Pub Date : 2022-03-15DOI: 10.15625/2615-9783/16997
My Ngo Thi Diem, Phap Ton That, Thuy Duong Thi, Q. Le Thi Phuong, Lien Nguyen Thi Thu
This study investigated the variation of the cyanobacterium Raphidiopsis raciborskii population under the influence of physicochemical parameters from May 2019 to April 2020 in the Buon Phong reservoir. The correlations between these parameters were explored by using Principal Component Analysis (PCA) and Pearson correlation analysis. The cylindrospermopsin (CYN) toxin in isolated strains from the reservoir was confirmed by using High-performance liquid chromatography (HPLC) analyses. R. raciborskii presented throughout the year in the reservoir with a biovolume from 0.12 to 9.14 mm3 L-1. Four R. raciborskii strains (CBP2, CBP3, CBP4, and CBP5) were successfully isolated and confirmed to produce CYN by the HPLC results. The highest concentration in isolated strains was 0.345 μg g-1 DW in the CBP4 strain. The PCR results of genes responsible for CYN biosynthesis showed that the PCR amplicons of cyrB and CyrC were amplified in two toxic strains (CBP2 and CBP3), while the amplicons of both cyrB and cyrC were not observed in two remaining toxic strains. In addition, such abiotic factors as temperature and nutrients played major roles in the abundance of R. raciborskii. Moreover, the biovolume of R. raciborskii positively correlated with the CYN concentrations in the Buon Phong reservoir.
{"title":"Cyanobacterium Raphidiopsis raciborskii and its toxin in Buon Phong reservoir, Dak Lak province, Vietnam","authors":"My Ngo Thi Diem, Phap Ton That, Thuy Duong Thi, Q. Le Thi Phuong, Lien Nguyen Thi Thu","doi":"10.15625/2615-9783/16997","DOIUrl":"https://doi.org/10.15625/2615-9783/16997","url":null,"abstract":"This study investigated the variation of the cyanobacterium Raphidiopsis raciborskii population under the influence of physicochemical parameters from May 2019 to April 2020 in the Buon Phong reservoir. The correlations between these parameters were explored by using Principal Component Analysis (PCA) and Pearson correlation analysis. The cylindrospermopsin (CYN) toxin in isolated strains from the reservoir was confirmed by using High-performance liquid chromatography (HPLC) analyses. R. raciborskii presented throughout the year in the reservoir with a biovolume from 0.12 to 9.14 mm3 L-1. Four R. raciborskii strains (CBP2, CBP3, CBP4, and CBP5) were successfully isolated and confirmed to produce CYN by the HPLC results. The highest concentration in isolated strains was 0.345 μg g-1 DW in the CBP4 strain. The PCR results of genes responsible for CYN biosynthesis showed that the PCR amplicons of cyrB and CyrC were amplified in two toxic strains (CBP2 and CBP3), while the amplicons of both cyrB and cyrC were not observed in two remaining toxic strains. In addition, such abiotic factors as temperature and nutrients played major roles in the abundance of R. raciborskii. Moreover, the biovolume of R. raciborskii positively correlated with the CYN concentrations in the Buon Phong reservoir.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43497825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-11DOI: 10.15625/2615-9783/16980
Hong Xuan Do, Manh -Hung Le, Hung Thanh Pham, Tu Hoang Le, Binh Quang Nguyen
Among the impacts of climate change and variabilities, change in the terrestrial water cycle has been investigated extensively due to the importance of water resources to the Earth System. The detection and attribution of changes in river flows, however, are usually complicated by the impacts of on-ground human activities such as urbanization or dam construction that have altered flow regimes. As a result, hydrological reference stations – gauges measuring river flows of catchments that are unregulated - have been identified in many countries to provide streamflow records that are suitable for climate studies. Such a network, to the best of our knowledge, has not been promoted widely in Vietnam, making it difficult to determine the actual impact of climate change and variability to river flow regimes at the national scale. To address this limitation, this study uses a data-driven approach to identify stations that have not been influenced substantially by human activities for Vietnam. Specifically, we have carefully assessed streamflow records at 68 locations that are not influenced by tidal regime to identify stations with relatively good data quality. The drainage area associated with each of these stations was then delineated following international standards, and then used to identify catchments that were not associated with large dams. The catchment boundary was also used to extract land surface information, available through an ensemble of different satellite-based data products, to further identify catchments that are not featured by large urban areas, or experienced a substantial change in land cover during the 2000-2019 period. Using these criteria, this study suggested two subsets of stations distributed across the countries, providing a good starting point for future investigations into the impacts of climate change on water resources in Vietnam. The investigation also suggests that more investments are required to maintain and expand the hydrologic reference network for Vietnam.
