5 years ago

Using hydrochemical, stable isotope and river water recharge data to identify groundwater flow paths in a deeply buried karst system

Baodong Xin, Xiaohong Wang, Wencai Liu, Yi Guo, Zhanfeng Zhao, Dajun Qin, Yong Yang, Yu Li, Muhammed Haji
The deeply buried river-connected Xishan Karst Aquifer (XKA)in western Beijing, China, hasbeen suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, thehydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km2. Results show that, (1)the river wateris characterized by high Na contents; (2) theδ2H and δ18O values in the river water are distinctively higher than those of groundwater samples, afterexperiencingthe long-time evaporative enrichment in the upstream reservoir; (3)theSr concentrations and 87Sr/86Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals, but excluded the water–silicate interaction; and (4) the groundwater samples in the direct recharge area of the XKA has the lowest Na concentrations as well as the δ2H and δ18O values. Based on the large differences in the Na contents and 18O values of groundwater and surface water, a simple two-component mixing model is developed for the study area andthe fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwaterfrom its source zone to the discharge area.Overall, our results suggest that the recharged surface water can be a useful evidence for delineation the groundwater flow path in river-connected karst aquifer.This studyimprovesour understanding of the heterogeneity in karst groundwater systems.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/hyp.11356

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