Qualidade da água e índice de estado trófico de lagos associados ao baixo Rio Tapajós, Amazônia, Brasil

Abstract

The degrees of anthropization are caused by deforestation, effluent discharge, which compromises water resources, in Amazonian cities. Due to the different types of degradation in lacustrine environments, studies on water quality and trophic classes of lakes are still incipient. In the city of Santarém, west of Pará, the lakes are connected to the Tapajós river and are bordered by white sands and clear waters, attractive for leisure and tourism. Thus, this study aimed to evaluate the Water Quality and Trophic State indices of the Juá and Taparí lakes, associated with the lower Tapajós river, in the municipality of Santarém-PA, taking into account the phases of the fluvial hydrograph (high water and low water ) and the intensity of anthropization. For this study, 4 sampling points were determined for each lake, with monthly collections being carried out in the year 2021, from January to June (high waters) and July to December (low waters). Analyzes of the physical, chemical and microbiological parameters were carried out in the field and in the laboratory and the Water Quality Index (WQI) and Trophic State Index (TEI) were determined. The results showed that the surface water quality conditions are in accordance with current environmental legislation in both lakes. The IQAs of Lakes Juá and Taparí weighted their waters in the good quality class, regardless of the fluvial hydrograph. The average index was better in Lake Taparí (IQA 74) and regardless of the lake environment, IQA values were better in high waters. As for the TSI, the lakes were classified as “ultraoligotrophic”, the TSI values reported significant differences between the phases of the fluvial regime and interaction between lakes and phase, with higher values in high waters, mainly in Lake Juá. Although the physical-chemical and microbiological parameters evaluated in the research are in accordance with the relevant environmental legislation and the final classification of the indices was satisfactory, the overall result allowed us to observe a greater deterioration in the quality of the water in Lake Juá; more anthropized; than on Lake Taparí.