Publications by authors named "Cyril Marchand"

19 Publications

  • Page 1 of 1

Exploring the Diversity of Fungal DyPs in Mangrove Soils to Produce and Characterize Novel Biocatalysts.

J Fungi (Basel) 2021 Apr 21;7(5). Epub 2021 Apr 21.

INRAE, UMR1163, Biodiversité et Biotechnologie Fongiques, Aix-Marseille Université, 13288 Marseille, France.

The functional diversity of the New Caledonian mangrove sediments was examined, observing the distribution of fungal dye-decolorizing peroxidases (DyPs), together with the complete biochemical characterization of the main DyP. Using a functional metabarcoding approach, the diversity of expressed genes encoding fungal DyPs was investigated in surface and deeper sediments, collected beneath either or trees, during either the wet or the dry seasons. The highest DyP diversity was observed in surface sediments beneath the area during the wet season, and one particular operational functional unit (OFU1) was detected as the most abundant DyP isoform. This OFU was found in all sediment samples, representing 51-100% of the total DyP-encoding sequences in 70% of the samples. The complete cDNA sequence corresponding to this abundant DyP (OFU 1) was retrieved by gene capture, cloned, and heterologously expressed in . The recombinant enzyme, called DyP1, was purified and characterized, leading to the description of its physical-chemical properties, its ability to oxidize diverse phenolic substrates, and its potential to decolorize textile dyes; DyP1 was more active at low pH, though moderately stable over a wide pH range. The enzyme was very stable at temperatures up to 50 °C, retaining 60% activity after 180 min incubation. Its ability to decolorize industrial dyes was also tested on Reactive Blue 19, Acid Black, Disperse Blue 79, and Reactive Black 5. The effect of hydrogen peroxide and sea salt on DyP1 activity was studied and compared to what is reported for previously characterized enzymes from terrestrial and marine-derived fungi.
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http://dx.doi.org/10.3390/jof7050321DOI Listing
April 2021

Respective contribution of urban wastewater and mangroves on nutrient dynamics in a tropical estuary during the monsoon season.

Mar Pollut Bull 2020 Nov 17;160:111652. Epub 2020 Sep 17.

Faculty of Fisheries and Aquatic Resources, Mae Jo University, Chiang Mai, Thailand.

Estuaries of Southeast Asia are increasingly impacted by land-cover changes and pollution. Here, our research objectives were to (1) determine the origins of nutrient loads along the Can Gio estuary (Vietnam) and (2) identify the processes that affect the nutrient pools during the monsoon. We constructed four 24-h time-series along the salinity gradient measuring nutrient concentrations and stable isotopes values. In the upper estuary, urban effluents from Ho Chi Minh City were the main input of nutrients, leading to dissolved oxygen saturation <20%. In the lower estuary, ammonium and nitrite concentration peaks were explained by mangrove export. No contribution from aquaculture was detected, as it represents <0.01% of the total river discharge. Along the salinity gradient, nutrient inputs were rapidly consumed, potentially by phytoplankton while nitrate dual-stable isotopes indicated that nitrification occurred. Thus, even in a large and productive estuary, urban wastewater can affect nutrient dynamics with potentially important ecological risks.
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http://dx.doi.org/10.1016/j.marpolbul.2020.111652DOI Listing
November 2020

Sedimentological and geochemical data in bed sediments from a tropical river-estuary system impacted by a developing megacity, Ho Chi Minh City - Vietnam.

Data Brief 2020 Aug 27;31:105938. Epub 2020 Jun 27.

CARE, Ho Chi Minh City University of Technology, VNU-HCM, Viet Nam.

