Environmental controls for the formation of sulphides of Fe in surficial sediments of the Odiel River Estuary (SW Spain)

This paper studies the relationships between Organic Carbon, Sulphur, Pirite, total Fe and oxalate-extractable Fe, present in the superficial sediment on a subtidal-intertidal topographic profile at the Odiel River estuary. The studied samples present high Fe concentrations (9,27 %) and amounts of pyrite varying between 0,42 % in the salt marsh sediments and 0,83 % in the subtidal channel and intertidal channel ■r margin. The C/S ratios obtained for the channel and channel margin are characteristic of well oxigenated • >.• > -.marine environments, whereas those observed at the salt marsh reflect sulphur deficit conditions. The , formation of sulphides in salt marsh zones Is clearly limited by the amount of sulphur that are present, because of their high topographical location and due to the long exposition periods that they experiment, inducing a decreasing of the amount of sulphur available for bacterial reduction processe