Metal partitioning and availability in estuarine surface sediments: Changes promoted by feeding activity of Scrobicularia plana and Liza ramada

Several works have evidenced in the past the importance and influence of plants and terrestrial invertebrates in metal availability in soils and sediments through changes in metal speciation. In contrast, the impact of estuarine invertebrates and fishes in this process has been poorly explored. The partition of metals in estuarine surface sediments was studied in a controlled environment according to four operationally defined fractions. Sediments were analyzed before and after the passage through the gut of two detritivorous species. Scrobicularia plana feeds on the bottom and suspended sediment particles through the inhalant siphon. Liza ramada is an interface feeder, filtering the superficial layer of the sediment and suspended particles in the water column. Cd, Cu and Ni bound to carbonates increased in the pellets of S. plana, compared with the ingested sediment, as did exchangeable Zn. Similarly, Cd and Zn bound to carbonates have also increased in the pellets of L. ramada; on the contrary, a decrease of Ni was observable in the pellets of this fish. The outcome of the controlled experiments pointed to a potential increase in some metals' availability in the estuarine environment, as a result of the more mobile metal forms in the excreted fecal pellets. This draws the attention to a relevant impact of the trophic activity of both species, alongside with the potential enhancement brought to it by the bioturbation promoted by them, in the role that the estuary itself has as a contaminants' buffer.