Refine
Has Fulltext
- no (3)
Year of publication
- 2022 (3)
Document Type
- Article (3) (remove)
Language
- English (3) (remove)
Is part of the Bibliography
- yes (3)
Keywords
- Bac Lieu (1)
- Ca Mau (1)
- Ca Mau peninsula (1)
- Delta aquifer system (1)
- Freshwater (1)
- Hau Giang (1)
- Hydrogeology (1)
- Kien Giang (1)
- Salinity (1)
- Seawater intrusion (1)
- Soc Trang (1)
- aquifers system (1)
- groundwater modeling (1)
- hydrogeology (1)
- validation of model (1)
- water balance; (1)
Institute
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.
The optical properties, chemical composition, and potential chromophores of brown carbon (BrC) aerosol particles were studied during typical summertime and wintertime at a kerbside in downtown Karl-sruhe, a city in central Europe.
The average absorption coefficient and mass absorption efficiency at 365 nm (Abs(365) and MAE(365)) of methanol-soluble BrC (MS-BrC) were lower in the summer period (1.6 +/- 0.5 Mm(-1), 0.5 +/- 0.2 m(2) g(-1)) than in the winter period (2.8 +/- 1.9 Mm(-1), 1.1 +/- 0.3 m(2) g(-1)). Using a parallel factor (PARAFAC) analysis to identify chromophores, two different groups of highly oxygenated humic-like substances (HO-HULIS) dominated in summer and contributed 96 +/- 6 % of the total fluorescence intensity.
In contrast, less-oxygenated HULIS (LO-HULIS) dominated the total fluorescence intensity in winter with 57 +/- 12 %, followed by HO-HULIS with 31 +/- 18 %. Positive matrix factorization (PMF) analysis of organic compounds detected in real time by an online aerosol mass spectrometer (AMS) led to five characteristic organic compound classes.
The statistical analysis of PARAFAC components and PMF factors showed that LO-HULIS chromophores were most likely emitted from biomass burning in winter. HO-HULIS chromophores could be low-volatility oxy-genated organic aerosol from regional transport and oxidation of biogenic volatile organic compounds (VOCs) in summer.
Five nitro-aromatic compounds (NACs) were identified by a chemical ionization mass spectrometer (C7H7O3N, C7H7O4N, C6H5O5N, C6H5O4N, and C6H5O3N), which contributed 0.03 +/- 0.01 % to the total organic mass but can explain 0.3 +/- 0.1 % of the total absorption of MS-BrC at 365 nm in winter.
Furthermore, we identified 316 potential brown carbon molecules which accounted for 2.5 +/- 0.6 % of the organic aerosol mass. Using an average mass absorption efficiency (MAE(365)) of 9.5 m(2)g(-1) for these compounds, we can es-timate their mean light absorption to be 1.2 +/- 0.2 Mm(-1), accounting for 32 +/- 15 % of the total absorption of MS-BrC at 365 nm.
This indicates that a small fraction of brown carbon molecules dominates the overall ab-sorption. The potential BrC molecules assigned to the LO-HULIS component had a higher average molecular weight (265 +/- 2 Da) and more nitrogen-containing molecules (62 +/- 1 %) than the molecules assigned to the HOHULIS components.
Our analysis shows that the LO-HULIS, with a high contribution of nitrogen-containing molecules originating from biomass burning, dominates aerosol fluorescence in winter, and HO-HULIS, with fewer nitrogen-containing molecules as low-volatility oxygenated organic aerosol from regional transport and oxidation of biogenic volatile organic compounds (VOC), dominates in summer.
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).