Geoaccumulation of Heavy Metals in the Sediment of Lake Guaíba Transitional Waters,Southern Brazil

Abstract

Abstract

Sediment in the region of transitional waters (riverine-lacustrine) of the Lake Guaíba has physical and chemical diversity influenced by its tributaries and the water dynamic. The aim of this study was to characterize sediment characteristics of bottom sediments in this region of transitional waters and evaluate the relationship of these characteristics with pollution. Surface bottom sediments (0–5 cm), as composite samples (with three subsamples), were collected at six sites in the Lake Guaíba transitional waters (during June 2016) with a drag bucket sampler. These samples were dried and sieved (2 mm) and pH, bulk density, particle density, particle size, electrical conductivity, total organic carbon, total Kjeldahl nitrogen, bioavailable phosphorus, metals, and X-ray diffraction determined on sieved samples. Particle size of the bottom sediment decreased along the course from Jacuí's Delta to Lake Guaíba. Particle size had a strong influence on sorption potential of elements and compounds, increasing the values of carbon, nitrogen, phosphorus, and metals. Results indicate that particle size has a major influence on concentrations of metals in bottom sediments. Although these results indicate only a minor metal enrichment, they raise the possibility of punctual pollution in Lake Guaíba surpassing the natural quality. Concentrations of metals (especially zinc, copper, chromium, nickel, and lead) are largely controlled by particle size in the Lake Guaíba transitional waters and particle size differences are the result of depositional processes within the lake.