Sedimentological and geochemical data were obtained for bed sediments from a tropical estuary environment in Vietnam in October 2014, January 2016, and November 2016. The data include grain-size distribution, percentage of clay, silt and sand, percentage of organic matter, concentration of total particulate phosphorus (TPP), concentration of particulate inorganic phosphorus (PIP), concentration of particulate organic phosphorus (POP), percentage of total nitrogen (TN), percentage of total carbon (TC), trace metals concentrations (V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Pb) and major elements (Al, Fe, Mn). Geochemical indexes (Enrichment factor EF and Geo-accumulation Index I-geo) and sediment quality guideline (mean Effect Range Median quotients) were calculated.
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http://dx.doi.org/10.1016/j.dib.2020.105938DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7339034PMC
August 2020

Trace metal dynamics in soils and plants along intertidal gradients in semi-arid mangroves (New Caledonia).

Mar Pollut Bull 2020 Jul 22;156:111274. Epub 2020 May 22.

IMPMC, Institut de Recherche pour le Développement (IRD), UPMC, CNRS, MNHN, Noumea, New Caledonia, France; ISEA, University of New Caledonia BP R4, 98851 Noumea, New Caledonia.

Trace metal dynamics were investigated in mangroves developing in semi-arid New Caledonia, where Avicennia and Rhizophora stands grow in the upper and lower intertidal zone, respectively. We collected soil samples and mangrove tissues in an undisturbed site, a mining-influenced site and in a mining and aquaculture-influenced site. Differences in duration of immersion and organic matter (OM) cycling resulted in a sharp decrease of metal concentrations in soils and plants from landside to seaside. Both species were tolerant to metals mainly via exclusion, (i.e. metal bioaccumulation restricted to roots and leaf litter). Strong correlations (p < 0.05) were found between Na and Fe, Mn, Cu and Zn in green and senesced leaves of Avicennia marina, indicating a possible role of those metals in mechanisms to cope with hypersaline conditions. Increasing metal pollution, aridity and sea-level rise are likely to result in a decrease in mangrove efficiency in filtering trace metals seaward.
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http://dx.doi.org/10.1016/j.marpolbul.2020.111274DOI Listing
July 2020

Temporal variations of trace metals and a metalloid in temperate estuarine mangrove sediments.

Environ Monit Assess 2019 Nov 30;191(12):780. Epub 2019 Nov 30.

Institute for Applied Ecology, School of Science, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand.

Mangrove sediments are strong modulators of organic matter (OM) content and pollutant dynamics, acting both as sinks and sources of these components. This study aimed to assess temporal dynamics of OM within temperate mangrove sediments and their ability to sequester pollutants. Specifically, levels of trace metals (Fe, Cu, Zn, Pb, Cd) and a metalloid (As) were examined within mangrove and mudflat sediments located in a high-energy environment in Mangawhai Harbour Estuary, northern New Zealand. Sediment cores were collected from a mangrove stand and adjacent mudflats at three sediment depths during different months over a year. Variations in OM and elements were compared to rainfall and temperature patterns observed during the sampling period. All element concentrations, except for those of As, were significantly higher in mangrove compared to mudflat sediments during the entire sampling period. This is consistent with the well-reported ability of mangroves to trap suspended particles and OM. In addition, we observed a decreasing trend in trace metal concentrations with increasing sediment depth within mangrove habitat, which correlated well with decreasing OM content. Our results also suggested that most elements had different, but significant, temporal variations throughout the year, especially in mangrove sediments. Overall, the concentrations of Cu, Zn, Pb, Cd, and As in mangrove sediments increased during summer, whereas maximum levels of Fe and OM were observed in winter. This temporal pattern was determined to be related to OM and redox cycling as a result of changes in effluent input rates and physical/chemical environments during different seasons.
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http://dx.doi.org/10.1007/s10661-019-7916-zDOI Listing
November 2019

Fatty acids, C and N dynamics and stable isotope ratios during experimental degradation of shrimp pond effluents in mangrove water.

Mar Environ Res 2019 Sep 26;150:104751. Epub 2019 Jun 26.

BOREA Biologie des Organismes et Ecosystèmes Aquatiques, UMR 7208 MNHN CNRS SU UA UCN IRD 207, Muséum National d'Histoire Naturelle, 75005, Paris, France.

