Stable isotope and hydrochemical evolution of shallow groundwater in mining area of the Changzhi Basin, northern China

The Changzhi Basin of China is an economically and ecologically important area with intensive human activities. To foster the sustainable development of groundwater resources and the economy, a total of 57 shallow groundwater samples were collected in shallow aquifers, including 46 H-2 and O-18 isotope samples, to improved understanding of the natural geochemical processes and the impacts of anthropogenic activities on the groundwater chemistry. Synthetical application of the multivariate statistical techniques, stable isotopes, Piper diagram, Gibbs diagram, ionic ratios and saturation indices to data analysis led to identification of hydrochemical zones for shallow groundwater from west to east of the basin. Three different water types had been identified using HCA in the study area. Isotopic analyses suggested that the groundwater recharge mainly comes from infiltration of rain water, hydraulic interaction between surface water and shallow groundwater, and lateral recharge from fissure water at the edge of the basin. The predominant natural geochemical processes include mineral dissolution in conjunction with the cation exchange. The excess deuterium method revealed that evaporation and mineral dissolution contributed 0.2-4.7% and 81-98% to the total salinity of shallow groundwater. Anthropogenic activities were secondary contributions to the hydrochemical evolution with fertilizer application, human waste and sewage discharges causing an increase in NO3-N content and coal mining activities affecting the ion content of Na+, Cl-, SO42-, and HCO3- in shallow groundwater.