Water surface variability in oceanic and estuarine coasts of Amapá, Brazil

The coast of Amapá state is the most preserved and least populated region in Brazil, characterized by a variety of complex ecosystems subject to hydroclimatic variability and anthropogenic pressures. Despite its significant hydrological and ecological importance, the area is also the least studied and understood in the country. This study aimed to analyze the water surface variability in both oceanic and estuarine Amapá coastal areas between 1985 and 2022, correlating them with hydroclimatic (precipitation and sea level rise) and anthropogenic (soy and mining) variables. The methodology included the following steps: (1) obtaining water surface time-series data for each coastal municipality and considering hydroclimatic and anthropogenic variables, followed by spatiotemporal analysis using geographic information systems (GIS); (2) conducting analyses of the environmental and physiographic features of the coastal basins; and (3) performing statistical integration and data modeling to test for potential correlations that explain water surface variations. We found that the water surfaces experienced distinct and significant variations, mainly influenced by the expansion of soy cultivation and sea level rise (p < 0.05). Furthermore, the oceanic region had a greater simultaneous impact from anthropogenic and hydroclimatic variables (R²_aj = 90.55%) than the estuarine region (R²_aj = 62.46%). We conclude that considerable hydrological changes have been occurring on the coast of Amapá, and thus this region should be a priority in terms of management and conservation of its vulnerable coastal ecosystems.