Hydrochemical Characteristics and Genetic Analysis of Groundwater in Zhanjiang City, Guangdong Province, South China

Groundwater serves as a vital water source in Zhanjiang City. This study analyzed the chemical components of 35 samples to understand the hydrochemical characteristics and evolution mechanism of groundwater in Zhanjiang City. A comprehensive analysis was conducted using statistical methods, including the use of Piper trilinear diagrams, the Gibbs method, ion ratios, and other techniques, to investigate the sources and control factors of the main ions in groundwater in the area. The findings reveal that all the groundwater is freshwater, with the main cations and anions being Na+ and HCO3−, respectively. Shallow water is mainly of the Cl•SO4 mixed cation type, followed by the HCO3•ClNa•Ca type. Middle and deep pore water is mainly of the HCO3Na type, followed by the HCO3Na•Mg type and HCO3Na•Ca type. The hydrochemical classifications of pore and fissure water are Cl•HCO3Mg•Na type and Cl•HCO3Na type water. The primary hydrogeochemical process is water–rock interaction, particularly the dissolution of silicate minerals. Additionally, evaporation and concentration contribute significantly to the chemical composition of shallow water, and ion exchange is also an important hydrogeochemical process affecting middle and deep pore water. Shallow water commonly contains nitrates, with 37.5% of shallow water showing contamination with NO3−. This study aims to provide insights into the development and utilization of local water resources.