Chemical composition, radioactive and stable isotopes in several selected thermal waters in North Vietnam

Nguyen Dinh Chau, Katarzyna Wątor, Piotr Rusiniak, et al. Ecological Indicators, 138: 108856, 2022.

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Abstract: This work presents the chemical composition and concentration of radioactive and stable isotopes in water samples collected from nine well-known therapeutic centers located in north Vietnam. Excluding the Thanh Thuy – Phu Tho waters, which are hosted in Pleistocene sandstone with marble and gravel, the rest of studied waters are hosted in Paleozoic limestone formations. The thermal waters are extracted from 10 to 400 m below the surface, but the Keng Ga Ninh Binh intake is of an artesian nature. The temperature measured in the outlet waters ranges from 39 °C to 61 °C. The δ18O and δ2H (δD) vary from −9.13 to −5.09 ‰ and −63.9 to −34.1 ‰ respectively. All the thermal waters examined originate from infiltration water. This is also confirmed by the values of selected calculated hydrochemical indices. The hydrochemical types of the waters are HCO3-Ca-Mg, HCO3-Na, Cl-Na, SO4-HCO3-Ca-Mg, SO4-Ca-Mg and SO4-Ca. The mineralization of the concerned waters varies from 244 mgL−1 to more than 11,500 mgL−1. The concentrations of uranium and radium in the waters are in the broad interval from about 4 mBqL−1 to 680 mBqL−1 for 238U and from below 5 mBqL−1 (limit of detection - LOD) to above 3400 mBqL−1 for 226Ra. There is no 228Ra in most of the waters (below 10 mBqL−1- LOD), excluding two waters in the Thanh Thuy-Phu Tho district, where 228Ra is present with 18 and 27 mBqL−1. In all the waters studied, there is a very low concentration of polonium (210Po) which varies from 0.5 mBqL−1 to 8.2 mBqL−1. High mineralization and high radium concentration should be associated with a long residence time in the given geological formation. The linear relationship between the depth of the host water formations and the water temperature suggests that the study waters are mostly heated from the geogradient of heat energy. But the water from the My Lam district is probably heated by intrusive magmatic fluid. From a radiological point of view, the waters used for therapeutic and relaxation purposes are safe, however, there would be some problems if they were to be used for drinking purposes.

The degree of integrated water resources management implementation in the Mekong River Delta in Viet Nam

Tran Van Tra, Tu Anh Nguyen, Le Van Linh, et al. World Water Policy, n/a(n/a).

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Abstract: Abstract A comprehensive approach in water resources management, referred to as integrated water resources management (IWRM), is required for successful water resource management. This study determined the degree of IWRM implementation in the Mekong River Delta in Viet Nam using indicator 6.5.1 from the United Nation's Sustainable Development Goal 6. A Delphi questionnaire approach was used in the study with a set of Knowledge Acquisition for Multiple Experts with Time Scales. The questionnaire was conducted with 21 selected experts for three rounds. The results showed that the degree of IWRM implementation in the Mekong River Delta in Viet Nam is at a medium-high level. Enabling environment scores significantly better than the three other components, while the finance dimension falls short. This reflects the government's efforts to effectively manage water resources in the region. However, given the limitations in technical and financial capacity for IWRM implementation, this effort is deemed inadequate. The results thus provide an assessment baseline to assist decision makers in addressing the shortcomings of the current state of IWRM.

 Groundwater arsenic content in quaternary aquifers of the Red River delta, Vietnam, controlled by the hydrogeological processes

Jolanta Kazmierczak, Trung Trang Dang, Rasmus Jakobsen, et al. Journal of Hydrology, 609: 127778, 2022.

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 Abstract: The relation between arsenic groundwater concentrations and hydrogeological processes was investigated in the proximal part of the Red River delta, Vietnam, west of the depression cone formed by the exploitation of groundwater in Hanoi. Flow paths in the Quaternary aquifers were modeled based on previously interpreted geological structure and hydrogeological data gathered during field work in 2014–2017. Sedimentary structures and simulated flow patterns were compared with the spatial distribution of the groundwater arsenic concentration. The regression of the sea in the area started 4 ka BP in the Holocene. The low tectonic subsidence rate of the Red River delta led to intensive erosion and replacement of fine grained sediments of the sea level high stand by sandy channel belts, resulting in hydraulic connections between the Pleistocene and Holocene aquifers. The Pleistocene aquifer is recharged by both regional flow paths and naturally occurring vertical recharge through Holocene sand and clay layers. Young groundwater (<40 a) in the shallow Holocene aquifer generally discharges to surface water bodies. The shallow flow system is also seasonally recharged with surface water, as indicated by δ18O enrichment of groundwater and oscillating groundwater ages in wells in the vicinity of water channels. The deeper flow system discharges into the Red River and Day River or flows parallel to the rivers, toward the sea. The overall pattern of arsenic groundwater concentrations (decreasing with increasing sediment age) is modified by groundwater flow. The arsenic contamination of the Pleistocene aquifer of the Red River delta is not only caused by the intensive groundwater abstraction in Hanoi, as reported previously, but also by the natural flow of high arsenic groundwater from Holocene to Pleistocene aquifers in areas located outside of the depression cone. Groundwater with < 50 µg L-1 arsenic is found in the Pleistocene aquifer close to the recharge zone in the mountains bordering the Red River delta and in the Holocene and Pleistocene aquifers where clay deposits were eroded. Close to the recent Red River channel, recharge of older Holocene and Pleistocene sediments occurs partially by arsenic-contaminated groundwater from the youngest Holocene aquifers, and here arsenic concentrations exceed 50 µg L-1. A high arsenic concentration is also present in the early Holocene-Pleistocene aquifer, beneath thick clay layers, indicating a limited extent of flushing and the inflow of fresh organic matter.

