Comparação dos índices de qualidade da água e usos do fator contaminação e índice de geoacumulação para os sedimentos da microbacia do arroio João Corrêa, São Leopoldo, RS, Brasil

Abstract

The João Corrêa creek, with 7 km length and a 9.7 km2 micro basin (MbaJC), has its main source into the forested hilly landscape of Sapucaia county and flows trough out the São Leopoldo city, receiving along his course several urban wastes and industrial effluents. Looking for a quantified evaluation of environmental impacts related to human activities, mainly due organic matter, nutrients and heavy metals, it was focused by this research a simultaneous assessment of water and bottom sediments quality and its relationship with hydrologic dynamics. Concerning the choice of environmental indicators, it was used first a widespread range of physical, chemical and microbiological parameters, (dissolved and suspended solids, grain size of sediments, electrical conductivity, color, smell, total solids, temperature, turbidity, alkalinity, aluminum, barium, cadmium, inorganic carbon, chlorides, chromium, lead, chemical demand of oxygen, hardness, iron, phosphates, manganese, nitrogen, ammoniac nitrogen, nitrite and nitrate, dissolved oxygen, hydrogen and redox potentials, sulfides, zinc, heterotrophic bacterias, thermotolerant coliformes, total coliformes, chlorophyll, biochemical oxygen demand and organic substances). The adopted analyses methodology was the described in Standard Methods for the Examination of Water and Wastewater 20ª Ed (1998). By the way, statistical correlation and multivariate analysis were applied to build up statistical indexes of quality (IQA) and metallic load of the stream water. So far, some current water quality indexes were compared, as CETESB, NSF, FEAM, COMITESINOS, statistical, trophic state (TEI) and metallic load, as well accumulation factor and geoaccumulation indexes to bottom sediments. Finally, a full comparison of water indexes and sediments contamination rates was carried out. The water quality was found regular to very poor by statistical index; the most restrictive was the COMITESINOS index. Eutrophic and hipereutrophic water conditions were found by TEI method, what could be related to hydrological dynamics. It was also found a low to moderated contamination of sediments, but the geoaccumulation indexes pointed a strong contamination of cadmium in the final river course. The recommended uses of freshwater along the water stream were classified in level 4 following the CONAMA Resolution N° 357/2005. The levels found to Barium, Cadmium and Lead are pointing a strong influence of antropic activities in the micro basin.