He is a Senior Lecturer at the University and has more than 40 year experiences in teaching and researching on water resources. His field is more focused on groundwater
Silicon has versatile functions in plant biology, especially in plant defense and tolerance to bo... more Silicon has versatile functions in plant biology, especially in plant defense and tolerance to both biotic and abiotic stressors. In this study, it was investigated if silicon could reduce the toxic effect of aluminum on rice. Aluminum was applied to OM4900 rice seedlings, and then their growth and sugar metabolism were determined. At doses of aluminum chloride of 100 and 200 µM, plant height was significantly enhanced and root elongation was reduced. The accumulation of photosynthetic pigments was tightly correlated with the aluminum concentration showing highest amounts at 400 µM. Sugar levels in roots and endosperm decreased upon aluminum addition. Aluminum toxicity in rice seedlings was relieved by addition of silicon in the form of sodium silicate. In the presence of 200 µM aluminum chloride, the addition of 100 mg/L sodium silicate to the hydroponic solution showed no contribution to plant growth or buildup of photosynthetic pigments. At this concentration, root development wa...
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2019
Multitemporal synthetic aperture radar (SAR) interferometry (InSAR) is a widely used technique to... more Multitemporal synthetic aperture radar (SAR) interferometry (InSAR) is a widely used technique to measure the ground subsidence and has already shown its ability to map such phenomena on a large spatial scale with millimetric accuracy from space. In Vietnam, to have independent SAR data for surface risk applications, a new X-band SAR mission (JV-LOTUSat) has been scheduled for launch for the 2019-2020 timeframe. However, Vietnam is located in tropical regions where their conditions are impacted by strong atmosphere. The aim of this article is to provide a better understanding of the capabilities of the X-band for estimating the ground subsidence under tropical atmospheric conditions. Analysis is carried out on two stacks, TerraSAR-X and Cosmos SkyMed X-band, from 2011 to 2014 in Ha Noi. We show that the results on the ground subsidence from InSAR processing can describe consistently the subsidence area based on ground measurements. This article demonstrates that the InSAR technique can be effective at detecting and estimating the subsidence phenomena even with the X-band and under conditions typical of tropical regions. The displacement results from TerraSAR-X and Cosmos SkyMed datasets are consistent, with a correlation coefficient (R 2) of 0.91 for the period during which their coverage overlaps. Groundwater overexploitation is one of the main causes of the ground subsidence in Ha Noi. This study provides strong support for the scientific potential of the X-band SAR space-borne mission in Vietnam and other tropical countries because it demonstrates the feasibility of the ground subsidence estimates by the X-band SAR, even in conditions impacted by strong atmosphere.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The research aimed to study 24 rock slope surfaces along the road around Hon Lon Island, Kien Hai... more The research aimed to study 24 rock slope surfaces along the road around Hon Lon Island, Kien Hai district, Kien Giang province, Vietnam. The analytical results have determined slope failure, wedge failure, and toppling, which occurred on almost slope surface and the average percentage of plane failure is the largest. The average percent of plane failure is 19.23%, the wedge failure is 15.35%, and the toppling fault is 6.73%. Besides, the analytical results have also identified the slope surfaces which can be the key blocks: ND-13, 18, 23, 25, 34, 37, 45, 51, 62, 63. The other analytical results show that the existence of key blocks at the rock slope surfaces in the N-S direction, dip to E at the survey locations: ND-13, 23, 63 and dip to W at the survey locations: ND-37, 45; in the NE-SW direction, dip to SE at the survey locations: ND-15, 62 and dip to NW at the survey locations: ND-18, 34; in the NW-SE direction, dip to SW at the survey location ND-51. These results have importan...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Regarding transport of macroplastic (>5 mm) in rivers, its division over bifurcations is still an... more Regarding transport of macroplastic (>5 mm) in rivers, its division over bifurcations is still an understudied topic. However, this is a critical knowledge to estimate plastic emission to oceans from rivers. To quantify the spatiotemporal variability of plastics in the Hong-Duong bifurcation, we executed a field campaign on a weekly basis and applied visual counting method where we count the floating plastics flowing through three cross sections to determine cross-sectional distribution of floating plastic and classify polymer categories of plastics from bridges located in the Hong-Duong bifurcation. These bridges include Nhat Tan located in northern Hanoi in the Red River, Long Bien is about 8km to the south from Nhat Tan in the Red River, and Dong Tru located in the tributary Duong River (˜7km from Nhat Tan). We aim to determine the spatiotemporal changes of macroplastics across the Hong-Duong bifurcation over the period from May 2021 to November 2021. Until July 2021, we found that the total average macroplastic fluxes at the cross sections in Nhat Tan, Long Bien, and Dong Tru were 698, 159, and 113 items/hour, respectively. Notably, these values do not follow the expected plastic balance between total plastic flux in the parent river and its tributaries, which is likely explained by the accumulation, transport below the surface, or sedimentation of plastics in the space between measurement locations. Additionally, over three months of May, June, and July, the total average plastic fluxes in all cross sections showed an increasing trend (˜10%). Furthermore, we also found that most plastics were distributed in the right side (downstream perspective) of Nhat Tan and Long Bien, while Dong Tru saw the opposite.
