Vietnam Journal of Marine Science and Technology

How Cs-137 dispersions due to atmospheric deposition to East Vietnam Sea: a hypothetical level 7 incident from the Fangchenggang Nuclear Power Plant (China)

Duy Vinh Vu — 2024-05-21

Only about 50 km from the Quang Ninh coastal area in Vietnam, the Fangchenggang Nuclear Power Plant (China) operation causes excellent concerns for the environment, especially the marine environment, if an incident occurs. Based on topographic and hydrometeorological data and assumptions about radiation release conditions when an incident occurs, the Delft3D-Part modeling system was set up to assess/forecast the effect of Cs-137 radioactive activity on the source of air deposition in the water environment of Vietnam. The results showed that the sources of the drop from the air significantly affected and caused a faster impact than direct radioactive sources after the incident. Under the influence of marine circulation, wind radioactive material after falling into the sea will quickly disperse and may affect the entire East Vietnam Sea after 3–6 months. The area with high radioactivity is concentrated mainly in the Tonkin Gulf and along the coast of Vietnam. Especially in the Gulf of Tonkin, the radioactivity can reach 300–1,200 Bq/m³ after the 5-day incident. The amount of radiation then gradually decreases to almost less than 100 Bq/m³ after one year and below 20 Bq/m³ after two years. According to depth, the amount of radioactive Cs-137 tends to shift between layers from the surface to the bottom: higher at first in the upper layers, then gradually decreasing and increasing in the lower layers. Radioactivity significantly reduced after two years of the incident but still exceeded QCVN 10: 2008/BTNMT.

Evaluating of the accuracy of the DTU22MDT mean dynamic topography model based on the tidal gauge data in Vietnam’s coastal areas

Thi Hong Tham Bui — 2024-05-21

In this study, the accuracy of the latest mean dynamic topography model (MDT), DTU22MDT, is determined based on data collected from 14 tide gauge stations along the coast of Vietnam, from the North to the South. The process of assessing the accuracy of the DTU22MDT model is carried out carefully and precisely, involving determining the model’s height at tide gauge stations, quality checks of the data, and evaluation of the model’s accuracy. The research results indicate that, compared to the local sea surface in Vietnam, the DTU22MDT model has a higher height of approximately 0.7 meters. This model represents the global MDT with the highest accuracy in Vietnam, with a mean square error of about 9.0 cm. This information provides a basis for applying the model in scientific research and practical applications, such as constructing a national height system, planning the economic development of coastal areas, generating specialized maps, designing structures, and other activities in the maritime regions of Vietnam. The method used to evaluate the accuracy of the MDT in this study can be applied to other research areas and to different MDTs.

Research of fresh/salt water in Upper-middle Pleistocene
(qp_2–3) in Bac Lieu Province

Hoai Thu Trinh — 2024-05-21

This study identified the relationship between Total Dissolved Solids (TDS) and Electrical Conductivity (EC) with the TDS = 0.6628*EC = 0.1706 correlation, in which the correlation coefficient is r = 0.984 and the Standard Error (±%) is 2.78%. The TDS content is determined by small relative error and a high correlation coefficient of the conductivity, which applies to calculate the TDS content of other groundwater samples in Bac Lieu Province. Also, the temperature difference in the electrical conductivity measurement affects the TDS content; thus, the study has determined that the temperature compensated constant between the electrical conductivity on the field and those at 25^oC is 0.002953. According to the data and the analysis of the TDS content, the fresh-salt water distribution map of the qp_2–3 aquifers has been established, and its boundary has been more detailed and standardized than in the previous study. In particular, TDS values range from 0.437 g/L to 2.0 g/L. The areas that contain brackish and salt water are distributed discontinuously, forming the saline zones in Loc Ninh, Phuoc Long communes in Hong Dan district; Phuoc Long, Hung Phu communes in Phuoc Long district; Vinh Hau, Vinh Binh communes in Hoa Binh district, and Thuan Hoa commune in Bac Lieu city. The saltwater area of the qp_2–3 aquifers is about 398 km², accounting for 16% of the study’s total area. The results fresh-salt water distributed mapping provide the environmental management institution with a comprehensive view of the distribution of fresh-salt water to propose effective groundwater exploitation policies.

