# Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests
## 2 Mangrove Blue Carbon: An Update
### Carbon Mass Balance Dynamics  
Using data reviewed in Alongi [43; 44], a mass balance of carbon flow through an idealized mangrove forest (Table 2) shows that about 63% of gross primary production GPP) is released as canopy respiration. Of net primary production (13.2 Mg C ha\({}^{-1}\) a\({}^{-1}\)), nearly equal amounts are vested in wood (3.71 Mg C ha\({}^{-1}\) a\({}^{-1}\)), litter (4.28 Mg C ha\({}^{-1}\) a\({}^{-1}\)), and root (5.21 Mg C ha\({}^{-1}\) a\({}^{-1}\)) production [43; 44]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Region** & **AGBC\({}_{\text{ORG}}\)** & **BGBC\({}_{\text{ORG}}\)** & **SC\({}_{\text{ORG}}\)** & **TEC\({}_{\text{ORG}}\)** \\ \hline Africa & 89.5 & 88.0 & 402.4 & 638.8 \\ \hline Southeast Asia & 115.7 & 44.9 & 656.1 & 806.4 \\ \hline South and East Asia & 94.2 & 35.9 & 445.4 & 482.8 \\ \hline Central and North America & 92.5 & 41.4 & 577.4 & 730.1 \\ and Caribbean & & & & \\ \hline South America & 104.3 & 85.2 & 236.9 & 419.4 \\ \hline Middle East & 30.6 & 41.2 & 150.9 & 224.9 \\ \hline Australia and New Zealand & 55.1 & 79.7 & 465.3 & 563.4 \\ \hline Pacific Islands & 213.7 & 172.9 & 599.7 & 987.4 \\ \hline \end{tabular}
\end{table} 
Table 1: Grand mean regional estimates of organic carbon stocks (Mg C\({}_{\text{ORG}}\) ha\({}^{-1}\)) in mangrove aboveground (AGBC\({}_{\text{ORG}}\)) and belowground (BGBC\({}_{\text{ORG}}\)) biomass and soil (SC\({}_{\text{ORG}}\)) to a depth of 1 m. Updated [9; 10; 11; 12; 13; 14; 15; 16] and summarized from [3]. TEC\({}_{\text{ORG}}\) = total ecosystem C\({}_{\text{ORG}}\) stock (Mg C\({}_{\text{ORG}}\) ha\({}^{-1}\)). Grand mean inputs and outputs are in overall balance (inputs-outputs \(\approx\) 1 Mg C ha\({}^{-1}\) a\({}^{-1}\)), considering the large variability in individual measurements among forests and estuaries in different locations with different geomorphological histories. Undoubtedly, allochthonous inputs from the sea and catchment also play an important, if unqualified, role in mangrove carbon dynamics considering that analysis of the origin of mangrove soil organic matter indicates that about 42% of OM may be derived from external sources [45; 46]. Thus, it is likely that some mangrove ecosystems will not be in metabolic balance with some systems being net importers and others being net exporters of carbon. The two main inputs were mangrove forest primary production and net DIC production in mangrove soils to a depth of 1 m. The latter is not usually considered in carbon mass balance estimates, but evidence suggests that centuries-old, sequestered carbon is still susceptible to remineralization and tidal DOC and DIC export [47], supporting the idea that organic carbon deposited prior to mangrove colonization continues to be decomposed as all mangroves colonize intertidal flats that have considerable stores of C\({}_{\text{ORG}}\)[1]. This idea is supported by the fact that radiocarbon dating of mangrove soil profiles of the upper 1-3 m [32; 34; 38; 39; 40] indicate subsurface mangrove deposits that are centuries-old, and certainly older that the existing mangrove vegetation. Another unqualified pathway is groundwater which can in many locations provide significant quantities of carbon- and nutrient-rich subsurface water [6]. Second to canopy respiration as a significant carbon loss is DIC + DOC export (Table 2), as nearly all carbon respired within the entire soil horizon is released in dissolved form via advective porewater exchange and/or lateral transport and subsurface tidal pumping to adjacent tidal waters. This large export term contributes nearly 60% of DIC and 27% of DOC discharge to the tropical coastal ocean [43]. Mangroves inhabit only 0.3% of the global ocean coastal area but contribute 55% of air-sea exchange, 14% of C\({}_{\text{ORG}}\) burial, 28% of DIC export, and 13% of DOC + POC export from the world's coastal wetlands and estuaries to the atmosphere and global coastal ocean [43].