Coastal Areas Of Vietnam Research Articles

Dynamics of Farming Systems under the Context of Coastal Zone Development: The Case of Xuan Thuy National Park, Vietnam

The study was conducted in Xuan Thuy National Park to provide a comparative assessment of different farming systems under the context of the coastal zone development of Vietnam. Based on a sample of 234 farmers in this area, SCP (Structure–Conduct–Performance) analysis revealed three farming systems: integrated aquaculture–mangrove (IAM), intensive shrimp (ISH), and rice-based (RB) farming. The evaluation of farm performance among the systems indicated that ISH incurred the highest values of variable cost and sustainable family income. Meanwhile, IAM obtained the lowest production cost due to the availability of allocated natural resources. The imbalance of applying synthesized fertilizers and an overdependence on nitro-based fertilizers were reported in the case of RB systems. In comparison with the other coastal areas of Vietnam, these farming systems achieved a lower level of production efficiency. It is urgent for policy makers to take action to promote sustainable farming practices in accordance with the stringent enforcement of environmental standards to reduce potential impacts and strengthen the coexistence of systems. Additionally, the purpose of securing rural livelihood under coastal development is aligned with the recommended solutions for economic improvement in this study.

Effect of Tides and Storm Surges on Storm Waves at the Northern Coastal Areas of Vietnam

Abstract: In this study, the effect of tides and storm surges on storm waves at the Northern coastal area of Vietnam is investigated by a coupled model of surge wave and tide (called: SuWAT). In particular, tide and storm surge are simulated by two-dimensional long wave equations taking into account the wave radiation stress, obtained from the SWAN model. The numerical was then applied to simulate storm waves and surges for typhoon Frankie (7/1996), Washi (7/2005) and Doksuri (9/2017). In the case of the super typhoon, the intensity of typhoon Washi is increased to level 16 (super typhoon level) but remains the same trajectory and operating time. The numerical results showed relatively well with observation data on storm surge and wave height. In general, the wave height is higher in the region near the coast and lower at offshore when considering the effect of tide and storm surge on storm wave. It also indicated that the effect of storm surge on storm wave is more significant than the tide. The results of the study are the basis for proposing to improve the wave forecasting technology in the study area.
 Keywords: Storm wave, tides, storm surge, super typhoon.

Effect of Water-Binder Ratio and Complex Organic-Mineral Additive on Properties of Concrete for Marine Hydrotechnical Constructions

Large-scale construction of marine structures in the coastal and offshore areas of Vietnam requires the development of new compositions of hydrotechnical concrete and innovative technologies for the preparation of concrete mixes, as well as their transportation to the place of placement. A preliminary composition of heavy concrete was determined and its properties were studied. The effect of the water-binder ratio (W/B) and the effect of using the developed complex organo-mineral modifying additive consisting of fly ash (FA) of Vung Ang TPP, microsilica SF-90 (SF90) and polycarboxylate superplasticizer SR 5000F (SP) on the concrete properties. To process the obtained results, the method of mathematical planning of the experiment with the construction of a four-factor plan was used. As a result of the studies conducted, first-order regression equations were obtained depending on the objective functions - the mobility of the concrete mixture on the cone sediment, the compressive strength of concrete and the deformations of concrete on input factors - x1 (W/B), x2 (amount of SP), x3 (amount of FA) and x4 (amount of SF90). From the obtained regression equations, it follows that the water-binder ratio, as well as the content of superplasticizer, fly ash and microsilica in the composition of the additive have a significant impact on the mobility of concrete mixtures. When reducing W/B and the amount of FA, as well as the increase in the amount of SF90 (x4) concrete compressive strength in 28 days also increases. The result of this study showed the relative deformation of concrete also increases with an increase in the content of FA and reducing W/B and the amount of SF90. At the same time, the effect of the water-binder relationship is most pronounced. It can be assumed that, in the composition of the developed modifying additive, the particles FA and SF90 played the role of a kind of “sliding bearings” between the grains of cement, with which you can control the dispersion of cement and finely dispersed mineral grains in the concrete mixture, and hence its mobility and persistence construction sites in the coastal areas of Vietnam. In addition, SF90, containing 91.65% of amorphous silica, binds free calcium hydroxide to less soluble low-basic calcium silicate silicates, compresses the structure of concrete and increases its compressive strength.

