ABSTRACT High concentrations of ammonia nitrogen (NH4+–N) are a dominant water pollutant in ionic rare earth mining basins, threatening aquatic ecosystems and drinking-water safety. To quantify these dynamics, this study developed a coupled SWAT–WASP model for the upper Dongjiang River Basin (UDRB), integrating remote sensing and long-term monitoring data; the model was calibrated and validated with 2016–2018 monthly observations, and quantitative evaluation via Nash–Sutcliffe Efficiency (NSE) and Percent Bias (PBIAS) showed good performance (runoff: NSE = 0.77–0.80; NH4+–N: SWAT NSE = 0.56–0.61, SWAT–WASP NSE = 0.65–0.87), confirming its reliability. 2022 simulations revealed strong NH4+–N spatial heterogeneity, with concentrations 1.8 mg L−1 near mining zones versus 0.5 mg L−1 in upstream natural areas; geodetector analysis identified population density combined with industrial–agricultural activity as the top driver of spatial differentiation (q 0.40), while interactions between precipitation, temperature, and land use further amplified variability. Overall, the SWAT–WASP framework provides a robust tool for evaluating NH4+–N dynamics and supports targeted pollution control and ecological restoration in rare earth mining watersheds.
Wu et al. (Mon,) studied this question.