Sixteen samples of surface and groundwater from the most southern part of the Hanoi city (Vietnam... more Sixteen samples of surface and groundwater from the most southern part of the Hanoi city (Vietnam) has been taken and analyzed for the soluble major ions, namely
The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on ... more The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on the Red River flood plain near Hanoi, Vietnam. The groundwater chemistry was investigated in a transect of 100 piezometers. Results show an anoxic aquifer featuring organic carbon decomposition with redox zonation dominated by the reduction of Fe-oxides and methanogenesis. Enhanced P CO 2 pressure causes carbonate dissolution to take place but mainly in the soil and unsaturated zone. The concentration of As increases over depth to a concentration of up to 550 lg/L. Most As is present as As(III) but some As(V) is always found. Arsenic correlates well with NH 4 , relating its release to organic matter decomposition and the source of As appears to be the Fe-oxides being reduced. Part of the produced Fe(II) is apparently reprecipitated as siderite containing less As. Results from sediment extraction indicate most As to be related to the Fe-oxide fractions. The measured amount of sorbed As is low. In agreement, speciation calculations for a Fe-oxide surface suggest As(III) to constitute only 3% of the surface sites while the remainder is occupied by carbonate and silica species. The evolution in water chemistry over depth is homogeneous and a reactive transport model was constructed to quantify the geochemical processes along the vertical groundwater flow component. A redox zonation model was constructed using the partial equilibrium approach with organic carbon degradation in the sediment as the only rate controlling parameter. Apart from the upper meter a constant degradation rate of 0.15 C mmol/L/yr could explain the redox zonation throughout the aquifer. Modeling also indicates that the Fe-oxide being reduced is of a stable type like goethite or hematite. Arsenic is contained in the Fe-oxides and is first released during their dissolution. Our model further suggests that part of the released As is adsorbed on the surface of the remaining Fe-oxides and in this way may be retarded.
Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respe... more Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using M??ssbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO 4 from the sediment were investigated in leaching experiments with HCl and 10mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers. ?? 2010 Elsevier Ltd.
In the Red River Delta, the concentrations of Arsenic in groundwater of alluvial dominated system... more In the Red River Delta, the concentrations of Arsenic in groundwater of alluvial dominated systems are very high, exceeding the WHO’s permissible. The correlation between the Arsenic concentrations in groundwater and the age of Holocene sediment as a key controlling groundwater Arsenic concentration in the Red River delta has been investigated. The evolution of sediments in the Holocene is closely related to paleo-riverbed migration in the past. A combination of methods is implemented including remote sensing, multi-electrode profiling (MEP), gamma-logging, drilling, soil sample and groundwater modeling. The resul has identified the shape, sediment compositions and location of the six paleo-riverbed periods. The age of the paleo-riverbed is determined by drilling, soil sampling and optically stimulated luminescence (OSL) in the laboratory. The oldest sediments is 5.9±0.4 ka BP in Phung Thuong near the mountain, the youngest one is from 0.4÷0.6 ka BP in H-transect near the Red River ...
VNU Journal of Science: Earth and Environmental Sciences
Fresh groundwater was found in the Pleistocene aquifer in the southern part of the Red River Delt... more Fresh groundwater was found in the Pleistocene aquifer in the southern part of the Red River Delta in 70’s of last century. It is located mainly in the south of Nam Dinh province and small part in southeast of Ninh Binh province. The fresh-saline boundary seems to migrate southward recently and downsize the area of fresh groundwater. It is necessary to find out the mechanisms of salt intrusion into the zone of freshwater in order to mitigate the negative impacts to the quality of water supply. Based on the survey data of groundwater chemistry, transient electromagnetic sounding, borehole logging, drilling, and chemical analysis of pore water squeezed from the low permeable sediment in the study region, it was determined the current spatial distribution of saline water in the Pleistocene aquifer and in marine clay layers. By combining these data with the results from previous studies, this study has determined the mechanisms of the salt intrusion into the freshwater zone. It was foun...
