Terrestrial Particulate Organic Matter Degradation in Estuarine and Coastal Areas: Coupling Lipid Tracers and Molecular Tools to Better Understand Deltaic Biogeochemical Cycles
Marie-Aimee Galeron1, John K Volkman2, Jean-François Rontani1, Olivier Radakovitch3, Bruno Charriere4 and Rémi Amiraux1, (1)Mediterranean Institute of Oceanography, Marseille Cedex 09, France, (2)CSIRO, Oceans and Atmosphere Flagship, Hobart, Tasmania, Australia, (3)CEREGE - UMR 7330, Aix-en-provence, France, (4)Aix Marseille Université, CNRS/INSU,IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 13288, Marseille, France
Abstract:
Deltaic and coastal areas have been studied extensively worldwide, due to their high economic and ecosystemic value. It was long thought that terrestrial particulate organic matter (TPOM) degraded during river transport was refractory to further degradation upon its arrival at sea. But studies on coastal sediments and in the Mackenzie delta (Canada) showed that, on the contrary, TPOM was undergoing intense degradation upon reaching seawater. In order to generalize these results to worldwide river basins, we propose to trace degradation processes impacting TPOM during in-stream transport as well as coastal distribution. We selected the Rhône River (France) for its differences with the Mackenzie River (latitude, temperature, coastal salinity) and carefully researched lipid tracers to help us pinpoint both the origin of the POM and the degradative processes undergone. Betulin, α-/β-amyrins, dehydroabietic acid, sitosterol and their specific degradation products were selected.
While the Rhône delta has been studied for decades, there is very little research on its in-stream processes, and how they can be linked with coastal cycles and fluxes.
Coupling new specific lipid tracers especially selected for the monitoring of higher plant degradation and molecular biology tools, we were able to better trace the origin of TPOM transported along the Rhône River, as well as better understand its degradation state in the river, the delta, and upon its arrival at sea. We show here that autoxidation (free radical induced oxidation), long overlooked, is a major degradation process impacting TPOM transported along the Rhone River, and is even more intense upon the arrival of TPOM at sea. Salinity, metal ion desorption, bacterial and biochemical activity are amongst the factors studied as inducers of such an intense degradation.
This understanding is crucial if we want a truly extensive knowledge of terrestrial particulate organic matter transport and deposition, as well as complete carbon fluxes and budgets that could be generalized to all river deltas.