Intensive shrimp farming generates high loads of wastewaters that are released along tropical coastlines with potential impacts on the ecosystems. In this study, we used an experimental approach to analyze the behavior of shrimp pond effluents released in the Can Gio mangrove waterways (Southern Vietnam). We incubated shrimp pond effluents (EF), river water (RV), and a mixture of both (MI; 90% RV + 10% EF) in a dark room and measured fatty acid (FA) compositions, C and N concentrations and stable isotopes ratios (δC and δN) of suspended particulate matter during 16 days. Fatty acid concentrations rapidly decreased in EF with a 50% loss of FA during the first 24 h of the experiment and a 75% loss after 4 days of incubation. Proportions of the FA 18:1ω7 increased in MI during incubation, suggesting that this FA may be used as a tracer of anthropogenic substances release in marine environments.
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http://dx.doi.org/10.1016/j.marenvres.2019.104751DOI Listing
September 2019

Patterns of fish utilisation in a tropical Indo-Pacific mangrove-coral seascape, New Caledonia.

PLoS One 2019 19;14(4):e0207168. Epub 2019 Apr 19.

College of Science and Engineering, James Cook University, Townsville, Queensland, Australia.

Mangrove forests are important habitats for fish. However, their utilisation by fish, and the specific values they confer, are still not fully understood. This study describes how fish use mangrove forests in an Indo-Pacific mangrove-coral reef seascape. Sampling was conducted using underwater video cameras (UVCs) to describe spatial and temporal variations in fish assemblages across a small-scale (~ 2.5 km2) system, and over the tidal and lunar cycle. UVCs were deployed in the two main component habitats of mangrove forests: at the mangrove forest edge, and inside the forest (5 m from the forest edge), to establish patterns of utilisation of fish across the tidal and lunar cycle. Proximity to coral reefs had a strong influence on the mangrove fish community, as most fish recorded were reef-associated. Juveniles of 12 reef species were observed, including two species classified as vulnerable on the IUCN list, and one endemic species. Fish assemblages on the mangrove edge differed significantly from those inside the forest. Most fish utilised the forest edge, with few species making regular use of in-forest habitats, supporting the contention that most fish species remain on the edge and potentially retreat into the forest for opportunistic feeding, or when threatened by larger predators. Species-specific patterns of utilisation varied across the tidal and lunar cycle. Small differences in depth profiles and substrate across the small-scale system had a significant effect on fish assemblages, highlighting the importance of accounting for spatial heterogeneity in these factors. These data provide important information for managers to implement adequate conservation strategies that include broader interconnected habitat mosaics.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0207168PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6474647PMC
December 2019

Bioaccumulation of some trace elements in tropical mangrove plants and snails (Can Gio, Vietnam).

Environ Pollut 2019 May 25;248:635-645. Epub 2019 Feb 25.

Faculty of Chemical Engineering and Food Technology, Nguyen Tat Thanh University, Viet Nam.

