Benthic fluxes of inorganic carbon in shallow coastal ecosystems of the Iberian Peninsula

The benthic fluxes of inorganic carbon, total alkalinity and oxygen were measured in five shallow coastal ecosystems located along the coast of the Iberian Peninsula (Southern Europe). The measured values ranged between 135 and 447 mmol m−2 day−1 for inorganic carbon, between 22 and 206 mmol m−2 day−1 for total alkalinity, and between 98 and 199 mmol m−2 day−1 for oxygen. These are higher than most fluxes reported previously in other coastal systems. They presented a linear correlation with the organic carbon content of surface sediments found in the systems studied. For the two sampling stations situated in the Bay of Cádiz, a significant dependence of the benthic fluxes on the temperature has been observed, with an activation energy value ranged between 45 and 53 kJ mol−1 based on inorganic carbon flux data, and ranged between 34 and 44 kJ mol−1 based on oxygen flux data. The relationship between the fluxes of inorganic carbon and oxygen increases with the concentration of organic carbon in the surface sediments, from values close to 1 up to values in excess of 3, and is found to be affected by variations in temperature. From the vertical profiles in the interstitial water, sulfate-reduction appears to be one of the principal routes of anaerobic oxidation of the organic matter in these systems, and is to a large extent responsible for the variations in pH found and the variation of the ratio of DIC/DO fluxes.