Papers by Truong Van Vinh
Can Gio mangrove is the largest in Vietnam, developing on approximately 35000 hectares. This fore... more Can Gio mangrove is the largest in Vietnam, developing on approximately 35000 hectares. This forest was partially destroyed during the Vietnamese war. A restoration program was developed between the late 70s and the early 90s, using Rhizophora apiculata Blume propagules. Currently, the Can Gio mangrove forest regenerates naturally and presents a specific species zonation along the intertidal elevation gradient. Rhizophora dominates the inner forest at the highest elevation, while at an intermediate location, Rhizophora and Avicennia cohabit with other scattered species. The lowest position is colonized by Avicennia. Within this context, the main objectives of this study were to determine the soil physicochemical characteristics, as well as the quality (C/N ratios and δ 13 C) and the quantity (carbon content and stocks) of the organic matter stored beneath each mangrove stand. In addition, we were interested in determining the above-ground biomass and the total carbon stocks of the ecosystem (without considering the below-ground biomass). Carbon stocks of the Can Gio mangrove forest ranged from 150 to 479 Mg C ha-1 , with up to 86 % of the C stored in the upper meter of the soil. The inner forest has the highest stock, followed by the transitional forest, and the fringe forest. The depth extension of the root system of the current forest was estimated, and its contribution to the soil carbon stock was calculated, using the adjacent mudflat as a proxy for the antecedent stocks. Our results show that, for the last 40 years, the current mature planted Rhizophora forest stored 25.26 Mg C ha-1. Consequently, mangrove plantation and restoration after the war was a success in terms of carbon storing. We suggest that the destruction of the Can Gio mangrove forests for urban development would induce the loss of an efficient CO2 sink.
Atmospheric Environment, 2019
Seasonal variability of CO 2 fluxes at different interfaces and vertical CO 2 concentration profi... more Seasonal variability of CO 2 fluxes at different interfaces and vertical CO 2 concentration profiles within a Rhizophora mangrove forest (Can Gio, Viet Nam)
Chemosphere, 2018
Mangrove sediments act as natural biogeochemical reactors, modifying metals partitioning after th... more Mangrove sediments act as natural biogeochemical reactors, modifying metals partitioning after their deposition. The objectives of the present study were: to determine distribution and partitioning of metals (Fe, Mn, Ni, Cr, Cu, Co and As) in sediments and pore-waters of Can Gio Mangrove; and to assess their ecological risks based on Risk Assessment Code. Three cores were collected within a mudflat, beneath Avicennia alba and Rhizophora apiculata stands. We suggest that most metals had a natural origin, being deposited in the mangrove mainly as oxyhydroxides derived from the upstream lateritic soils. This hypothesis could be supported by the high proportion of metals in the
Marine pollution bulletin, 2018
In New Caledonia, shrimp ponds are built not on cleared mangroves but on salt flats behind the ma... more In New Caledonia, shrimp ponds are built not on cleared mangroves but on salt flats behind the mangroves. The objectives of this study were to determine the variability of CO fluxes from a semi-intensive shrimp pond during active and non-active periods of the farm and to determine the carbon dynamics from the upstream tidal creek to the downstream creek, which receives the farm's effluents. CO emissions from the active pond were estimated at 11.1 ± 5.26 mmol CO m d. By modifying the hydrodynamics of the creeks, farm practices also influenced CO emissions from both the upstream and downstream creeks. After tillage, all the organic carbon deposited at the pond bottom during the active period was mineralized, resulting in CO emissions to the atmosphere estimated at 7.9 TCO ha. Therefore, shrimp farming is an anthropogenic source of CO to the atmosphere, but suitable and optimized rearing practices limit these emissions.
