The Guajará Bay is the main water body of Belém, characterized by strong hydrodynamic, and coupled with the Guamá River is used as a receiver of the waste of the population. The organic carbon is one of the most important macronutrients in aquatic systems, as it provides energy, acting on biological communities. The phosphorus in the environment comes from the weathering of rocks, mainly in the form of apatite and also contributed through manure, when present at high concentrations, phosphorus can accelerate the process of eutrophication. This study aimed to investigate the total organic carbon and total phosphorus and its fractions, as well as granulometry, at the mouths of the major drainage channels along the Guamá River and Guajará Bay and correlate the values obtained with the particle size characteristics of the points. Water samples were collected to determine in situ the basic physicochemical parameters such as temperature, pH, conductivity and dissolved solids through a multiparameter analyzer. The average temperature was 29.5 °C, characteristic of a tropical estuary, pH values had a mean of 6.37, reflecting a greater influence of river water to the sea front. The electrical conductivity had average value of 0.12 mS cm-1, while the total dissolved solids average’s was 0.05 g L-1. The TOC was determined by the method of Gaudette in 7 points along the edge of Belém, the average values found were 3.54 %, with a minimum of 2.80 in the Una’s channel and maximum of 3.88 at the port of Miramar. The granulometry was composed by fine sediments, where the sand content indicated a strong hydrodynamic. The determination of phosphorus was based on Ruttenberg’s method by absorption spectrophotometry, obtaining 5 fractions: P- bioavailable iron bound to the P, switched biogenic apatite connected to P and P detrital organic apatite, the sum of these fractions results in total phosphorus. The value of total phosphorus ranged from 22.86 to 31.91 μmol P g -1, on the Island of the Jaguars and Miramar, respectively. Unless representative fraction was in general P- bioavailable as the fraction of bound phosphorus biogenic apatite was responsible for over 50% of phosphorus values at all points. The results of TOC were remarkably close to previous works in the region, the values of phosphorus when compared to studies from other regions show that the estuary Guajará is not strongly influenced by human action, but this action shows already present when comparing values of the edge of Belém with the most distant points.
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