Avaliação dos impactos provocados pela descarga de efluente tratado na microbacia do Cintra – Botucatu SP

Abstract

Botucatu is a municipality located in the central south region of São Paulo State, 230km away from the capital, at altitudes ranging from 400 to 950m. The landforms in this region favor the formation of waterfalls; the relief, called "Cuesta", is a water divisor for the watersheds of Paranapanema and Tietê Rivers. Cintra Stream Micro- watershed is situated in the northwest region of Botucatu; its headwaters are inside the campus of São Paulo State University-UNESP, Rubião Junior District, and runs to the north towards Tietê Watershed. This study aimed to evaluate the impacts caused by treated and non-treated effluent discharge; detect, qualitatively and quantitatively, possible punctual and diffuse contamination sources; analyze morphometric parameters; and suggest conservation and recovery measures for the headwaters and riparian forests of Cintra Micro-watershed. The analyzed parameters were: organoleptic and physicochemical properties, chemical species, microbiological elements, pesticides, and morphometric parameters of the micro-watershed. Water samples were bimonthly collected for 12 months, between June/2005 and May/2006, in 8 different sites over the stream, of which 6 collection sites (1–6) are inside the micro-watershed and 2 sites (7 and 8) are downstream to its mouth. The latter is a water divisor for Araquá River Micro-watershed, where Pavuna Ecological Park and its waterfalls are located. The data from water quality analysis were discussed considering annual means, standard deviation and comparison of means (Tukey’s test). All physicochemical parameters and chemical species indicated punctual contamination in sites 1 and 2. For pesticides, there were significant pyrethroid concentrations, 5.5-fold higher than the maximum index allowed by the Edict of the Ministry of Health for waters destined to human consumption; also, organochlorines were detected in several collections, which is worrying since they are forbidden. Besides, punctual contamination by thermotolerant coliforms reached 2400 MPN/100ml. The morphometric characteristics of Cintra Micro-watershed suggest this stream is not prone to overflow and presents excellent conditions for agroecology and water quality preservation from its headwaters to mouth. However, there is the need of rural management guiding, riparian reforestation and actions directed to eliminate existing sites of punctual discharge, aiming at preserving the headwaters for riparian population use, animal consumption, and recreation in the waterfalls with no harm to the health of users, minimizing thus the influence of Cintra Stream on Barra Bonita reservoir (Tietê) concerning eutrophication.