Abstract: The spatial and temporal distribution characteristics of the major elements in water body reflects its chemical,physical,and biological processes.The assessment of the concentration of main ions and their spatio-temporal variation can provide important evidence in understanding the elements distribution and the cycle of matter of the water body.In this study,we collected 95 shallow groundwater samples from different regions of Shanxi Province,China during different seasons in 2015 and 2016.According to the results of the average concentrations of major ions and pH value,the hydrochemical characteristic of shallow groundwater were analyzed and the temporal and spatial variation for the concentration of each major ion was revealed using the methods of descriptive statistics,spatial interpolation analysis,Gibbs diagram and Piper diagram.The results indicated that the groundwater as a whole belongs to the fresh water and the water quality was good.A significant spatial variation was found in the TDS (Total Dissolved Solids) of the shallow groundwaters.Higher TDS was observed in the central region and southwestern region of Shanxi Province and it was changed with the season.While in the northwestern and southeastern regions of Shanxi Province,the TDS of shallow groundwaters is relatively lower and its seasonal variation is not obvious.The concentrations of the Na⁺,Ca²⁺ were higher than that of other cations and the HCO₃^- concentration was higher than that of other anions.Compared with the dry season,the concentration of the Na⁺ and Cl^- in the shallow groundwater in the wet season showed a significant increasing trend,which might be affected by topography and seasonal precipitation.There were multiple hydrochemical types observed in the shallow groundwater samples,which can be classified into HCO₃^--Ca²⁺ type,HCO₃^--SO^2-₄-Na⁺ type,HCO₃^--SO^2-₄-Ca²⁺-Na⁺ type and HCO₃^--Cl^--Na⁺ type.Based on the Gibbs analysis,the main ions were mainly affected by rock weathering process.The anthropogenic influence and evaporation effects were observed in the shallow groundwater samples in the central basin area.There was a significant seasonal variation on the ions concentrations.Compared with the dry season,the concentrations of Na⁺ and Cl^- were significantly increased in the wet season which might be affected by the soil eluviation.The knowledge of these can promote effective management of water resources.

Key words: shallow groundwater, hydrochemical type, temporal and spatial variation, controlling factor, Shanxi Province