Chemical aspects of water and sediment from the Ibitinga reservoir (São Paulo í Brasil í 21° 45’ S and 48° 50’ W)

Abstract

The aim of this paper was to investigate the water quality of the Ibitinga reservoir, based on limnological variables of sediment and water, between October 1989 and November 1990, in a spatial and seasonal approach. The water column was sampled in three stations (E-1, E-2 and E-3). In addition, two other sampling stations, located at the mouths of the Jacaré Pepira (EJP) and Jacaré Guaçu rivers (EPG), were also selected. The results show that the reservoir is turbulent, polymictic and mesotrophic (Trophic State Index: chlorophyll a = 47; PO₄^3- = 41; Secchi = 48). In the reservoir water, the analyzed variables presented higher average values at the wet season, mainly in the station E-1. The DO median values varied from 6.7 mg.L^-1 (E-3 bottom, wet season) to 9.2 mg.L^-1 (E-3 surface, dry season). The pH, BOD, NO₂-N and Total Inorganic Carbon (TIC) varied according to season and spatial variation (P<0.05), while water temperature, color, NH₄⁺ and PO₄^3- followed only the seasonality. The chlorophyll a varied among the sampling stations and turbidity was affected by seasonality and water depth. For all parameters analyzed in water, only NO₃-N was co-varied with the Ibitinga reservoir and the rivers (P< 0.05). In the sediment, TIC showed a spatial variation and total P was affected by season and spatial variation, with interaction effect (P<0.05). The Tietê river exerted a strong influence on the water quality of the Ibitinga reservoir, while the diluting effect provided by Jacaré Pepira and Jacaré Guaçu rivers was less relevant.