Dissolved nutrient fluxes in macrotidal estuary in the Amazonian region, Brazil

This paper aimed to characterize the transport of dissolved nutrients through São Marcos Bay, in Brazilian Amazonian region, and to understand if it acts as a sink or a source of dissolved nutrients for the adjacent marine system of the region. Water sample collections were distributed in two profiles (P1 and P2) in different seasons: dry and rainy. River discharge, temperature, pH, salinity, dissolved oxygen and turbidity were measured in situ. Dissolved nutrients in the water, such as the nitrite, phosphate and silicate were determined with colorimetric method. During the dry season, when occured the flood tide in the estuary, salinity and pH increased and the other parameters decreased, because of the processes occurring in water are commonly connected by acid-base reactions and oxidation-reduction in the environment. During the rainy season the inverse process occurred, due to rainfall intensity in the region. All the nutrient fluxes had same variability in P1, both spatial and temporal, obtaining the highest values during the rainy season. Whereas P2 showed different variations of the fluxes, indicating that most nutrients that entered the estuarine were retained between profiles, suggesting that the São Marcos Bay acts predominately as a nutrient sink from the draining basin.Keywords: nitrite, phosphate, silicate, water, São Marcos Bay.