Avaliação da qualidade da água do Lago Igapó e seus tributários na cidade de Londrina/PR

Abstract

The assessment of water quality in urban water bodies has become an essential activity in the face of constant population increase and the growing rate of urbanization. The water quality was evaluated through field work, divided in two campaigns with 15 collection points distributed between the source of the Ribeirão Cambé microbasin and the Igapó I Lake dam in the city of Londrina/PR. The campaigns were carried out in 2021, in the months of January and August, as they are periods with different climatic conditions, characterized by rainy and dry seasons, respectively. Eleven physicochemical and microbiological parameters were evaluated: temperature, electrical conductivity (EC), hydrogenic potential (pH), turbidity, dissolved oxygen (DO), total solids, total nitrogen, total phosphorus, biochemical oxygen demand (BOD), coliforms thermotolerants and Escherichia coli. The water quality index (WQI) was calculated and multivariate data analysis was performed using Principal Component Analysis (PCA). The results were compared to the limit values of CONAMA Resolution Nº 357/2005. The study showed that in the 1st campaign, the site was heavily impacted by the runoff into the lake. The excess amount of organic matter and sediments has led to its advanced silting state, demonstrated by the high values of BOD, turbidity and fecal coliforms. In the 2nd campaign, the contamination was more localized at specific points, in addition to the accumulation of contaminants in the sediment. This is verified by the high concentration of salts, due to the lower runoff, confirmed by the parameters of EC, total phosphorus and total solids. The results suggest that the contamination of anthropic origin is present in both sampling campaigns. In general, the lake's WQI could be rated as "good", and, in addition to the PCA analysis, was an important tool to assess the water quality of the microbasin. The invariability of the WQI demonstrates that changes in climatic conditions promote the intermittence of parameters. However, the degraded nature of the water bodies studied prevails over seasonality. In view of this, for the planning of actions to mitigate the problems of the Igapó, it is highly recommended to pay close attention to the parameters implicit in the calculation of the WQI.