Hydro-biogeochemical processes of surface water leakage into groundwater in large scale karst water system: A case study at Jinci, northern China
2021
Li, Chengcheng | Gao, Xubo | Wang, Wanzhou | Zhang, Xin | Zhang, Xiaobo | Jiang, Chunfang | Wang, Yanxin
Surface water leakage and anthropogenic inputs into groundwater prevail in karst areas in China. In this paper, surface and ground water were collected and multiple isotopic tracers were integrated with hydrogeochemical parameters to characterize the residence time, recharge history, biogeochemical processes, surface leakage and anthropogenic influences in Jinci karst system. Most karst groundwater have depleted δ¹⁸O and δ²H values together with ¹⁴C ages of 3000–11,085 years. Several karst groundwater along the Fenhe River channel show remarkable enrichment of oxygen and hydrogen and young apparent ¹⁴C ages (60–1845 years), signifying recently communicating with surficial environment. Major anthropogenic components in the surface water (Na⁺, Cl⁻ and NO₃⁻) and nutrients leak into groundwater along Fenhe River. Additionally, surface water leakage changes the microbial community in phylum and family levels for groundwater. The calculated river water leakage flux for the possible affected groundwater range from 61% to 87%, with the highest serious leakage found in Hekou county. Dominated by Ca²⁺, Mg²⁺, HCO₃⁻ and SO₄²⁻, the hydrogeochemical evolution of surface and ground water in the study area are largely controlled by dissolution of calcite, dolomite with gypsum and dedolomitization. Discharge of coal mine drainages and unregulated disposal of domestic sewage also contribute substantially to the groundwater hydrogeochemistry along the river leakage section, confirmed by lower δ³⁴S values (1.8‰–4.7‰), depleted δ¹³C compositions (−12.2‰ to −10.4‰) and enriched δ¹⁸O and δ²H values. Karst groundwater in Hekou county show the highest contribution of coal mine drainage (36.4%) and moderate contribution of domestic sewage (8.6%).
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