Evolution–University of Arizona algorithm was used to determine the best-fit parameter values according to the root-mean-square error (RMSE). Calibration and validation results were evaluated by calculating the Nash-Sutcliffe efficiency coefficient (NSE) and the RMSE. The GNTM accurately reproduced nitrate concentration fluctuations: during the validation period the values of RMSE were 0.135 and 1.432 and NSE were 0.821 and 0.661 in Wells W1 and W2, respectively. These results indicate that this model provides a simple way to accurately simulate nitrate concentrations in groundwater.