Geochemical Signatures of Recent Holocene Estuarine Sediments of the Jaboatão River, Pernambuco, Brazil

The Jaboatao River Basin, northeastern Brazil, is characterized by urban and industrial land uses, although it includes extensive sugarcane plantations with a marked deterioration of the native forests. Heavy metal (HM) concentrations in estuarine sediments of the river have been measured to assess possible historical sources of pollution. The trace metals were investigated based on samples from a drill core taken 4 km from the mouth of the river. The sediments of the core were analysed for chemistry, particle size, and organic matter (OM) content. The chemical species analysed (As, Cr, Pb, Hg, Ni, and Zn) show higher concentrations in the 30–35 cm interval of the core. This indicates that the accumulation of HMs has been constant over the last few decades and confirms the existence of two well-differentiated compartments, one above and one below the 30–35 cm horizon. The partitioning of the sedimentary and geochemical profiles highlights varying environmental conditions in the estuary. This behaviour is marked by a conspicuous dichotomy in the C/N ratio, specifying signatures dependent on the geochemistry of the sediments and on hydrodynamic variations, in an essentially organo–siliciclastic depositional context. The OM present in the sediments indicates a progressive evolution of continental environment conditions at the bottom to more estuarine conditions at the top, which could indicate a small and progressive drowning of the Jaboatao River mouth, probably related to sea-level rise in the range considered.