Nguyen Tai Tue

Sources and Exchange of Particulate Organic Matter in an Estuarine Mangrove Ecosystem of Xuan Thuy National Park, Vietnam

The spatio-temporal variations in stable isotope signatures (δ13C and δ15N) and C/N ratios of particulate organic matter (POM), and physicochemical parameters in a creek water column were examined in an estuarine mangrove ecosystem of Xuan Thuy National Park, Vietnam. The objective was to examine the factors influencing creek water properties, and the sources and exchange of POM in this important mangrove ecosystem. The diel and seasonal variations in water temperature, flow velocity, pH, dissolved oxygen, and salinity demonstrated that tidal level, season, and biological factors affected the creek water properties. Mangroves had relatively low δ15N and very low δ13C values, with respective average values of 1.5 ± 0.9‰ and −28.1 ± 1.4‰. The low mangrove leaf δ15N indicated minor anthropogenic nitrogen loading to the mangrove forests. A significant positive correlation between POM–δ13C and salinity along the axis of Ba Lat Estuary, Red River, indicated that marine phytoplankton (δ13C value, −21.4 ± 0.5‰) was the predominant source of POM at the estuary mouth. Based on the co-variation of δ13C and C/N ratios, marine phytoplankton and mangrove detritus were predominant in POM of major creeks and small creeks, respectively. During the diurnal tidal cycle, the dynamics of POM were affected by sources of organic matter, tidal energy, and seasonal factors. The contribution of mangrove detritus to POM reached a maximum at the low tide and was enhanced during the rainy season, whereas marine phytoplankton contribution was highest at high tide.

Dual isotope study of food sources of a fish assemblage in the Red River mangrove ecosystem, Vietnam

The food source utilization and trophic relationship of the fish assemblage in the Red River mangrove ecosystem, Vietnam were examined using dual isotope analysis. The carbon and nitrogen stable isotope signatures of 23 fish species ranged from −24.0 to −15.7‰ and from 8.8 to 15.5‰, respectively. Cluster analysis based on the δ13C and δ15N signatures clearly separated the mangrove fish into five feeding groups, representing detritivores, omnivores, piscivores, zoobenthivores, and zooplanktivores, which concurred with the dietary information. The results suggested that mangrove carbon contributed a small proportion in the diets of the mangrove fish, with dominant food sources coming from benthic invertebrates, including ocypodid and grapsid crabs, penaeid shrimps, bivalves, gastropods, and polychaetes. The δ15N values showed that the food web structure may be divided into different trophic levels (TLs). The lowest TLs associated with Liza macrolepis, Mugil cephalus, and Periophthalmus modestus; 18 fish species had TLs between 3.0 and 3.8; and Pennahia argentata had the highest TL (c. 4.0).

Enhancing Resilience to Climate Change and Disasters for Sustainable Development: Case Study of Vietnam Coastal Urban Areas

Climate change is likely to intensify severe impacts of disasters and extreme weather events on resilience and sustainability of coastal urban areas. The solutions for enhancing sustainability and climate resilience of the coastal urban areas depend on multivariables and dimensions such as social, human, institutional, economic, and natural conditions and resources. It is therefore needed to develop a set of indicators for evaluating the adaptive capacity of urban systems and communities to climate change. In this chapter, we analyzed the status quo of climate variability, climate-related disasters, vulnerability, and adaptive capacity to climate change of Da Nang city, Vietnam, for developing a proposal of response measures to climate change. Results showed that Da Nang city has been impacted by several disasters, consisting of typhoons, floods, sea level rise, drought, saline intrusion, landslides, erosions, and forest fires. The vulnerability to climate change and disasters of Da Nang city is classified into low, average, high, and very high levels. The measures for reducing vulnerability and enhancing resilience to climate change and sustainability include increasing the resilience of natural environments and ecosystems and social systems, enhancing the urban governance for climate change adaptation, and promoting the transformative capacity from climate change to sustainable development opportunities.

RETRACTED ARTICLE: Application of stable isotope analysis methods for reconstructing paleoenvironment and paleoclimate in sediment cores

This article has been retracted due to the quality, at the request of the editors-in-chief. The Publisher apologizes for any inconvenience this may cause.

CHARACTERISTICS OF MARINE ENVIRONMENTAL GEOCHEMISTRY FROM NGA SON TO CUA HOI, THANH HOA PROVINCE (0-30 METERS WATER DEPTH)

The aim of this study is to clarify characteristics of marine environmental geochemistry from Nga Son to Cua Hoi (0-30 m water depth). The water and sediment samples were collected from March to April of each year during the period 2011 - 2013. Results indicated that salinity of seawater ranged from 1.2‰ to 33.3‰. The seawater environment was classified into neutral-weak oxidation in the layer from 0-10 m water depth and weak alkaline-weak oxidation in the layer 10-30 m water depth. Concentrations of most anions and elements in seawater had a decreasing trend from nearshore to offshore regions and with depth, with the exception of SO 4 2- , CO 3 2- , Mg, B - , Br - , I - . Sedimentary environment was highly dominated by neutral-strong oxidization and weak alkaline-weak oxidization for the zone from 0-10 m water depth and 10-30 m water depth, respectively. Concentrations of anions and elements tended to be higher in nearshore region than those in offshore zone, with the exception of SO 4 2- , PO 4 3- , NO 3 - and positively correlated with fine-grained sediment compositions. Total PCBs concentration increased from north to south, yet HCHs and DDTs had opposite trends. Compared with environmental quality guidelines, marine sediments and seawater were not polluted by heavy metals and organic compounds of PCBs and OCBs.

Quantifying organic carbon storage and sources in sediments of Dong Rui mangrove forests, Tien Yen district, Quang Ninh province using carbon stable isotope

The objective of this study is to quantify the organic carbon (OC) storage and its sources in sediments of Dong Rui mangrove forests, Tien Yen district, Quang Ninh province by analyzing TOC (total organic carbon), TN (total nitrogen), C/N ratios, δ13C isotopes and sediment grain sizes. The results showed that the fine-grained sediment fraction (<63 μm) ranged from 8.58 to 82.10%; TOC, TN contents, C/N ratios and δ13C values ranged from 0.21 to 10.20%, 0.01 to 0.34%, 15.07 to 46.09 and –27.75 to –25.84‰, respectively. The variation of δ13C and C/N ratios, and the correlation between TOC, TN and the fine-grained sediment fractions indicated that mangrove forests play important roles in OC sequestration and accumulation of fine-grained sediments. The OC storage in sediments varied from 16.7 to 78.3 MgC ha-1 with an average of 57.2±14.9 MgC ha-1. Nowadays, the mangrove forest area in Dong Rui is about 2194.1 ha, thus, the total OC in sediment pool up to 45 cm in depth, contained 1.26(±0.3)×105 MgC, equivalent to 4.6(±1.2)×105 Mg CO2. These results demonstrated that the conservation of Dong Rui mangrove forest not only provides opportunities for coastal protection and disaster mitigation and other provision values, but also enhancing carbon sequestration and offsetting greenhouse gas emissions.