LAUSR

Reclaimed water has been extensively used as an alternative resource for irrigation, but can affect groundwater quality due to salt and nitrogen leaching. We conducted field investigations of a shallow groundwater monitoring well at the Research Center for Eco-Environmental Sciences, China, and irrigated sample sites of turf grass with reclaimed water for 8 years. The HYDRUS-1D and MODFLOW models were integrated to study the transport and distribution of electrical conductivity (ECgw) and nitrate–N (N–NO3−) in the shallow groundwater under long-term reclaimed water irrigation. Model calibration and validation showed that the integrated model could simulate the fates of ECgw and N–NO3− in the shallow groundwater. Field experiments and the model simulation showed that reclaimed water irrigation can increase salinity and N–NO3− concentration in shallow groundwater and predicted, assuming the continuation of current irrigation practices, that the annual average ECgw and N–NO3− would reach a steady level of 0.72 dS m−1 and 2.18 mg L−1, respectively. Because ECgw increased with increasing irrigation water salinity and amount, there is a risk of increased salinity in the shallow groundwater under long-term reclaimed water irrigation. Under all simulation scenarios, annual average N–NO3− concentrations in the shallow groundwater at an equilibrium state did not exceed the class II groundwater quality standard (2–5 mg L−1). After proper calibration and validation, the integration of HYDRUS-1D and MODFLOW models offers an effective tool for analyzing irrigation management of low-quality water in water-scarce regions.