Mangrove sediments can store high amount of pollutants that can be more or less bioavailable depending on environmental conditions. When in available forms, these elements can be subject to an uptake by mangrove biota, and can thus become a problem for human health. The main objective of this study was to assess the distribution of some trace elements (Fe, Mn, Co, Ni, Cr, As, and Cu) in tissues of different plants and snails in a tropical mangrove (Can Gio mangrove Biosphere Reserve) developing downstream a megacity (Ho Chi Minh City, Vietnam). In addition, we were interested in the relationships between mangrove habitats, sediment quality and bioaccumulation in the different tissues studied. Roots and leaves of main mangrove trees (Avicennia alba and Rhizophora apiculata) were collected, as well as different snail species: Chicoreus capucinus, Littoraria melanostoma, Cerithidea obtusa, Nerita articulata. Trace elements concentrations in the different tissues were determined by ICP-MS after digestion with concentrated HNO and HO. Concentrations differed between stands and tissues, showing the influence of sediment geochemistry, species specific requirements, and eventually adaptation abilities. Regarding plants tissues, the formation of iron plaque on roots may play a key role in preventing Fe and As translocation to the aerial parts of the mangrove trees. Mn presented higher concentrations in the leaves than in the roots, possibly because of physiological requirements. Non-essential elements (Ni, Cr and Co) showed low bioconcentration factors (BCF) in both roots and leaves, probably resulting from their low bioavailability in sediments. Regarding snails, essential elements (Fe, Mn, and Cu) were the dominant ones in their tissues. Most of snails were "macroconcentrators" for Cu, with BCF values reaching up to 42.8 for Cerithidea obtusa. We suggest that high quantity of As in all snails may result from its high bioavailability and from their ability to metabolize As.
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http://dx.doi.org/10.1016/j.envpol.2019.02.041DOI Listing
May 2019

Contrasted ecological niches shape fungal and prokaryotic community structure in mangroves sediments.

Environ Microbiol 2019 04 19;21(4):1407-1424. Epub 2019 Mar 19.

CNRS, UMR5557; Ecologie Microbienne, INRA, UMR1418, Université Lyon 1, 69220, Villeurbanne Cedex, France.

Mangroves are forest ecosystems located at the interface between land and sea where sediments presented a variety of contrasted environmental conditions (i.e. oxic/anoxic, non-sulfidic/sulfidic, organic matter content) providing an ideal ecosystem to study microbial communities with niche differentiation and distinct community structures. In this work, prokaryotic and fungal compositions were investigated during both wet and dry seasons in New Caledonian mangrove sediments, from the surface to deeper horizons under the two most common tree species in this region (Avicennia marina and Rhizophora stylosa), using high-throughput sequencing. Our results showed that Bacteria and Archaea communities were mainly shaped by sediment depth while the fungal community was almost evenly distributed according to sediment depth, vegetation cover and season. A detailed analysis of prokaryotic and fungal phyla showed a dominance of Ascomycota over Basidiomycota whatever the compartment, while there was a clear shift in prokaryotic composition. Some prokaryotic phyla were enriched in surface layers such as Proteobacteria, Euryarchaeota while others were mostly associated with deeper layers as Chloroflexi, Bathyarchaeota, Aminicenantes. Our results highlight the importance of considering fungal and prokaryotic counterparts for a better understanding of the microbial succession involved in plant organic matter decomposition in tropical coastal sediments.
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http://dx.doi.org/10.1111/1462-2920.14571DOI Listing
April 2019

Metals geochemistry and ecological risk assessment in a tropical mangrove (Can Gio, Vietnam).

Chemosphere 2019 Mar 30;219:365-382. Epub 2018 Nov 30.

Department of Analytical Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City, Viet Nam; Faculty of Chemical Engineering and Food Technology, Nguyen Tat Thanh University, Viet Nam.

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 residual fraction (mean values (%): 71.9, 30.7, 80.7, 80.9, 67.9, 53.4 and 66.5 for Fe, Mn, Ni, Cr, Cu, Co, and As respectively, in the mudflat). The enrichment of mangrove-derived organic matter from the mudflat to the Rhizophora stand (i.e. up to 4.6% of TOC) played a key role in controlling metals partitioning. We suggest that dissolution of Fe and Mn oxyhydroxides in reducing condition during decomposition of organic matter may be a major source of dissolved metals in pore-waters. Only Mn exhibited a potential high risk to the ecosystem. Most metals stocks in the sediments were higher in the Avicennia stand than the Rhizophora stand, possibly because of enhanced dissolution of metal bearing phases beneath later one. In a context of enhanced mangrove forests destruction, this study provides insights on the effects of perturbation and oxidation of sediments on metal release to the environment.
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http://dx.doi.org/10.1016/j.chemosphere.2018.11.163DOI Listing
March 2019

Biofilm and temperature controls on greenhouse gas (CO and CH) emissions from a Rhizophora mangrove soil (New Caledonia).

