Spatial and temporal characteristics of isotopes of different water sources and implications for water circulation in mining areas

This study aimed to characterize the temporal and spatial variation in isotopes of different water sources of the Pingshuo mining area to identify the significance of coal mining activities to the regional water cycle. Surface water, groundwater, and mine water samples were collected in August and December, 2020. The hydrogen and oxygen stable isotopes of the samples were measured and analyzed. The contributions to mine water from different water sources were calculated using the MixSIAR Bayesian mixed model. The results indicate that the summer δD and δ¹⁸O isotopes of surface water and mine water exceeded those in winter. There was no obvious seasonal difference in groundwater δD and δ¹⁸O. Hydrogen and oxygen isotopes of surface water increase along the flow path, but were partially depleted in mine water. The hydrogen and oxygen isotopes of groundwater gradually increased along the direction of runoff. Hydrogen and oxygen isotopes of water in the coal mining area exceeded those in the non-mining area. Seasonal effects resulted in the area of high shallow groundwater hydrogen and oxygen isotopes in August significantly exceeding those in December. Plotting of δD and δ¹⁸O showed that surface water was affected by evaporative fractionation after being recharged by atmospheric precipitation. Sources of recharge of shallow groundwater were more complex. Deep groundwater was recharged by shallow groundwater and surface water through infiltration of the fracture zone formed by coal mining. Mine water was recharged by surface water, shallow groundwater, and deep groundwater. Deep groundwater was the main source of mine water recharge, accounting for 61.60% to 67.20% of total mine water recharge, with its contribution higher in winter than in summer. Recharge of mine water by shallow groundwater demonstrated significant seasonal differences.