Groundwater nitrate contamination, coupled with long-term overexploitation and intensive anthropogenic perturbations, has become a critical environmental challenge in the northwestern North China Plain, underscoring the urgent need to elucidate groundwater hydrochemical characteristics and their genetic mechanisms. Taking the upper section of the Yongding River alluvial–proluvial fan as the study area, this research aims to quantitatively decipher the hydrochemical characteristic and genetic mechanism of high-nitrate groundwater, identify the sources of nitrate contamination, and assess the associated human health risks. By leveraging over a decade of continuous hydrochemical monitoring data, an integrated analytical approach is adopted, including hydrochemical ionic ratio analysis, Positive Matrix Factorization, and Human Health Risk Assessment. The results indicate that the groundwater is characterized by HCO3-Ca. The pH values range from 7.2 to 8.2 while the total dissolved solids concentrations vary between 695 mg/L and 949 mg/L. Ionic ratio analysis demonstrates that water–rock interaction is the dominant controlling process, involving silicate hydrolysis, dissolution of carbonates, gypsum dissolution, and cation exchange. The Positive Matrix Factorization model quantitatively identifies four key factors controlling the hydrochemical characteristics of groundwater. Factor 1 is dominated by NO3− (76.67%) and associated with exogenous nitrate inputs from nitrogen fertilizer application. Factor 2 is dominated by Na+ (72.26%) and Mg2+ (81.67%), deriving from silicate weathering and dolomite dissolution. Factor 3 is governed by pH (59.62%) and K+ (71.65%), with its driving mechanism being the weathering and dissolution of potassium-bearing silicate minerals. Factor 4 is dominated by SO42− (50.12%) and constitutes a mixed source associated with sulfur-containing fertilizer application and livestock breeding. Groundwater NO3− concentrations range from 4.2 mg/L to 23.3 mg/L, with 69% of dry-season and 77% of wet-season samples exceeding the 10 mg/L threshold, primarily originating from manure and domestic wastewater. HHRA results show that nitrate poses significant non-carcinogenic health risks, with the highest risk observed in children (100% of samples at high risk), followed by adult females (92% at high risk) and adult males (77~92% at high risk). This study provides quantitative insights into the genetic mechanisms of groundwater nitrate contamination and offers a scientific basis for groundwater quality management and health risk mitigation in the NCP and other similar agricultural regions worldwide.
Yang et al. (Mon,) studied this question.
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