Hydrogeochemical Investigations of Groundwater in the Lingbei Area, Leizhou Peninsula

Abstract

Groundwater is an important source of water supply in the Leizhou Peninsula. In August 2018, five surface water samples, 18 shallow pore water samples, 14 middle-deep pore water samples, and 27 pore fissure water samples were collected in the Lingbei area, the northern part of the Leizhou Peninsula. Major ion concentrations, as well as H, O isotope composition (of δ18O and δ2H) were analyzed. The results show that groundwater pH values, total hardness, concentrations of K+, TDS, Cl-, and SO42- are low, while H2SiO3(aq) and NO3- concentrations are relatively high. For pores and fissures water, hydrochemical types are mainly Mg-Ca-HCO3, Mg-Ca-HCO3-Cl, and Cl- loadings are significantly increased along the flow path. Ca-Cl, Na-Ca-HCO3-Cl, and Na-Ca-Mg-HCO3-Cl types predominate in shallow pore water. For middle-deep pore water, the types are primarily Mg-Ca-HCO3, Na-Ca-Mg-HCO3, K-Na-HCO3-SO4, and concentrations of K+, Na+, Cl-, and SO42- are modestly increased along the flow path. We find that the groundwater is of meteoric origin, groundwater Cl- and Na+ originate from marine atmospheric precipitation, Mg+, Ca2+, and HCO3- are mainly derived from silicate weathering, and NO3- principally arises from chemical fertilizer. Shallow pore water and fissure pore water are affected by evaporation concentration, whereas cation exchange is important for middle-deep pore water. The milligram equivalent ratio of nitrate in groundwater reaches 28.3%. After taking into account the nitrate, 50.85% of the sampling water is NO3 type, and displays a pollution trend. Our results contribute to the sustainable utilization of groundwater in the study area and other similar areas.