Environmental drivers of blue carbon burial and soil carbon stocks in mangrove forests

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

“…However, this result is likely due to the small number of observations used to constrain biomass predictions for that region (only two AGB values available for Rio Grande do Norte at the time Rovai et al, 2021b study was conducted; Supplementary Table 1). Regarding SOC stocks, deltaic mangroves in Piauí, Amapá, Pará and Maranhão states had lower soil carbon density due to higher inorganic-to-organic ratio per soil volume characteristic of coastal deltaic floodplains when compared to predominantly estuarine or lagoonal mangroves (Rovai et al, 2018;Sanderman et al, 2018;Jennerjahn, 2020;MacKenzie et al, 2020) found in other Brazilian states (Table 2). When summed, carbon stocks in biomass (AGB+BGB) and soils across Brazilian mangroves averaged 341 MgC ha −1 (range: 297-397 MgC ha −1 ), showing little variation among states (e.g., maximum difference of 23% or ∼80 MgC ha −1 ) (Table 2).…”

“…While there were no differences (P > 0.05, results not shown) across the coastal geomorphic types found along Brazil's shoreline, this value is 15-30% higher than recent global estimates (e.g,. 1.94-2.39 MgC ha −1 yr −1 ; Jennerjahn, 2020;MacKenzie et al, 2020;Wang et al, 2020), likely due to the predominance of minerogenic coastlines (deltaic, which accounts for >80% of the country's mangrove area, and meso-and macrotidal estuarine systems) where deposition of both autochthonous (mangrove detritus) and allochthonous (terrestrial and marine detritus) sediments are amplified (Adame et al, 2010;Kusumaningtyas et al, 2019;Cragg et al, 2020). Importantly, when this national median value is multiplied by the country's mangrove area coverage, annual carbon sequestration in Brazilian mangroves soils was estimated at 2.14 TgC yr −1 , corresponding to about 13.5% of the total amount of carbon buried annually in the world's mangroves.…”

“…Among tidal saline wetlands, mangroves are known for high rates of carbon sequestration in soils (mean = 222 gC m −2 yr −1 ; Jennerjahn, 2020;MacKenzie et al, 2020;Wang et al, 2020), that are 50 times higher than reported for terrestrial tropical and temperate forested biomes (mean = 4.5 gC m −2 yr −1 ; McLeod et al, 2011). Combined with comparable carbon sequestration rates in woody biomass (mean = 82.7 gC m −2 yr −1 , range = 13-2,160 gC m −2 yr −1 ; Xiong et al, 2019), these intertidal wetlands can be a cost-effective strategy for some nations to compensate for part of their carbon dioxide (CO 2 ) emissions (Taillardat et al, 2018).…”

Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests

“…Multiplying the median by both low and high estimates of mangrove area [29,30], carbon burial in the world's mangrove forests equates to 9.6-15.8 Tg C ORG a −1 which is several times greater than for the tropical coastal ocean (3.9 Tg C ORG a −1 ), slightly greater than for salt marshes (11.7 Tg C ORG a −1 ) but less than in seagrass meadows (35.3 Tg C ORG a −1 ) [8]. The wide variability in C ORG burial rates reflects large differences in forests of different ages, types, and locations; rates are more likely to be a function of multiple interrelated drivers such as geomorphology, tidal inundation frequency, forest age, species composition, storms, tidal prism, soil grain size, and oceanic, riverine, and anthropogenic inputs, as sequestration rates exhibited no significant relationship with latitude [41]. Further, in many tropical river deltas, sediment deposition and subsequent C ORG accumulation and burial in mangroves are often highly dynamic with episodes of sediment starvation due to damming and episodes of massive bedload transport and deposition that smother mangroves, as found in the Mekong delta [32,42].…”

Preface: Blue carbon studies in Asia‐Pacific regions: Current status, gaps, and future perspectives

“…Much of the carbon is autochthonous or sequestered within the system, but external sources are also important. Ecosystem connectivity can influence blue carbon dynamics because these BCEs can receive OC from upland forest as well as exchange OC among themselves (MacKenzie et al, 2021; Sasmito et al, 2020). The second paper in this special feature by Hidayah et al (2022) found that macroalgal and mangrove‐derived OC are important contributors to seagrass OC sequestration and OC stocks (Hidayah et al, 2022).…”