Quantification of ragworm (Nereididae: Tylorrhychus) density in soil macrofauna communities in the Northern coastal area of Vietnam

The study aims were focused on ragworms (Nereididae: Tylorrhynchus), their relations to other soil macrofauna animals as well as their distributional characteristics. We recorded 20 soil macrofauna orders belonging to 9 classes: Adenophorea: Araeolaimida, Gastropoda: Mesogastropoda & Stylommatophora, Polychaeta: Aciculata, Oligochaeta: Haplotaxida & Tubificidea, Hirudinea: Arhynchobdellida, Arachnida: Araneida, Crustacea: Decapoda, Myriapoda: Symphyla, Oniscomorpha, Juliformia & Scolopendromorpha, Insecta: Odonata, Orthoptera, Hemiptera, Homoptera, Coleoptera, Hymenoptera and Diplura, and one unidentified. Soil macrofauna diversity decreases following order of habitat types: (d) Grassland and (e) Cultivated field > (a) Thai Binh river bank and (b) Ragworm rearing rice field > (c) Dike. The soil macrofauna population densities decreases in the following order of habitat types: (c) > (d) > (a) > (e) > (b). Their biomass decreases in the following order: (d) > (c) > (e) > (b) > (a). Soil macrofauna diversity and their population densities decreases in the following order of soil vertical layers: (1) > (-2) > (-3) > (-4) > (-5). Their biomass decreases in the following order: (-1) > (-4) > (-2) > (-3) > (-5). Ragworm Tylorrhynchus was recorded in only one habitat type, the (b) ragworm reaing rice field, in which recorded were eight other macrofauna orders: Mesogastropoda (Gastropoda), Aciculata (Polygochaeta), Tubificidea (Oligochaeta), Arhynchobdellida (Hirudinea), Decapoda (Crustacea), Hemiptera, Coleoptera and Hymenoptera (Insecta), and an unidentified one. The macrofauna density was smallest in the habitat (b).
 Rươi (Nereididae: Tylorrhynchus) được khảo sát trong mối liên hệ với các nhóm động vật đất Macrofauna khác, cùng đặc điểm phân bố theo sinh cảnh và tầng đất thẳng đứng. Xác định được 20 bộ động vật macrofauna đất thuộc 9 lớp: Adenophorea: Araeolaimida, Gastropoda: Mesogastropoda & Stylommatophora, Polychaeta: Aciculata, Oligochaeta: Haplotaxida & Tubificidea, Hirudinea: Arhynchobdellida, Arachnida: Araneida, Crustacea: Decapoda, Myriapoda: Symphyla, Oniscomorpha, Juliformia & Scolopendromorpha, Insecta: Odonata, Orthoptera, Hemiptera, Homoptera, Coleoptera, Hymenoptera & Diplura, một nhóm không xác định. Đa dạng các bộ động vật đất Macrofauna giảm theo thứ tự loại sinh cảnh sau: (d) & (e) >(a) & (b) >(c). Mật độ quần thể của động vật đất Macrofauna giảm theo thứ tự sau: (c) > (d) > (a) > (e) > (b). Sinh khối của chúng giảm theo thứ tự sau: (d) > (c) > (e) > (b) > (a). Đa dạng các bộ động vật đất Macrofauna và mật độ quần thể giảm theo thứ tự tầng đất thẳng đứng sau: (-1) > (-2) > (-3) > (-4) > (5). Sinh khối của chúng giảm theo thứ tự sau: (-1) > (-4) > (-2) > (-3) > (-5). Loài rươi (Tylorrhynchus sp.) chỉ ghi nhận được ở sinh cảnh (b) ruộng lúa nuôi rươi. Trong sinh cảnh này còn xác định được 8 bộ Macrofauna khác là Gastropoda: Mesogastropoda, Polygochaeta: Aciculata, Oligochaeta: Tubificidea, Hirudinea: Arhynchobdellida, Crustacea: Decapoda, Insecta: Hemiptera, Coleoptera, Hymenoptera, và không xác định được tên.

Pilot Study of Brackish Water Treatment using Dual Stage Nanofi ltration for Domestic Use in Thu Bon Basin, Vietnam

Due to the impact of climate change, the process of salinity intrusion occurs frequently in coastal areas of Vietnam. The main objective of this study is therefore to try diff erent nanofi ltration (NF) processes (such as single-stage and dual-stage NF) to treat brackish water for residential areas in Thu Bon river basin, where the salinity varies signifi cant with seasons. Results have shown that during the rainy season, the salinity was less than 8.5‰, so the single stage NF worked perfectly. When season changes from rainy season to dry season, the river’s salinity increases up to 17.5‰, application of dual NF is most appropriate. This dual NF process not only guarantees the effl uent quality to meet National Technical Regulation, but also off ers reasonable energy cost and fi nally can prolong the membrane lifespan.

Modeling of Atmospheric Corrosion in the Tropical Climate of Vietnam

The kinetics of corrosion losses of carbon steel, copper, and zinc in the continental and coastal areas of Vietnam is studied by in situ testing. The dominant climate and aerochemical atmospheric factors are revealed with respect to the metals tested in different periods of their exposure. The mathematical models that characterize the relationship between the time of wetness of metal surface, atmospheric pollution, and corrosion rate are developed. Based on power law model M = At k , the values of constants A and k are calculated for each metal and test site, where parameter A characterizes corrosion losses of metal for the first year of exposure and k denotes the protective properties of a layer of corrosion products.

