The study of 12 sediment traps located in the Tinto and Odiel river estuary show the influence of the acid
contributions in the seasonal variation of the contents in organic carbon, inorganic carbon and sulfur. The
seasonal relations between organic carbon and sulfur (C/S) have allowed determining environmental
conditions of the estuarine system. Of this form, the winter conditions correspond to a normal marine
environment, whereas rest of the year varies between euxinic and semi-euxinic conditions due to the high
rate of evaporation that takes place in the intertidal zone that favors sulphate precipitation