DETERMINATION OF TROPHIC STATE INDEX FOR PHOSPHORUS AT DIFFERENT POINTS OF THE RIVER POMBA

Abstract

To assess the calculated trophic state of the watercourse, the trophic state index (TSI) of the River Pomba, Minas Gerais, was determined during dry and rainy period. The water samples were collected from nine different points of the river. The TSI values were calculated by replacing the variable by the total phosphorus in the equation proposed by CARLSON (1977) and modified by TOLEDO Jr. (1990). The maximum concentration of P was found in sectors where the River Pomba received domestic and industrial effluents, and phosphate fertilizers used in agricultural areas. The data revealed that during the dry period, the River Pomba was partially eutrophic, while in the rainy season, the entire evaluated route was characterized as eutrophic, with a TSI varying predominantly between 54 and 74. The results indicated that the surface washing of anthropic surface areas was higher during rainy season, which most contributed to the phosphorus load in the river, thus increasing its concentration even with increased flow of the watercourse.