Long-term water nutrient variations along the easternmost south American estuarine and coastal areas

The estuarine ecosystem is the connection between the river basin and the ocean. The ecological role of this ecosystem is essential for socioeconomic and subsistence activities. However, this ecosystem faces significant threats from domestic, industrial and agricultural effluents. To assess the influence of factors that could be influencing these impacts, this study investigated the spatio-temporal dynamics of ammonia (NH₃) and phosphorous (P) concentration in the lower portion of the river basins located in the most eastern South American region located in Pernambuco State of Brazil. The monitoring data collected between 2005 and 2019 reveal significant NH₃ and P concentration variations, influencing annual, seasonal, and spatial factors. The Generalized Addictive Model for Location, Scales, and Shape (GAMLSS) was utilized to assess the data NH₃, and P water concentrations often exceed the ideal limits (NH₃ ≤ 0.7 mg.L-¹ and P ≤ 0.186 mg.L-¹). The environmental variables of dissolved oxygen, distance from the coastline, rainfall, and ENSO were the most important factors influencing the concentration of NH₃ and P in this portion of South America. The highest concentrations of these nutrients were found principally in the metropolitan sector during the dry season (NH₃ = 4.1 mg.L-¹ e P = 0.604 mg.L-¹). The La Niña phenomenon, particularly during moments of extreme drought (e.g. 2006 and 2017), has led to a significant increase in the concentration of these pollutants, indicating potential risks for the occurrence of eutrophication events in these estuarine ecosystems. Based on our findings, intensifying efforts to sustain and expand the monitoring program is necessary. These measures will enhance the effectiveness of habitat restoration and help achieve optimal environmental conservation.