Status and impacts to sea turtles in Vietnam

Dang Ngai Nguyen — 2024-05-21

Sea turtles face a great danger of extinction because of human impacts, and the number of turtle occurrence is decreasing. By interviewing fishermen, coastal residents and authorities combined with field surveys in some places where turtles regularly lay eggs, such as Con Dao and Ninh Thuan, the results show that 05 species of sea turtles were found in Vietnam: The Green (Chelonia mydas), Hawksbill (Eretmochelys imbricata), Olive Ridley (Lepidochelys olivacea), Loggerhead (Caretta caretta) and Leatherback (Dermochelys coriacea). Among them, Green turtles are the most abundant and distributed in all surveyed localities; Hawksbill and Olive Ridley were smaller in number; and Loggerhead and Leatherback were the two species with the least number. Only 03 species remaining to breed on the beaches: Green, Olive Ridley, and Leatherback. The Hawksbill turtles used to lay eggs in the past but have been no longer recorded. Con Dao is a home for the largest number of breeding Green turtles. The reasons for the decline of turtles in Vietnam were the collection of eggs and nesting turtles, fisheries bycatch, development of coastal infrastructure and waste pollution, habitat degradation, and illegal trade in sea turtle products.

Dinoflagellate composition and environmental conditions in the Xuan Dai Bay, South-Central Vietnam

Thi Ngoc Duyen Huynh — 2024-05-21

The dinoflagellate community was investigated in association with environmental factors using a data set in April 2021 and April 2022 in Xuan Dai Bay, South-Central Viet Nam. Environmental variables, including physical parameters and dissolved inorganic nutrients, were measured in April 2022. Seventy-three dinoflagellate taxa were identified for Xuan Dai Bay. There was a significant difference in the number and abundance of dinoflagellates between two parts of the bay, the upper and lower bay. The study showed that dinoflagellates favored an area with good water exchange and were less affected by aquaculture activities. Principal component analysis (PCA) was used to explore the relative abundances of different phytoplankton groups, their diversity indices, and environmental variables at the surface and bottom layers of the two parts of the bay. The results showed that dinoflagellates correlated to physical parameters (e.g., PAR, salinity, temperature) at the surface layer and nutrients at the bottom layer. Dinoflagellates and diatoms are mixotrophic and strongly correlated at the bottom layer in Xuan Dai Bay. This strong relationship in the bay was because of the dominance of a heterotrophic genus, Protoperidinium. The present study provided characteristics of the dinoflagellates in Xuan Dai Bay and the possible impacts of environmental parameters on their abundance. The results can be used for further studies and possibly managing of dinoflagellate blooms in coastal waters.

Study on lipid and fatty acid composition of Thelenota ananas collected from Bai Dong Island, Ha Long Bay, Vietnam

Thi Phuong Ly Dang — 2024-05-21

The paper studies the lipid and fatty acid composition of the sea cucumber Thelenota ananas collected on Bai Dong Island, Ha Long Bay, Vietnam. The total lipid content of dry sample weight was relatively high (11.89%). The triacylglycerol TG has the highest concentration in total lipids with a ratio of up to 66.73%; the PL and PI classes do not have a significant difference with the proportions of 13.44 and 11.65% in total lipids. Two classes of sterol ST, hydrocarbon-wax HW and free fatty acid FFA account for a small proportion. The two main classes of phospholipids are PC and PE, with a ratio of 47.10% and 33.29% of total phospholipids. There are 36 fatty acids identified, of which total saturated fatty acids (SFA) account for 41.61%; Monounsaturated fatty acids (MUFA) account for 32.15%, and polyunsaturated fatty acids (PUFA) account for 25.63%; the main fatty acids are stearic acid (18:0) accounting for 13.15% of the total fatty acids; 16:1n-9 accounts for 14.87%, and 20:5n-3 EPA fatty acids account for 15.3% of the total fatty acids. Among the fatty acids, n-9 (omega 9) accounts for the highest proportion with 25.16%; n-3 fatty acids (omega 3) account for 18.43%; n-6 (omega 6), n-7 (omega 7) fatty acids account for 5.8 and 6.5%, respectively. In this study, the n3/n6 ratio of the sea cucumber sample Thelenota ananas was 3.18%, consistent with the evaluation standards of the World Health Organization (WHO) of n3/n6 ratio ≥ 0.1%. It is classified as a good foodstuff for human health; therefore, it can be considered a source of food that can be used to serve community health care needs.

