Hydrogeochemical characterization of groundwater quality in the Weining Plain, northwest China

The Weining Plain relies heavily on groundwater to support human livelihoods and economic development. This research investigated the hydrochemical characteristics of groundwater in the Weining Plain, analyzed the processes controlling the changes in groundwater quality using multivariate statistics and graphical methods, and quantified the extent of the influence of water-rock interactions on the hydrochemical evolution by means of hydrogeochemical modeling. The results point to that the concentration sequence in which the dominant groundwater constituents in the Weining Plain unfold as follows: Na⁺>Ca²⁺>Mg²⁺>K⁺ among cations, while HCO₃⁻>SO₄²⁻>Cl⁻>CO₃²⁻ among anions, with hydrochemical types primarily categorized as SO₄·Cl–Ca·Mg, SO₄·Cl–Na, and HCO₃–Ca·Mg. Also, it revealed severe nitrate pollution in the region, with most groundwater not meeting drinking water standards. Principal component analysis identified that a combination of natural factors and human activities makes a difference in determining the quality of groundwater in the region. The water-rock processes are the primary natural controlling factor, coupled with strong shallow groundwater evaporation, which significantly regulate groundwater chemical changes, while human activities exacerbate groundwater chemistry degradation. Hydrogeochemical modeling of PHREEQC highlights that the dissolution of anorthite dominates the left bank path of the Yellow River with 5.32 mmol/L, whereas the cation exchange is significant in the right bank path, with 4.32 mmol/L of Na⁺. The dissolution of halite, gypsum, anorthite, coupled with cation exchange from Ca²⁺ to Na⁺, are key hydrogeochemical reactions driving changes in groundwater quality within the study region. This study provides a solid scientific basis for the management of groundwater resources in the region.