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<p>Saline groundwater poses significant challenges for freshwater use in the eastern coastal area of the Jeju volcanic island, South Korea, also being utilized for industrial purposes such as aquaculture and the production of food and beverages. Ensuring the sustainable use of saline groundwater requires effective water management based on a comprehensive understanding of fresh–saltwater mixing dynamics. This study investigates the hydrogeochemical processes and salinization mechanisms in the eastern coastal region of Jeju Island through integrated analysis of water chemistry, stable water isotopes (δ<sup>1</sup><sup>8</sup>O and δD), and an age tracer (<sup>3</sup>H). The relationships between the major ions with Cl<sup>−</sup> indicate that the salinity of groundwater was primarily driven by simple seawater mixing, with the degree of mixing significantly influencing water chemistry across different salinity groups: freshwater (FZ), fresh–saltwater transition (FSTZ), and saline (SZ) zones. The FZ samples exhibited depleted δ<sup>1</sup><sup>8</sup>O values (−7.2‰ to −6.9‰) and high <sup>3</sup>H concentrations (2.6–4.0 TU), indicating relatively young groundwater recharged by recent local rainfall. In contrast, the FSTZ and SZ samples showed enriched δ<sup>1</sup><sup>8</sup>O values (−6.5‰ to 0.1‰) and low <sup>3</sup>H concentrations (1.2–2.8 TU), reflecting the mixing of modern seawater (δ<sup>1</sup><sup>8</sup>O: 0.3‰; <sup>3</sup>H: 1.5 TU). Notably, several inland FSTZ and SZ samples showed lower <sup>3</sup>H concentrations than expected based on the seawater mixing ratios, likely due to longer residence times during the circulation of the saltwater wedge. These samples also had higher SiO₂ concentrations than the other seaward samples, resulting from prolonged basaltic mineral dissolution as the contact time with the coastal aquifer medium increased. Overall, the hydrogeochemical characteristics of the saline groundwater in the study area were influenced by simple mixing with modern seawater, which was recharged by upstream fresh groundwater, and the increased dissolution of basaltic minerals during the circulation of the saltwater wedge in the coastal aquifer system.</p>

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Hydrogeochemical and isotopic interpretation of fresh–saltwater interactions in the coastal aquifer of Jeju volcanic island, South Korea

  • 期刊论文

  • 发表日期：

    2025年2月27日

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  • Eun-Hee Koh,
  • Ki-Ju Kim

摘要

Saline groundwater poses significant challenges for freshwater use in the eastern coastal area of the Jeju volcanic island, South Korea, also being utilized for industrial purposes such as aquaculture and the production of food and beverages. Ensuring the sustainable use of saline groundwater requires effective water management based on a comprehensive understanding of fresh–saltwater mixing dynamics. This study investigates the hydrogeochemical processes and salinization mechanisms in the eastern coastal region of Jeju Island through integrated analysis of water chemistry, stable water isotopes (δ18O and δD), and an age tracer (3H). The relationships between the major ions with Cl− indicate that the salinity of groundwater was primarily driven by simple seawater mixing, with the degree of mixing significantly influencing water chemistry across different salinity groups: freshwater (FZ), fresh–saltwater transition (FSTZ), and saline (SZ) zones. The FZ samples exhibited depleted δ18O values (−7.2‰ to −6.9‰) and high 3H concentrations (2.6–4.0 TU), indicating relatively young groundwater recharged by recent local rainfall. In contrast, the FSTZ and SZ samples showed enriched δ18O values (−6.5‰ to 0.1‰) and low 3H concentrations (1.2–2.8 TU), reflecting the mixing of modern seawater (δ18O: 0.3‰; 3H: 1.5 TU). Notably, several inland FSTZ and SZ samples showed lower 3H concentrations than expected based on the seawater mixing ratios, likely due to longer residence times during the circulation of the saltwater wedge. These samples also had higher SiO₂ concentrations than the other seaward samples, resulting from prolonged basaltic mineral dissolution as the contact time with the coastal aquifer medium increased. Overall, the hydrogeochemical characteristics of the saline groundwater in the study area were influenced by simple mixing with modern seawater, which was recharged by upstream fresh groundwater, and the increased dissolution of basaltic minerals during the circulation of the saltwater wedge in the coastal aquifer system.