Vietnam Journal of Marine Science and Technology

Simulation of typhoon-induced hydrodynamic conditions in the Hai Phong coastal area: a case study of Son Tinh typhoon 2012 and 2018

2023-05-16T10:45:01+07:00

The Hai Phong coastal area is one of the places that is often affected by storms and tropical depressions, with significant impacts on hydrodynamics and geomorphological changes. The influence of typhoons on hydrodynamic conditions in the Hai Phong coastal area has yet to be thoroughly studied. Accordingly, the above study has evaluated the influence of storms with different trajectories on the hydrodynamic field in the Hai Phong coastal area under complex, non-linear impacts to contribute to a better understanding of the influence of storms on hydrodynamic processes and to improve research capacity on hydrodynamic regimes in coastal estuaries using modeling tools. Observational and reanalysis data from global sources were collected systematically and homogeneously to create open boundary conditions (time-serial) for the model. The NESTING method created sea boundary conditions for the model from another model with a larger grid outside. The Delft3D model system was set up with five vertical layers in Sigma coordinates and was validated, showing a fair agreement with measurement data at some places in the study area. Results of scenarios showed typhoons have an extreme impact on hydrodynamic conditions in the Hai Phong coastal area, especially raising the water level and increasing the flow velocity and wave height in the coastal area. Different typhoons effect the hydrodynamics differently, but they all share that the estuary areas with narrow channels are more strongly affected than the remaining areas. When the typhoons make landfall at the Lach Huyen estuary in Nam Trieu, the flow velocity can be up to 0.8–1.2 m/s (an increase of 0.5 m/s compared to the flow velocity in normal conditions), and the wave height can be up to 1.2–2.5 m (a rise of 0.4–2 m compared to the wave height in without typhoon).

Applying machine learning for hydraulic flow unit classification and permeability prediction: case study from carbonate reservoir in the Southern part, Song Hong basin

2024-08-07T20:11:00+07:00

Machine learning (ML) is an artificial intelligence (AI) that enables computer systems to classify, cluster, identify, and analyze vast and complex sets of data while eliminating the need for explicit instructions and programming. For decades, machine learning has become helpful for complex reservoir characterization such as carbonate reservoirs. Permeability prediction from well logs is a significant challenge, especially when the core data is rarely available due to its high cost. In this study, we aimed to bridge this gap by demonstrating the practical application of integrating Hydraulic Flow Units (HFU) and machine learning methods. Our goal was to provide a reliable estimation of permeability using core and wireline logging data in the complex Middle Miocene carbonate reservoir of the CX gas field in the southern part of the Song Hong basin. In the first step, due to the reservoir’s heterogeneity, the core plug dataset was classified into 5 HFUs based on the flow zone indicators (FZI) concept from the modified Kozeny-Carman equation using unsupervised machine learning - K-means method. The porosity - permeability for each HFU was defined after HFU clustering. In the second step, we designed three different workflows to predict permeability and HFU using supervised machine learning from a combination of core and log data. These workflows were rigorously test and compared with the core data. The most accurate result was chosen as the base, providing a high confidence level in our predictions’ reliability.

Grain-size distribution characteristics of sediments in coastal shallow waters from Van Don to Tien Yen - Ha Coi, Northwest Gulf of Tonkin, Vietnam, according to End-member modelling analysis

2024-08-07T20:10:50+07:00

The study involved the collection of eighteen surface sediment samples from the coastal shallow water area from Van Don to Tien Yen - Ha Coi in the Northwestern section of the Gulf of Tonkin to analyze their particle size composition. Utilizing the EMMAgeo end-member analysis model, four characteristic particle sizes (4EM) of 0.34, 7.7, 130, and 230 µm, corresponding to clay, fine silt, and fine sand of varying sizes were identified. In conjunction with the sedimentary environment, the spatial distribution analysis of these end members allowed a detailed determination of the formation conditions and distribution of the sediment components. Clay deposits (EM1) are primarily intercalated between the islands. At the same time, fine silt (EM2) is concentrated in the northern part of the study area, transported by flows, and deposited in a low-energy environment. Fine sand sediments (EM3 and EM4) are distributed along the coast of the Van Don peninsula in the Southern part of the study area and likely formed in association with tidal-wave processes under higher energy conditions compared to the North.