{"title":"Identifying hydrologic reference stations to understand changes in water resources across Vietnam - a data-driven approach","authors":"Hong Xuan Do, Manh -Hung Le, Hung Thanh Pham, Tu Hoang Le, Binh Quang Nguyen","doi":"10.15625/2615-9783/16980","DOIUrl":"https://doi.org/10.15625/2615-9783/16980","url":null,"abstract":"Among the impacts of climate change and variabilities, change in the terrestrial water cycle has been investigated extensively due to the importance of water resources to the Earth System. The detection and attribution of changes in river flows, however, are usually complicated by the impacts of on-ground human activities such as urbanization or dam construction that have altered flow regimes. As a result, hydrological reference stations – gauges measuring river flows of catchments that are unregulated - have been identified in many countries to provide streamflow records that are suitable for climate studies. Such a network, to the best of our knowledge, has not been promoted widely in Vietnam, making it difficult to determine the actual impact of climate change and variability to river flow regimes at the national scale. To address this limitation, this study uses a data-driven approach to identify stations that have not been influenced substantially by human activities for Vietnam. Specifically, we have carefully assessed streamflow records at 68 locations that are not influenced by tidal regime to identify stations with relatively good data quality. The drainage area associated with each of these stations was then delineated following international standards, and then used to identify catchments that were not associated with large dams. The catchment boundary was also used to extract land surface information, available through an ensemble of different satellite-based data products, to further identify catchments that are not featured by large urban areas, or experienced a substantial change in land cover during the 2000-2019 period. Using these criteria, this study suggested two subsets of stations distributed across the countries, providing a good starting point for future investigations into the impacts of climate change on water resources in Vietnam. The investigation also suggests that more investments are required to maintain and expand the hydrologic reference network for Vietnam.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":"1 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41590180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-04DOI: 10.15625/2615-9783/16969
Chien Hoang Thi, M. Kirby, Lan Dinh Tran
Tourism development plays a crucial role in creating employment, boosting the revenue of the economy, supporting to improve the living standard. While tourism provides many opportunities to improve the well-being of local communities, the expansion of tourism needs to be effectively managed to avoid the degradation of natural capital. Assessing resource awareness and use behavior is an effective way to determine the public’s commitment to natural resource conservation and restoration in protected areas. The research was performed in Bach Long Vy Island (BLVI) in Hai Phong city, Viet Nam which is the first National Marine protected area designated by the Vietnamese Government. The aim of this study was to estimate tourists’ Willingness to pay (WTP) for natural resource conservation at BLVI through using Contingent valuation method (CVM) with the single-bounded dichotomous choice technique and the random utility model. We estimate the average visitor WTP is VND 153 370 per year (approx. US$6.58), while the aggregate WTP of tourists for the environmental conservation is VND 7.67 million per year (approx. US$32 900) (currency conversions taken as the average rate in September 2020; US$1 to VND 23280). The calculated results show that income and gender factors have significant effects visitors WTP whereas age and education have opposite effects. The outcomes of this research demonstrate the potential tourism value of this island due to the natural amenities and high biodiversity, particularly originating from its marine ecosystems. This result provides valuable scientific information for decision makers and local authorities and should be useful in establishing strategies to prevent the deterioration of ecosystems at BLVI (e.g., an environmental charge or entrance fee), thus contributing to sustainable tourism development.
