Qualidade da água em nascentes da bacia do Vacacaí-mirim com diferentes usos e coberturas do solo

Abstract

Several factors can modify the qualitative features of water resources in watershed areas. Such changes are due to natural processes and from human activities such as agriculture, livestock and removal of riparian vegetation which interfere in the original conditions of use and soil cover. Because of these practices in springs areas the water quality may be degraded. In such context, this study aimed to evaluate the influence of different uses and soil covers on the physical, chemical and biological features in the water of springs located in the Arroio Manoel Alves watershed, Itaara town, RS. Therefore, six springs (N1, N2, N3, N4, N5 and N6) as its pipeline (CC), were monitored under different land uses and covers (agriculture, buildings, eucalyptus, grass, native forest, water resource and access roads). The study was developed between January 2015 and January 2016, with a bi-weekly water sampling and analysis of the following qualitative parameters: temperature, turbidity, pH, EC, OD, BOD5,20, total coliforms, Escherichia coli, TS, DS, SS, PO4-, NO2-, NO3-, SO42- and Cl-. There were installed two rain gauges to quantify the rainfall in the watershed, which corresponded to the annual total of 2267,2 mm. The flow rates were hourly monitored reaching maximum values of 5,67 L.s-1, the N1, N2, N3, N4 and N6, 14,17 L.s-1 to N5 and 255,5 L.s-1 to CC. The retention curves and the resolution of the framework classes 357/2005 CONAMA revealed that the N5 and the CC overcame class 4 for variable turbidity. For BOD5,20, all areas exceeded the limits of class 4 for the major part of the period. For E. coli, N6 remained in class 4 at most of the time. For the DS parameter, the N1, N2, N3, N4 and N6 did not fit in classes 1, 2 and 3 in the analyzed period. WQI got "average" standards in the springs N3, N4 and N6, and "good" standards for N1, N2, N5 and CC. FA formed three components in N1, designated as climate, weathering and diffuse pollution factors. The N2 showed three components, explained by weathering, climate and pollution diffuse factors. The N3 was explained by the superficial, environment and microbiological factors. The N4 obtained the three components, characterized by leaching, diffuse pollution and decay factors. For N5 three components formed were described by decomposition, weathering and microbiological factors. In N6, the components were classified by superficial, environment and microbiological factors. For CC, formed three components, explained by diffuse pollution, weathering and climate factors. In general, the methodologies used for evaluation and analysis of the influence by use and soil covers on water quality of monitored areas shown to be satisfactory, where the N3 had livestock activity interference, the N6 of rural household s effluents and, N1 and N2, indicated results of forest protection on water quality. The N5 expressed influence of external factors on water quality, the N4, characterized by low concentrations of pH and DO, and the pipeline, demonstrated influence by the flow rates, the tributaries and by the land use and soil covers of the watershed.