TY  - JOUR
A1  - Bauer, Jonas
A1  - Börsig, Nicolas
A1  - Pham, Van Cam
A1  - Hoan, Tran Viet
A1  - Nguyen, Ha Thi
A1  - Norra, Stefan
T1  - Geochemistry and evolution of groundwater resources in the context of salinization and freshening in the southernmost Mekong Delta, Vietnam
JF  - Journal of Hydrology: Regional Studies
N2  - Study region: 
Ca Mau Province (CMP), Mekong Delta (MD), Vietnam. 

Study focus: 
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. 

New hydrological insights for the region: 
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.
KW  - Ca Mau
KW  - Hydrogeology
KW  - Delta aquifer system
KW  - Salinity
KW  - Freshwater
KW  - Seawater intrusion
Y1  - 2022
U6  - https://doi.org/10.1016/j.ejrh.2022.101010
SN  - 2214-5818
VL  - 40
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Hoan, Tran Viet
A1  - Richter, Karl-Gerd
A1  - Borsig, Nicolas
A1  - Bauer, Jonas
A1  - Ha, Nguyen Thi
A1  - Norra, Stefan
T1  - An improved groundwater model framework for aquifer structures of the quaternary-formed sediment body in the southernmost parts of the Mekong Delta, Vietnam
JF  - Hydrology : open access journal
N2  - The Ca Mau peninsula (CMP) is a key economic region in southern Vietnam. In recent decades, the high demand for water has increased the exploitation of groundwater, thus lowering the groundwater level and leading to risks of degradation, depletion, and land subsidence, as well as salinity intrusion in the groundwater of the whole Mekong Delta region. By using a finite element groundwater model with boundary expansion to the sea, we updated the latest data on hydrogeological profiles, groundwater levels, and exploitation. The basic model setup covers seven aquifers and seven aquitards. It is determined that the inflow along the coastline to the mainland is 39% of the total inflow. The exploitation of the study area in 2019 was 567,364 m(3)/day. The most exploited aquifers are the upper-middle Pleistocene (qp(2-3)) and the middle Pliocene (n(2)(2)), accounting for 63.7% and 24.6%, respectively; the least exploited aquifers are the upper Pleistocene and the upper Miocene, accounting for 0.35% and 0.02%, respectively. In the deeper aquifers, qp(2-3) and n(2)(2), the change in storage is negative due to the high exploitation rate, leading to a decline in the reserves of these aquifers. These groundwater model results are the calculations of groundwater reserves from the coast to the mainland in the entire system of aquifers in the CMP. This makes groundwater decision managers, stakeholders, and others more efficient in sustainable water resources planning in the CMP and Mekong Delta (MKD).
KW  - groundwater modeling
KW  - hydrogeology
KW  - aquifers system
KW  - water balance;
KW  - validation of model
KW  - Ca Mau peninsula
KW  - Kien Giang
KW  - Soc Trang
KW  - Hau Giang
KW  - Bac Lieu
Y1  - 2022
U6  - https://doi.org/10.3390/hydrology9040061
SN  - 2306-5338
VL  - 9
IS  - 4
PB  - MDPI
CY  - Basel
ER  -