Environmental Engineering Reference
In-Depth Information
aquatic mammals also frequent the sites including Hippo-
potamus amphibious and Trichechus senegalensis (Mana-
tees) especially in valleys of River Monoor lakes and
terrestrial mammals especially red-bellied monkeys (Cer-
copithecus erythrogaster).
subplot is fixed with painted PVC plastic pipe with bound-
aries demarcated by strong ropes. All plots were well map-
ped from their GPS coordinates. Four transects were
established in sites with different levels of degradation of
mangrove vegetation from non-woody, very degraded,
medium or less degraded to non-degraded mangroves in
Kpétou, Djègbadji, Adounko (1), and Adounko (2) sites,
respectively (Table
1
; Figs.
2
,
3
). Pre-qualitative criteria for
the characterization of different degradation regimes were
based on the characteristics of the canopy (closure, open),
trees (diameter, height, density) and undergrowth (density),
and the frequency of indicator species later compared with a
unique post-quantitative criteria of basal surface (m
2
) per ha.
The monitoring protocol consisted of species identification,
mapping, tagging, and measurements of all trees inside the
plot using modified forestry techniques for mangroves (Pool
et al.
1977
; Cintron and Novelli
1984
; Kauffman and Donato
2012
). Four carbon pools were considered in the present
study, including vegetation carbon pools (both above- and
belowground), litter, coarse deadwood, and soil.
Socioeconomic Environment and Human Activities
This complex is full of unique assets: natural, landscape,
religious, tourist, economic, etc. Indeed, the area is subject
to high anthropogenic pressure manifested by uncontrolled
exploitation of its resources, which have consequences of
increased erosion, ecological change affecting biodiversity,
etc. The region is characterized by a wide range of ethnic
diversity with a population of over 1 million people mostly
made up of two (02) groups:
• On the coast: the Pla between Pahou and Avlékété, the
Pédah between Ouidah and Djègbadji, the Aizo between
Cococodji and Godomey, the Fon and the Keta were
found along the coast and everywhere, Gengroup and
Ewe, late comers occupy the entire coast from Ghana
(origin) to Nigeria.
• At North coast, mostly the Adja, Fon, Nago, and Mina
were found.
The most prominent human activities in the area are
fishing in nearby lakes and lagoonal systems. Agriculture
includes vegetable and arable crop farming, especially
tomatoes, beans, onions, pepper, maize, and cassava. Small
livestock production systems (domestic birds, rabbits, goats,
and sheep) are mostly based on free-ranging systems around
homesteads. Salt is also produced around the mangrove
areas and conversion of palm wine into alcohol. The large
amounts of clay in the mangrove area are used in local
pottery industry.
Measurement of Vegetation Carbon
The most commonly assessed carbon stock in forestry is
usually in the aboveground component because trees dom-
inate the aboveground carbon pools and serve as indicator
of the ecological conditions of most forests. Inside the plots,
all trees with diameter of the stem at breast height
(dbh
130
) C 1.0 cm were identified, measured, tagged, and
mapped (Fig.
4
). Data on species, dbh, live/dead, and height
were recorded for all individuals. In Rhizophora, dbh was
taken 30 cm above highest stilt root. Aboveground roots
and saplings (dbh B 1 cm) were sampled inside five 1-m
2
quadrants placed systematically at 1-m intervals along the
10 9 10 m plot (Fig.
2
b).
Establishment of Permanent Sample Plots
and Quantification of Carbon Pools
Dead and Downed Wood
Deadwood was estimated using the transect method whose
application is given in Kauffman and Donato (
2012
). The
line intersect technique involves counting intersections of
woody pieces along a vertical sampling transect. The
diameters of deadwood (usually more than 0.5 cm in
diameter) lying within 2 m of the ground surface were
measured at their points of intersection
The method used was that of permanent sample plots
described and applied to the rainforest by Condit (
1998
),
adapted to the mangrove forests in Cameroon by Cameroon
Wildlife Conservation Society (CWCS) (see Ajonina
2008
);
it should be noted that the same method was used in Ghana
(Ajonina
2011
), and most recently in the mangrove countries
of the Congo Basin under the UNEP REDD + Central
African mangroves evaluation of multiple services man-
grove ecosystem in the Congo Basin (Cameroon, Congo,
DRC, and Gabon) (Ajonina et al.
2013
). Transects of
100 9 10 m (0.1 ha) were established following a random
azimuth from a random fixed point. Each transect was
divided into three plots of 0.02 ha (10 9 20 m) separated by
an interval of 10 m along the transect with further division
into six square subplots of 10 9 10 m. The angle of each
with the main
transect
axis.
Each
deadwood
measured
was
given
a
decomposition ranking: rotten, intermediate, or sound.
Soil Samples
Mangrove soils have been found to be major reservoirs of
organic carbon (Donato et al.
2011
). Soil carbon is mostly
concentrated in the upper 1.0 m of the soil profile. This
layer is also the most vulnerable to land-use change, thus
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