Concentrations and Fractionation of Carbon, Iron, Sulfur, Nitrogen and Phosphorus in Mangrove Sediments Along an Intertidal Gradient (Semi-Arid Climate, New Caledonia)

Abstract

Abstract:In mangrove ecosystems, strong reciprocal interactions exist between plant and substrate. Under semi-arid climate, Rhizophora spp. are usually predominant, colonizing the seashore, and Avicennia marina develops at the edge of salt-flats, which is the highest zone in the intertidal range. Along this zonation, distribution and speciation of C, Fe, S, N, and P in sediments and pore-waters were investigated. From the land-side to the sea-side of the mangrove, sediments were characterized by I/ increase in: (i) water content; (ii) TOC; (iii) mangrove-derived OM; II/ and decrease in: (i) salinity; (ii) redox; (iii) pH; (iv) solid Fe and solid P. Beneath Avicennia and Rhizophora, TS accumulated at depth, probably as a result of reduction of iron oxides and sulfate. The loss of total Fe observed towards the sea-side may be related to sulfur oxidation and to more intense tidal flushing of dissolved components. Except the organic forms, dissolved N and P concentrations were very low OPEN ACCESSJ. Mar. Sci. Eng. 2015, 3 53beneath Avicennia and Rhizophora stands, probably as a result of their uptake by the root systems. However, in the unvegetated salt-flat, NH4 + can accumulate in organic rich and anoxic layers. This study shows: (i) the evolution of mangrove sediment biogeochemistry along the intertidal zone as a result of the different duration of tidal inundation and organic enrichment; and (ii) the strong links between the distribution and speciation of the different elements.

Mangrove Methane Biogeochemistry in the Indian Sundarbans: A Proposed Budget

“…The range of SO 2− 4 -S concentrations between sediment depths of 20-25 cm was 27.16-27.70 mM, were 1.34 times higher than surface sediment values. Once again, if we compare these SO 2− 4 -S concentrations to the mangrove system in New Caladonia, they are considerably lower (Deborde et al, 2015). One other difference was that in the Lothian Island Sundarbans sediment, SO 2− 4 -S concentrations had a significant decrease only within upper 15 cm depth of sub-surface mangrove sediment consistent with patterns of peak sulfate reduction, with methanogenesis occurring deeper in the sediments (more discussion on this later).…”

“…These observed redox condidions, which are highly conducive for anearobic microbial metabolism favors significant production of biogenic trace gases such as N 2 O, CH 4 , and H 2 S in this mangrove system . In contrast to the Sundarbans mangrove ecosystem, mangrove sediments of New Caledonia were found to have positive redox potential values, to a sediment depth of 30 cm, with negative E h values only found in considerably deeper sediments (Deborde et al, 2015). Such extreme differences sediment redox potential across different mangrove systems can typically be attributed to the geological setting (sediment porosity, organic matter supply), ecological factors (floral and faunal activities), hydrologic regime (tidal inundation and flushing).…”

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

“…Unlike other tropical forests, mangroves are composed of a relatively small number of tree species, which have developed specific adaptations to grow in such peculiar environments, characterized by a fluctuating salinity and the lack of oxygen (Kathiresan and Bingham, 2001). Consequently, mangrove zonation creates sharp lateral and vertical sedimentary physicochemical gradients (Deborde et al, 2015). On the west coast of New Caledonia, which is characterized by a semi-arid climate, Rhizophora spp.…”

“…This is mainly due to the fact that mangrove sediments provide a unique set of ecological niches to diverse organisms and especially to Bacteria and Fungi representing 91% of the total microbial biomass in mangrove sediments (Alongi, 1988;Simões et al, 2015). In those ecosystems, organic carbon is mainly composed of plant lignocellulosic compounds (Marchand et al, 2005) that are decomposed by both Fungi and Bacteria, and accumulated among the deeper layers of sediments, which are anoxic and hypersaline (Deborde et al, 2015). In those ecosystems, organic carbon is mainly composed of plant lignocellulosic compounds (Marchand et al, 2005) that are decomposed by both Fungi and Bacteria, and accumulated among the deeper layers of sediments, which are anoxic and hypersaline (Deborde et al, 2015).…”

Long-distance electron transport by cable bacteria in mangrove sediments

“…Therefore, it is not unsurprising that mangrove sediments also sustain cable bacteria activity: mangrove sediments have a high organic carbon content due to litterfall (Aller et al 2004, Deborde et al 2015, and in most cases sulphate reduction is the most important pathway of organic matter mineralization (Kristensen et al 2008). However, unlike previously sampled sites, mangroves are subject to a bioturbation regime imposed by macrofauna such as fiddler crabs and ghost shrimps (Kristensen & Alongi 2006).…”