Details

Autor(en) / Beteiligte

• Bauer, Jonas
• Börsig, Nicolas
• Pham, Van Cam
• Hoan, Tran Viet
• Nguyen, Ha Thi
• Norra, Stefan

Titel

Geochemistry and evolution of groundwater resources in the context of salinization and freshening in the southernmost Mekong Delta, Vietnam

Ist Teil von

• Journal of hydrology. Regional studies, 2022-04, Vol.40, p.101010, Article 101010

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2022

Link zum Volltext

Quelle

EZB-FREE-00999 freely available EZB journals

Beschreibungen/Notizen

• Ca Mau Province (CMP), Mekong Delta (MD), Vietnam. Groundwater from deep aquifers is the most reliable source of freshwater in the MD but extensive overexploitation in the last decades led to the drop of hydraulic heads and negative environmental impacts. Therefore, a comprehensive groundwater investigation was conducted to evaluate its composition in the context of Quaternary marine transgression and regression cycles, geochemical processes as well as groundwater extraction. The abundance of groundwater of Na-HCO3 type and distinct ion ratios, such as Na+/Cl-, indicate extensive freshwater intrusion in an initially saline hydrogeological system, with decreasing intensity from upper Pleistocene to deeper Miocene aquifers, most likely during the last marine regression phase 60–12 ka BP. Deviations from the conservative mixing line between the two endmembers seawater and freshwater are attributed to ion-exchange processes on mineral surfaces, making ion ratios in combination with a customized water type analysis a useful tool to distinguish between salinization and freshening processes. Elevated salinity in some areas is attributed to HCO3- generation by organic matter decomposition in marine sediments rather than to seawater intrusion. Nevertheless, a few randomly distributed locations show strong evidence of recent salinization in an early stage, which may be caused by the downwards migration of saline Holocene groundwater through natural and anthropogenic pathways into deep aquifers. •This study presents the first detailed geochemical groundwater study in Ca Mau.•Geochemical and water type analysis reveal freshening of an initial saline aquifer.•The change of water type in early stages of salinization is linked to ion exchange.•Early signs of vertical saline intrusion from Holocene aquifers into deeper aquifers.•We delineate recent and past influences on groundwater in the southern Mekong Delta.