A new research led by Brazilian scientists, carried out by a multidisciplinary team involving researchers from UFES, USP and UFPA, with support from the National Geographic Society, CCARBON/USP, FAPES and CNPq, revealed that the mangroves of the Amazon coast hide a valuable and vulnerable secret: vast deposits of peat (accumulated organic matter) under their roots. The finding, published today in the journal PeerJ, indicates that these ecosystems store much more carbon than previously thought, but are being rapidly destroyed by coastal erosion, releasing greenhouse gases at alarming levels.
The study, carried out on Maracá Island, in Amapá, identified for the first time that possibly about 46% of the mangroves in the northern Brazilian Amazon overlap with coastal peatland areas. This combination creates a “super-stock” of carbon, but also a fragility: when the sea advances and erodes the coast, this ancient carbon is exposed and released into the atmosphere.
The Carbon Hidden Beneath the Mud
Unlike common mangroves, which grow on mineral soils, the mangroves of the Amazon are superimposed on layers of peat of millennial age that can be meters deep. “We discovered that these organic layers have a carbon concentration up to 25 times higher than the typical mangrove soils of the Amazon coast,” explains Professor Angelo Bernardino, a researcher at the Federal University of Espírito Santo (UFES) and coordinator of the study.
The research quantified that erosion in these areas removes about 72% of the carbon stored in the soil. This means that the natural loss of mangroves, driven by rising sea levels and changes in sea currents, is generating greenhouse gas emissions that were not being accounted for in current climate models. The organic carbon content of the peat layers under the mangroves reaches 46%, compared to 1-2% of typical soils of mangrove forests on the Amazon coast. Carbon stocks in soils up to 2 meters deep in mangroves over peatlands are 600 tons per hectare, about 2 times higher than that found in mangrove forests in the Amazon (250 to 360 tons/ha).
Implications for Global Climate
The discovery has a direct impact on Brazil’s conservation strategies. With almost 367,000 hectares of mangroves on peatlands in the Amazon region, the protection of these areas becomes critical for the country to achieve its emission reduction goals.
“Recognizing these mangroves as distinct ecosystems is critical to accurate carbon accounting,” Bernardino says. “Coastal erosion in the Amazon is now one of the main factors in the degradation of these stocks, and we need urgent strategies to monitor and mitigate these losses.”
The study reinforces that the “blue carbon” (stored in marine ecosystems) of the Amazon is one of the greatest climate treasures on the planet, but that its permanence depends on the delicate balance between the forest and the ocean.