Groundwater arsenic content related to the sedimentology and stratigraphy of the Red River delta, Vietnam

Jolanta Kazmierczak, Dieke Postma, Trung Dang, et al. The Science of the total environment, 814: 152641-41, 2022.

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 Abstract: Arsenic (As) is highly toxic and over 100 million people living on the floodplains of Asia are exposed to excessive groundwater As. A very large spatial variability over small distances has been observed in the groundwater As concentrations. Advances in the prediction of the As distribution in aquifers would support drinking water management. The application of remote sensing of geomorphic paleo river features combined with geological, geophysical and archeological data and available groundwater As measurements may be used to predict groundwater As levels in rural areas, as shown by the example from the Red River delta, Vietnam. Groundwater in sediments deposited in the marine environment is low in As, probably due to the precipitation of As in sulfide minerals under anoxic conditions. Groundwater As levels in freshwater alluvial deposits in undisturbed floodplain areas are slightly increased and the highest As concentrations are associated with meander belts. The meander belts remain clearly visible in remote sensing and may well reflect the youngest preserved alluvial sediments. High As levels in the meander belt aquifers are probably related to the availability of highly reactive organic matter and consequent reduction of iron oxyhydroxides and As release. Furthermore, given similar hydrogeological conditions, the extent of flushing of As from the youngest alluvial sands is limited compared to the older Pleistocene sands. Even within abandoned meander belts a high spatial variability of As concentrations was observed. The younger channel belts (<1 ka BP) and old Holocene aquifers below undisturbed floodplain environments deposited during a period with high sea level host groundwater enriched in As. Low As groundwater is found in sandy channel belts deposited during the regression of the sea and in Pleistocene islands preserved within the floodplain. The decisive influence of the depositional environment of the aquifer sediments on groundwater As content is revealed. [Display omitted] •Arsenic (As) hazard maps improved by Remote Sensing (RS) and archeological data.•Sedimentary structure of a delta plain interpreted from RS and ground based methods.•Significant insight into groundwater As provided from detailed geology.•Extent of low As groundwater in the marine deposits derived from RS.•High As groundwater associated with meander belts and thick clay layers. 

Responding to transboundary water challenges in the Vietnamese Mekong Delta: In search of institutional fit

Thong Anh Tran and Cecilia Tortajada. Environmental Policy and Governance, 2022. Free full text

Abstract: The operations of large hydropower dams in the Mekong basin, while posing detrimental transboundary effects downstream, are not fully recognised in Vietnamese government policies, especially at the regional scale. This study adopts the concept of institutional fit to investigate policy gaps in addressing the transboundary water challenges characterised by falling floodwater flows and accelerating saltwater intrusion in the Vietnamese Mekong Delta. Based on interviews with key stakeholders (including central and provincial government officials,  environmental experts, and academics) as well as desk reviews of policy documents, we argue that, while the transboundary water repercussions are increasingly evident on the ground, they are not adequately factored in water policies and strategic development planning for the delta. This study suggests that failure to incorporate co-evolving effects of climate change and Mekongwide hydropower dynamics into local water governance will cause institutional constraints to tackle water stressors (too much or too little water) over the long term. Achieving institutional fit will therefore help align the national water policy framework with local development strategies and reduce policy-practice gaps at the delta scale. To this end, two key aspects need to be considered: first, how, and in which forms, innovative management decisions and water governance policies can be effectively undertaken towards securing the living delta and its resilience to present and future environmental risks; and second, how reframed water policy and development agendas can holistically capture and resolve the transboundary hydrological problems, while leveraging the Vietnamese government's policy engagement at higher levels to address related impacts.

Towards Sustainable Groundwater Management of Transboundary Aquifers in the Lower Mekong Region.

Das Gupta, S. Shrestha, TPL. Nguyen, et al., 2022.

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 Abstract: The management of a transboundary aquifer shared by two or more countries is quite complex and is a challenging task. A pragmatic action plan to develop and implement sustainable groundwater development and management of a transboundary aquifer system is proposed. An Institutional system in the form of a Coordinating Council or a Multi-Country Consultative Body at the Government Level is recommended for the management of TBA. Adequate knowledge and in-house capacity with the know-how and expertise is imperative at different administrative levels to address development and management issues.

 Vũ Thị Nha (World Bank Group)

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