Seasonality and nutrient-uptake capacity of Sargassum spp. in Western Australia

The eight-band high resolution multispectral WorldView-2 satellite imagery demonstrated potential for mapping and monitoring Sargassum spp. beds and other associated coastal marine habitats around Rottnest Island and Point Peron. Sargassum spp. in Western Australian coast showed seasonal changes in canopy cover and mean thallus length which are also significantly influenced by the nutrient concentrations. This study documented the life cycle of Sargassum spinuligerum and successfully cultivated the species for the first time in Western Australia

ADSORPTIVE CATHODIC STRIPPING VOLTAMMETRIC DETERMINATION OF SEVERAL HEAVY METALS (Ni, Co, Cu, Pb) IN NATURAL WATERS

Joint Research on Environmental Science and Technology for the Eart

Growth and morphological responses of Halophila beccarii to low salinity

Halophila beccarii Ascherson is classified as a threatened seagrass species by IUCN because of the reductive tendency of ​​its distribution area. This seagrass is considered a euryhaline species adapted to a wide range of salinities from freshwater and brackish water to marine water. Previous studies showed that the species tends to grow better under low salinity; however, its optimum salinity has not been determined. In Vietnam, H. beccarii grows in habitats with low salinity (0–20 ppt). The results show that salinity affects the growth, survival rate, shoot density, biomass, and morphological characteristics of the grass. The leaf dimension is more prolonged and broader; the petiole and shoot length are longer at 10 ppt salinity. In contrast, both the number of shoots and biomass peak at 5 ppt and decrease at lower and higher salinities. The study reveals that H. beccarii can grow better under mesohaline conditions than freshwater and hypersaline conditions with an optimum salinity at 5–10 ppt. These findings would explain the species’ distribution dynamics in coastal environments and be helpful information for conserving the seagrass populations in habitats with fluctuating salinity as coastal lagoons in Central Vietnam

KHẢ NĂNG LƯU TRỮ CACBON CỦA THẢM CỎ BIỂN TẠI ĐẦM LĂNG CÔ, TỈNH THỪA THIÊN HUẾ

Seagrass beds play an essential role in mitigating climate change by absorbing CO2 from the atmosphere and converting carbon into biomass through photosynthesis. We used remote sensing and GIS technology with field survey data to establish the distribution and above-ground dry biomass maps of seagrass beds in 2021. A Landsat 8 OLI satellite image was used in the interpretation process. An above-ground dry biomass map was established by building the regression function between the above-ground dry biomass and the reflectance spectrum of the image bands. The overall accuracy and the Kappa coefficient of the classification process were 95.5% and 0.94. At Lang Co Lagoon, the seagrass bed area in 2021 was about 36.18 ha, distributed primarily in the area between Lang Co Town and the north of the lagoon; and scattered in the north of the lagoon, Hoi Can, Hoi Dua, and Hoi Mit. In addition, the total carbon stock of seagrasses in Lang Co Lagoon was estimated at 5.54 tons, equivalent to 20.32 tons of CO2, in which the contribution of Halodule uninervis accounted for 61% of the total carbon stock.Thảm cỏ biển đóng vai trò quan trọng trong việc giảm thiểu biến đổi khí hậu thông qua việc hấp thụ CO2 từ khí quyển và chuyển cacbon thành sinh khối nhờ quá trình quang hợp. Chúng tôi đã sử dụng công nghệ viễn thám và GIS, kết hợp với dữ liệu khảo sát thực địa, để thành lập bản đồ phân bố và sinh khối khô trên mặt đất của hệ sinh thái thảm cỏ biển tại Đầm Lăng Cô vào năm 2021. Một ảnh vệ tinh Landsat 8 OLI đã được sử dụng trong quá trình giải đoán. Một bản đồ sinh khối khô trên mặt đất được thành lập thông qua việc xây dựng hàm hồi quy giữa sinh khối khô trên mặt đất và phổ phản xạ của các kênh ảnh Landsat. Độ chính xác tổng thể và hệ số Kappa là 95,5% và 0,94. Tại Đầm Lăng Cô, diện tích thảm cỏ biển năm 2021 chiếm khoảng 36,18 ha, phân bố chủ yếu ở các khu vực giao giữa Thị trấn Lăng Cô và phía Bắc của đầm; rải rác tại phía Bắc của đầm, Hói Cạn, Hói Dừa và Hói Mít. Ngoài ra, tổng trữ lượng cacbon của cỏ biển ở Đầm Lăng Cô là 5,54 tấn cacbon, tương đương với 20,32 tấn CO2; trong đó, sự đóng góp của loài Halodule uninervis chiếm 61% tổng trữ lượng cacbon

