Forçantes naturais e antrópicas sobre os manguezais de Salinópolis - Pará.

Abstract

Mangroves stand out for their resilience and important role in environmental balance. Still, globally, mangrove areas have suffered losses of around 35% between 1980 and 2000, caused by changes in salinity gradients, wave and current action, relative sea level changes and urban expansion. The Brazilian coastal zone is distributed in 395 municipalities, among them Salinópolis, located on the Paraense coast, with a wide occurrence of mangroves that have also presented degradation. A spatial-temporal analysis based on Landsat, Quickbird and drone images was used to investigate the main forces driving the natural and anthropogenic mangrove dynamics in Salinópolis. These data allowed for individualizing the vegetation and geomorphology units between 2009 and 2019. An aerial photogrammetric survey based on drone data between Feb / 2019 and Sep / 2019 enabled the identification of changes in the topography of the tidal flats and cliffs. These data indicated an increase in mangrove areas of around 104 ha between 2009 and 2017 in the study area. However, there was a loss of this forest of approximately 52.3 ha between 2017 and 2019, when there was an increase in unregulated urbanization of coastal areas. The area comprising the so-called “Praia do Maçarico” presented losses of mangroves of around 15.2 and 28.8 ha in 2010 - 2017 and 2017 – 2019 periods, respectively. In the Atalaia area, there was a loss of about 23.5 ha between 2017 and 2019. The expansion of the mangroves occurred over higher coastal plains (~2.8 m above mean sea level), distant from human intervention, and probably caused by a relative sea level rise. However, the retraction of mangrove areas occurred mainly due to unregulated urban expansion over the higher tidal flats. In addition, the spatio-temporal analysis indicated erosion on the Maçarico cliff, with a retreat from the top of the cliff of up to 20 m between Feb / 2019 and Sep / 2019. In the year 2022 there were urban infrastructure works in this area with new sediment input to try to stabilize the cliff. It should be highlighted that the eroded material from the cliff caused an increase of up to 1 m on the tidal flat near the base of the cliff, where some mangroves occur, causing the burial of their roots and the death of these trees. The data showed that interventions on the coast with mangroves have caused losses in these forest areas that tend to migrate to topographically higher sectors due to the relative sea level rise, characterizing a conflict between the current expansion trend of this ecosystem and anthropogenic interventions on the coast. The coast of Salinópolis, with a vulnerability degree between very high (4,6) and high (3,6) requires the inclusion of projects with a quali-quantitative analysis of the interaction of the main coastal characteristics (e.g. geomorphology, topographic gradients of the coast, tidal range, vegetation, angle and speed of currents and surface runoff) before implementing works on the Salinópolis coast.