Tracing the sources of strontium in karst groundwater in Chongqing, China: a combined hydrogeochemical approach and strontium isotope

摘要

Groundwater quality in karst regions is largely controlled by natural processes and anthropogenic activities. Over the past 10 years, dissolved Sr and its radiogenic isotope, ~(87)Sr/~(86)Sr, were widely used to trace the sources of solutes in groundwater. However, there is little research about hydrogeochemistry and Sr isotopic compositions of the karst groundwater in Chongqing karst area. In this paper, thirty-five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO_3 type or Ca(Mg)-HCO_3 type. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the ~(87)Sr/~(86)Sr varied from 0.70751 to 0.71627. The groundwater samples from different aquifers and land use types showed distinctive dissolved Sr concentrations and ~(87)Sr/~(86)Sr. The very positive relationship between Ca/Sr and Mg/Sr in dolomite and limestone aquifers suggests that Ca, Mg and Sr element come mainly from the release of carbonate rock under the groundwater-rock-CO_2 gas interaction. According to the ~(87)Sr/~(86)Sr ratio, the Sr element in karst groundwater in Chongqing was controlled by the weathering of limestone, dolomite and silicate rock (allogenic water in a non-karst area). The relationship ~(87)Sr/~(86)Sr versus Sr~(2+)/[K~+ + Na~+] shows that the anthropogenic inputs also obviously contribute to the Sr contents. The research results show that the karst ground-water in Chongqing is facing serious crisis of water quality, and needs to be protected further.