Land-based activities, pollution sources and levels in water and sediment in the coastal and marine area of Kenya
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Kenya has a land area of 580,000 km2 and lies astride the equator. It has a coastline bordering the Indian Ocean, which runs about 600 km long in a south-westerly direction with varying, marine and coastal wetlands rich in biodiversity. The coastline is characterised by a fringing coral reef broken at places where rivers discharge and estuarine creeks open into the sea. The estuaries are typically fringed with highly productive and extensive mangrove swamps. In the nearshore areas between the mangroves and fringing coral reef are lagoons that harbour highly productive and diverse seagrass meadows. These ecosystems receive considerable quantities of riverine and coastal watershed discharge which include high loads of nutrients, sediments, suspended particulate matter, heavy metals and petroleum hydrocarbons associated with municipal wastewater and agricultural runoff that impact on the water and sediment quality, productivity, biodiversity and system functioning. It is recognized that the systems are multiple use ecosystems providing various goods and services of ecological and socio-economic significance. It is instructive that major urban and commercial centres have developed around such marine systems. Indeed coastal and marine resources are under relentless pressure from rapid population growth and urbanization. Thus, about 9 % of the total population of Kenya is based in the Coast Province and growing at 3.1 % p.a. which is significantly faster than the national average of 2.9 % p.a. (GOK – 1999 Census). There are two major drainage basins, namely the Tana and Sabaki-Galana-Athi basins which drain into the Indian Ocean. The Tana River, which is the longest, drains a catchment area extending from Mt. Kenya and discharges into the Ungwana bay. The Sabaki-Galana-Athi River basin has its tributaries rising from the Aberdare Range and discharges into the Malindi Bay. Other river systems and streams discharging into the sea include Ramisi, Mkurumuji, Kombeni, Tsalu, Mwache and Umba (which rises from the Kilimanjaro-Usambara hills in Tanzania). The river discharge areas are major sources of the freshwater and sediments entering the sea as shown in Figure. 1.