Trends and extremes of drought episodes in Vietnam sub-regions during 1980–2017 at different timescales

This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regions of Vietnam during the 1980–2017 period. This assessment was performed using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at 1 to 24 months timescales. Results show that the main periods of extreme drought occurred simultaneously throughout the country in 1992–1993 and 2003–2004, except for 2015–2016, when it was not identified in the southern region. In addition, a slight temporal lag was identified latitudinally (north–south) at the beginning of dry conditions, revealing the largest difference between the northern and southern regions. A positive trend in the time series of both indices (SPEI and SPI) prevailed in all sub-regions, with the SPEI minus SPI difference always being negative, suggesting the importance of temperature and evapotranspiration for this trend. Further detailed analyses were then performed using SPEI at 1-month and 12-months timescales for all climate sub-regions, as well as the main indicators to characterize duration and severity. Results show that the number of drought episodes did not vary much between regions, but they did vary in duration and severity at the annual scale. Moreover, changes in the soil root zone are largely associated with dry and wet conditions not only from season to season, but also in longer accumulation periods and more strongly in the northern regions of Vietnam. Indeed, a study of the most severe drought episodes also revealed the occurrence of negative anomalies of the root-soil moisture in the subsequent four or more months. Dynamic atmospheric conditions associated with the peak of most severe drought episodes show the crucial role of subsidence of dry air in the middle and high atmosphere, which prevents convection in the lower troposphere. Finally, the linkages between drought conditions in Vietnam and large-scale atmospheric and oceanic teleconnection patterns were revealed to be quite different among northern and southern sub-regions. During the positive phase of El Niño–Southern Oscillation (ENSO), drought episodes at different timescales were identified in the southern climate sub-regions, while the negative phase was associated with drought conditions in the northern regions.Xunta de Galicia | Ref. ED481B 2019/070Fundação para a Ciência e a Tecnología | Ref. UIDB/50019/2020–IDLXunta de Galicia | Ref. ED481B 2018/062Xunta de Galicia | Ref. ED431C 2017/64-GRCMinisterio de Ciencia, Innovación y Universidades | Ref. RTI2018-095772-B-I00Fundação para a Ciência e a Tecnología | Ref. PTDC/CTA-MET/29233/201

Current advances in seagrass research: A review from Viet Nam

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total Corg stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity

Remote-Sensed Mapping of Sargassum spp. Distribution around Rottnest Island, Western Australia using High Spatial Resolution WorldView-2 Satellite Data

Satellite remote sensing is one of the most efficient techniques for marine habitat studies in shallow coastal waters, especially in clear waters where field observations can be easily carried out. However, such in situ observations have certain limitations: they are time consuming, have a limited ability to capture spatial variability, and require an interdisciplinary approach between marine biologists and remote-sensing specialists. The main objective of this study was to survey and map Sargassum beds around Rottnest Island, Western Australia, through a combination of high spatial resolution WorldView-2 imagery, using a validated depth invariant index model for water-column correction, and in-field observations. The combination of field survey data and four classification methods resulted in highly accurate classification outcomes that showed the distribution patterns of Sargassum spp. around Rottnest Island during the austral spring season (October 2013). Overall, the minimum distance and Mahalanobis classifiers yielded the highest overall accuracy rates of 98.32% (kappa coefficient, κ = 0.96) and 98.30% (κ = 0.96), respectively. The K-means classification method gave the lowest accuracy percentage of 42.50% (κ = 0.22). Thus, the primary results of this study provide useful baseline information that is necessary for marine-conservation strategic planning and the sustainable utilization of brown macroalgae resources around the Western Australian coast

