Carbon Balance in Salt Marsh and Mangrove Ecosystems: A Global Synthesis

Abstract

Mangroves and salt marshes are among the most productive ecosystems in the global coastal ocean. Mangroves store more carbon (739 Mg CORG ha−1) than salt marshes (334 Mg CORG ha−1), but the latter sequester proportionally more (24%) net primary production (NPP) than mangroves (12%). Mangroves exhibit greater rates of gross primary production (GPP), aboveground net primary production (AGNPP) and plant respiration (RC), with higher PGPP/RC ratios, but salt marshes exhibit greater rates of below-ground NPP (BGNPP). Mangroves have greater rates of subsurface DIC production and, unlike salt marshes, exhibit active microbial decomposition to a soil depth of 1 m. Salt marshes release more CH4 from soil and creek waters and export more dissolved CH4, but mangroves release more CO2 from tidal waters and export greater amounts of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), to adjacent waters. Both ecosystems contribute only a small proportion of GPP, RE (ecosystem respiration) and NEP (net ecosystem production) to the global coastal ocean due to their small global area, but contribute 72% of air–sea CO2 exchange of the world’s wetlands and estuaries and contribute 34% of DIC export and 17% of DOC + POC export to the world’s coastal ocean. Thus, both wetland ecosystems contribute disproportionately to carbon flow of the global coastal ocean.

Environmental conditions to support blue carbon storage in mangrove forest: A case study in the mangrove forest, Nusa Lembongan, Bali, Indonesia

“…According to Figure 5, most carbons were stored in the soil, which accounts for 64% of total carbon stock. This observation is quite close to a previous study that states 77% of total carbon stock in the mangrove ecosystem was stored in soil (Alongi 2020;Kauffman et al 2014;Sasmito et al 2020b). Coastal ecosystem are known to have higher carbon accumulation in sediments/soil compared to terrestrial vegetation mainly because of high autochthonous and allochthonous inputs and low decomposition rates of organic matter due to the mostly anoxic conditions in the sediment (Kristensen 2000;Donato et al 2011;Kida and Fujitake 2020).…”

“…Globally mangrove ecosystem has a total carbon stock of 738 ± 27.9 Mg C ha -1 of which 77% of the carbon is stored in soil (Alongi 2020). Although mangrove forests in the world only account for 0.2% of terrestrial vegetation coverage (Hamilton and Casey 2016), in a country that has extensive mangrove area, it is essential to consider the mangrove ecosystem as a mitigation plan.…”

Nitrogen Cycling and Mass Balance in the World’s Mangrove Forests

“…Mangrove PON export accounts for only 1.5% of the entire world's river discharge [249]. The contributions of mangrove N 2 O emissions, denitrification, and burial to the global coastal ocean [250] are modest (0.4%, 0.5-2.0% and 6%, respectively), but are disproportionate relative to their small area (0.31%) [251].…”

Carbon and alkalinity outwelling across the groundwater‐creek‐shelf continuum off Amazonian mangroves

“…Mangroves have one of the highest aerial carbon burial rates due to high primary production and complex root systems that allow organic matter deposition and long-term storage in the anoxic soil layers (Alongi 2020;Jennerjahn 2020). Part of the mangrove soil carbon might be released to the atmosphere after microbial decomposition and exported to ocean as particulate and dissolved matter (Bouillon et al 2008;Volta et al 2020).…”