Sci Total Environ 2019 Feb 8;650(Pt 1):1019-1028. Epub 2018 Sep 8.

Université de la Nouvelle-Calédonie, ISEA, EA 7484, BPR4, 98851 Noumea, New Caledonia.

Seasonal variations of CO and CH fluxes were investigated in a Rhizophora mangrove forest that develops under a semi-arid climate, in New Caledonia. Fluxes were measured using closed incubation chambers connected to a CRDS analyzer. They were performed during low tide at light, in the dark, and in the dark after having removed the top 1-2 mm of soil, which may contain biofilm. CO and CH fluxes ranged from 31.34 to 187.48 mmol m day and from 39.36 to 428.09 μmol m day, respectively. Both CO and CH emissions showed a strong seasonal variability with higher fluxes measured during the warm season, due to an enhanced production of these two gases within the soil. Furthermore, CO fluxes were higher in the dark than at light, evidencing photosynthetic processes at the soil surface and thus the role of biofilm in the regulation of greenhouse gas emissions from mangrove soils. The mean δC-CO value of the CO fluxes measured was -19.76 ± 1.19‰, which was depleted compared to the one emitted by root respiration (-22.32 ± 1.06‰), leaf litter decomposition (-21.43 ± 1.89‰) and organic matter degradation (-22.33 ± 1.82‰). This result confirmed the use of the CO produced within the soil by the biofilm developing at its surface. After removing the top 1-2 mm of soil, both CO and CH fluxes increased. Enhancement of CH fluxes suggests that biofilm may act as a physical barrier to the transfer of GHG from the soil to the atmosphere. However, the δC-CO became more enriched, evidencing that the biofilm was not integrally removed, and that its partial removal resulted in physical disturbance that stimulated CO production. Therefore, this study provides useful information to understand the global implication of mangroves in climate change mitigation.
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http://dx.doi.org/10.1016/j.scitotenv.2018.09.093DOI Listing
February 2019

Effects of elevated atmospheric CO and increased tidal flooding on leaf gas-exchange parameters of two common mangrove species: Avicennia marina and Rhizophora stylosa.

Photosynth Res 2018 Nov 9;138(2):249-260. Epub 2018 Aug 9.

Université de la Nouvelle-Calédonie, ISEA, EA 7484, BPR4, 98851, Noumea, New Caledonia, France.

In this study, we examined interactive effects of elevated atmospheric CO, concentrations, and increased tidal flooding on two mangroves species, Avicennia marina and Rhizophora stylosa. Leaf gas-exchange parameters (photosynthesis, transpiration rates, water-use efficiency, stomatal conductance, and dark respiration rates) were measured monthly on more than 1000 two-year-old seedlings grown in greenhouses for 1 year. In addition, stomatal density and light curve responses were determined at the end of the experiment. Under elevated CO concentrations (800 ppm), the net photosynthetic rates were enhanced by more than 37% for A. marina and 45% for R. stylosa. This effect was more pronounced during the warm season, suggesting that an increase in global temperatures would further enhance the photosynthetic response of the considered species. Transpiration rates decreased by more than 15 and 8% for A. marina and R. stylosa, respectively. Consequently, water-use efficiency increased by 76% and 98% for A. marina and R. stylosa, respectively, for both species, which will improve drought resistance. These responses to elevated CO were minimized (by 5%) with longer flooding duration. Consequently, future increases of atmospheric CO may have a strong and positive effect on juveniles of A. marina and R. stylosa during the next century, which may not be suppressed by the augmentation of tidal flooding duration induced by sea-level rise. It is possible that this effect will enhance seedling dynamic by increasing photosynthesis, and therefore will facilitate their settlements in new area, extending the role of mangrove ecosystems in carbon sequestration and climate change mitigation.
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http://dx.doi.org/10.1007/s11120-018-0570-4DOI Listing
November 2018

Variability of CO emissions during the rearing cycle of a semi-intensive shrimp farm in a mangrove coastal zone (New Caledonia).