{"title":"User willingness to pay for natural resource conservation at Bach Long Vy Island, Vietnam","authors":"Chien Hoang Thi, M. Kirby, Lan Dinh Tran","doi":"10.15625/2615-9783/16969","DOIUrl":"https://doi.org/10.15625/2615-9783/16969","url":null,"abstract":"Tourism development plays a crucial role in creating employment, boosting the revenue of the economy, supporting to improve the living standard. While tourism provides many opportunities to improve the well-being of local communities, the expansion of tourism needs to be effectively managed to avoid the degradation of natural capital. Assessing resource awareness and use behavior is an effective way to determine the public’s commitment to natural resource conservation and restoration in protected areas. The research was performed in Bach Long Vy Island (BLVI) in Hai Phong city, Viet Nam which is the first National Marine protected area designated by the Vietnamese Government. The aim of this study was to estimate tourists’ Willingness to pay (WTP) for natural resource conservation at BLVI through using Contingent valuation method (CVM) with the single-bounded dichotomous choice technique and the random utility model. We estimate the average visitor WTP is VND 153 370 per year (approx. US$6.58), while the aggregate WTP of tourists for the environmental conservation is VND 7.67 million per year (approx. US$32 900) (currency conversions taken as the average rate in September 2020; US$1 to VND 23280). The calculated results show that income and gender factors have significant effects visitors WTP whereas age and education have opposite effects. The outcomes of this research demonstrate the potential tourism value of this island due to the natural amenities and high biodiversity, particularly originating from its marine ecosystems. This result provides valuable scientific information for decision makers and local authorities and should be useful in establishing strategies to prevent the deterioration of ecosystems at BLVI (e.g., an environmental charge or entrance fee), thus contributing to sustainable tourism development.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45870601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-22DOI: 10.15625/2615-9783/16942
Huy Hoang-Cong, T. Ngo‐Duc, Tuyet Nguyen-Thi, Long Trinh-Tuan, Chung Jing Xiang, F. Tangang, Santisirisomboon Jerasorn, T. Phan‐Van
This study first evaluates the performance of three model experiments in representing rainfall over part of Vietnam and the Lower Mekong Basin for the historical period 1986-2005. The three experiments include the Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-EARTH Global Climate Model (GCM) and two downscaling runs based on a regional climate model at 25km resolution with the GCM forcing (RCM-25km) and at 5km resolution with the RCM-25km forcing (RCM-5km). Verifications against observations show that the experiments generally capture the spatial distribution of climatological rainfall. While the GCM well represents the observed average rainfall cycles, its coarse resolution limits its capability in reproducing extreme rainfall values. The downscaling experiments do not clearly show their advantage in simulating average rainfall but exhibit significant added values when representing extreme rainfall in the study region. The RCM-5km does not outperform its driving 25km experiment in representing the mean and extreme rainfall values, suggesting that having a better resolution may not compensate for having a good model configuration with appropriate physical schemes. Analysis of climate projection for the far future period 2080-2099 under two representative concentration pathways (RCP) scenarios, RCP4.5 and RCP8.5, reveals that the downscaling experiments can modify the change direction of future rainfall obtained with the GCM. While the EC-EARTH GCM generally projects wetter tendencies of up to 50%, the downscaling experiments project a general decrease of down to -50% under both scenarios over the study domain. Regarding extreme rainfall, the annual maximum 1-day rainfall amount (RX1day) is projected to increase for the three experiments. The simple daily intensity index (SDII) future changes follow those of the annual rainfall values.
