Environmental Engineering Reference
In-Depth Information
unregulated and where environmental protection may be
inadequate (Fonesca et al.
2011
; Li et al.
2007
; Manning
2011
; Nriagu
1992
; Oyeyiola et al.
2013a
). The ocean's
ecosystem and the changes in it induced by pollution and
climate change are of worldwide concern. To predict how
this ecosystem will respond to further global change and
what role the ocean's biota will play requires detailed
studies of biological, physical and chemical data of marine-
related sample matrices (water, sediment and biota). One of
the main concerns at present is the pollution of the marine
environment by contaminants whose levels are growing at
an alarming rate. Pollutants such as potentially toxic metals,
persistent organic pollutants such as pesticides, dioxins,
polychlorinated biphenyls and PAHs, and nutrients have
been found to be a major threat to the marine ecosystem and
thus a major global problem. This is because pollutants
released in one part of the world can be transported to
regions far from their source of origin through the atmo-
sphere, waters and other pathways. Their effect on human
health can be felt directly and/or via the food web (Chaney
et al.
1996
).
of sawdust and other municipal waste take places near the
Third Mainland Bridge—the longest bridge in West Africa
which crosses the Lagos lagoon and links the Lagos
Mainland in the north of Lagos Megacity to the Lagos
Island in the south of the city.
The Lagos Lagoon is a brackish coastal lagoon—the
largest in the West African coast—located between longi-
tude 3
o
23
0
and 3
o
40
0
E and between latitude 6
o
27
0
and
6
o
48
0
N. It is a fairly shallow expanse of water (0.3-3 m
deep) which is about 50 km long and 3-13 km wide and
separated from the Atlantic Ocean by a narrow strip of
barrier bar complex. The lagoon borders the forest belt and
empties directly into the Atlantic Ocean at the harbour
(Fig.
1
). During the rainy season, large volumes of fresh
water passes through the harbour into the sea. In view of its
complexity (linkages to land, freshwater, sea, salinity fluc-
tuations, dynamics), the lagoon is a fragile ecosystem prone
to environmental degradation through pollution from
industry, household, resource over-exploitation, etc. The
loading of pollutants into the lagoon affects the quality of
the water. This is reflected in the colour and appearance of
the lagoon water, ranging from oily at some locations to
grey, slightly yellow, turbid and dark at others. There is a
high spatial and temporal variability of constituents (pol-
lutants) in surface sediments throughout the lagoon. This is
reflected by the variation in sediment type and colour at
different locations of the lagoon.
Lagos lagoon serves the huge population of Lagos,
approximately 15 million. The Lagoon finds its use in
artisanal fishing, transport and recreational purposes. It is an
important habitat for a wide array of fish and marine
organisms and is the major source of sea foods for the
people of Lagos (Isebor et al.
2006
). Some abuses of the
Lagoon include serving as a direct dumpsite for industrial,
agricultural and municipal wastes, and even a dumpsite for
sewage at some locations. Dredging of sediment from the
lagoon for sand-filling and land reclamation although illegal
is commonplace to satisfy local demand for building con-
structions. Pollutants from this lagoon may affect the pop-
ulation directly through contact with contaminated sediment
or water and via the food chain.
However, despite rapid industrialization in the region,
coupled with the importance of this waterbody, currently,
there is a dearth of detailed information on the pollution and
pollutant status of the Lagos Lagoon system.
The Lagos Lagoon System
Lagos is the Africa's biggest city and the fastest growing
metropolis in the world. It is the most heavily industrialized
and urbanized city in Nigeria, with much of the nation's
wealth and economic activities located there, and 12 % of
the total population (150 million). The City of Lagos is
currently undergoing an extensive programme of expansion
and development with the aim of becoming a 'megacity'
and major international focus for trade and industry
(Howden
2010
; This Day's Special International Project
2007
). The urban area is built on a number of floodplains
and encompasses a network of marshes, swamps, streams,
creeks, rivers and estuaries which receive large quantities of
rain water run-off, domestic, municipal and industrial waste
effluents, and each of these receptors discharge finally into
the Lagos Lagoon. We describe here the entire hydrological
system of the Lagos Lagoon System in Nigeria.
The city of Lagos has about 91 waterways (canals) and
their tributaries draining the entire city and discharging into
the Lagos Lagoon at different locations. Most of the major
markets and industries in Lagos (Iddo, Otto, Yaba, Oshodi,
Mushin, Idioro, Balogun, Ebute-Ero, Idumota, Abule Egba,
Alaba Rago, Alaba International, Mile2 and Mile 12 mar-
kets) generate huge quantities of municipal wastes which
are either dumped directly into the lagoon or are incinerated
at sites that drain into the lagoon at different locations. Open
waste incineration, in some cases on the shores of Lagos
lagoon, is a very common sight in Lagos. One of such open
incinerators is found at Okobaba, where incessant burning
Physicochemical Properties of the Lagos
Lagoon
Our extensive studies of the physicochemical status of the
water in the Lagos Lagoon System have been revealing on
the
pollution
status
of
the
waterbody.
Water
samples
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