1898 / 2019-08-30 14:55:22

Groundwater salinization in deep aquifers constrained by isotopic and minor elements in the Yuncheng Basin, northern China

12、水文地质与水科学 > 专题4：污染水文地质及水化学过程

In this study, we establish the origin of saline groundwater in deep aquifers at Yuncheng Basin, through field studies in 2015 and by using major, trace elements and multiple isotopes (oxygen, hydrogen, sulfur, carbon and strontium). The TDS contents of deep groundwater samples from Yuncheng Basin range from 230 to 1,720 mg/L, and 50% of the samples are saline (TDS > 1,000 mg/L). The δ18O and δ2H data indicate that these deep groundwater are recharged during a previous wetter and/or cooler period and the paleo-temperature is approximately 3 °C cooler than the modern temperature. Groundwater ages estimated from 14C activities further indicate that these deep groundwater mostly recharge between c. 5000 and 11000 years ago in the late Pleistocene and the early Holocene.
Three types of saline sources for deep groundwater are delineated in the Yuncheng Basin. The correlation between groundwater Br/Cl and B/Cl molar ratios reflects the dominant effects of freshening of depleted-δ18O and δ2H palaeo-saline waters on locally distributed groundwater salinity in the Qiji and Wenxi. Saline groundwater sampled near the faults show strong evidences of a geothermal origin, while downward vertical leakage of shallow saline groundwater suffering from pyrite oxidation contributes to elevation of TDS contents in deep groundwater near the depression cone.
Major ion chemistry and δ34S data reflect the important impact of evaporite salts dissolution on groundwater salinization. Strontium and carbon isotopes indicate that substantial DIC and Sr in groundwater are derived from carbonate dissolution. In spite of the ample evidences of carbonate weathering, groundwater is Na-rich and Ca-poor. This is due to cation exchange, removing Ca and enriching Na contents during flow through the aquifer. Bacterial sulfate reduction results in low salinities in deep groundwater in the E’mei Plateau, although the effect of BSR is masked by the strong influence of carbonate weathering to a certain extent. Groundwater in the southern part of Zhongtiao Mountain has much lower Sr concentrations and higher 87Sr/86Sr ratios than those in other groundwater, indicating that silicate minerals may contribute small amounts of Sr in the groundwater from the recharge area.