Water quality of urban streams, Santa Cruz do Sul, Rio Grande do Sul, Brazil, based on physical, chemical and biological analyses

Schuch, MariliaFiedler de Abreu Júnior, EdsonLobo Alcayaga, Eduardo

The purpose of the study was to evaluate the water quality of urban streams in Santa Cruz do Sul, in the Brazilian state of Rio Grande do Sul, using physical, chemical and microbiological parameters. Eight sampling sites were distributed over the upper and lower reaches of four streams. Four sampling campaigns were carried out, two in 2007 and two in 2008. The parameters analyzed were: temperature, pH, turbidity, dissolved oxygen, biochemical oxygen demand, nitrate, ammonia nitrogen, phosphate, total dissolved solids and thermotolerant coliforms. Simultaneously, epilithic diatom samples were collected, the species identified and the respective relative abundance determined. The assessment of water quality was performed applying resolution 357/200 of the National Environment Council, and the Biological Water Quality Index. The results indicated that the streams are polluted by organic contamination and show advanced stages of eutrophication, mainly in the lower reaches, and are classified according to the National Environment Council resolution as Class 4, corresponding to poor water quality. The results of the Biological Water Quality Index ranged from strong to very strong in most sampling sites, highlighting Cyclotella meneghiniana, Fallacia monoculata, Nitzschia palea and Sellaphora pupula as the species most tolerant to eutrophication. Two sampling groups were separat