Determination of multi-element composition of Vietnamese marine sediment and tuna fish by k 0-standardized neutron activation analysis

The k0-standardized neutron activation analysis (k0-NAA) has been applied for determination of multiple elements (25 elements: Al, As, Ba, Br, Ca, Cl, Co, Cr, Cs, Cu, Eu, Fe, Hg, K, La, Mg, Na, Rb, Sc, Se, Sm, Th, Ti, V and Zn) in marine sediment and tuna fish. About 50 marine sediment and 9 tuna fish samples were collected in two coastal areas of Vietnam. The health risk index (HRI) values of As and Br were higher than 1.0 for the tuna fish. Also, HRI value of Hg was 8.92 × 10−1 indicating a relatively high potential health risk, whiles Co and Mn with HRIs = 1.56 × 10−4 and 8.56 × 10−4, respectively, have the lowest potential health risks. Average enrichment factors using Al as a reference element (EFAl) were higher than 1.5 for Eu, La, Zn, Th, Cs and As in which the highest EFAl value for As was higher than 10. This study showed that the HRI value of As in the tuna fish correlated positively with the EFAl value for the element in the marine sediment.

Socio-Ecological Risk Factors for Prime-Age Adult Death in Two Coastal Areas of Vietnam

BackgroundHierarchical spatial models enable the geographic and ecological analysis of health data thereby providing useful information for designing effective health interventions. In this study, we used a Bayesian hierarchical spatial model to evaluate mortality data in Vietnam. The model enabled identification of socio-ecological risk factors and generation of risk maps to better understand the causes and geographic implications of prime-age (15 to less than 45 years) adult death.Methods and FindingsThe study was conducted in two sites: Nha Trang and Hue in Vietnam. The study areas were split into 500×500 meter cells to define neighborhoods. We first extracted socio-demographic data from population databases of the two sites, and then aggregated the data by neighborhood. We used spatial hierarchical model that borrows strength from neighbors for evaluating risk factors and for creating spatially smoothed risk map after adjusting for neighborhood level covariates. The Markov chain Monte Carlo procedure was used to estimate the parameters. Male mortality was more than twice the female mortality. The rates also varied by age and sex. The most frequent cause of mortality was traffic accidents and drowning for men and traffic accidents and suicide for women. Lower education of household heads in the neighborhood was an important risk factor for increased mortality. The mortality was highly variable in space and the socio-ecological risk factors are sensitive to study site and sex.ConclusionOur study suggests that lower education of the household head is an important predictor for prime age adult mortality. Variability in socio-ecological risk factors and in risk areas by sex make it challenging to design appropriate intervention strategies aimed at decreasing prime-age adult deaths in Vietnam.

The size and age structure of Tridacna crocea Lamarck, 1819 (Bivalvia: Tridacnidae) in the coastal area of islands of the Cön Dao Archipelago in the South China Sea

In May 2010, an expedition on the research vessel Akademik Oparin explored the populations of the clam Tridacna crocea on reefs of the Bay Canh and Cau islands of the Con Dao Archipelago in the South China Sea. A retrospective approach using phototechniques revealed a great similarity of the vertical distribution, growth, size, and age composition of the tridacna at these islands. The maximum density of tridacna (25 ind/m2) was characteristic of a depth of about 3 m in the area of reef flat transition to reef slope. The growth of clams can be approximated by a Bertalanffy-type equation: Lt = 133.8[1 − e−0.1181(t − 0.2596)]. The lack of discreteness in the size and age compositions of populations of T. crocea indicated that population recruitment was quite stable over the years. This tends to maintain the population in a relatively stable condition, which enabled us to consider it as a possible reserve for the artificial restoration of populations of the species in impoverished coastal areas of Vietnam.

Yielding Potential of Rubber (Hevea brasiliensis) in Sub-Optimal Environments

SUMMARY Rubber production has been extended to many sub-optimal environments worldwide during late 1970s. Prominent among them are northeast India, highlands and coastal areas of Vietnam, southern China and southern plateau of Brazil. In addition to near-ideal growing conditions, these areas offer stresses like low temperature, higher altitude, diseases and wind. South China experiences all these stresses due to expanse of land mass and extremely diverse climate. A number of rubber clones are being evaluated along with derivation of new recombinants adaptable to these areas. Rubber clones are seen to exhibit specific adaptation in these areas. A negative relationship of yield with minimum temperature, wind velocity and evaporation is very distinct in all clones in Tripura (NE India). While RRIM 600 can be adjudged as a universally adapted clone with moderate yield under all these sub-optimal environments, specificity in yield adaptation goes in favor of PB 235, RRII 208, RRII 203 and HAIKEN 1 (India); RRIM 600, GT 1 (Vietnam); REYAN 8-333, PB 235 (China) and PB 235, FX-3864 (Brazil). Though PB 235 gave higher yield in these areas, recommendations for commercial cultivation are impeded as a result of high wind damage. Clonal specificity for adaptation is distinct.