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The Sierra Leone continental shelf is located in a unique
position on the West African coast where it comes under
the influence of the Guinea Current, southern off-spins
of the Canary Current, the Equatorial Counter Current
and the coastal drift occurring in the shallower waters.
The resultant effect of these forces is crucial to the ecology
of the shelf by creating a vacuum in the northern parts
of the shelf and generating some amount of upwelling so
necessary for primary production.
The physical and chemical processes of a marine
environment determine the quality of its biodiversity
and habitats. The overall health of marine ecosystems
can therefore be assessed by examining the status and
trends of the major physical and chemical processes
taking place in it. Such processes as erosion of rock
and sediments, volcanic activity, gas exchange with the
atmosphere, the metabolic and breakdown products
of organisms and precipitation, affecting the coastal
morphology, marine biota, biological productivity and
the structure of marine assemblages.
The continental shelf of Sierra Leone is very broad in the
north and tapers towards the south. Wave action and tidal
activity play a significant role in the shallow areas. Besides
regulating the diurnal life of aquatic organisms they are
involved in the transport of pollutants and the disposal of
waste especially along the beaches.
6. Physical, chemical and
ecological processes
Sixteen physical and chemical processes have been assessed.
Most of them were found to be in good condition (Fig. 6.1),
according to the assessment at the workshop (Fig. 6.2). Sediment
transportation is a problem (assessed to be in poor condition)
due to large amounts of sediments of agricultural and mining
activities entering some of the rivers, estuaries and lagoons.
In addition to the physical and chemical processes that have
been assessed, two ecological processes have been assessed
as well (Fig. 6.3). These are related to disturbances in the
physical environment. In general the processes are still in
good condition and functioning due to the fact that the
coasts of Sierra Leone remain largely undeveloped.
The impacts of spatial or physical disjunctions are high
around harbours and seem to have increased over the past
5 years. Some wetlands have been affected by dredging and
development, with an impact on their function as stop-over
site for migrating birds.
6.1. Sea water Temperature
Sea surface temperatures, derived from COADS 1950-
1990, show a temperature range from 27 to 28.5°C between
February and May, a temperature drop to 26.8°C between
May and August and again a rise to 27°C from August and
November. The average temperature in December is 28.5°C
and 27.8°C in January.
Figure 6.1:
Summary of the physical and chemical processes. Average, high and low for the
condition of the physical and chemical processes in the best 10%, most and worst 10% of places