Hydro-biogeochemical processes of surface water leakage into groundwater in large scale karst water system: A case study at Jinci, northern China

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 delta O-18 and delta H-2 values together with C-14 ages of 3000-11,085 years. Several karst groundwater along the Fenhe River channel show remarkable enrichment of oxygen and hydrogen and young apparent C-14 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 delta S-34 values (1.8 parts per thousand-4.7 parts per thousand), depleted delta C-13 compositions (12.2 parts per thousand to 10.4 parts per thousand) and enriched delta O-18 and delta H-2 values. Karst groundwater in Hekou county show the highest contribution of coal mine drainage (36.4%) and moderate contribution of domestic sewage (8.6%).

Automated summary

This study investigated surface water leakage and anthropogenic inputs into karst groundwater in the Jinci karst system. The results showed that groundwater along the Fenhe River has been affected by oxygen and hydrogen enrichment, anthropogenic components, and nutrient leakage from surface water, leading to changes in the microbial community of the groundwater. The hydrogeochemical evolution in the study area is mainly controlled by dissolution of calcite, dolomite with gypsum, and dedolomitization, with contributions from coal mine drainage and unregulated disposal of domestic sewage.