DSpace Collection:

Sea-level rise in Hai Phong coastal area (Vietnam) and its response to ENSO - evidence from tide gauge measurement of 1960-2020

Sat, 01 Jan 2022 00:00:00 GMT

Title: Sea-level rise in Hai Phong coastal area (Vietnam) and its response to ENSO - evidence from tide gauge measurement of 1960-2020 Authors: Nguyen, Minh Hai; Ouillon, Sylvain; Vu, Duy Vinh Abstract: The Hai Phong coastal area (Northwest of the Vietnam East Sea) is prosperous and densely populated, but it is also a place that is considered likely to be severely affected by sea-level rise. Based on the tide gauge measurement data at Hon Dau station during 1960-2020, the sea-level rise trends were analyzed and linked to the El Niño Southern Oscillation (ENSO). The analyses were carried out separately for the whole period (1960-2020) and for the last 19 years (2002-2020) by the Mann-Kendall test and Sen’s slope estimator. The Empirical Mode Decomposition method was used to identify the role of ENSO on the water level variability. The results showed a significant sea-level rise trend with a 95% confidence level. The average annual rates of sea-level were 3.56 mm/year and 7.78 mm/year over the periods 1960-2020 and 2002-2020, respectively, indicating a sea-level rise of about 21.4 cm over 60 years and a significant acceleration in sea-level rise recently (14.7 cm over the last 19 years). Sea-level that rose during El Niño events and declined during La Niña, related to ENSO with cycles of 2 and 6.1 years. From 1960 to 2020, ENSO events took four months to impact the sea-level in the Hai Phong coastal area, causing sea-level variability within -3.7 to 7.2 cm over 1972-2020.

Benthic habitat mapping and assessment of seagrass species diversity in Da Lon Reef, Truong Sa Islands, Vietnam, using very high-resolution satellite imagery and in situ data

Sun, 01 Jan 2023 00:00:00 GMT

Title: Benthic habitat mapping and assessment of seagrass species diversity in Da Lon Reef, Truong Sa Islands, Vietnam, using very high-resolution satellite imagery and in situ data Authors: Nguyen, Dang Hoi; Ngo, Trung Dung; Vu, Viet Dung Abstract: Benthic habitats are critical in shallow sea areas; they regulate the diversity and richness of organisms in each area. Mapping benthic habitats elucidates natural sea characteristics and aids in managing and using natural resources, as well as conserving marine biodiversity. This study established a benthic habitat map for the Da Lon Reef area, Truong Sa Islands, Vietnam, using Pléiades high-resolution remote sensing imaging materials and field survey results from 2020 and 2021. We identified seven classes of benthic habitats with a 91.64% overall accuracy, corresponding to a Kappa coefficient of 0.88. In the Da Lon Reef, seagrass biomes occupy a large area (more than 200 ha) and are distributed mainly inside lagoons at depths of 2–6 m. The field survey results identified five seagrass species and the biodiversity and biomass of seagrass populations in the lagoon of Da Lon Reef. The study results confirm the fundamental value of resources, biodiversity in general and seagrass in particular, in managing and protecting shallow sea ecosystems and biodiversity conservation in the Da Lon Reef area, an important part of the Truong Sa Islands, Vietnam.

Quaternary stratigraphy of southern Vietnam continental margin

Sun, 01 Jan 2023 00:00:00 GMT

Title: Quaternary stratigraphy of southern Vietnam continental margin Authors: Nguyen, Nhu Trung; Bui, Viet Dung; Bui, Van Nam; Pham, Nguyen Ha Vu; Nguyen, Van Kieu Abstract: This study investigates the stratigraphic architectures of the South Vietnam continental margin (SVCM) from the Pliocene to the recent period. We have utilized high-resolution seismic data and sediment core data to achieve this. The study reveals that the Quaternary sequences on the continental margin are bounded by composite erosional surfaces, which were formed due to sub-aerial erosion during periods of sea level fall and subsequent reworking processes during sea level rise. The Quaternary sequence can be divided into two subsequences: the Early Pleistocene and the Middle Pleistocene-Holocene. The Middle Pleistocene-Holocene sequences can be subdivided into six fourth-order sequences, each lasting approximately 100 to 120 thousand years. These sequences are well-preserved on the outer shelf at a modern water depth of around 100 to 120 meters. Seismic stacking patterns indicate that regressive deposits predominantly dominate the Quaternary stratigraphy of the SVCM. This means that sediment deposition during the Quaternary period was more pronounced during periods of sea-level fall. The outer shelf margin of the modern continental margin shows a south-to-southeastward migration of prograding clinoforms, indicating sediment progradation in these directions. The thick Quaternary regressive deposits preserved on the outer shelf are attributed to various factors. These factors include the low shelf gradient, tectonic subsidence, regional hinterland uplift, monsoon strengthening, and high sediment supply from the Palaeo-Mekong Delta during sea-level fall. The interaction of these factors facilitated the accumulation of thick sedimentary deposits during falling sea levels. The mid-late Pleistocene stratigraphy of the SVCM shows similarities to many other continental margins worldwide. These margins are mainly shaped under the influence of asymmetric 4th-order Milankovitch cycles. These cycles are driven by variations in Earth's orbital parameters and are characterized by longer phases of relative sea-level fall followed by shorter periods of stabilization and rise.