Mar Pollut Bull 2018 Apr 22;129(1):194-206. Epub 2018 Feb 22.

IMPMC, Institut de Recherche pour le Développement (IRD), UPMC, CNRS, MNHN, Noumea, New Caledonia; University of Sciences of Ho Chi Minh City, Analytical Chemistry Department, 225 Nguyen Van Cu, District 5, Ho Chi Minh City, Viet Nam. Electronic address:

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.
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http://dx.doi.org/10.1016/j.marpolbul.2018.02.025DOI Listing
April 2018

Tidal variability of CO and CH emissions from the water column within a Rhizophora mangrove forest (New Caledonia).

Sci Total Environ 2018 Aug 16;631-632:334-340. Epub 2018 Mar 16.

Université de la Nouvelle-Calédonie, ISEA, EA 7484, BPR4, 98851 Noumea, New Caledonia.

We performed a preliminary study to quantify CO and CH emissions from the water column within a Rhizophora spp. mangrove forest. Mean CO and CH emissions during the studied period were 3.35±3.62mmolCmh and 18.30±27.72μmolCmh, respectively. CO and CH emissions were highly variable and mainly driven by tides (flow/ebb, water column thickness, neap/spring). Indeed, an inverse relationship between the magnitude of the emissions and the thickness of the water column above the mangrove soil was observed. δCO values ranged from -26.88‰ to -8.6‰, suggesting a mixing between CO-enriched pore waters and lagoon incoming waters. In addition, CO and CH emissions were significantly higher during ebb tides, mainly due to the progressive enrichment of the water column by diffusive fluxes as its residence time over the forest floor increased. Eventually, we observed higher CO and CH emissions during spring tides than during neap tides, combined to depleted δCO values, suggesting a higher contribution of soil-produced gases to the emissions. These higher emissions may result from higher renewable of the electron acceptor and enhanced exchange surface between the soil and the water column. This study shows that CO and CH emissions from the water column were not negligible and must be considered in future carbon budgets in mangroves.
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http://dx.doi.org/10.1016/j.scitotenv.2018.03.006DOI Listing
August 2018

Trace metals partitioning between particulate and dissolved phases along a tropical mangrove estuary (Can Gio, Vietnam).

Chemosphere 2018 Apr 30;196:311-322. Epub 2017 Dec 30.

Department of Analytical Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City, Viet Nam; IMPMC, Institut de Recherche pour le Développement (IRD), UPMC, CNRS, MNHN, Noumea, New Caledonia, France.

Mangroves can be considered as biogeochemical reactors along (sub)tropical coastlines, acting both as sinks or sources for trace metals depending on environmental factors. In this study, we characterized the role of a mangrove estuary, developing downstream a densely populated megacity (Ho Chi Minh City, Vietnam), on the fate and partitioning of trace metals. Surface water and suspended particulate matter were collected at four sites along the estuarine salinity gradient during 24 h cycling in dry and rainy seasons. Salinity, pH, DO, TSS, POC, DOC, dissolved and particulate Fe, Mn, Cr, As, Cu, Ni, Co and Pb were measured. TSS was the main trace metals carrier during their transit in the estuary. However, TSS variations did not explain the whole variability of metals distribution. Mn, Cr and As were highly reactive metals while the other metals (Fe, Ni, Cu, Co and Pb) presented stable log K values along the estuary. Organic matter dynamic appeared to play a key role in metals fractioning. Its decomposition during water transit in the estuary induced metal desorption, especially for Cr and As. Conversely, dissolved Mn concentrations decreased along the estuary, which was suggested to result from Mn oxidative precipitation onto solid phase due to oxidation and pH changes. Extra sources as pore-water release, runoff from adjacent soils, or aquaculture effluents were suggested to be involved in trace metal dynamic in this estuary. In addition, the monsoon increased metal loads, notably dissolved and particulate Fe, Cr, Ni and Pb.
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http://dx.doi.org/10.1016/j.chemosphere.2017.12.189DOI Listing
April 2018

Changes in soil characteristics and C dynamics after mangrove clearing (Vietnam).

