Evaluation of groundwater geochemical characteristics and quality in the central and Northern Shaanxi Province,China

Groundwater is of vital importance to many aspects of ecosystem services,especially in the central and northern Shaanxi Provence,China,-an area covered by loess deposits and short of water resources.We studied the solute geochemistry and water quality of groundwater in this area to improve the understanding of hydrogeochemical processes in loess deposits area.The results showed that the average pH of groundwaters was 8.03±0.36(1 SD)with large ranges(324-83,379 mg/L)of the total dissolved solids(TDS).The cations and anions followed the order of Na^+>Ca^2+>Mg^2+>K^+>SiO2 and HCO3>Cl^->SO4^2->F^->NO3^-.Most groundwater samples show the HCO3^--Na^+-Ca^2+water type and a small number of samples the Na^+-Cl^-type.Irrigation water quality assessments showed that 40%of the groundwater has good water quality,42%moderate water quality,and 18%(the upper reaches of Wuding River and Wei River)poor water quality with very high salinity.About 40%of groundwater samples were not suitable for drinking due to the high TDS,fluoride,sulfide,and chloride.Gibbs plot and stoichiometry analysis showed that carbonate weathering is the main source of groundwater chemistry in central Shaanxi Province while evaporite dissolution dominates in northern Shaanxi Provence.The loess weathering significantly influences the dissolved solutes of groundwater in the Loess Plateau.The ion-exchange between Mg^2+and Ca^2+in groundwater and Na^+in clay minerals and the deposition of carbonate minerals increased Na^+but decreased the Ca^2+in groundwater.Our research results improve our understanding of hydrogeochemical processes that affect the solutes chemistry of groundwater in the loess area and provide essential data to the global groundwater database.