Index of Trophic Status of Clear Water Lakes Associated with the Lower Tapajós River, Amazonia, Brazil

Abstract

The Trophic State Index (TSI) is a mathematical tool capable of classifying the trophic status of a water body, evaluating the water quality with respect to chlorophyll-a and total phosphorus concentrations, which are used to evaluate the Index. The results corresponding to phosphorus (P) should be understood as a measure of the eutrophication potential, since this nutrient acts as the causative agent of this process. This study purpose was to identify the trophic status of clear water lakes, associated with the lower Tapajós-river, using the Trophic State Index (TSI). The study considered a spatial and temporal approach, in which two samplings were carried out in four lakes on the right bank of the lower Tapajós-river, one in October 2016 in the low water period, and another in March 2017 in the high-water period. The limnological parameters were analyzed from water sampling of the Limnetic region, 30 cm below the water surface, against the direction of water flow. The average values of (TSI) index among the lakes do not have a significant difference. Only between periods of low and high water, the latter having higher values. The weighted values of Total Phosphorusand Chlorophyll-a indicated that nowadays the waters of Lakes Verde, Jacundá, Taparí and Juá are in the ultraoligotrophic state. According to resolution 357/05, the four lakes had concentrations of Total Phosphorus and Chlorophyll-a within the range allowed by legislation, having little variation in the distribution of these