Environmental Engineering Reference
In-Depth Information
Fig. 6
Aboveground carbon
stocks of selected terrestrial
rainforest in Congo basin and the
mangroves sampled in this study
300
250
200
150
100
50
0
Dja Biosphere
Reserve
Campo Maan
National Park
Korup National
park
average Central
Africa
rainforest
Average
mangroves of
central Africa
1,023 ± 88 MgC/ha in the Indo-Pacific (Donato et al.
2012) and 987 ± 338 MgC/ha in Mexico (Adame et al.
2013
).
Although it is clear that undisturbed forests contain the
largest amounts of carbon, the difference between moder-
ately exploited and highly exploited systems is less clear.
The relatively high carbon contents in exploited systems
could be explained by the fact that soils in exploited sys-
tems could be receiving carbon input from outside the
system through flood water, alluvial deposits and tides.
High soil carbon figures in highly exploited as well as
moderately exploited forests in RoC and DRC were influ-
enced by a peri-urban setting that suffers pollution effects.
Furthermore, the relatively high carbon deposits in soils of
exploited systems shows that not all soil carbon is oxidized
and emitted to the atmosphere when the system becomes
degraded; part of this remains captured in the soil column.
The significant difference in carbon stocks between non-
disturbed and moderately exploited systems points to the
possibility that mangroves release carbon stocks relatively
quickly after degradation, even if degraded moderately, and
that it is important for mangroves to remain in completely
undisturbed states if they are to maintain maximum carbon
values.
be released per ha of cleared pristine mangrove in Central
Africa. A recent report estimates that 771 km
2
of mangrove
were cleared in Central Africa between 2000 and 2010
(UNEP-WCMC
2012
), equating to estimated emissions of
100,152,000 Mg of carbon dioxide. Of course, not all the
carbon dioxide is released immediately, and these emissions
occur over decades.
Comparison with Adjacent Central African
Rainforests of the Congo Basin
Ecosystem carbon storage reported in the mangroves of
Central Africa is among the largest for any tropical forest
(IPCC 2007). We made comparisons of mangrove carbon
stocks with some of the reported carbon stocks of the ter-
restrial Congo basin rainforest (Fig.
6
). For consistency, we
have only utilized aboveground biomass, as most of the
studies in terrestrial forests lacked belowground carbon
stocks. Aboveground carbon pools were 209 Mg/ha in Dja
Biosphere Reserve (Djuikouo et al.
2010
), 188 Mg/ha
Campo Ma'an National Park (Kanmegne
2004
) and
178.5 Mg/ha in Korup National Park (Chuyong, unpub-
lished data), all in Cameroon. The average aboveground
carbon pool for undisturbed rainforest in Central Africa was
154 Mg/ha. This is lower than the 538 MgC/ha found in the
mangroves of this study, underscoring the value of man-
groves as carbon stocks. When soil carbon is added to the
equation, the difference between the carbon storage poten-
tial of mangroves and terrestrial rainforests could become
even greater.
The extremely high carbon content of mangroves com-
pared to terrestrial forests is often explained by the high
levels of organic carbon in the soil, which is typical of many
coastal ecosystems including seagrasses and salt marsh. The
reason for the high organic carbon content in the soil is the
accretion rates of these ecosystems as they keep up with
sea-level rise, sometimes over thousands of years, and trap
detritus and sediments from tidal movement and alluvial
deposits. Most terrestrial ecosystems reach maximum car-
bon content in their soils over decades or even centuries, but
coastal ecosystems can keep on accreting over millennia
Carbon Dioxide (Greenhouse Gas) Emission
Potential
The most vulnerable carbon pools following mangrove
deforestation and degradation are the aboveground carbon
as well as soil carbon from the top 30 cm. Estimating
emissions from land-use change was conducted using the
uncertainty-propagation approach detailed in Donato et al.
(
2011
). For the mangroves of Central Africa, a conservative
low-end estimate of conversion impact was used, with 50 %
aboveground biomass loss, 25 % loss of soil C from the top
30 cm, and no loss from deeper layers. Use of low-end
conversion impact in the current study is justified by low-
level reclamation of mangroves for aquaculture and agri-
culture in Central Africa. Using these conservative esti-
mates, we estimate that 1,300 Mg of carbon dioxide would
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