Lateral Export and Sources of Subsurface Dissolved Carbon and Alkalinity in Mangroves: Revising the Blue Carbon Budget

• Published in: Journal of marine science and engineering Vol. 10; no. 12; p. 1916
• Main Author: Alongi, Daniel M.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.12.2022
• Subjects: Alkalinity; Allochthonous deposits; Autotrophy; Blue carbon; budget; By products; Carbon; Carbon sources; Coastal ecosystems; Creeks & streams; Decomposition; Dissolved inorganic carbon; Dissolved organic carbon; Ecosystems; Exports; Forests; Groundwater discharge; Hydrogen-ion concentration; Mangroves; Mineralization; Organic matter; Organic soils; Pore water; Precipitation; Primary production; Rivers; Salinity; Sediments; Soil; Soil microorganisms; Soil organic matter; Soil profiles; Soil properties; Tidal marshes; Tropical forests; Thailand; Australia; China; India
• ISSN: 2077-1312; 2077-1312
• DOI: 10.3390/jmse10121916

Mangroves are carbon-rich ecosystems that store large quantities of carbon, mostly in soils. Early carbon (C) budgets indicated that >50% of mangrove C fixation was unaccounted for. This ‘missing C’ has now been discovered to be a large release (423 Tg C a−1) of porewater dissolved DIC (dissolved inorganic carbon), dissolved organic carbon (DOC), and total alkalinity (17 TMOL a−1) via lateral export derived from bacterial decomposition of soil organic matter. This large export originates from DIC produced over at least a 1.0–1.5 m soil profile (280–420 Tg C a−1) via decomposition of autochthonous and allochthonous inputs and/or likely mineralization in deep (≥1 m) ancient soils. DOC and DIC export from mangroves equate to 41% and ≈100% of export from the world’s tropical rivers, respectively. A newly revised blue carbon budget for the world’s mangroves indicates a mean ecosystem gross primary production (GPPE) to ecosystem respiration (RE) ratio of 1.35 and a net ecosystem production (NEP) of 794 g C m−2 a−1 (= global NEP of 117 Tg C a−1), reflecting net autotrophy. CORG burial is 5% and 9% of GPPE and NEPE, respectively. Mean RE/GPPE is 0.74 and carbon use efficiency averages 0.57, higher than for tropical humid forests (0.35).