Recharge of Red River water into arseniccontaminated aquifers below Hanoi was investigated. The g... more Recharge of Red River water into arseniccontaminated aquifers below Hanoi was investigated. The groundwater age at 40 m depth in the aquifer underlying the river was 1.3 ± 0.8 years, determined by tritium−helium dating. This corresponds to a vertical flow rate into the aquifer of 19 m/year. Electrical conductivity and partial pressure of CO 2 (P CO 2) indicate that water recharged from the river is present in both the sandy Holocene and gravelly Pleistocene aquifers and is also abstracted by the pumping station. Infiltrating river water becomes anoxic in the uppermost aquifer due to the oxidation of dissolved organic carbon. Further downward, sedimentary carbon oxidation causes the reduction of As-containing Fe-oxides. Because the release of arsenic by reduction of Fe-oxides is controlled by the reaction rate, arsenic entering the solution becomes highly diluted in the high water flux and contributes little to the groundwater arsenic concentration. Instead, the As concentration in the groundwater of up to 1 μM is due to equilibrium-controlled desorption of arsenic, adsorbed to the sediment before river water started to infiltrate due to municipal pumping. Calculations indicate that it will take several decades of river water infiltration to leach arsenic from the Holocene aquifer to below the World Health Organization limit of 10 μg/L.
Saltwater intrusion is generally related to seawater-level rise or induced intrusion due to exces... more Saltwater intrusion is generally related to seawater-level rise or induced intrusion due to excessive groundwater extraction in coastal aquifers. However, the hydrogeological heterogeneity of the subsurface plays an important role in (non-)intrusion as well. Local hydrogeological conditions for recharge and saltwater intrusion are studied in a coastal groundwater system in Vietnam where geological formations exhibit highly heterogeneous lithologies. A three-dimensional (3D) hydrostratigraphical solid model of the study area is constructed by way of a recursive classification procedure. The procedure includes a cluster analysis which uses as parameters geological formation, lithological composition, distribution depth and thickness of each lithologically distinctive drilling interval of 47 boreholes, to distinguish and map well-log intervals of similar lithological properties in different geological formations. A 3D hydrostratigraphical fence diagram is then generated from the constructed solid model and is used as a tool to evaluate recharge paths and saltwater intrusion to the groundwater system. Groundwater level and chemistry, and geophysical direct current (DC) resistivity measurements, are used to support the hydrostratigraphical model.
Silicon has versatile functions in plant biology, especially in plant defense and tolerance to bo... more Silicon has versatile functions in plant biology, especially in plant defense and tolerance to both biotic and abiotic stressors. In this study, it was investigated if silicon could reduce the toxic effect of aluminum on rice. Aluminum was applied to OM4900 rice seedlings, and then their growth and sugar metabolism were determined. At doses of aluminum chloride of 100 and 200 µM, plant height was significantly enhanced and root elongation was reduced. The accumulation of photosynthetic pigments was tightly correlated with the aluminum concentration showing highest amounts at 400 µM. Sugar levels in roots and endosperm decreased upon aluminum addition. Aluminum toxicity in rice seedlings was relieved by addition of silicon in the form of sodium silicate. In the presence of 200 µM aluminum chloride, the addition of 100 mg/L sodium silicate to the hydroponic solution showed no contribution to plant growth or buildup of photosynthetic pigments. At this concentration, root development wa...