Sci Total Environ 2017 Sep 30;593-594:654-663. Epub 2017 Mar 30.

Faculty of Chemistry, University of Science - VNUHCM, 225 Nguyen Van Cu, Ho Chi Minh City, Viet Nam; Institut de Recherche pour le Développement (IRD), UMR 7590, UR 206, BP A5, 98848 Nouméa, New Caledonia, France.

Of the blue carbon sinks, mangroves have one of the highest organic matter (OM) storage capacities in their soil due to low mineralization processes resulting from waterlogging. However, mangroves are disappearing worldwide because of demographic increases. In addition to the loss of CO fixation, mangrove clearing can strongly affect soil characteristics and C storage. The objectives of the present study were to quantify the evolution of soil quality, carbon stocks and carbon fluxes after mangrove clearing. Sediment cores to assess physico-chemical properties were collected and in situ CO fluxes were measured at the soil-air interface in a mangrove of Northern Vietnam. We compared a Kandelia candel mangrove forest with a nearby zone that had been cleared two years before the study. Significant decrease of clay content and an increase in bulk density for the upper 35cm in the cleared zone were observed. Soil organic carbon (OC) content in the upper 35cm decreased by >65% two years after clearing. The quantity and the quality of the carbon changed, with lower carbon to nitrogen ratios, indicating a more decomposed OM, a higher content of dissolved organic carbon, and a higher content of inorganic carbon (three times higher). This highlights the efficiency of mineralization processes following clearing. Due to the rapid decrease in the soil carbon content, CO fluxes at sediment interface were >50% lower in the cleared zone. Taking into account carbonate precipitation after OC mineralization, the mangrove soil lost ~10MgOChayr mostly as CO to the atmosphere and possibly as dissolved forms towards adjacent ecosystems. The impacts on the carbon cycle of mangrove clearing as shown by the switch from a C sink to a C source highlight the importance of maintaining these ecosystems, particularly in a context of climate change.
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http://dx.doi.org/10.1016/j.scitotenv.2017.03.204DOI Listing
September 2017

Spatio-temporal variations in the composition of organic matter in surface sediments of a mangrove receiving shrimp farm effluents (New Caledonia).

Sci Total Environ 2015 Apr 26;512-513:296-307. Epub 2015 Jan 26.

UMR BOREA 7208 CNRS/MNHN/UPMC/IRD/UCBN, Muséum National d'Histoire Naturelle, CP 53, 61 rue Buffon, 75231 Paris cedex 5, France.

In order to investigate spatio-temporal variations in the composition and origin of the benthic organic matter (OM) at the sediment surface in mangrove receiving shrimp farm effluents, fatty acid (FA) biomarkers, natural stable isotopes (δ(13)C and δ(15)N), C:N ratios and chlorophyll-a (chl-a) concentrations were determined during the active and the non-active period of the farm. Fatty acid compositions in surface sediments within the mangrove forest indicated that organic matter inputs varied along the year as a result of farm activity. Effluents were the source of fresh particulate organic matter for the mangrove, as evidenced by the unsaturated fatty acid (UFA) distribution. The anthropogenic MUFA 18:1ω9 was not only accumulated at the sediment surface in some parts of the mangrove, but was also exported to the seafront. Direct release of bacteria and enhanced in situ production of fungi, as revealed by specific FAs, stimulated mangrove litter decomposition under effluent runoff condition. Also, microalgae released from ponds contributed to maintain high benthic chl-a concentrations in mangrove sediments in winter and to a shift in microphytobenthic community assemblage. Primary production was high whether the farm released effluent or not which questioned the temporary effect of shrimp farm effluent on benthic microalgae dynamic. This study outlined that mangrove benthic organic matter was qualitatively and quantitatively affected by shrimp farm effluent release and that responses to environmental condition changes likely depended on mangrove stand characteristics.
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http://dx.doi.org/10.1016/j.scitotenv.2014.12.082DOI Listing
April 2015

Temporal variability of CO₂ fluxes at the sediment-air interface in mangroves (New Caledonia).