Diversity of the dinoflagellate genus Tripos Bory 1823 (Dinophyceae) in the Western coastal waters of Tonkin Gulf, Vietnam

2024-08-07T20:10:40+07:00

Tripos is a genus of marine dinoflagellates in the family Ceratiaceae, the order Gonyaulacales (Dinophyceae). The genus Tripos has been studied in the western coastal waters of Tonkin Gulf, including 6 coastal sampling stations (Tra Co, Cua Luc, Do Son, Ba Lat, Sam Son, Cua Lo) and 2 offshore stations (Co To, Bach Long Vi) in four surveys conducted in March, June, August and November 2022. A total of 21 species belonging to the genus Tripos were initially identified in the study area. The number of species of this genus is lower in the estuarine area and higher in the offshore. The species occurred at all sampling stations, including Tripos furca, T. fusus, T. muelleri, T. trichoceros and T. breve, in which T. furca and T. fusus were the most common species. Species were common including Tripos candelabrus, T. ehrenbergii, T. gravidus, T. minutus, T. extensus and T. longipes. The species diversity in the dry season (March and November) was higher than in the rainy season (June and August). Cell density of the Tripos species varies spatially and temporally in the study area. The variation in Tripos density was related to the sampling stations, tide, sampling time, and water environment factors such as temperature, salinity, DO and pH.

Biodiversity of coral reefs and associated seagrass beds in Quy Nhon Bay, Binh Dinh Province

2024-08-07T20:10:47+07:00

The distribution of critical marine habitats in Quy Nhon Bay, Binh Dinh Province, was assessed with the combination of resolution of Google Earth images and local knowledge through local consultations and ground truthing using small boats to check the sites supporting coral reefs and seagrass beds with local involvement. Detailed surveys on species diversity and conditions of marine habitats were conducted at 24 sites of coral reefs and four sites of seagrass beds at three sites (Nhon Ly, Nhon Hai, Ghenh Rang, and Nhon Chau) in 2016–2017. More than 152 ha of coral reefs, 5 ha of seagrass beds, and 720 species belonging to 7 key groups (290 species of fishes; reef-building corals: 194, molluscs: 123, seaweeds: 47, echinoderms: 40, crustaceans: 20 and seagrasses: 6 species) associated with the above habitats were recorded in the Bay. Among them, 92 species were facing different threats, in which 3 species were endangered (EN), including branching corals (Alveopora minuta), flat pen shells (Atrina vexillum), and top shells (Tectus pyramis); 38 species at vulnerable (VU); and 51 species at near threatened (NT) following the IUCN Red List and Vietnam Red Book. In general, the coral reefs and seagrass beds at Bai Dua and Seo Island (Nhon Ly); Kho Nho Island, Bo Dap (Nhon Hai); S. Ngang Island, Bai Nam and Bai Nom of Dat Island (Ghenh Rang); Da Ban, Bai Lang, Bai Lang Ba and Ong Gia Island (Nhon Chau) supported higher diversity and better conditions than other sites. Establishing restricted zones at these sites is an urgent need, but it also holds the premise of sustainable utilization and conservation of resources in the future.

The variation of organic carbon concentrations in the surface water in Cua Luc Bay, Ha Long Bay, Vietnam

2024-08-07T20:10:37+07:00

The total organic carbon (TOC) in the marine environment, which includes dissolved organic carbon (DOC) and particulate organic carbon (POC), is essential to the ocean’s carbon cycling system. This research was carried out in 2023 to assess the variation in organic carbon concentration in the environment of Cua Luc Bay and Ha Long Bay at 22 survey stations. The results show that the average concentrations of DOC and POC are 1.59 ± 0.21 mgC/L and 0.74 ± 0.35 mgC/L, respectively. However, DOC and POC concentrations are still considered low compared with other rivers and estuaries in Vietnam and worldwide. The ratios of organic carbons like DOC/POC and POC/Chl-a in this study area were also calculated. The ratios’ results are evidence of many fluctuations in the water environment in Ha Long Bay, Vietnam, in 2023.

Diversity of fatty acids in different coral species collected in the coastal sea of Nha Trang, Khanh Hoa

