Sediment pollution in an urban water supply lake in southern Brazil

摘要

Urbanization and anthropogenic activities create many environmental issues in urban water supply reservoirs, especially in metropolitan regions. Thus, this study was carried out aiming to evaluate the variance in the physical-chemical characteristics of bottom sediment along the Lake Guaiba, Brazil. Lake Guaiba is a freshwater lake situated in a metropolitan region in southern Brazil, being the main water supply to the region. Surface sediment was evaluated to pH, electrical conductivity, particle-size, total organic carbon and nitrogen, metals and inorganic elements (Fe, Al, Ca, Ba, Sr, Co, Tl, Zn, Cu, Cr, Ni, Pb, Cd, and Hg), and organic compounds. The sediments in the Lake Guaiba show a wide range in the physical-chemical characteristics. Metals Zn, Cu, Cr, and Ni appear in higher concentrations near to the margin of southern Porto Alegre, where there was also more clay plus silt. Sediments of Lake Guaiba have physical-chemical variability by the settle tendency and water flow from the riverine to lacustrine areas. The sediment in Lake Guaiba had a median of: Zn, 132; Cu, 78; Cr, 42; Ni, 28; Pb, 33; Cd, 0.3; and Hg, 0.07g/g. Bed sediments of Lake Guaiba are polluted with Zn, Cu, Cr, and Ni, major in the east margin (near to Porto Alegre). The potential toxic metals and organic compounds found in Lake Guaiba are commonly reported in urban regions around the world. Those elements and compounds derive from many anthropic activities, as industries, sewage, and vehicles. With diffuse sources in the region, the pollution control in Lake Guaiba is very complex.