Chemical Characteristics and Controlling Factors of Shallow Groundwater in the Lower Reaches of Changhua River Basin, Hainan Island, China

Abstract

In order to ensure a sustainable water resource for residents of the lower reaches of the Changhua River on Hainan Island, it is crucial to understand the chemical characteristics and formation mechanisms of their shallow groundwater. To achieve this, we collected and analyzed 100 groundwater samples using various methods. Our findings indicate that the groundwater is generally near-neutral to weakly alkaline, suggesting an oxidized environment. We identified 56 chemical types, with Ca•Na-HCO3 and Ca-HCO3 being the most common. Water–rock interactions—particularly with silicate rocks—are the primary factor influencing the water’s chemical characteristics, with Na+ and K+ coming from the leaching of silicate rocks, and Ca2+ and Mg2+ originating from the dissolution of carbonate rocks. Unfortunately, human activities such as agricultural practices and domestic sewage have had a significant impact on the groundwater, with NO3− levels surpassing SO42− in most samples. These findings provide valuable insights into the development and protection of the shallow groundwater in this area.