Marine Chemistry, 2019
, et al., Assessing nutrient dynamics in mangrove porewater and adjacent tidal creek using nitrat... more , et al., Assessing nutrient dynamics in mangrove porewater and adjacent tidal creek using nitrate dual-stable isotopes: A new approach to challenge the Outwelling Hypothesis?, Marine Chemistry,
Journal of Sea Research
Abstract Tropical estuaries are characterised by high spatial and temporal variability in the con... more Abstract Tropical estuaries are characterised by high spatial and temporal variability in the conditions they provide for living organisms, which in turn may affect their biochemical composition. Anthropogenic contaminants such as nutrients, antibiotics, pesticides and trace metals may also affect the biochemical composition of these coastal organisms, notably with regard to fatty acids (FA), of which optimal species-specific polyunsaturated FA ratios are required to maintain living species in healthy conditions. The objective of this study was to evidence changes in the FA profile of four ubiquist benthic species in relation to the salinity gradient of a human impacted and mangrove dominated tropical estuary (Can Gio, Southern Vietnam). Among the four benthic species studied, two exhibited spatial and seasonal changes in their FA composition: the varunid crab Metaplax elegans and the predatory mangrove murex snail Chicoreus capucinus. Proportions of the FA 16:1ω7, proportions of highly unsaturated FA and ratios of eicosapentanoic acid/arachidonic acid in the tissues of both species seemed related to upstream inputs. Different relative abundances of benthic microalgae affected both claw muscle and hepatopancreas FA composition of M. elegans, while the FA composition of C. capucinus shows that the influence of prey's diet might be transferred within trophic chains. Finally, some species, such as Nerita balteata and Metapenaeus ensis might have more adaptive capacities, because of their mobility, or because of their specific metabolic pathways, minimizing the potential impact of spatial and/or temporal changes in food resources quality. A starvation experiment involving N. balteata actually revealed the metabolic synthesis of non-methylene interrupted FA that may confer cell membranes a higher resistance to external stressors than common polyunsaturated FA. Our study highlights the future possibility of using the FA composition of sentinel organisms (i.e. feeding on specific food resources and/or especially subject to environmental stresses) as a bioindicator tool to assess mangrove ecosystems health.
Frontiers in Environmental Science
Mangrove soils are considered as sinks for trace metals, protecting coastal waters from pollution... more Mangrove soils are considered as sinks for trace metals, protecting coastal waters from pollutions. However, the cycling of trace metals in mangroves is complex due to various biogeochemical processes across the intertidal zone, notably the dissolution of bearing phases resulting in high trace metal concentrations in porewaters. Previous studies demonstrated a decrease of trace metal stocks in mangrove soils seaward, possibly due to the export of dissolved metals through tidal pumping. Can Gio mangrove is the largest one in Vietnam, developing downstream Ho Chi Minh City (Viet Nam’s biggest industrial city). The objectives of the present study were to characterize the dynamics of trace metals in a tidal creek of the Can Gio mangrove that does not receive any upstream inputs and to identify the role of porewater seepage on their dynamics. To reach our goals, surface water and suspended particulate matters were collected every 2 h during two different tidal cycles (spring and neap tides) and at the two different seasons, dry and wet. Mangroves porewaters were also collected. In addition to particulate and dissolved trace metals, physico-chemical parameters and a groundwater tracer (Radon – 222Rn) were measured. The results showed that trace metal concentrations at flood tides, both in the dissolved and the particulate phases, were in the same range that those measured in the Can Gio Estuary. Then during ebb tides, we evidenced high inputs of dissolved Fe, Mn, Co, and Ni from mangrove soils. However, the dynamics of these inputs differed depending on the element considered. Mn was exported from the tidal creek in its dissolved form. However concerning Fe, and to a lesser extent Co and Ni, we suggest that, when delivered to the creek from the soils under dissolved forms, these trace metals precipitated because of different physicochemical characteristics between mangrove soils and tidal creek, notably higher dissolved oxygen concentrations and higher pH. Consequently, these elements were exported to the estuary in particulate forms. We suggest that budget studies of trace metals in mangroves should be developed like the ones concerning carbon to efficiently determine their role as a barrier for pollutants between land and sea.
Marine Pollution Bulletin
Frontiers in Environmental Science, Feb 13, 2020
Mangroves are highly productive ecosystems, being key components of trophic food chains along tro... more Mangroves are highly productive ecosystems, being key components of trophic food chains along tropical coastlines. In Southern Vietnam, planted Rhizophora apiculata develops in the upper intertidal zone, while Avicennia alba naturally colonizes areas at lower elevation along tidal creeks. The main objective of this study was to quantify the seasonal variability of leaf litter decomposition rates considering that in previous studies we observed a strong influence of the monsoon on C and nutrients cycling within the mangrove and in adjacent creeks. We were also interested in changes in the quality of the leaf litter during its decomposition, focusing on nutrients, δ 13 C, and trace metals. To reach our goals, we used the litterbag technique. During the monsoon, leaf litter decay rates were increased in the Avicennia stand, most probably because of enhanced leaching resulting from a higher level of the river due to heavy rainfall. In addition, the enhanced decay rates measured in the Avicennia stand during the rainy season resulted in a strong 13 C depletion, while 13 C enrichment was measured in the other conditions. Elemental concentrations changes during decay were not clearly influenced by season, but depended on the element considered. K, Mg, Na, and Ca had t 50 values lower than the one of the bulk material. P and S contents also rapidly decreased during the first decomposition stages, but these elements had longer t 50 values than the bulk leaves. Conversely, an enrichment in most trace metals was observed during leaf litter decomposition whatever the season. We suggest that these metals were either trapped from the water column and the forest floor by organic molecules composing the litter, or subjected to litter decomposers uptake. Consequently, this study shows that the release or the uptake of elements during mangrove leaf litter decomposition varied with different parameters, which may have ecological implications on the nature of the elements exported toward adjacent ecosystems, and on their primary productivity.