{"title":"A high-resolution climate experiment over part of Vietnam and the Lower Mekong Basin: performance evaluation and projection for rainfall","authors":"Huy Hoang-Cong, T. Ngo‐Duc, Tuyet Nguyen-Thi, Long Trinh-Tuan, Chung Jing Xiang, F. Tangang, Santisirisomboon Jerasorn, T. Phan‐Van","doi":"10.15625/2615-9783/16942","DOIUrl":"https://doi.org/10.15625/2615-9783/16942","url":null,"abstract":"This study first evaluates the performance of three model experiments in representing rainfall over part of Vietnam and the Lower Mekong Basin for the historical period 1986-2005. The three experiments include the Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-EARTH Global Climate Model (GCM) and two downscaling runs based on a regional climate model at 25km resolution with the GCM forcing (RCM-25km) and at 5km resolution with the RCM-25km forcing (RCM-5km). Verifications against observations show that the experiments generally capture the spatial distribution of climatological rainfall. While the GCM well represents the observed average rainfall cycles, its coarse resolution limits its capability in reproducing extreme rainfall values. The downscaling experiments do not clearly show their advantage in simulating average rainfall but exhibit significant added values when representing extreme rainfall in the study region. The RCM-5km does not outperform its driving 25km experiment in representing the mean and extreme rainfall values, suggesting that having a better resolution may not compensate for having a good model configuration with appropriate physical schemes. Analysis of climate projection for the far future period 2080-2099 under two representative concentration pathways (RCP) scenarios, RCP4.5 and RCP8.5, reveals that the downscaling experiments can modify the change direction of future rainfall obtained with the GCM. While the EC-EARTH GCM generally projects wetter tendencies of up to 50%, the downscaling experiments project a general decrease of down to -50% under both scenarios over the study domain. Regarding extreme rainfall, the annual maximum 1-day rainfall amount (RX1day) is projected to increase for the three experiments. The simple daily intensity index (SDII) future changes follow those of the annual rainfall values.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45501569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-17DOI: 10.15625/2615-9783/16929
Viet-Ha Nhu, Tinh T. Bui, L. My, Hoe Vuong, Hoang Nhat Duc
The research approaches a new machine learning ensemble which is a hybridization of Random subspace (RS) and C4.5, named RandSub-DT, for improving the performance of the landslide susceptibility model. This is based on the GIS database, including 170 landslide polygons and ten predisposing landslide factors, i.e., slope, aspect, curvature, TWI, land use, distance to road, distance to the river, soil type, distance to fault, and lithology. We carried out this study in the Halong and Cam Pha City areas which are important economic centers in the Quang Ninh province, Vietnam, where landslides seriously influence the daily life of the citizen causing economic damage. We then used a GIS database to construct and validate the proposed RandSub-DT model. The model performance was assessed using a confusion matrix and a set of statistical measures. The result showed that the RandSub-DT model with the classification accuracy of 90.34% in the training dataset and the prediction capability of 77.48% had a high performance for landslide prediction. This research proved that an ensemble of the C4.5 and RS provided a highly accurate estimate of landslide susceptibility in the research area.
{"title":"A new approach based on integration of random subspace and C4.5 decision tree learning method for spatial prediction of shallow landslides","authors":"Viet-Ha Nhu, Tinh T. Bui, L. My, Hoe Vuong, Hoang Nhat Duc","doi":"10.15625/2615-9783/16929","DOIUrl":"https://doi.org/10.15625/2615-9783/16929","url":null,"abstract":"The research approaches a new machine learning ensemble which is a hybridization of Random subspace (RS) and C4.5, named RandSub-DT, for improving the performance of the landslide susceptibility model. This is based on the GIS database, including 170 landslide polygons and ten predisposing landslide factors, i.e., slope, aspect, curvature, TWI, land use, distance to road, distance to the river, soil type, distance to fault, and lithology. We carried out this study in the Halong and Cam Pha City areas which are important economic centers in the Quang Ninh province, Vietnam, where landslides seriously influence the daily life of the citizen causing economic damage. We then used a GIS database to construct and validate the proposed RandSub-DT model. The model performance was assessed using a confusion matrix and a set of statistical measures. The result showed that the RandSub-DT model with the classification accuracy of 90.34% in the training dataset and the prediction capability of 77.48% had a high performance for landslide prediction. This research proved that an ensemble of the C4.5 and RS provided a highly accurate estimate of landslide susceptibility in the research area.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48174490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-12DOI: 10.15625/2615-9783/16874
Vinh Vu Duy, S. Ouillon, Hai NGUYEN MİNH
Based on the Mann-Kendall test and Sen’s slope method, this study investigates the monthly, seasonal, and annual sea surface temperature (SST) trends in the coastal area of Hai Phong (West of Tonkin Gulf) based on the measurements at Hon Dau Station from 1995 to 2020. The results show a sea surface warming trend of 0.02°C/year for the period 1995-2020 (significant level α = 0.1) and of 0.093°C/year for the period 2008-2020 (significant level α = 0.05). The monthly SSTs in June and September increased by 0.027°C/year and 0.036°C/year, respectively, for the period 1995-2020, and by 0.080°C/year and 0.047°C/year, respectively, for the period 2008-2020. SST trends in winter, summer, and other months were either different for the two periods or not significant enough. This may be due to the impact of ENSO, which caused interannual SST variability in the Hai Phong coastal with two intrinsic mode functions (IMF) signals a period of ~2 (IMF3) and ~5.2 years cycle (IMF4). A combination of these signals had a maximum correlation of 0.22 with ONI (Oceanic Niño Index) delayed by 8 months. ENSO events took ~8 months to affect SST at Hai Phong coastal area for 1995-2020 and caused a variation of SST within 1.2°C.