Sci Total Environ 2015 Jan 7;502:617-26. Epub 2014 Oct 7.

Université de la Nouvelle-Calédonie, PPME, EA 3325, BP R4, 98851 Noumea, New Caledonia.

Carbon budgets in mangrove forests are uncertain mainly due to the lack of data concerning carbon export in dissolved and gaseous forms. Temporal variability of in situ CO2 fluxes was investigated at the sediment-air interface in different seasons in different mangrove stands in a semi-arid climate. Fluxes were measured using dynamic closed incubation chambers (transparent and opaque) connected to an infra-red gas analyzer. Microclimatic conditions and chl-a contents of surface sediments were determined. Over all mangrove stands, CO2 fluxes on intact sediments were relatively low, ranging from -3.93 to 8.85 mmolCO₂·m(-2)·h(-1) in the light and in the dark, respectively. Changes in the fluxes over time appeared to depend to a great extent on the development of the biofilm at the sediment surface. We suggest that in intact sediments and in the dark, CO2 fluxes measured at the sediment-air interface rather reflect the metabolism of benthic organisms than sediment respiration (heterotrophic and autotrophic). However, without the biofilm, sediment water content and air temperature were main drivers of seasonal differences in CO2 fluxes, and their influence differed depending on the intertidal location of the stand. After removal of the biofilm, Q10 values in the Avicennia and the Rhizophora stands were 1.84 and 2.1, respectively, revealing the sensitivity of mangrove sediments to an increase in temperature. This study provides evidence that, if the influence of the biofilm is not taken into account, the in situ CO2 emission data currently used to calculate the budget will lead to underestimation of CO2 production linked to heterotrophic respiration fueled by organic matter detritus from the mangrove.
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http://dx.doi.org/10.1016/j.scitotenv.2014.09.066DOI Listing
January 2015

Multiple markers pyrosequencing reveals highly diverse and host-specific fungal communities on the mangrove trees Avicennia marina and Rhizophora stylosa.

FEMS Microbiol Ecol 2012 Feb 25;79(2):433-44. Epub 2011 Nov 25.

INRA, UMR1163 - Biotechnologie des Champignons Filamenteux, ESIL, Marseille Cedex 09, France.

Fungi are important actors in ecological processes and trophic webs in mangroves. Although saprophytic fungi occurring in the intertidal part of mangrove have been well studied, little is known about the diversity and structure of the fungal communities in this ecosystem or about the importance of functional groups like pathogens and mutualists. Using tag-encoded 454 pyrosequencing of the ITS1, ITS2, nu-ssu-V5 and nu-ssu-V7 regions, we studied and compared the fungal communities found on the marine and aerial parts of Avicennia marina and Rhizophora stylosa trees in a mangrove in New Caledonia. A total of 209,544 reads were analysed, corresponding to several thousand molecular operational taxonomic units (OTU). There is a marked zonation in the species distribution, with most of the OTU being found specifically in one of the microhabitat studied. Ascomycetes are the dominant phylum (82%), Basidiomycetes are very rare (3%), and 15% of the sequences correspond to unknown taxa. Our results indicate that host specificity is a key factor in the distribution of the highly diverse fungal communities, in both the aerial and intertidal parts of the trees. This study also validates the usefulness of multiple markers in tag-encoded pyrosequencing to consolidate and refine the assessment of the taxonomic diversity.
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http://dx.doi.org/10.1111/j.1574-6941.2011.01236.xDOI Listing
February 2012