92
(Alongi et al. 2005); 22–230 g OC m
−2
year
−1
in Fukido Estuary, Japan (Tateda et al.
2005); and 100–600 g OC m
−2
year
−1
in Trat, Thailand (Tateda et al. 2005). Such
local variation probably reflects site-specific biological and physicochemical factors
(Amundson 2001; Davidson and Janssens 2006; De Deyn et al. 2008; Kristensen
2008; Smith et al. 1991). Breithaupt et al. (2012) compared rates between core sites
with and without river inputs and reported a mean rate of 268 ± 227 g OC m
−2
year
−1
for sites with rivers and 114 ± g OC m
−2
year
−1
for sites without rivers. They attributed the higher burial rates at sites with rivers to high organic carbon input rates
from riverine or tidal sources, in addition to input from autochthonous production.
For example, in Hinchinbrook Channel, Australia (Alongi et al. 1999), mangrove
carbon accounted for only 56% of the total organic carbon input, and the contribution of mangrove materials varied widely both over time and at different coring
locations (Gonneea et al. 2004).
Not only do area-based mangrove OC burial rates vary widely depending on site
characteristics, but estimates of the global mangrove area also differ (see Sect. 3.2.).
At present, the global amount of buried mangrove OC can be estimated only by
multiplying the mean global OC burial rate by the global mangrove area. Breithaupt
et al. (2012) used 163 g m
−2
year
−1
as the mean global OC burial rate and 160,000 km
2
as the global mangrove area and estimated the mean global mangrove OC burial rate
as 26.1 Tg C year
−1
(95% CI 21.0–32.4 Tg C year
−1
). This corresponds to 9.6–14.9%
of the global annual mangrove production (218 ± 72 Tg C year
−1
) estimated by
Bouillon et al. (2008), and to 8.3–15% of the total annual marine OC burial rate
(213.7–252.4 Tg C year
−1
) estimated by Duarte et al. (2005) and recalculated by
Breithaupt et al. (2012).
3.5.2.2 Necromass Stocks
Published data suggest that mangrove soils contain large carbon stocks (Donato
et al. 2011; Atwood et al. 2017; Sanderman et al. 2018). Donato et al. (2011) measured whole-ecosystem carbon storage in mangrove ecosystems in the Indo-West
Pacific region and found that the carbon was stored mainly as necromass in soils
(49–98% of the whole-ecosystem carbon storage). The amount of carbon stored in
mangrove soils is extremely high compared with that in upland forest soils (Fig. 3.8;
see also Table 2.1 in Chap. 2 of this volume). Donato et al. (2011) also found that
necromass carbon was higher in estuarine than in oceanic mangrove ecosystems
(Fig. 3.9). In both types of ecosystems, the carbon concentration (% dry mass) in the
top 100 cm of soil was high and gradually decreased with depth, but the mean soil
carbon density in oceanic settings (0.061 g C cm
−3
) was larger than that in estuarine
settings (0.038 g C cm
−3
). This density difference might reflect autochthonous versus allochthonous sources of sediment or litter. Despite the greater soil carbon density in oceanic settings, the thicker organic (peat) soils in estuarine settings (usually
>3 m) than in oceanic settings (<2 m) mean that estuarine soils store more carbon
per unit area than oceanic soils. Donato et al. (2011) reported that belowground
carbon storage was positively but only weakly correlated with aboveground carbon
T. Inoue
(Alongi et al. 2005); 22–230 g OC m
−2
year
−1
in Fukido Estuary, Japan (Tateda et al.
2005); and 100–600 g OC m
−2
year
−1
in Trat, Thailand (Tateda et al. 2005). Such
local variation probably reflects site-specific biological and physicochemical factors
(Amundson 2001; Davidson and Janssens 2006; De Deyn et al. 2008; Kristensen
2008; Smith et al. 1991). Breithaupt et al. (2012) compared rates between core sites
with and without river inputs and reported a mean rate of 268 ± 227 g OC m
−2
year
−1
for sites with rivers and 114 ± g OC m
−2
year
−1
for sites without rivers. They attributed the higher burial rates at sites with rivers to high organic carbon input rates
from riverine or tidal sources, in addition to input from autochthonous production.
For example, in Hinchinbrook Channel, Australia (Alongi et al. 1999), mangrove
carbon accounted for only 56% of the total organic carbon input, and the contribution of mangrove materials varied widely both over time and at different coring
locations (Gonneea et al. 2004).
Not only do area-based mangrove OC burial rates vary widely depending on site
characteristics, but estimates of the global mangrove area also differ (see Sect. 3.2.).
At present, the global amount of buried mangrove OC can be estimated only by
multiplying the mean global OC burial rate by the global mangrove area. Breithaupt
et al. (2012) used 163 g m
−2
year
−1
as the mean global OC burial rate and 160,000 km
2
as the global mangrove area and estimated the mean global mangrove OC burial rate
as 26.1 Tg C year
−1
(95% CI 21.0–32.4 Tg C year
−1
). This corresponds to 9.6–14.9%
of the global annual mangrove production (218 ± 72 Tg C year
−1
) estimated by
Bouillon et al. (2008), and to 8.3–15% of the total annual marine OC burial rate
(213.7–252.4 Tg C year
−1
) estimated by Duarte et al. (2005) and recalculated by
Breithaupt et al. (2012).
3.5.2.2 Necromass Stocks
Published data suggest that mangrove soils contain large carbon stocks (Donato
et al. 2011; Atwood et al. 2017; Sanderman et al. 2018). Donato et al. (2011) measured whole-ecosystem carbon storage in mangrove ecosystems in the Indo-West
Pacific region and found that the carbon was stored mainly as necromass in soils
(49–98% of the whole-ecosystem carbon storage). The amount of carbon stored in
mangrove soils is extremely high compared with that in upland forest soils (Fig. 3.8;
see also Table 2.1 in Chap. 2 of this volume). Donato et al. (2011) also found that
necromass carbon was higher in estuarine than in oceanic mangrove ecosystems
(Fig. 3.9). In both types of ecosystems, the carbon concentration (% dry mass) in the
top 100 cm of soil was high and gradually decreased with depth, but the mean soil
carbon density in oceanic settings (0.061 g C cm
−3
) was larger than that in estuarine
settings (0.038 g C cm
−3
). This density difference might reflect autochthonous versus allochthonous sources of sediment or litter. Despite the greater soil carbon density in oceanic settings, the thicker organic (peat) soils in estuarine settings (usually
>3 m) than in oceanic settings (<2 m) mean that estuarine soils store more carbon
per unit area than oceanic soils. Donato et al. (2011) reported that belowground
carbon storage was positively but only weakly correlated with aboveground carbon
T. Inoue