A cross-section analysis of sedimentary organic matter in a mangrove ecosystem under dry climate conditions: The Somone estuary, Senegal

Abstract

International audienceMangrove sediments are an important organic matter (OM) reservoir and play a major role in the carbon cycle. Since the 1990s, these ecosystems were subjected to numerous studies, in order to quantify the sed-imentary sink for organic carbon (OC) and to characterize the organic matter sources, but remain poorly studied in Western Africa. The aim of our study is to quantify the organic carbon content and to identify the OM origin stored in the Somone mangrove sediments. Studied area is characterized by a (i) dry climate conditions with a higher rate of evaporation, (ii) lack of freshwater input by river, and (iii) tide dominated system. Here, we focus on physico-chemical properties of sediments (temperature, pH and redox), sedi-ment grain size, water content, particulate organic carbon and dissolved organic carbon from a series of 40 cm-deep cores in four tidal contexts: mudflat, Rhizophora, and Avicennia mangroves and barren area. Results show that total organic carbon (TOC) contents range between 0.34 and 3.92 wt.% and are higher in sediments from mudflat and Rhizophora mangrove than in sediments from Avicennia mangrove and barren area. Indeed, sediments stored under Avicennia is subjected to suboxic conditions initiated by roots system and crabs bioturbation; while under Rhizophora and mudflat, local anoxic conditions are prevalent as suggest the negative Eh values and the occurrence of framboidal pyrites. Mangrove sediments of the Somone estuary contain an autochthonous lignocellulosic-derived organic matter. The youngest and stunted form of the Somone mangrove explains the low organic carbon content of sediments; where dry climate conditions limit the organic matter production by the mangrove forest. The shallow depth at which the organic matter of the former mudflat was found confirms that the Somone mangrove is subjected to a low sedimentation rate. This suggests that organic carbon burial depends on others processes than sedimentation. Then, in the Somone mangrove ecosystem, both of pneumatophores and burrowing crab activities are the main factors that control OM degradation (Avicennia station) while anaerobic conditions (mudflat and Rhizophora) promote OM preservation

Plankton and benthos similarity indices as indicators of the impact of mangrove plantation on the environmental quality of silvofishery ponds

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Evaluating, predicting and mapping belowground carbon stores in Kenyan mangroves

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“…At present, the effects of variables influencing BGC are poorly understood, and further research is justified. Whilst some studies have treated mangrove sediments within forests as homogenous systems, others have found significant differences in BGC between different species (Lacerda et al ., ; Alongi et al ., ; Bouillon et al ., ; Huxham et al ., ; Liu et al ., ; Wang et al ., ; Sakho et al ., ) and distances from the coast (Fujimoto et al ., ; Donato et al ., ; Kauffman et al ., ). The geomorphological setting of a mangrove forest will potentially influence the import of allochthonous material, and the production and export of autochthonous material, through river discharge, tidal amplitude, wave power and turbidity (Adame et al ., ; Saintilan et al ., ; Yang et al ., ), and therefore the effects of these variables may vary between sites.…”

The influence of crab burrows on sediment salinity in a Rhizophora-dominated mangrove forest in North Brazil during the dry season

“…Mangrove forests are species-rich, highly productive systems, and they provide numerous ecosystem services. These forests can considerably affect the biogeochemical cycles of coastal regions (Alongi et al, 1989;Alongi, 2008;Rivera-Monroy et al, 1995;Sakho et al, 2015;Schwendenmann et al, 2006), serve as feeding grounds and nursery sites for oceanic and coastal nekton, and provide habitat for a range of terrestrial, intertidal and marine fauna and flora (Ellison, 2008;Faunce and Serafy, 2006).…”