Application Earth Observation Data for Monitoring Coastal Marine Ecosystes in Vietnam

<p>Poster presented at the "Oceans and Society: Blue Planet"  Symposium in São Paulo, Brazil in November 2012.</p> <p><strong>Abstract</strong></p> <p>The data on spatial distribution, qualitative and quantitative characteristics of coastal habitats can be considered as fundamental and essential information for the planning, policy making on sustainable developing and utilizing these coastal marine ecosystems under impacts of economic development and natural disaster pressures. Coastal wetland habitats of Huong Phong Commune belongs to Huong Tra District, in the central province of ThuaThien Hue, Vietnam was selected as a pilot site for this study. Through analysis of survey and earth observation data, seagrass meadows, mangroves and agriculture ecosystems were mapped.</p

Historical Monitoring of Shoreline Changes in the Cua Dai Estuary, Central Vietnam Using Multi-Temporal Remote Sensing Data

Cua Dai is one of the major estuarine areas in Central Vietnam that plays a significant role in local maritime transport, fisheries, and tourism activities. This paper presents a study that monitored the shoreline dynamics of the Cua Dai estuary over a period of 50 years (1964–2014) by using field survey data, geographic information systems techniques, and multi-temporal satellite remote sensing images (ALOS-AVNIR2 and Landsat imageries). The assessment of shoreline changes was divided into three phases: 1964–1980, 1981–2000, and 2001–2014. The results revealed that over the last 50 years, shoreline changes dramatically occurred between 1964 and 1980. The general trends of erosion and accretion at the Cua Dai estuary show that the river mouth moved towards the south due to the erosion of shorelines in the north and the river bank in the south of the Cua Dai estuary. The study outcomes can provide essential information for planning, zoning, and sustainable development activities of the coastal zones in the context of climate change

Mapping Submerged Aquatic Vegetation along the Central Vietnamese Coast Using Multi-Source Remote Sensing

Submerged aquatic vegetation (SAV) in the Khanh Hoa (Vietnam) coastal area plays an important role in coastal communities and the marine ecosystem. However, SAV distribution varies widely, in terms of depth and substrate types, making it difficult to monitor using in-situ measurement. Remote sensing can help address this issue. High spatial resolution satellites, with more bands and higher radiometric sensitivity, have been launched recently, including the Vietnamese Natural Resources, Environment, and Disaster Monitoring Satellite (VNREDSat-1) (V1) sensor from Vietnam, launched in 2013. The objective of the study described here was to establish SAV distribution maps for South-Central Vietnam, particularly in the Khanh Hoa coastal area, using Sentinel-2 (S2), Landsat-8, and V1 imagery, and then to assess any changes to SAV over the last ten years, using selected historical data. The satellite top-of-atmosphere signals were initially converted to radiance, and then corrected for atmospheric effects. This treated signal was then used to classify Khanh Hoa coastal water substrates, and these classifications were evaluated using 101 in-situ measurements, collected in 2017 and 2018. The results showed that the three satellites could provide high accuracy, with Kappa coefficients above 0.84, with V1 achieving over 0.87. Our results showed that, from 2008 to 2018, SAV acreage in Khanh Hoa was reduced by 74.2%, while gains in new areas compensated for less than half of these losses. This is the first study to show the potential for using V1 and S2 data to assess the distribution status of SAV in Vietnam, and its outcomes will contribute to the conservation of SAV beds, and to the sustainable exploitation of aquatic resources in the Khanh Hoa coastal area.</jats:p