Antimicrobial secondary metabolites from a marine-derived fungus Penicillium sp. OM07

Thi Dao Phi — 2024-05-21

Eight compounds, diketopiperazine dimer WIN 64821 (1), ergosterol peroxide (2), ergosterol (3), 3β,5α,9α-trihydroxyergosta-7,22-dien-6-one (4), 3,4-dihydroxy-6,7-dimethyl-quinolin-2-carboxylic (5), norhaman (6), dihydrocitrinin (7), and phenol A acid (8) were isolated and characterized from the culture broth of the marine-derived Penicillium sp. OM07 strain was isolated from sediment collecting at Son Cha, Hue, Vietnam. Their structures were determined by analyses of MS and NMR data. All compounds were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Most showed high antifungal activity against Candida albicans ATCC10231 strain with MIC values ranging from 8 µg/mL to 256 µg/mL. All compounds had inhibitory activity against from one to three Gram-positive tested strains with MIC values from 64–256 µg/mL.

Research on application of bromelain and alcalase for production of hydrolyzed powder from round scads
(Decaterus punctatus)

Tat Thanh Le — 2024-05-21

Round scad (Decaterus punctatus) is a species with high nutritional value and is used mainly as food for humans, and partly as food for aquatic animals. There are no processed products from scad fish in our country; thus, the value of scad fish products still needs to be higher. In this report, we have established the hydrolysis procedure by the enzyme mixture of bromelain and alcalase with the following conditions: the enzyme alcalase/bromelain ratio of 1/3; the enzyme and substrate ratio of 1%; hydrolysis temperature at 50oC; nature pH of fish; the incubated time of 6 h; the speed of 200 rpm; The hydrolyzed powder product is rich in protein (74.5%), and minerals (calcium, potassium, phosphorus, copper), thus has many potential applications in functional foods.

Assessing the Antifouling Effectiveness of the Novel Organic Coating for Adherent Species in the Seawater of the coastal area of Ha Long City, Quang Ninh Province (Vietnam)

Xuan Thai Nguyen — 2024-05-21

This paper presents the results of a 12-month testing period in seawater at Vung Oan, Ha Long City marine area, Quang Ninh Province (Vietnam), assessing the fouling organism’s removal effectiveness of polysiloxane (PS)/Ag-Zn zeolite/Cu₂O nanocomposite coatings. This experiment is a substantial base to evaluate impact of Ag-Zn/zeolite and Cu₂O nanoparticles (NPs) on growth of bacteria and macro-fouling organisms compared to a control coating without the above additives. The results indicated that the coating loaded with Ag-Zn/zeolite and Cu₂O NPs exhibited a lower bacterial count than the coating without biocide additives. Specifically, the bacterial count was 9.6 × 10⁵ for the coating with biocide and 2 × 10⁷ for the coating without biocide. Regarding macro-fouling species, the analysis and identification of organisms attached to the coating samples revealed the presence of three fouling species: Perna viridis, Balanus amphitrite, and Haliclona cinerea. Modiolus barbatus, Nereis sp., and Xanthidae were only observed on surface of the control samples, suggesting that Ag-Zn/zeolite and Cu₂O NPs can impede the development of Modiolus barbatus, Nereis sp., and Xanthidae on the coating surface. Furthermore, the average weight of macro-fouling organisms on the coating containing Ag-Zn/zeolite and Cu₂O NPs was significantly lower (90 g/sample) than that of the macro-fouling organisms on the control coating (333 g/sample). Notably, one of the three samples with the Ag-Zn/zeolite and Cu₂O NPs had the lowest weight of macro-fouling organisms, measuring only 35 g. Based on these findings, it can be concluded that polysiloxane/Ag-Zn/zeolite/Cu₂O nanocomposite coatings show promise as antifouling paints for marine work applications.