Avaliação espacial e temporal da qualidade da água da sub-bacia do Rio Ivinhema, MS

Abstract

The pollution of an aquatic environment means the occurrence of any alteration on its physical, chemical or biological conditions endangering humans´ and elements of biota´s health, originating, thus, the contamination. The aim of this study was to evaluate the quality of the superficial water of Ivinhema River Basin and to attribute the origin of the pollution from natural and/or anthropogenic activities and the punctual or diffuse sources based on spatial and temporal variations of the study area. The study intervals reached the days 09/11/2011, 23/02/2012, 20/03/2012, 25/05/2012, 20/07/2012 and 09/10/2012 corresponding to six collects taken in four different places along the Ivinhema River Sub-Basin. The analysis variables were based on physicochemical parameters: temperature, pH, conductivity, dissolved oxygen, BOD5, organic matter (oxygen consumption), total nitrogen, total phosphorus, total acidity, total alkalinity, chloride, hardness, turbidity, total solids and total dissolved solids (TDS), and the metals aluminum, cadmium, lead, iron and zinc. We observed among the months of evaluation that the pluviometric index was the factor that influenced the most the quality of the water from the Ivinhema River Sub-Basin that, through the process of soil leaching provoked by the rains, results on the superficial outflow either in agricultural or in livestock areas taking to waterbodies the sediments originated from the mineral supplements for cattle, fertilizers and pesticides, soil amendments inter alia. The average of concentrations obtained for the physicochemical variables did not overreach the established limits by the Resolution 357/2005 of CONAMA for water Class II in all points, characterizing a good quality of the basin water, excluding, thus, any restriction related to its use for the analysis. The good situation of the PPA´s (Permanent Preservation Areas) on the sub-basin riverfront has contributed to reducing pollution, as we can observe mainly on the low variables values such turbidity, conductivity and TDS. Some changes on the results were verified on the determination of the metals, based on the limits established by CONAMA Resolution 357/2005 for water Class II, whose presence of aluminum and iron may be especially attributed to natural environment factors such as the erosion and rocks and soil leaching around the region, although there´s a small contribution from anthropogenic sources; the origin of zinc and lead refers to human activities with local contribution of the natural environment, such as the soil. However, the contribution of the metal ions, resulted from anthropogenic factors demonstrates the need to investigate the sites of their occurrence, in order to know the real source of pollution and/or contamination by such elements and thus provide the data that will help on future management projects and also on the recovery of the study area and on environmental education.