Hydrogeochemistry of water courses: the influence of human occupation on physicochemical parameters in the City of Porto Alegre, Southern Brazil

Abstract

This paper presents the results of environmental impact study in three hydrographic sub-basins located in different urban-landscape contexts in the city of Porto Alegre, State of Rio Grande do Sul. The influence of human activities on chemical composition of water and sediments sampled seasonally was determined from the analysis in laboratory of physicochemical parameters such as Fe, Mn, Al, Cu, Zn, Cr, Cd, Pb, Hg, BOD₅ , COD and organic matter, as well in situ determinations such as potential of hydrogen-pH, temperature-T, reduction potential-Eh, electrical conductivity-EC and dissolved oxigen-DO, in order to establish the distinction between wastewater charges generated in each scenario. The results show that urban-landscape contexts influence substantially the chemical composition of water courses. Moreover, seasonality displays a secondary role, whereas there was no significant variation in pollutant concentrations during the water surplus period, between April and October. Thus, it appears that the degree of pollution follows the logical sequence of patterns of urbanization in Brazil: Suburban is the zone where the production of wastewater is the smallest; the mixed urban zone is one with high population density, presence of industries and other potentially polluting activities; and the sparse urban zone that presents intermediate characteristics. At the same time, it appears that, in both scenarios, the riverine environment is exposed to continuous processes of degradation, since wastewater charges are released directly on it, fact that contribute with the raise of the financial costs of water treatment.