Assessment and evaluation of metal contents in sediment and water samples within an urban watershed: an analysis of anthropogenic impacts on sediment and water quality in Central Brazil

Abstract

The aim of this study was to assess the distribution of metals in sediments and surface water within the Lago Paranoa catchment in Central Brazil, and to evaluate metal enrichments due to anthropogenic activities. Concentrations of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sr, Ti and Zn were analyzed in sediment samples from sediment sources under different land uses, in alluvial sediment profiles, and in water samples. Principal component analysis was used to investigate the impact of different land use types on metal concentrations in source sediments. The anthropogenic impact of different land uses on metal concentrations in sediments was quantified by the calculation of enrichment factors, using the local geological background as reference. The data showed that different anthropogenic activities are related to specific metal enrichments in source and alluvial sediments. Particularly urban areas with high-density block development were characterized by higher enrichments of Cd, Cr, Pb, Sr and Zn compared to the local background values. Sediments from agricultural areas had higher concentrations of Cr, Cu and Ni compared to urban areas, which is caused by higher contents of clay and not due to human impact. The concentrations of Cd, Cr, Cu and Pb in surface water samples of the main rivers discharging into Lago Paranoa were very low. The values of Al, Fe, Mn, Sr and Zn differed between the sub-catchments and showed seasonal variation. Metal concentrations depended substantially on terrestrial inputs from anthropogenic and natural sources. The analysis of effluent water samples indicated that there is a temporary metal input into the lake from the two wastewater treatment plants, which might have caused metal enrichments in sediments and water. The regression analyses showed that there is a strong correlation between metal concentrations in alluvial sediments and corresponding water samples, as well as between metal accumulation in the alluvial sediments and shares of urban areas in the sub-catchment.