Carolina Fiorillo Mariani

The Rio Grande branch is a part of Billings Complex and is isolated from the central body by Anchieta Dam. This reservoir is located in São Paulo Metropolitan Region and has multiple uses, including water supply, recreation, leisure, receptor of domestic and industrial wastewater. At the present work, the water column was studied in 6 stations along the reservoir, in two different days (one in March and the other in October, 2004). We measured pH, temperature, electric conductivity, dissolved oxygen (DO), transparence of water column, suspended material, total solid, chlorophyll a, feoftin, nitrogenated substances. The data was treated by means of a PCA, a multivariate non-parametric analysis. During March, the water column was stratified because of temperature, pH and electric conductivity. During October, there were higher chlorophyll a concentrations and lower transparence. Trofic State Index was calculated from chlorophyll a and from Secchi disc data, and showed a meso to eutrofic environment. Some NH4+, DO and chlorophyll a concentrations are those of classes designated for less noble uses according to Brazilian law CONAMA n° 357 of 17/03/2005. The statistical analysis showed that the first two axis where responsible for 55% of the total data variance. Total nitrogen and pH were the variables that contributed most for the composition of axis 1 and 2. This reflects the importance of trofic state for the reservoirs characteristics. The stations were segregated according to the sampling date, with no high-low direction pattern. Rio Grande reservoir, Billings Complex, is located in São Paulo Metropolitan Region. It is an important recreation place from where water is extracted in order to supply cities nearby. Lacustrine sediments are concentrated pool for chemicals, among which are trace metals. These metals may be taken up by organisms, accumulated by them and transferred along the food web (bioaccumulation and biomagnification) or may remain biologically unavailable as insoluble, stable and refractory complexes. In anoxic environments, sulfide may be responsible for metal free ion availability control, since it reacts with metal ions and forms an insoluble salt, potentially not bioavailable. At the present work, it was used a weak-acid extraction method for the acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) determination. Cd, Cu, Ni, Pb, Cr and Zn were quantified by means of an ICP-AES and AVS by means of visible spectrophotometer. Organic matter (OM) and clay-silt percentiles, important phases for metal complexation, were also measured. Results were compared to sediment quality guidelines suggested by USEPA (∑ MES-SVA molar relation) and by Canadian Council of Ministers of Environment (CCME) as well by Regional Reference Values (RRV) established for the Alto-Tietê basin. There was an increase of AVS concentration of 100 folds from station 4 (near the riverine region) to station 26 (near the dam). Results showed excess of sulfide compared with metals, what means a low toxic potential. On the other hand, metal concentrations were above RRV, specially Cu (102,7 times greater), Cd (46,2 times greater) and Pb (12,5 times greater). There were also concentrations greater than values suggested by CCME (9,3; 8,3 and 2,9 times greater for Cu, Pb and Cd, respectively). Excepted by Zn, all metals showed increasing patterns from upper to lower regions of the reservoir. PCA statistical analysis demonstrated that the metal data variation has a correlation with OM variation, instead with AVS, and suggests the importance of OM in controlling metal bioavailability in the studied system.

"Rio Grande Reservoir: limnological characteristics of the water and metal bioavailability in sediment." / "Reservatório Rio Grande: caracterização limnológica da água e biodisponibilidade de metais-traço no sedimento"

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