Abstract
Urban water supply reservoirs, their quality and quantity of water are affected by anthropogenic activities and environmental changes. They are aquatic ecosystems that respond to the dynamics of organic loads and nutrients, and episodes of eutrophication. Past disturbances in the watersheds and the water column can be noticed by the vertical distribution of heavy metals and trace metals in the sedimentary core. In this study, two sediment cores from the Passauna reservoir in Curitiba, Brazil were examined to assess the accumulation of heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), and nickel (Ni), and other major elements such as aluminum (Al), iron (Fe), manganese (Mn), potassium (K) and barium (Ba), and their association to pollution. Enrichment factor (EF) and geoaccumulation index (Igeo) were applied to the identified accumulation of metals as well as to the level of pollution. The decay of radionuclides, including 210Pb and 137Cs, were used to find the rate of sedimentation over 136 years. The results showed a spatial variation, with the highest concentration of metals found in the upstream part of the reservoir. The EF values of the following metals decreased: in core I, EF(Fe) > EF(Mn) > EF(Cd) > EF(Sb) > EF(Zn) > EF(Cu) > EF(Cr) > EF(Pb); and in core II, EF(Sb) > EF(Pb) > EF(Cd) > EF(Cr) > EF(Fe) > EF(V) > EF(Zn) > EF(Cu) > EF(Ni) > EF(Mn). The Igeo values of the metals decreased in core I Igeo(Fe) > Igeo(Sb) > Igeo(Al) > Igeo(Zn) > Igeo(Cd) > Igeo(Cd) > Igeo(Ni) > Igeo(Cr) > Igeo(Mn) > Igeo(Pb) > Igeo(V); and in core II, Igeo(Sb) > Igeo(Cd) > Igeo(Pb) > Igeo(Al) > Igeo(Cr) > Igeo(V) > Igeo(Fe) > Igeo(Cu) > Igeo(Ni) > Igeo(Zn) > Igeo(Mn). We used the Mn/Fe, Cu/Ni, and V(V + Ni) ratio to evidence changes in productivity and redox conditions in the water column over time.We observed that during the period 1930–1970 anthropogenic activities controlled the impacts on reservoir and water quality. The changes in the distribution of metals coincided with the expansion of agriculture and urban area. In addition, redox and productivity showed periods with different rates of productivity as well as alternate periods of trophic levels. In sum, this paper provides information on how the depositional environment affects the geochemical characteristics of sediment, explaining past environmental changes.
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