Hydrogeochemical and isotopic evidence for flow paths of karst waters collected in the Heshang Cave, Central China

Abstract

Understanding of hydrological processes in caves is important to help us interpret paleoclimate records from speleothems. In this study, we integrated hydrogeological and hydrogeochemical properties to characterize the hydraulic behavior of karst waters in the Heshang Cave, Central China. Using geological and topographical analyses, we identified regional watershed boundaries and hydrogeological connections that were controlled by anticlinal geometry and faults. Water samples were collected from the Heshang Cave and potential recharge sites. Geochemical data of c(Sr²⁺)/c(Ca²⁺) and c(Mg²⁺)/c(Ca²⁺) ratios suggest that the drainage system in Heshang Cave consists of two flow paths. For vadose waters, including drip water and rimstone pool water, c(Sr²⁺)/c(Ca²⁺) ratio ranges from 0.000 6 to 0.001 1, and c(Mg²⁺)/c(Ca²⁺) ratio ranges from 0.97 to 1.1, indicating that recharge was mainly from rainfall infiltration through the overlying Cambrian dolomite stratum. In contrast, slope current and underground river waters have higher c(Sr²⁺)/c(Ca²⁺) ratios (values from 0.002 2 to 0.002 8), and lower c(Mg²⁺)/c(Ca²⁺) ratios (values from 0.50 to 0.64). These waters show homogeneous isotopic composition (δ¹⁸O: −7.15‰–−6.95‰; δD: −52.73‰–−51.31‰), implying recharge of allogeneic water from the Xiaoer River via karst conduits that pass through Ordovician limestone and Cambrian dolomite stratum.

Keywords

karst water / hydrogeochemistry / stable isotope / flow path / Heshang Cave

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