Avaliação dos aspectos físico-químicos e microbiológicos para determinação do índice de qualidade da água – IQA no Rio Toledo – PR

Abstract

The Toledo river has its route in both rural and urban areas, being subject to different forms of environmental impacts. Changes in water characteristics may be related to the use and occupation of the soil in the vicinity of the river, generating anthropogenic processes. Thus, the purpose of this work was to analyze the water quality of the Toledo River in order to verify the effects of urbanization and agricultural activities under the water body. The Water Quality Index (WQI) and cadmium trace elements, lead, manganese, nickel and zinc were used. The WQI was calculated, according to the methodology proposed by CETESB (2015), where the physical variables were obtained: turbidity and water temperature; Chemical variables: BOD; pH; Dissolved oxygen; Total nitrogen and total phosphate; Biological variables: fecal coliforms. Limnological analyzes were performed following the methodology described in APHA (2005). The values of the analyzes were compared to those established by the Conama Resolution nº 357/2005, for Class II waters. The concentrations of the trace elements were obtained through the ICP-OES equipment by acid digestion. In order to do this, monthly water collections were carried out in five distinct points, three points located in the rural region, and two points in the urban region, during the period from July 2015 to June 2016, totaling one year of monitoring. The WQI values at the five collection points ranged from (78.06 to 36.44). Point 1 had an annual average of (67.75) and point 4 (39.92). Points 4 and 5 showed critical points regarding contamination of organic origin (BOD), phosphate (total phosphate) and microbiological (fecal coliforms). The values obtained exceeded the limits established by the legislation in force in practically all monitoring. These values allowed to classify the water body in the categories of Regular to Good. The trace elements presented in all points values discordant of the limits recommended by the resolution Conama no 357/2005 for waters of Class II. The analysis of land use and occupation showed that the urban area occupies an area of 2,902.93 (Ha), totaling 2.42% of occupancy. The agricultural area occupies 98,643.02 (Ha), with 82.33% of area in use. In this way the use and occupation of the soil improperly can directly influence the quality and availability of water resources, either by accelerated urbanization, by the suppression of vegetation or by the use of agriculture. Impacts may vary depending on the use, organic load, nutrients, metallic contaminants and sediment trapping, compromising the quality and balance of the aquatic ecosystem.