Brazilian Mangroves: Blue Carbon Hotspots of National and Global Relevance to Natural Climate Solutions

Abstract

Mangroves are known for large carbon stocks and high sequestration rates in biomass and soils, making these intertidal wetlands a cost-effective strategy for some nations to compensate for a portion of their carbon dioxide (CO2) emissions. However, few countries have the national-level inventories required to support the inclusion of mangroves into national carbon credit markets. This is the case for Brazil, home of the second largest mangrove area in the world but lacking an integrated mangrove carbon inventory that captures the diversity of coastline types and climatic zones in which mangroves are present. Here we reviewed published datasets to derive the first integrated assessment of carbon stocks, carbon sequestration rates and potential CO2eq emissions across Brazilian mangroves. We found that Brazilian mangroves hold 8.5% of the global mangrove carbon stocks (biomass and soils combined). When compared to other Brazilian vegetated biomes, mangroves store up to 4.3 times more carbon in the top meter of soil and are second in biomass carbon stocks only to the Amazon forest. Moreover, organic carbon sequestration rates in Brazilian mangroves soils are 15–30% higher than recent global estimates; and integrated over the country’s area, they account for 13.5% of the carbon buried in world’s mangroves annually. Carbon sequestration in Brazilian mangroves woody biomass is 10% of carbon accumulation in mangrove woody biomass globally. Our study identifies Brazilian mangroves as a major global blue carbon hotspot and suggest that their loss could potentially release substantial amounts of CO2. This research provides a robust baseline for the consideration of mangroves into strategies to meet Brazil’s intended Nationally Determined Contributions.

Blue Carbon Ecosystems in Brazil: Overview and an Urgent Call for Conservation and Restoration

“…Amazon mangroves represent 27.9% of the total mangrove area of the country (Ferreira & Lacerda, 2016). These results demonstrate the global importance of Brazilian mangroves as carbon hotspots (Rovai et al, 2022) (Table 1). Mangroves in North Brazil (Amazon mangroves) are part of the world's largest continuous belt of mangroves (760,000 ha) (Souza Filho, 2005).…”

“…However, the overall focus of current BC research on the estimations of total stocks and burial rates (habitat-bound carbon) has overlooked the mobile BC fraction, that is, carbon outwelling (lateral fluxes or horizontal exports of C to the ocean; Santos et al, 2021). Therefore, the sequestration capacity of BCEs can be largely underestimated (Santos et al, 2021;Rovai et al, 2022).…”

“…Surveys of the TECS registered in Amazon mangroves (511 MgC ha −1 ) do not significantly differ from the mangroves of semiarid tropical coasts in Brazil [413 MgC ha −1 (Kauffman et al, (Hamilton and Friess, 2018;Rovai et al, 2022).…”

“…The aboveground (AGB) and belowground (BGB) biomass and TECS in Brazilian mangroves (Figure 2B) may present heterogeneity based on geomorphic and sedimentary settings, soil depth, tidal height, salinity, climate, environmental protection measures, and forest structure (Kauffman et al, 2018a;Kauffman et al, 2018b;Nobrega et al, 2018;Rovai et al, 2018;Kauffmann et al, 2020;Hatje et al, 2020;Matos et al, 2020;Rovai et al, 2020;Rovai et al, 2022) (Table 2). The belowground portion (including soils and roots) represents approximately 70%-86% of the total carbon stocks in mangroves (Hamilton and Friess, 2018;Kauffman et al, 2018a;Kauffmann et al, 2020).…”

Amazonian vegetated estuarine ecosystem as a global hotspot in carbon sequestration

“…This is in part due to the large extent of the mangrove area and the di culty to access large parts of this region, in particular around the island of Marajó. A recent review of carbon sequestration rates in mangroves of Brazil, suggested that they appear to sequester 15-30% more carbon than other global regions, but it is unknown if this is related to a paucity of data or genuinely re ects the situation in Brazil 10 , particularly considering the fact that only one study was considered for north Brazil, where 77% of the mangroves are located.…”