Acumulação de carbono e emissão de gases de efeito estufa na planície costeira de Soure, leste da Amazônia

Abstract

Estuarine environments are characterized by being dynamic, resulting from river and marine interactions, influenced by hydrodynamic, biological and geomorphological processes, with direct action of depositional processes linked to river currents and tides. Estuarine areas have a variety of ecosystems, including mangroves. Mangroves stand out for their ecological and climatic role, in addition to acting as a nursery for biodiversity. The organic-rich fine sediments retained and the conditions favoring preservation of organic matter in mangroves contribute to the accumulation of carbon in the soil, characterizing them as a natural sink for blue carbon. However, anthropogenic impacts threaten this ecosystem, which results in the release of greenhouse gases (GHG) such as carbon dioxide (CO2) and methane (CH4) into the atmosphere. Mangrove forests play an important role in climate regulation by capturing and storing CO2 in the soil, helping to reduce the concentration of GHG in the atmosphere, and playing a very important role as a mitigator of climate change. Therefore, the objective of this study was to evaluate the relationship between sedimentary facies, carbon storage, and CO2 and CH4 emissions in the coastal-estuarine plain located in the municipality of Soure (PA). The coastal plain of the study area is formed by depositional processes of slow to moderate hydrodynamic gradients, reflected in the alternation between muddy and sandy layers. TOC levels of up to 9% were observed accumulated in the most superficial sedimentary layers of the mangroves. The analysis of stable carbon isotopes indicates a predominance of organic sediments derived from higher plants (trees and shrubs). Radiocarbon dating of organic-rich muddy layers reveals the establishment of this ecosystem in the eastern portion of Marajó during the mid-Holocene approximately 3626 cal. B.P. Measurements of CO2 and CH4 fluxes in tidal channels adjacent to the mangroves demonstrate significant variations during tidal cycles. CO2 concentrations and fluxes were higher during low tide. For CH4, fluxes were predominantly diffusive, especially at Barra Velha, while for the Pesqueiro area at high tide, total diffusive fluxes were higher, in addition to recording ebullitive flux. Both fluxes (diffusive and ebullitive) are indicative of CH4 emissions into the atmosphere. The Soure coastal plain has presented facies characteristic of mangrove ecosystems since at least approximately 3600 years BP, with substrate formed by intercalations of muddy and sandy sediments. The integration of stable carbon isotope data, TOC, 14C dating and GHG flux measurements was of paramount importance to understand the carbon cycle in the region and its relationship with past and current events in the face of climate change, emphasizing the need to preserve and conserve these ecosystems.