Hydrogeochemical Characteristics and Sulfate source of Groundwater in Sangu Spring Basin

Abstract

Sangu Spring Basin is located in an important economic area，and groundwater is the main source of water for local life and industry. Understanding the sources of chemical components in groundwater is important for the development and utilization of groundwater. In this paper, we analyzed the origin of the chemical components of groundwater and their evolution in the Sangu Spring Basin using statistical analysis, Piper diagram, Gibbs diagrams, ion ratios, and combined hydrochemistry-isotope analyses. The results show that groundwater is the origin of atmospheric precipitation, the groundwater in stagnant and confined environment zones is formed under colder climatic conditions, and the surface water (SW) has a close hydraulic relation with the groundwater. Water-rock interaction is the main factor controlling the composition of groundwater. The compositions of groundwater are mainly derived from carbonate weathering, silicate weathering and dissolution of gypsum. Na+ and K+ in groundwater mainly come from the dissolution of albite and potassium feldspar, rather than rock salt. Ion exchange occurs in KGW and FGW, and the ion exchange is dominated by the exchange of Mg2+ and Ca2+ in the groundwater by Na+ and K+ in the rock or soil. De-dolomitization of KGW in deeply buried and stagnant flow zones occurred, causing elevated Mg2+ and SO42- concentrations. Nitrates and chlorides in groundwater are affected by a combination of agricultural activities, industrial activities, and weathering of rocks. Sulfate in groundwater is derived from dissolution of gypsum, infiltration of atmospheric precipitation and leakage of SW. Groundwaters with the highest sulfate content are located in the vicinity of SW, as a result of receiving recharge from SW seepage. Groundwaters with higher sulfate contents are located in the stagnant and deeply buried zones, where sulfate is mainly derived from the dissolution of gypsum. SW seepage recharges groundwater, resulting in the increased levels of Cl-, NO3- and SO42- in groundwater. These insights can provide assistance in groundwater protection and effective management.