Heavy Metals & Mineralogy in Sediment Cores from a Tropical Coastal Lagoon, Mexico

Abstract

Concentrations of Fe, Co, Ni and Cd in this lagoon are comparable to similar but affected systems. Cu, Zn, Cr and Pb are, however, lower than those found in contamined estuaries. One core (CP-3) shows an exponential increase of all metals toward the surface. This distribution may lead to erroneous interpretations, attributing it to pollutant input. Clay minerals of the cores consist of kaolinite (41-69%), illite (21-52%), montmorillonite (1-12%) and traces of gibbsite. Variable proportions of illite and kaolinite in the Copala river core can be explained by a depositional environment with varying influence from non-marine to marine conditions. Quartz, feldspar and amphiboles found in the silt fraction of all cores indicate that the sediments in all parts of the lagoon are composed mainly of detrital material.