{"title":"Sea surface temperature trend analysis by Mann-Kendall test and sen’s slope estimator: a study of the Hai Phong coastal area (Vietnam) for the period 1995-2020","authors":"Vinh Vu Duy, S. Ouillon, Hai NGUYEN MİNH","doi":"10.15625/2615-9783/16874","DOIUrl":"https://doi.org/10.15625/2615-9783/16874","url":null,"abstract":"Based on the Mann-Kendall test and Sen’s slope method, this study investigates the monthly, seasonal, and annual sea surface temperature (SST) trends in the coastal area of Hai Phong (West of Tonkin Gulf) based on the measurements at Hon Dau Station from 1995 to 2020. The results show a sea surface warming trend of 0.02°C/year for the period 1995-2020 (significant level α = 0.1) and of 0.093°C/year for the period 2008-2020 (significant level α = 0.05). The monthly SSTs in June and September increased by 0.027°C/year and 0.036°C/year, respectively, for the period 1995-2020, and by 0.080°C/year and 0.047°C/year, respectively, for the period 2008-2020. SST trends in winter, summer, and other months were either different for the two periods or not significant enough. This may be due to the impact of ENSO, which caused interannual SST variability in the Hai Phong coastal with two intrinsic mode functions (IMF) signals a period of ~2 (IMF3) and ~5.2 years cycle (IMF4). A combination of these signals had a maximum correlation of 0.22 with ONI (Oceanic Niño Index) delayed by 8 months. ENSO events took ~8 months to affect SST at Hai Phong coastal area for 1995-2020 and caused a variation of SST within 1.2°C.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47223495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-05DOI: 10.15625/2615-9783/16864
Hoan Hoang Van, F. Larsen, Nhan Pham Quy, Long Tran Vu, Giang Nguyen Thị Thanh
In Nam Dinh province, in the Red River delta plain in Northern Vietnam, groundwater in the shallow Holocene aquifer shows elevated total dissolved solids up to 35 km from the coastline, indicating a saltwater intrusion from the Gulf of Tonkin. High groundwater salinities have been encountered below and adjacent to the Red River in the deep Pleistocene aquifer. Since 1996, large-scale groundwater abstraction was initiated from the deep aquifer, and the observed elevated salinities now raise concerns about whether the groundwater abstraction is undertaken sustainably. We have conducted a study to obtain a fundamental understanding of the recharge mechanisms and salinization processes in the Nam Dinh province. A holistic approach with multiple methods including transient electromagnetic sounding and borehole logging, exploratory drilling, sampling and analyzing primary ion and stable isotope compositions of water and pore water, groundwater head monitoring, hydraulic experiments laboratory of clay layers, and groundwater modeling by using the SEAWAT code. Results reveal that saline river water is leached from the Red River and its distributaries into the shallow aquifers. The distribution and occurrence of salty pore water in the Holocene aquitard clay shows that meteoric water has not been flowing through these low permeable clay layers. Marine pore water has, however, been leached out of the Pleistocene clay. When this layer is present, it offers protection of the lower aquifer against high salinity water from above. Salinity as high as 80 % of oceanic water is observed in interstitial pore water of the transgressive Holocene clay. Saltwater is transported into the Pleistocene aquifer, where the Holocene clay is directly overlying the aquifer.