Mangrove forests can fix and store high quantities of carbon both in their soil and in their biom... more Mangrove forests can fix and store high quantities of carbon both in their soil and in their biomass, the latter peaking in the equatorial regions and decreasing with latitude. In Vietnam, more than 80% of the mangroves develop either in the Mekong Delta or in the Can Gio Estuary, which are characterized by tropical monsoon climates. Most of these mangroves were planted and are dominated by Rhizophora apiculata Blume. The main objectives of this study were to determine forest structure, above-ground biomass and carbon conversion factors for each tree component in order to obtain allometric equations and to derive carbon stocks for managed Rhizophora stands of different ages developing within this context. Thirty-six trees, having a diameter at breast height (DBH) ranging from 7.0 to 36.2 cm, from a planted mangrove forest were harvested in Ca Mau (Mekong Delta) to determine allometric equations. In addition, thirteen plots were established in both Ca Mau and Can Gio mangrove forests, to determine above-ground carbon densities. We proposed the following specific allometric equation to estimate total above-ground biomass (kg) for managed R. apiculata mangrove stands in Southern Vietnam: W Total = 0.38363 * DBH 2.2348 (R 2 = 0.976, SE = 1.17, F = 1401, P < 0.001). The total above-ground biomass ranged from 135.4 to 523.6 Mg ha −1 depending on forest age and tree density. Consequently, and taking into account a carbon conversion factor of 44.09%, carbon stocks in the above-ground biomass of R. apiculata mangrove forests in Southern Vietnam ranged from 59.7 to 230.9 Mg C ha −1. The mean carbon partitioning in the tree biomass was: 77.11% for trunks, 11.87% for branches, 8.66% for prop roots, and 2.36% for leaves. However, this distribution, as well as annual height increments and biomass increase rates, also varied with forest age and tree densities. We suggested that tree density reduction through thinning activities allowed easier tree development, resulting in an increased biomass with enhanced allocation to branches and above-ground prop roots for the stability of the trees. Using the specific allometric equation and specific carbon conversion factor reduced the uncertainty in the estimation of above-ground biomass and carbon stocks.
Despite being organic-rich, mangrove soils are usually characterized by low rates of CO 2 emissio... more Despite being organic-rich, mangrove soils are usually characterized by low rates of CO 2 emissions due to waterlogged conditions, mangroves being thus considered as valuable blue carbon sinks. However, these emissions are highly variable, notably depending on climatic parameters. Can Gio mangrove is a tropical one, being the largest in Vietnam, having being replanted after the war in the late 70's. The main objectives of this study were to quantify the seasonal variability of CO 2 emissions at different interfaces (soil-air, water-air, and trunk-air) within a mature Rhizophora stand, and to assess the influence of these emissions on the vertical CO 2 concentration profiles in the canopy. CO 2 emissions from the soil in the dark were the highest of the different interfaces studied, and were among the highest measured for a mangrove soil, with a mean yearly value reaching more than 270 mmol CO 2 m −2 d −1. We suggest that the very high temperatures characterizing Southern Vietnam all year round were responsible for these elevated CO 2 emissions. In addition to temperature, the first rainfall pulse of the monsoon resulted in the highest CO 2 fluxes both from the soil, reaching up to 500 mmol CO 2 m −2 d −1 , and from the trunks, reaching almost 230 mmol CO 2 m −2 d −1. Because rainfall pulses are usually followed by a period of increasing rates of ecosystem photosynthesis, and a decrease of ecosystem respiration, we measured lower CO 2 fluxes during the middle of the wet season. Additionally, it is possible that, during the rainy season, part of the CO 2 produced within the soil was exported trough pore-water seepage, which was enhanced because of the higher level of the river. Concerning CO 2 emissions at high tide within the Rhizophora stand, the seasonal trend followed the one of precipitation. During the rainy season, estuarine waters are enriched in organic matter and CO 2 due to increased runoff in watersheds, and consequently CO 2 fluxes from the water column were the highest. However, these emissions were much lower than those from the soil at low tide or from the trunks. Eventually, CO 2 concentrations profiles in the canopy varied with the season, the tide, and the night-day alternation. Elevated CO 2 concentrations at the root level may imply that prop roots can produce high amount of CO 2 but also that they may trap gas emitted from the soil or the water column, possibly acting as physical barriers to air movement. Further studies using eddy-covariance technique should be developed to confirm the hypothesis suggested in this preliminary study.
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Papers by Truong Van Vinh