干旱区生态环境知识资源中心

Karst groundwater is the major source of water supply for economic development and drinking water in Liulin spring area, north China. Thus, karst groundwater quality and its variation have aroused wide public concern. The primary hydrogeochemical processes that dominate karst groundwater quality, including dissolution of carbonate rocks and evaporite, mixing, and dedolomitization, are analyzed by hydrogeochemical method in combination with multivariate statistical theory and computer simulation technology. The results show that the redox state of groundwater environment transforms gradually from oxidation state to reducing state with increasing temperature and total dissolved solids (TDS) and decreasing pH value along flow path. The hydrogeochemical types of groundwater range from HCO3-Ca center dot Mg to Cl center dot SO4-Na. The Ca2+, Mg2+, and HCO3 (-) in karst groundwater mainly originate from dissolution of calcite and dolomite. Dissolution of calcite occurs in infiltration of rainfall into soils and unsaturated zones and then reaches to saturation before arriving groundwater level. Though saturation index of dolomite (SID) is greater than 0 in most of the samples, dolomite still dissolves along flow path due to the dedolomitization. The SO4 (2-) derives basically from the dissolution of gypsum rather than oxidation of pyrite. The dissolution of gypsum causes dedolomitization that increases the concentrations of Ca2+, Mg2+, and SO4 (2-) while the concentration of HCO3 (-) has smaller changes. The concentrations of Na+ and Cl- are mainly controlled by dissolution of halite. The enrichment of Na+ relative to Cl- in most samples may result from leakage of surface water enriched Na+ and dissolution of mirabilte fragments.