Alteração nas características físico-químicas e biológicas da água com a introdução da atividade de silvicultura de eucalipto em microbacias na região do Pampa - RS

Abstract

This study was conducted in order to investigate possible changes in the quality characteristics of the water resources, with the introduction of eucalyptus afforestation to replace the traditional use of the Pampa biome, in watersheds located in the city of Rosário do Sul (RS). Therefore, the investigation included two experimental areas (watersheds), one of them, using forestry with Eucalyptus sp. (ME) with a catchment area equal to 95 ha and other native pasture and extensive livestock (MC) with an area equal to 21 ha. During the period from August 2011 to August 2012, there was monitoring of hourly water levels of streams (dataloggers), daily rainfall (funnels collectors), and biweekly, of the surface water physical, chemical and biological processes, which corresponds to pH, EC, temperature, turbidity, and the concentrations of NH4+, NO2-, NO3-, PO4-, SO42-, K+, Ca2+, Mg2+, F-, Cl-, Na2+, BOD5,20, DO, SS, TS, DS, alkalinity, total coliforms and Escherichia coli. The rainfall and average flow rates recorded for the period was 583,8 (1,55) and 721,6 mm (2,77 L s-1), respectively, for MC and ME. According classes framework of Resolution n° 357/05 of CONAMA, through the retention curves of the quality parameters BOD5,20, turbidity, Escherichia coli and TS, in general, the ME framework presented in larger classes MC, except for the variable E. coli, which showed class 4 for MC. The principal components analysis yielded a reduction of 19 to 12 variables analyzed. Four components explained 82,3 % of the total variance of the data for ME, the pH, EC, turbidity, alkalinity, DS, Mg2+ and Ca2+ were the variables which best characterize the sampled water (PC1). In MC 81,9 % of the total variance was accounted for five main components, being EC, alkalinity, K+, Mg2+ and Ca2+, which best represented the water quality. The introduction of forestry, along with the areas of environmental protection required by the legislation (PPA + LR), to replace the traditional use of the Pampa biome (extensive livestock) contributed to a reduction of up to nine times the E. coli concentration, when assessed by dilution of the variable in the curve of permanence flow.