Integration of HYDRUS-1D and MODFLOW for evaluating the dynamics of salts and nitrogen in groundwater under long-term reclaimed water irrigation
2019
Lyu, Sidan | Chen, Weiping | Wen, Xuefa | Chang, Andrew C.
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.
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