The distribution and variation of total organic matter (TOM) during the rainy season, was studied in the sediments of the coastal lagoon of Huizache-Caimanero, Sinaloa. Two well defined areas werw detected: one with more than 9% TOM, NE of the lagoon, and other with less than 9% TOM, SW of the lagoon. An almost homogeneous TOM concentration was found from the surface to 15-20 cm depth of the sediment core. This is probably due to the continuous addition of TOM from the terrestrial and submerged vegetation.
