Hydrochemistry and Isotope Hydrology for Groundwater Sustainability of the Coastal Multilayered Aquifer System (Zhanjiang, China)‎

Abstract EN

Groundwater sustainability has become a critical issue for Zhanjiang (China) because of serious groundwater level drawdown induced by overexploitation of its coastal multilayered aquifer system.

It is necessary to understand the origins, material sources, hydrochemical processes, and dynamics of the coastal groundwater in Zhanjiang to support its sustainable management.

To this end, an integrated analysis of hydrochemical and isotopic data of 95 groundwater samples was conducted.

Hydrochemical analysis shows that coastal groundwater is fresh; however, relatively high levels of Cl−, Mg2+, and total dissolved solid (TDS) imply slight seawater mixing with coastal unconfined groundwater.

Stable isotopes (δ18O and δ2H) values reveal the recharge sources of groundwater in the multilayered aquifer system.

The unconfined groundwater originates from local modern precipitation; the confined groundwater in mainland originates from modern precipitation in northwestern mountain area, and the confined groundwater in Donghai and Leizhou is sourced from rainfall recharge during an older period with a colder climate.

Ionic relations demonstrate that silicate weathering, carbonate dissolutions, and cation exchange are the primary processes controlling the groundwater chemical composition.

Declining trends of groundwater level and increasing trends of TDS of the confined groundwater in islands reveal the landward extending tendency of the freshwater-seawater mixing zone.