Sierra Leone - State of the Marine Environment 2015

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.

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.

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

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