Chapter 16 – Freshwater Ecology of Kenyan Highlands and Lowlands
Nyingi, Dorothy Wanja
Ogada, Mordecai O
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Freshwater ecosystems of Kenya are the lifeline of economic and social development; however, most of these are threatened or on the verge of collapse. The need to maintain them in their natural condition, reduce disturbance and conserve their biodiversity has been stressed in the face of severe drought, food insecurity and water stress conditions including inability to maintain constant hydroelectric power. However, without a clear picture of how many freshwater rivers, wetlands and lakes exist and their precise locality, size, sources and uses, it would be impossible for the authorities charged with their protection to put in place management or mitigation measures. Highland freshwater ecosystems of Kenya include Mount Kenya, Aberdares, Mau Forest, Mount Elgon and Cherangani Hills, which are referred to Kenya's water towers since they jointly supply most of the freshwater resources of the country. They are fragile ecosystems with streams flowing through montane forest belts and are critical reservoirs of biodiversity. They are characterized by high rainfall; steep slopes and erodible soils induce severe surface runoff, soil erosion and landslides. Sediments from erosion cause pollution of water in the streams. In countries with limited resources such as Kenya only small portions of rivers can be effectively conserved. It is imperative that significant effort is targeted at the upper reaches, because any conservation effort in the lower reaches of the river are easily negated by upstream disturbances. Their importance is primarily due to their ability to store and distribute water to lowlands and for ground water recharge. For example, 90% of dry season flow of the Northern Ewaso Ng'iro River is derived from the Mount Kenya. Montane areas in Kenya are also often associated with sacred sites and areas of cultural and social importance to the communities around them. Kenya's highland ecosystems face great anthropogenic threats due to deforestation and agricultural pressure. These areas have been ideal for tea and coffee plantations and human settlements. The Mau Forest, which is the largest indigenous forest in Kenya, has had vast areas cleared for settlements by immigrants, which in turn has caused reduction of flows of the Sondu Miriu River, which is dammed downstream for hydroelectric power. Even though sections of the Aberdares and Mount Kenya occur in protected areas, the lack of management and inability to patrol large areas has had led to various conflicts over land and water uses. Lowland freshwater ecosystems include those occurring on the lower sections of the eastwards-flowing rivers of Kenya including Rivers Tana, Athi, Northern Ewaso Ng'iro and the Ramisi. These are areas of low altitude and the rivers are slow moving and characterized by high sediment load, which is rich in nutrients and important for agriculture along the banks of these rivers. However, reductions and changes in flow regimes in the lowlands are more recently becoming a reason for concern. In the Tana River Delta, a large number of communities and biodiversity rely on the water for agriculture, pastoralism, fishing and other socioeconomic uses related to ecosystem services. The two main factors affecting river flows in lowlands are water abstractions and land-use change and intensification, both related to growing human populations. Climate change poses a further complication to both highland and lowland ecosystems due to changes in rainfall patterns reducing not only river flows but also the high rainfall events that cause unprecedented floods.