Environmental Engineering Reference
In-Depth Information
mangroves) following mangrove degradation and 43 t CO
2
e (10 %) avoided CO
2
e emissions
from undisturbed mangrove forests.
Keywords
Mangroves
Degradation
Carbon budget
CO
2
emission
Benin
Introduction
The present study was carried out to assess carbon stocks
in mangrove ecosystems subjected to various level of deg-
radation as part of a larger initiative to set up a CDM tree
planting project to restore degraded mangrove areas of
southern Benin.
Mangroves are among the carbon-richest forests in the
tropics, containing an average of 1,023 t carbon per ha.
Mangrove deforestation generates global emissions of
0.02-0.12 Pg carbon per year, while storing up to 20 Pg C
annually (Donato et al.
2011
), roughly equivalent to 2.5
times annual global carbon dioxide (CO
2
) emissions despite
accounting for only around 0.7 % (around 140,000 km
2
)of
global tropical forests (Giri et al.
2010
). Apart from high
carbon storage potentials, mangroves provide other valuable
ecosystem services like protection from storms, floods, and
erosion; provision of timber and non-timber forest products
(Daïnou et al.
2008
); processing of waste and nutrient
pollution; aquaculture and agriculture support; and habitat
for aquatic and terrestrial species.
In Benin, the total mangrove cover is about 66 km
2
within its 120 km littoral zone consisting largely of a sandy
coast without developed estuaries and deltas. The man-
groves of Benin tend to be limited to the edge of the
extensive network of brackish coastal lagoons in the south
of the country. Despite replanting efforts, these mangroves
are in an advanced state of degradation (UNEP
2007
).
Because of their large ecosystem, carbon stocks, their vul-
nerabilities to land use, and the numerous other ecosystem
services they provide, mangroves are increasingly consid-
ered as prime ecosystems participating in climate change
mitigation strategies through reforestation and restoration
(Alongi
2002
; Donato
2012
).
To participate in global climate change-related pro-
cesses, such as reduced emissions from deforestation and
degradation (REDD+), and Clean Development Mechanism
(CDM), it is necessary to determine carbon stocks and
emissions baselines. Many carbon stock assessments in
mangrove ecosystems have been carried out recently around
the world (Donato et al.
2011
; Kauffman and Donato
2012
;
Adame et al.
2013
) mainly assessing mangroves from more
or less temporal sample plots in mostly undisturbed states.
Until recently in Central Africa (Ajonina et al.
2013
), lack
of permanent mangrove sample plots made it difficult to
gauge mangrove ecosystem recovery dynamics from
increasing degradation pressures for its vital ecosystem
services that sustain coastal rural economies, especially in
the west-central African region.
Materials and Methods
Site Description
Biophysical Characteristics
Mangroves in southern Benin are concentrated within a
wetland complex area that includes Ahémé Lake, the Aho
Channel coastal lagoon mouth, and Roy Ramsar site 1017
(latitude 7
o
N and longitudes 1
o
35
0
and 2
o
30
0
E) (see Fig.
1
)
(UNEP
2007
). The climate is equatorial with a mean total
rainfall of 1,200 mm/year mostly within two seasons
(March-late July and September-November) and two dry
seasons (late July-early September and late November-
early March). Average daily temperatures are around 27 C,
relative humidity ranges from a low of 78 % in January-
February to a maximum of 95 % in September. The western
wetland complex is located in the western part of the coastal
sedimentary basin whose main series are the Upper Creta-
ceous, Eocene, the Continental Terminal, and recent for-
mations. The region has a dense hydrological network with
three major rivers: the Couffo, Mono, and Sazué. The
Couffo, 190 km long, is a small river in the Guinean regime
with two seasons of flood. It has its source in Togo country
at 240 m altitude, near the border village of Tchetti, and
empties into Lake Ahémé. The Mono, with 148 km of its
course in Benin, has a bed slope within the watershed of
southern Benin that is very low (0.06 to 0.4 m/km). The
Sazué, 63 km long, is formed by the meeting of two rivers:
the Dévédon (22 km) and Salédo (40 km). The slopes of the
bed are extremely low. Apart from these major rivers, there
are others with various physiognomies:
Zoko lakes, Dévé, Togbadji, Egbo, Doukon, Toho
Godogba, Wozo, and DatchiDofe; Large marshy depres-
sions south of Athiémé and west of Comè districts, where
several vegetation formations can be encountered especially
pockets of mangrove, riparian forests, periodically flooded
swamp forests, marshes, grasslands, and floating aquatic
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