2024-08-07T20:10:32+07:00

The total of 15 coral samples belonging to soft coral species Sinularia flexibilis, hard coral Acropora sp., and the hydrocoral Millepora platypylla, were collected in the coastal sea of Nha Trang, Khanh Hoa, Vietnam. In these samples, 39 fatty acids were identified in which Sinularia flexibilis sample identified 26 fatty acids, Acropora sp. identified 27 fatty acids, and Millepora platyphylla has the most diverse fatty acid composition with 35 fatty acids. In the coral samples of S. flexibilis, the difference between the ratio of total saturated fatty acids and the polyunsaturated fatty acids was much smaller than that of the other two species. The n-3/n-6 ratio is the highest among Millepora species, up to 4.45; in S. flexibilis and Acropora, this ratio can be lower than 1. Fatty acids 16:0 and 18:0 are the two main fatty acids in total; the content varies between samples of different species but is quite similar amongst samples of the same species. Fatty acids characterized by symbiotic microalgae 16:2n-7, 18:3n-6, 18:4n-3 Fatty acids 18:3n-6 were absent in S. flexibilis samples, minor content in M. platyphylla samples, and relatively significant in Acropora sp. (from 7.07% to 9.59% total fatty acids). Two fatty acids 16:2n-7 and 18:4n-3 were present in all 3 species, the highest in the sample S. flexibilis. The tetracosapolyenoic fatty acids 24:5n-6 and 24:6n-3 are soft coral marker fatty acids, present in only 5 samples of S. flexibilis with 24:5n-6 content ranging from 2.56% to 5.58% total fatty acids, 24:6n-3 is much lower (0.24% to 0.76%). The two PUFAs with the highest concentration were 20:4n-6 and 22:6n-3. 20:4n-6 was present in the total fatty acids of S. flexibilis with a quite high content (9.76% to 17.12% of the total axb), in contrast, the proportion was very low in five Millepora samples and five Acropora samples. 22:6n-3 was significantly high in the five Millepora samples (12.63% to 25.29% total fatty acids) and minor in the samples of the other two species.

Antioxidant and cytoprotective activities of marine fungi isolated from brown seaweeds in Nha Trang Bay, Khanh Hoa Province, Central Vietnam

2024-08-07T20:10:56+07:00

This study aims to evaluate the antioxidant and cytoprotective activities of 32 fungal strains isolated from brown seaweeds collected from Nha Trang Bay, Khanh Hoa Province, Central Vietnam. These fungal extracts were screened for antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) free radical scavenging assay. In contrast, cytoprotective activity on rat cardiomyocytes H9c2 cell line was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay. The results indicated the capacity for free DPPH and ABTS radical scavenging of fungal crude extracts with 31.25% (n = 10) and 81.25% (n = 26), respectively. Among the fungal strains with high antioxidant activity, the three fungal extracts 2104NT-1.3, 2104NT-3.3, and 2104NT-7.7 increased the viability of rotenone-exposed cardiomyocyte cells by 9.9%, 15.2%, and 13.6%, respectively. Three fungal strains with significant antioxidant and cytoprotective activities were identified as Penicillium chermesinum 2104NT-1.3, Aspergillus sp. 2104NT-3.3, and Penicillium sp. 2104NT-7.7 based on sequence analysis of internal transcribed spacer (ITS) region. This study provided the potential fungal strains isolated from Nha Trang Bay for further investigation of antioxidant and cytoprotective compounds.

Study of nitrogen and phosphorus nutrient dynamics in concentrated marine fish farming water environment in Long Son - Vung Tau

2024-08-07T20:10:44+07:00

The nutritional content of N and P in concentrated marine fish farming water in the Cha Va - Long Son - Vung Tau estuary area increased sharply during 2013–2016; notably, the N-NH₄⁺ content increased in 2017–2019. The N-NO₂^- and N-NO₃^- content in the dry season (0.051 mg/L and 0.190 mg/L) was higher than in the rainy season (0.044 mg/L and 0.133 mg/L). In contrast, the N-NH₄⁺ and P-PO₄^3- contents in the rainy season (0.321 mg/L and 0.1 mg/L) are higher than in the dry season (0.154 mg/L and 0.093 mg/L). The N and P nutrient dynamics in water fluctuate according to the semi-diurnal tide regime; the nutrient content decreases during high water - daytime, increases during low water in the evening, and is high during high water at night and in the morning, early the next day. In dry and rainy seasons, the N-NH₄⁺ content is always the highest (0.024–0.761 mg/L) among the nitrogen-based nutritional parameters. N and P nutrients in water are correlated: N-NH₄⁺ parameter pairs with Total P, N-NO₂^- with Total P, Total N with Total P, N-NO₂^- and N-NO₃^-, P-PO₄^3- with Total P, and the parameter pair N-NO₂^- with P-PO₄^3- have low positive correlation coefficients (r), from 0.1–0.21. Conversely, the parameter pairs N-NO₃^- and Total N, N-NO₃^- and N-NH₄⁺, and N-NO₂^- and N-NH₄⁺ have low negative correlation coefficients (r), from -0.12 to -0.26. From 2010–2021, the number of cages increased beyond planning, causing environmental pollution in the water in the farming area. The nutritional RQ value of the water is high at level 4 every year (very high risk of environmental pollution).