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International Journal of Marine Science 2014, Vol.4, No.42, 1-11
http://ijms.biopublisher.ca
3
provide the needed information in the understanding
of ecosystem functioning and buttress the underlying
principles relating to plant-animal interaction in
estuarine ecosystems.
1 Materials and Methods
1.1 Description of study area
The Lagos Lagoon is located in the heart of the Lagos
metropolis, occupying the southern part of the
metropolis, linking the Atlantic Ocean in the west and
south through the Lagos Harbour, and connecting with
Lekki and Epe Lagoons in the east. It is about
6,354.788 sq km in area and 285 km in perimeter. The
lagoon sediment range from mud, sandy mud, muddy
sand, to sand (Ajao and Fagade, 1991). It is generally
between 0.5 - 2 m deep in most parts with a maximum
of about 5 m in the main lagoon and 25 m in some
dredged parts of the Lagos Harbour. The lagoon
serves as means of recreation, transport, and a
dumpsite for residential and industrial discharges. It
also serves as a natural shock absorber to balance
forces within the natural ecological system.
More than 60 % of the industries in Nigeria are
located in Lagos State and they all discharge their
effluents directly or indirectly into the Lagos Lagoon.
Most of the effluents discharged are untreated as many
of the industries do not have treatment plants. In
addition to wastewater from industries, there are
domestic sewage discharges, garbage and wood
shavings from sawmill depots along the shores of the
lagoon. The proliferation of urban and industrial
establishments along the shores of the lagoon has
resulted in a complex mix of both domestic and
industrial wastes which eventually find their way into
the lagoon (Ajao, 1996).
The Lagos lagoon system consists of three main
segments namely; the Lagos Harbour Segment, the
Metropolitan Segment and the Epe Segment.
Commercial and industrial activities are mainly
concentrated in the Metropolitan Segment (Ajao,
1996). There are both spatial and seasonal differentials
in the salinity of the lagoon due to the effect of
Atlantic Ocean and rainfall pattern (Webb, 1958).
Seasonal and diurnal salinity fluctuations are greatest
in the Lagos Harbour Segment of the lagoon because
the influx of water from Atlantic Ocean and the
lagoon at different times of the day and year. This
salinity decreases as distance increases from Atlantic
Ocean.
Apart from waste discharged into the lagoon, Lagos
Lagoon is also faced with a lot of human pressure
such as sand filling and dredging, general habitat
destruction and unregulated fishery exploitation.
These have resulted in the general biodiversity
reduction in the lagoon as reported in previous studies
(Nwankwo and Akinsoji, 1999) on the lagoon biota.
Three sampling stations (Figure 1) from the
Metropolitan Segment were selected for this study and
care was taken in selection of the study stations to
adequately represent true estuarine conditions.
Station 1 is the Okobaba
(
6
o
34′24′′N and 3
o
31′52′′E),
this part of the lagoon is known for its wood waste
which is indiscriminately released into the lagoon.
Tidal influence is strong in this area of the lagoon.
Colour of the water was brownish green and sediment
colour was black. Station 2 is located at the Iddo
(
6
o
47′36′′N and 3
o
27′29′′E) area of the lagoon. Most
notable human activity here is sewage dump. Station 3
is at the Tin Can
Island Port
slightly adjacent the
Lagos Harbour (6
o
52′19′′N and 3
o
43′41′′E). Colour of
the water was brownish green and sediment colour
was black. The texture of the sediment collected in
this station was muddy. Boating activities is a major
feature of the study area.
1.2 Data collection and laboratory analyses
Depth of study stations was measured using a
graduated wooden pole while water transparency was
determined using a 20 cm diameter Secchi Disk
painted black and white. Turbidity of water samples
was determined according to the methods described in
APHA (1998). From each station, samples of benthic
macrofauna were taken in three replicates with a van
Veen grab of 0.1 m
2
in area. Samples were washed
through a sieve of 0.5 mm mesh size and organisms
retained by the sieved were collected in sample
containers and preserved with 10 % formaldehyde
solution
in situ
. Water samples for chl-a analysis were
collected in BOD bottles and corked properly while
samples of sediment for chl-a analysis were collected
in BOD bottle and resuspended with water from the
site. In the laboratory fixed benthic samples were
washed with tap water to remove the fixative and any
remaining sediment and other debris for easy sorting.
The animals were sorted into different taxonomic
groups using suitable identification manuals including