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2019
Multitemporal synthetic aperture radar (SAR) interferometry (InSAR) is a widely used technique to... more Multitemporal synthetic aperture radar (SAR) interferometry (InSAR) is a widely used technique to measure the ground subsidence and has already shown its ability to map such phenomena on a large spatial scale with millimetric accuracy from space. In Vietnam, to have independent SAR data for surface risk applications, a new X-band SAR mission (JV-LOTUSat) has been scheduled for launch for the 2019-2020 timeframe. However, Vietnam is located in tropical regions where their conditions are impacted by strong atmosphere. The aim of this article is to provide a better understanding of the capabilities of the X-band for estimating the ground subsidence under tropical atmospheric conditions. Analysis is carried out on two stacks, TerraSAR-X and Cosmos SkyMed X-band, from 2011 to 2014 in Ha Noi. We show that the results on the ground subsidence from InSAR processing can describe consistently the subsidence area based on ground measurements. This article demonstrates that the InSAR technique can be effective at detecting and estimating the subsidence phenomena even with the X-band and under conditions typical of tropical regions. The displacement results from TerraSAR-X and Cosmos SkyMed datasets are consistent, with a correlation coefficient (R 2) of 0.91 for the period during which their coverage overlaps. Groundwater overexploitation is one of the main causes of the ground subsidence in Ha Noi. This study provides strong support for the scientific potential of the X-band SAR space-borne mission in Vietnam and other tropical countries because it demonstrates the feasibility of the ground subsidence estimates by the X-band SAR, even in conditions impacted by strong atmosphere.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The research aimed to study 24 rock slope surfaces along the road around Hon Lon Island, Kien Hai... more The research aimed to study 24 rock slope surfaces along the road around Hon Lon Island, Kien Hai district, Kien Giang province, Vietnam. The analytical results have determined slope failure, wedge failure, and toppling, which occurred on almost slope surface and the average percentage of plane failure is the largest. The average percent of plane failure is 19.23%, the wedge failure is 15.35%, and the toppling fault is 6.73%. Besides, the analytical results have also identified the slope surfaces which can be the key blocks: ND-13, 18, 23, 25, 34, 37, 45, 51, 62, 63. The other analytical results show that the existence of key blocks at the rock slope surfaces in the N-S direction, dip to E at the survey locations: ND-13, 23, 63 and dip to W at the survey locations: ND-37, 45; in the NE-SW direction, dip to SE at the survey locations: ND-15, 62 and dip to NW at the survey locations: ND-18, 34; in the NW-SE direction, dip to SW at the survey location ND-51. These results have importan...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Regarding transport of macroplastic (>5 mm) in rivers, its division over bifurcations is still an... more Regarding transport of macroplastic (>5 mm) in rivers, its division over bifurcations is still an understudied topic. However, this is a critical knowledge to estimate plastic emission to oceans from rivers. To quantify the spatiotemporal variability of plastics in the Hong-Duong bifurcation, we executed a field campaign on a weekly basis and applied visual counting method where we count the floating plastics flowing through three cross sections to determine cross-sectional distribution of floating plastic and classify polymer categories of plastics from bridges located in the Hong-Duong bifurcation. These bridges include Nhat Tan located in northern Hanoi in the Red River, Long Bien is about 8km to the south from Nhat Tan in the Red River, and Dong Tru located in the tributary Duong River (˜7km from Nhat Tan). We aim to determine the spatiotemporal changes of macroplastics across the Hong-Duong bifurcation over the period from May 2021 to November 2021. Until July 2021, we found that the total average macroplastic fluxes at the cross sections in Nhat Tan, Long Bien, and Dong Tru were 698, 159, and 113 items/hour, respectively. Notably, these values do not follow the expected plastic balance between total plastic flux in the parent river and its tributaries, which is likely explained by the accumulation, transport below the surface, or sedimentation of plastics in the space between measurement locations. Additionally, over three months of May, June, and July, the total average plastic fluxes in all cross sections showed an increasing trend (˜10%). Furthermore, we also found that most plastics were distributed in the right side (downstream perspective) of Nhat Tan and Long Bien, while Dong Tru saw the opposite.
Sixteen samples of surface and groundwater from the most southern part of the Hanoi city (Vietnam... more Sixteen samples of surface and groundwater from the most southern part of the Hanoi city (Vietnam) has been taken and analyzed for the soluble major ions, namely
The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on ... more The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on the Red River flood plain near Hanoi, Vietnam. The groundwater chemistry was investigated in a transect of 100 piezometers. Results show an anoxic aquifer featuring organic carbon decomposition with redox zonation dominated by the reduction of Fe-oxides and methanogenesis. Enhanced P CO 2 pressure causes carbonate dissolution to take place but mainly in the soil and unsaturated zone. The concentration of As increases over depth to a concentration of up to 550 lg/L. Most As is present as As(III) but some As(V) is always found. Arsenic correlates well with NH 4 , relating its release to organic matter decomposition and the source of As appears to be the Fe-oxides being reduced. Part of the produced Fe(II) is apparently reprecipitated as siderite containing less As. Results from sediment extraction indicate most As to be related to the Fe-oxide fractions. The measured amount of sorbed As is low. In agreement, speciation calculations for a Fe-oxide surface suggest As(III) to constitute only 3% of the surface sites while the remainder is occupied by carbonate and silica species. The evolution in water chemistry over depth is homogeneous and a reactive transport model was constructed to quantify the geochemical processes along the vertical groundwater flow component. A redox zonation model was constructed using the partial equilibrium approach with organic carbon degradation in the sediment as the only rate controlling parameter. Apart from the upper meter a constant degradation rate of 0.15 C mmol/L/yr could explain the redox zonation throughout the aquifer. Modeling also indicates that the Fe-oxide being reduced is of a stable type like goethite or hematite. Arsenic is contained in the Fe-oxides and is first released during their dissolution. Our model further suggests that part of the released As is adsorbed on the surface of the remaining Fe-oxides and in this way may be retarded.
Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respe... more Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using M??ssbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO 4 from the sediment were investigated in leaching experiments with HCl and 10mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers. ?? 2010 Elsevier Ltd.
In the Red River Delta, the concentrations of Arsenic in groundwater of alluvial dominated system... more In the Red River Delta, the concentrations of Arsenic in groundwater of alluvial dominated systems are very high, exceeding the WHO’s permissible. The correlation between the Arsenic concentrations in groundwater and the age of Holocene sediment as a key controlling groundwater Arsenic concentration in the Red River delta has been investigated. The evolution of sediments in the Holocene is closely related to paleo-riverbed migration in the past. A combination of methods is implemented including remote sensing, multi-electrode profiling (MEP), gamma-logging, drilling, soil sample and groundwater modeling. The resul has identified the shape, sediment compositions and location of the six paleo-riverbed periods. The age of the paleo-riverbed is determined by drilling, soil sampling and optically stimulated luminescence (OSL) in the laboratory. The oldest sediments is 5.9±0.4 ka BP in Phung Thuong near the mountain, the youngest one is from 0.4÷0.6 ka BP in H-transect near the Red River ...
VNU Journal of Science: Earth and Environmental Sciences
Fresh groundwater was found in the Pleistocene aquifer in the southern part of the Red River Delt... more Fresh groundwater was found in the Pleistocene aquifer in the southern part of the Red River Delta in 70’s of last century. It is located mainly in the south of Nam Dinh province and small part in southeast of Ninh Binh province. The fresh-saline boundary seems to migrate southward recently and downsize the area of fresh groundwater. It is necessary to find out the mechanisms of salt intrusion into the zone of freshwater in order to mitigate the negative impacts to the quality of water supply. Based on the survey data of groundwater chemistry, transient electromagnetic sounding, borehole logging, drilling, and chemical analysis of pore water squeezed from the low permeable sediment in the study region, it was determined the current spatial distribution of saline water in the Pleistocene aquifer and in marine clay layers. By combining these data with the results from previous studies, this study has determined the mechanisms of the salt intrusion into the freshwater zone. It was foun...
Recharge of Red River water into arseniccontaminated aquifers below Hanoi was investigated. The g... more Recharge of Red River water into arseniccontaminated aquifers below Hanoi was investigated. The groundwater age at 40 m depth in the aquifer underlying the river was 1.3 ± 0.8 years, determined by tritium−helium dating. This corresponds to a vertical flow rate into the aquifer of 19 m/year. Electrical conductivity and partial pressure of CO 2 (P CO 2) indicate that water recharged from the river is present in both the sandy Holocene and gravelly Pleistocene aquifers and is also abstracted by the pumping station. Infiltrating river water becomes anoxic in the uppermost aquifer due to the oxidation of dissolved organic carbon. Further downward, sedimentary carbon oxidation causes the reduction of As-containing Fe-oxides. Because the release of arsenic by reduction of Fe-oxides is controlled by the reaction rate, arsenic entering the solution becomes highly diluted in the high water flux and contributes little to the groundwater arsenic concentration. Instead, the As concentration in the groundwater of up to 1 μM is due to equilibrium-controlled desorption of arsenic, adsorbed to the sediment before river water started to infiltrate due to municipal pumping. Calculations indicate that it will take several decades of river water infiltration to leach arsenic from the Holocene aquifer to below the World Health Organization limit of 10 μg/L.
Saltwater intrusion is generally related to seawater-level rise or induced intrusion due to exces... more Saltwater intrusion is generally related to seawater-level rise or induced intrusion due to excessive groundwater extraction in coastal aquifers. However, the hydrogeological heterogeneity of the subsurface plays an important role in (non-)intrusion as well. Local hydrogeological conditions for recharge and saltwater intrusion are studied in a coastal groundwater system in Vietnam where geological formations exhibit highly heterogeneous lithologies. A three-dimensional (3D) hydrostratigraphical solid model of the study area is constructed by way of a recursive classification procedure. The procedure includes a cluster analysis which uses as parameters geological formation, lithological composition, distribution depth and thickness of each lithologically distinctive drilling interval of 47 boreholes, to distinguish and map well-log intervals of similar lithological properties in different geological formations. A 3D hydrostratigraphical fence diagram is then generated from the constructed solid model and is used as a tool to evaluate recharge paths and saltwater intrusion to the groundwater system. Groundwater level and chemistry, and geophysical direct current (DC) resistivity measurements, are used to support the hydrostratigraphical model.
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