{"title":"Recharge mechanism and salinization processes in coastal aquifers in Nam Dinh province, Vietnam","authors":"Hoan Hoang Van, F. Larsen, Nhan Pham Quy, Long Tran Vu, Giang Nguyen Thị Thanh","doi":"10.15625/2615-9783/16864","DOIUrl":"https://doi.org/10.15625/2615-9783/16864","url":null,"abstract":"In Nam Dinh province, in the Red River delta plain in Northern Vietnam, groundwater in the shallow Holocene aquifer shows elevated total dissolved solids up to 35 km from the coastline, indicating a saltwater intrusion from the Gulf of Tonkin. High groundwater salinities have been encountered below and adjacent to the Red River in the deep Pleistocene aquifer. Since 1996, large-scale groundwater abstraction was initiated from the deep aquifer, and the observed elevated salinities now raise concerns about whether the groundwater abstraction is undertaken sustainably. We have conducted a study to obtain a fundamental understanding of the recharge mechanisms and salinization processes in the Nam Dinh province. A holistic approach with multiple methods including transient electromagnetic sounding and borehole logging, exploratory drilling, sampling and analyzing primary ion and stable isotope compositions of water and pore water, groundwater head monitoring, hydraulic experiments laboratory of clay layers, and groundwater modeling by using the SEAWAT code. Results reveal that saline river water is leached from the Red River and its distributaries into the shallow aquifers. The distribution and occurrence of salty pore water in the Holocene aquitard clay shows that meteoric water has not been flowing through these low permeable clay layers. Marine pore water has, however, been leached out of the Pleistocene clay. When this layer is present, it offers protection of the lower aquifer against high salinity water from above. Salinity as high as 80 % of oceanic water is observed in interstitial pore water of the transgressive Holocene clay. Saltwater is transported into the Pleistocene aquifer, where the Holocene clay is directly overlying the aquifer.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42993984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Determination of naturally radionuclides have been known well as an important topic in environmental study in recently. One of the most toxic radioisotope in nature, a daughter product of 238U decay chain is 210Po (polonium). The improvement and optimizations methods for determination of this attractive isotope are still presenting so far. In this paper, a new improved method was elaborated for 210Po determination in thermal water sample. In the proposed method, analytical optimization of spontaneous/auto deposition does not use Teflon cup, magnetic stirring or any preparing equipment/item only normal glass and a side of square silver. In addition, the optimization was neglected with absent of purification of polonium (Liquid-liquid extraction methods/Ion exchange chromatography/Extraction chromatographic separations). The outcome of optimal procedure were simplify, less time consuming, great reduction of costs with chemical recovery >80% and could apply for any liquid environmental samples.
{"title":"Improvements of 210Po determination method in thermal water samples","authors":"Van- Hao Duong, Chau Nguyen Dinh, Trinh Phan Trong, Trung- Tien Chu","doi":"10.15625/2615-9783/16851","DOIUrl":"https://doi.org/10.15625/2615-9783/16851","url":null,"abstract":"Determination of naturally radionuclides have been known well as an important topic in environmental study in recently. One of the most toxic radioisotope in nature, a daughter product of 238U decay chain is 210Po (polonium). The improvement and optimizations methods for determination of this attractive isotope are still presenting so far. In this paper, a new improved method was elaborated for 210Po determination in thermal water sample. In the proposed method, analytical optimization of spontaneous/auto deposition does not use Teflon cup, magnetic stirring or any preparing equipment/item only normal glass and a side of square silver. In addition, the optimization was neglected with absent of purification of polonium (Liquid-liquid extraction methods/Ion exchange chromatography/Extraction chromatographic separations). The outcome of optimal procedure were simplify, less time consuming, great reduction of costs with chemical recovery >80% and could apply for any liquid environmental samples.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47558562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-23DOI: 10.15625/2615-9783/16842
Minh Pham, Hieu, Kenta Kawaguchi, Anh, Phuc
