Spatio-temporal variation of dissolved inorganic nutrients and chlorophyll a in a tropical Amazon estuary in northern Brazil

Abstract

The present study was carried out in the Muriá or Maripanema borehole estuary located in the Atlantic Coast sector of Salgado, Northern Brazil, with the objective of understanding the dynamics of the dissolved nutrients at the water-air interface and the mechanisms of their interaction with the abiotic and biotic parameters (chlorophyll a). This system is influenced by seasonality, which involves aspects of tidal regimes. For this, the spatial and temporal variability of dissolved inorganic nutrients was evaluated together with physical-chemical parameters through mixture diagrams, stoichiometric ratios, and Principal Component Analysis. Ammoniacal N was the most representative form of dissolved inorganic nitrogen in both seasons with maximum values around (~199 μM) subsidizing primary productivity, with a maximum chlorophyll value of (122 μg.m^-3). The high level of N-ammonia was also associated with the release of domestic effluents, aquaculture and degradation of organic matter that occur in the mangrove areas along the Muriá borehole. Phosphate, among the dissolved nutrients, was the one that suffered the most neutralizing action, with low concentrations, so as not to offer signs of eutrophication. Silica concentrations were influenced by variations in tides and water flows. In general, the results obtained allowed an excessive intake of nutrients to be observed along the Muriá borehole, with fluctuations in their concentrations influenced by seasonality, tides and anthropic activities indicating a highly dynamic environment that directly influences the primary productivity of the region.

Keywords:
nitrogen; phosphorus; silicate; estuaries