Identification of driving factors and water quality evaluation of groundwater in Quanzhou City, a typical coastal area in Southeast China

Identifying the drivers and threats to coastal groundwater quality has emerged as one of the critical environmental and resource management issues. In this study, 140 shallow groundwater samples were collected from the coastal plain of Quanzhou City in China. Methods applied included mathematical statistics, correlation analysis, ionic ratio, isotope techniques, hydrochemical facies evolution diagrams (HFE-D), entropy weight water quality index (EWQI), health risk evaluation model and Monte Carlo simulation. The results demonstrated that the groundwater in the study area was neutral to weakly acidic, mainly soft water and fresh water. The groundwater chemical types were mainly composed of Cl-Na (37.86%), HCO3-Ca-Na (32.14%) and HCO3-Ca (27.86%). The natural sources of groundwater chemical composition were mainly controlled by the rock weathering, evaporation and cation exchange action. Nitrate with relatively high content in groundwater was found to originate mainly from anthropogenic inputs including domestic sewage and agricultural activities. The results of the stable isotope analysis showed the contributions of potential nitrate sources were 66.6%, 21.5%, 15.0%, and 2.5% for sewage and manure, soil nitrogen, synthetic fertilizer, and atmospheric deposition, respectively. The results of EWQI indicated that the overall groundwater quality of this study area was relatively good and suitable for domestic use. However, health risk evaluation based on Monte Carlo simulation showed that the probabilities of non-carcinogenic risk from groundwater nitrate were 4.31% for males, 5.71% for females, 13.93% for children and 25.80% for infants, respectively. The intake of high nitrate content groundwater via drinking pathway would pose a threat to the health of the local residents and require attention.