Wave-induced sediment dynamics and seabed changes around the Truong Sa Island, Vietnam

Thu, 01 Jan 2026 00:00:00 GMT

Title: Wave-induced sediment dynamics and seabed changes around the Truong Sa Island, Vietnam Authors: Nguyen, Xuan Tung; Nguyen, Minh Huan; Nguyen, Kim Cuong; Pham, Duc Hung; Luu, Anh Tuan Abstract: This study investigated wave-induced suspended sediment dynamics and seabed morphological changes around the Truong Sa Island in the East Vietnam Sea. The analysis was conducted using the MIKE 21/3 Coupled Model FM, which integrates wave, hydrodynamic, sediment transport, and bed evolution modules to simulate seabed responses to both seasonal and interannual wave forcing during 2013–2015. The model was forced with ERA5 reanalysis data and validated using observed tidal and bathymetric datasets from the Vietnam Academy of Science and Technology (VAST). Results revealed that seabed changes were most pronounced in the northeastern nearshore region of the Truong Sa Island. It was driven by the prevailing northeast-directed wave conditions, which also contributed to elevated suspended sediment concentrations (SSCs). Seasonally, winter exhibited more dynamic seabed changes and greater suspended sediment variability than summer. Under the most severe wave conditions in 2015, the simulated domain experienced a net seabed incision with an average depth of -0.54 m. Spatially, the nearshore areas were characterized by significant seabed incision and high SSCs, whereas offshore regions showed minimal seabed changes and low SSCs. Moreover, persistent sediment deposition was observed in the harbor southwest of the Truong Sa Island, implying the need for regular dredging to maintain operational capacity. The findings underscore the need for integrated management strategies that balance coastal development, marine ecosystem protection, and navigational safety.

Ecological risk assessment of microplastics and heavy metals in Northern Vietnam's estuarine sediments: A case study of Ba Lat and Bach Dang

Thu, 01 Jan 2026 00:00:00 GMT

Title: Ecological risk assessment of microplastics and heavy metals in Northern Vietnam's estuarine sediments: A case study of Ba Lat and Bach Dang Authors: Pham, Thi Minh Hanh; Le, Thi Huong; Truong Manh, Chien; Dang, The Ba; Dinh, Hai Ngoc; Duong, Thanh Nghi; Doan, Thi Oanh; Le, Thi Phuong Quynh; Nguyen, Trung Kien; Dang, Anh Tien; Duong, Thi Thuy Abstract: Estuarine environments are highly productive and biodiverse ecosystems that are particularly vulnerable to environmental pollution. This study assessed the presence and ecological risks of microplastics (MPs) and ten heavy metals in surface sediments from two major estuaries of the Red-Thai Binh River system in northern Vietnam: Ba Lat and Bach Dang. Sediment samples were collected during the rainy season (July 2024) under low tide conditions. The average concentrations of heavy metals followed the order: Hg < Cd < As < Ni < Cu < Cr < Pb < Zn < Mn < Fe. While most metal concentrations, except for Fe, were below Vietnamese regulatory limits (QCVN 43:2025/BTNMT), several samples exceeded the U.S. EPA (1997) Threshold Effects Level (TEL), particularly for As, Pb, Hg, Cu, and Ni. The geo-accumulation index identified Pb as the most enriched element, followed by As and Zn. Despite localized exceedances, the overall ecological risk associated with heavy metals was classified as low. In contrast, microplastic contamination posed a more prominent ecological threat. MP concentrations ranged from 3,600 to 9,000 items/kg (mean: 5,908±1,790) in Ba Lat and from 1,900 to 4,800 items/kg (mean: 3,858.3±832.8) in Bach Dang, surpassing levels reported in previous regional studies. The dominant particle types were small-sized fibers (< 2 mm) and fragments (0.05–0.2 mm²), which are likely to have greater bioavailability and ecological impact. A Potential Ecological Risk Index (PERI), incorporating MP abundance, polymer types, and hazard scores, indicated high-to-dangerous risk levels in Bach Dang and medium-to-high risk levels in Ba Lat. These findings highlight the urgent need for effective mitigation strategies, including improved plastic waste management and routine MP monitoring, particularly in ecologically sensitive areas such as aquaculture zones, coastal habitats, and salt production sites.