Variação espacial e sazonal de nitrogênio em um estuário de baixo influxo do semiárido brasileiro

Abstract

Nitrogen is an essential element for maintaining vital processes in the biotic environment and is one of the main limiting factors of primary productivity. Thus, the objective of this study was to evaluate the spatial and seasonal variations of nitrogen in the Pacoti River estuary, a low-inflow estuary on the semi-arid coast of Brazil. Samples was collected at six stations along the estuary during the rainy, transition, and dry periods in 2022. The results indicated seasonal and spatial variations with differences in rainfall that resulted in variations in salinity gradients, dissolved oxygen concentrations and nitrogen forms. Salinity increased from the rainy (14.77) to the dry period (28.30), indicating enhanced saline intrusion due to reduced freshwater input. During the transition period, oxygen supersaturation occurred at the lower stations and anoxia at the upper stations. The highest concentrations of nitrogen forms were observed in the upper stations and in the dry period, with averages of 25.67 µM of ammoniacal N, 2.12 µM of nitrite, 4.15 µM of nitrate and 74.61 µM of total nitrogen. Ammoniacal-N was the dominant fraction of dissolved inorganic nitrogen (DIN), representing an average of 68.48% of DIN, being higher in the dry period, with an average of 89.98%, suggesting anthropogenic influence, such as the discharge of domestic effluents.