Long-term monitoring of hydrochemical characteristics and nitrogen pollution in the groundwater of Yinchuan area, Yinchuan basin of northwest China

Abstract

Research on the hydrochemical characteristics of groundwater can help to elucidate its evolution and distribution, as well as other hydrogeological conditions. The present study investigated the current status of groundwater hydrochemistry and nitrogen contamination in Yinchuan area, Yinchuan basin of northwest China. Piper and Gibbs diagrams were constructed and multivariate statistical methods were used to explore the groundwater hydrochemical characteristics and its controlling factors, as well as nitrogen contamination of groundwater and its sources. The results demonstrated that phreatic water was moderately salty with a large variation of TDS and major ion concentrations, while the confined water was mainly fresh water with TDS less than 1000 mg/L. Phreatic water was mainly HCO3·Cl–Na·Mg and HCO3·SO4–Na·Mg types, while the confined water was HCO3·Cl–Na·Ca and HCO3·SO4–Na·Ca types. The major ion chemistry of the confined water is governed by water–rock interactions, while evaporation plays a key role in phreatic water chemistry formation. Furthermore, the concentration of NO3− in phreatic water is significantly higher than that of confined water, and the opposite was observed for NH4+. The concentrations of NO3− and NH4+ exhibited an increasing tendency in groundwater in the last 26 years. The nitrogen sources in phreatic water involved human activities like nitrogen fertilizer application in agriculture, and industrial and domestic sewage. In confined aquifer, the higher NH4+ concentration is comprehensively affected by hydrogeological conditions, leakage of phreatic water and an anaerobic environment. Overall, the results of the present study are helpful for the groundwater protection in Yinchuan area, and will contribute to the effective management and reasonable development of groundwater resources in Yinchuan basin.