Electrochemical characterization of mangrove sediments: A proposal of new proxies for organic matter oxidation

The voltammetric response of microparticulate deposits resulting from solvent evaporation of ethanolic extracts of mangrove sediments in contact with aqueous acetate buffer is hereby described. Dated sediment cores sampled from the Peruvian mangrove system ("Manglares de Tumbes" National Sanctuary) presented voltammetric responses dominated by oxidative signals of organic components that exhibit significant variations depending on the depth. Voltammetric data allowed for the definition of electrochemical indexes representative of the electrochemically oxidable organic matter fraction. These electrochemical indexes were f(EAOM) (for the total amount of organic matter being electrochemically active), f(EROM) (for the fraction of organic matter electrochemically oxidizable in reversible form), f(RDOX) (for the proportion between the fractions of electrochemically active organic matter which is in an oxidized state and in a reduced state) and f(ROS) (capability for reaction with reactive oxygen species), while the spectroscopic index A(1650)/A(3400) (as a proxy analogous to fRDOX) was also applied. The mangrove forest presents a higher oxidized fraction of the electrochemically active organic matter, as confirmed by additional data obtained from infrared spectroscopy. These results indicate that the described electrochemical indexes may provide insights on organic matter degradation by oxidative processes in addition to chemical analyses of coastal vegetated systems that are currently used, such as mangrove wetlands.