together with abundant Permian-Triassic magmatic rocks. This magmatic complex provides important information to reconstruct the tectonic evolution of the Indochina block and surrounding areas. The Cha Val plutonic rocks mainly comprise diorite, quartz diorite, and granodiorite. Geochemically, they are metaluminous with low A/CNK (0.49 to 1.16 with an average of 0.85), medium to high K, low to medium SiO2, and Na2O/K2O>1. Trace and rare earth element compositions display enrichment in Cs, U, Pb, and Nd, but depletion in Ba, Nb, Ta, P, Eu, and Ti, similar to those of continental arc-related magmas. Rock-forming minerals of the Cha Val plutonic rocks are characterized by abundant hornblende. All observed petrographical and geochemical characteristics suggest that the Cha Val plutonic rocks are typical for I-type affinity generated from a subduction regime. LA-ICP-MS U-Pb zircon analyses of three representative samples yielded their crystallization ages between 258.0 Ma and 248.9 Ma, temporally coeval with Late Permian-Early Triassic magmatism previously reported in the Truong Son belt. The (87Sr/86Sr)i ratios (0.7081 to 0.7244), negative whole-rock εNd(t) values (-4.5 to -2.9), zircon εHf(t) values (-1.04 to 2.71), and whole-rock Nd and zircon Hf model ages (TDM2) (1394 Ma to 1111 Ma) indicate that the Cha Val plutonic rocks are derived from melting of Mesoproterozoic crustal materials with a minor contribution of mantle-derived melt. Together with other Permian-Triassic magmatic complexes along the Song Ma suture zone and the Truong Son Belt, the Cha Val plutonic rocks are a representative of magmatism associated with the subduction-collision that amalgamated the South China and Indochina blocks after the closure of a branch of Paleo-Tethys along the Song Ma suture zone during the Late Permian-Early Triassic Indosinian orogeny.
{"title":"Geochemistry, zircon U-Pb geochronology and Sr-Nd-Hf isotopic composition of the Cha Val plutonic rocks in central Vietnam: Implications for Permian-Triassic Paleo-Tethys subduction-related magmatism","authors":"Minh Pham, Hieu, Kenta Kawaguchi, Anh, Phuc","doi":"10.15625/2615-9783/16842","DOIUrl":"https://doi.org/10.15625/2615-9783/16842","url":null,"abstract":"together with abundant Permian-Triassic magmatic rocks. This magmatic complex provides important information to reconstruct the tectonic evolution of the Indochina block and surrounding areas. The Cha Val plutonic rocks mainly comprise diorite, quartz diorite, and granodiorite. Geochemically, they are metaluminous with low A/CNK (0.49 to 1.16 with an average of 0.85), medium to high K, low to medium SiO2, and Na2O/K2O>1. Trace and rare earth element compositions display enrichment in Cs, U, Pb, and Nd, but depletion in Ba, Nb, Ta, P, Eu, and Ti, similar to those of continental arc-related magmas. Rock-forming minerals of the Cha Val plutonic rocks are characterized by abundant hornblende. All observed petrographical and geochemical characteristics suggest that the Cha Val plutonic rocks are typical for I-type affinity generated from a subduction regime. LA-ICP-MS U-Pb zircon analyses of three representative samples yielded their crystallization ages between 258.0 Ma and 248.9 Ma, temporally coeval with Late Permian-Early Triassic magmatism previously reported in the Truong Son belt. The (87Sr/86Sr)i ratios (0.7081 to 0.7244), negative whole-rock εNd(t) values (-4.5 to -2.9), zircon εHf(t) values (-1.04 to 2.71), and whole-rock Nd and zircon Hf model ages (TDM2) (1394 Ma to 1111 Ma) indicate that the Cha Val plutonic rocks are derived from melting of Mesoproterozoic crustal materials with a minor contribution of mantle-derived melt. Together with other Permian-Triassic magmatic complexes along the Song Ma suture zone and the Truong Son Belt, the Cha Val plutonic rocks are a representative of magmatism associated with the subduction-collision that amalgamated the South China and Indochina blocks after the closure of a branch of Paleo-Tethys along the Song Ma suture zone during the Late Permian-Early Triassic Indosinian orogeny.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48535845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-01DOI: 10.15625/2615-9783/16764
An, Hiroshi, Nhan, Tien, Thien
In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.
{"title":"Pore water pressure responses of saturated sand and clay under undrained cyclic shearing","authors":"An, Hiroshi, Nhan, Tien, Thien","doi":"10.15625/2615-9783/16764","DOIUrl":"https://doi.org/10.15625/2615-9783/16764","url":null,"abstract":"In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44330323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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