The trace metal chemistry of a tropical hypersaline basin: Evidence from field and laboratory experiments

Abstract

Field observations were made of the distribution of trace metals in water and sediments along a chlorinity gradient from 20-160‰ in the seasonally hypersaline Ceuta lagoon, Sinaloa, Mexico. The observations revealed a non-consecutive behaviour of the metals (with respect to chlorinity) with a rapid loss of metals to the sediments from chlorinity 20-50‰, a net desorption of metals from the sediments from 50-155‰ and finally, precipitation with halite or the last bitters. Radiochemical laboratoty experiments were performed to examine possible solid-solution formation of Ni, Co and Mn with the calcium carbonate and gypsum phases formed during seawater evaporation and the partition of Co and Mn between suspended sediments and seawater throughout the chlorinity range of the lagoon. From the laboratory experiments and a simple descriptive model of a hypersaline basin, it was concluded that the behaviour of trace metals in the lagoon results from variations in the adsorption/desorption equilibria with the sediments rather than solid solution formation.