Hydrochemical characteristics and controlling factors of deep karst groundwater in Huaibei Plain, Huaihe River Basin, China

Introduction Deep karst groundwater is an important object for groundwater resources development and utilisation in the context of increasing water scarcity, as well as a potential threat of water hazards to the deep mining of hidden coalfields in Huaihe River Basin. Methods To elucidate the hydrochemical characteristics and controlling factors of deep karst groundwater, groundwater samples in Huaibei Plain were collected and discussed by comprehensively using mathematical statistics, the Piper trilinear diagram, Gibbs diagram, hydrogen and oxygen isotopes, saturation index, ion ratio relationship, and APCS-MLR receptor model. Results The absolute principal component score (APCS) with eigenvalues greater than 1 was extracted, where APCS1 could be defined as evaporite minerals and APCS2 could be defined as silicate minerals with a cumulative contribution of 88.63%. The linear fitting results showed that the R 2 values of were above 0.75 with the maximum value reaching 0.92, and the ratios of the measured values to the predicted values were generally close to 1, indicating that the analysis of the APCS-MLR receptor model were credible. Discussion The hydrochemical components of deep karst groundwater mainly came from three sources, including evaporite minerals, silicate minerals and unknown sources, and the contributions to the deep groundwater were 59.57%, 29.06% and 11.37%, respectively. The weathering and dissolution of evaporite minerals and silicate minerals were the main sources of the hydrochemical components, and also the main controlling factors for the hydrochemical evolution of deep karst groundwater in Huaihe River Basin.