Lake Turkana: World’s Largest Permanent Desert Lake (Kenya)
Located in the “cradle of mankind” of the East African Rift Valley, Lake Turkana is distinguished as both the world’s largest permanent desert lake and alkaline water body. With a surface area of about 7,560 km2, Lake Turkana is a highly pulsed, variable system as a result of its closed-basin nature, arid surroundings, and its strong dependence on River Omo for the majority of its inflow, which originates as rainfall over the Ethiopian highlands. In this article we describe the lake’s unique ecosystem and associated vicissitudes, diverse habitats and incredible biodiversity, and ecosystem services. Although parts of the lake and lower Omo Delta have been zoned as an international biosphere reserve, Lake Turkana and the region are facing immense threat from anthropogenic activities. A combination of external factors (hydropower dams, irrigation schemes, climate anomalies) and internal drivers (demography, economic growth) will strongly impact the Lake Turkana basin over the next decade. In turn, this will have significant negative consequences on resource productivity and the wellbeing of local communities.
KeywordsDesert Lake Alkaline Omo Delta Wetland Blue-green algae Transboundary Wetland Hydropower Dams Irrigation Schemes Dependent Communities
Despite its large size, Lake Turkana is a highly pulsed, variable system as a result of its closed-basin nature, arid surroundings, and its strong dependence on one river for the majority of its inflow. As a result, the lake is sometimes called an “amplifier lake ”, i.e., “amplifies” changes in climate (Street-Perrott and Roberts 1983). The water budget of the lake is balanced between river inflows, groundwater exchanges, and evaporation losses (Avery 2010). The surface area of the lake, which receives less than 200 mm year−1 of rainfall, is 5.7 % of its drainage area (Avery 2012a). An estimated mean evaporation rate of 2.5 m year−1 (Kolding 1989) requires an inflow compensation of about 600 m3 s−1 or 19 km3 year−1 to maintain the lake’s water balance. More recent water balance modeling suggested a similar but lower inflow of 550 m3 s−1 (Avery 2010). The Omo River’s catchment area makes up 56.6 % of the lake’s drainage basin but the river contributes approximately 90 % of the lake’s inflow (Avery 2012b, 2013). As a result, the lake’s water level fluctuations are almost entirely caused by variations in rainfall over the Ethiopian highlands. Rainfall in the lower Omo basin and over the lake is bimodal, as in the rest of Kenya, with peak rainfall in April and November. As one progresses north, the rainfall becomes unimodal, and in uppermost basin, the peak rains fall in July and August (Avery 2012a). This is the wettest part of the basin, and the lake peaks 1 month later (ibid.). At its present contemporary size, the lake has a relatively long residence time of about 12.5 years (Kolding 1992).
Geochemistry (Water Quality and Nutrients)
Lake Turkana has average conductivity levels of 3,500 μScm−1, making it a “high ion ” or “Class II” lake (Talling and Talling 1965). Due to its closed-basin nature, the conductivity of the lake has been increasing by approximately 0.45 μScm−1 year−1 (Hopson 1982). Current salinity levels are approximately 2.5 practical salinity units (psu) (Odada et al. 2003), with the system moving toward the limit of 3 psu defining true saline lakes. Lake Turkana is also the world’s largest alkaline lake, with a pH range of 8.6–9.5 (Cohen 1986). The annual surface temperature ranges between 27.2 °C and 29.4 °C and bottom temperatures vary only 1.0 °C from 25.4 °C to 26.4 °C. Turbidity levels are high in Lake Turkana and the euphotic zone extends to only 6 m in the open lake (Källqvist et al. 1988). The lake is known for its strong southeasterly winds, which create surface water currents to the northwest and deep reverse bottom water currents (Hopson 1982). Due to these currents and the lake’s relatively shallow nature, the lake is well mixed and the water is generally well oxygenated at all depths (Källqvist et al. 1988), with oxygen levels of ≥5 mgl−1 observed at all stations in a recent study (Ojwang et al. 2007).
Diversity of Wetland Ecosystems
The most notable wetland ecosystem in Lake Turkana is the Omo Delta. Other notable wetland ecosystems within the lake include Ferguson’s Gulf, Central Island National Park, and the mouths of the Kerio and Turkwel rivers (Fig. 1). In addition, the lake margins host many smaller but important wetlands, in some cases physically separate from the lake.
Omo Delta Wetland
The Omo Delta and fringing riverine wetlands are characterized by dense macrophyte vegetation, dominated by Potamogeton spp., and the emergent grasses Paspalidium geminatum and Sporobolus spicatus, which occur in shallow areas. Several submerged plants, including Ceratophyllum demersum and Hydrocotyle sp., and floating plants, including Lemna gibba, Nymphaea spp., and Ottelia ovalifolia, have been recorded in the area (Hughes and Hughes 1992). Besides the ubiquitous acacia tree (Acacia tortilis) that dominates the landscape, there is the gingerbread palm tree (Hyphaene thebaica), whose oval fruit is edible, and the doum palm (Hyphaene coriacea), used for making local raft boats. The presence and imminent impact of the noxious invasive weed water hyacinth (Eichhornia crassipes) is of great concern to many conservationists, though it presumably may not survive in the semi saline lake.
These two smaller deltas differ greatly from each other and are associated with the seasonal Kerio and Turkwel Rivers (Fig. 1). The Kerio River runs parallel to the primary direction of the wind in the region, so its mouth is situated on a low-energy shore. It is also protected from the direct north–south wave action that arises when winds change direction and has consequently developed a dense mass of riverine-associated macrophytes. The Turkwel River, on the other hand, drains directly into the part of the bay facing the strong SE winds for which the lake is known. As a result, rooted macrophytes have failed to take hold along the banks, and there is little permanent vegetation except for the invasive thorny shrubs of Prosopis juliflora.
Ferguson’s Gulf is the most important tilapia habitat in Lake Turkana, especially for the indigenous tilapia species Oreochromis niloticus. The Gulf generally experiences annual water level fluctuations of 0.5–1.5 m, but has also dried up completely three times in the last 25 years (Fig. 2). The Gulf, which is approximately midway down the lake’s western shoreline east of Kalokol market, is protected from the open lake’s wave action and direct mixing by the Longech/Namukuse spit. The relatively calm waters of the Gulf support a different phytoplankton community from the rest of the lake, with primary production rates up to three orders of magnitude higher than in the open lake (Källqvist et al. 1988). Intensive fishing activities conducted using small-mesh beach seine, set gillnets, and purse seines are rampant in the area. The fishery is characterized by boom and bust cycles that are largely dependent on the Omo River’s floods. The invasive shrub, P. juliflora, heavily covers the shores of the Gulf. Its thick interlocking thorny canopy blocks access to previously important fishing grounds and certain landing beaches.
Sibiloi/Koobi Fora Protected Area
Sibiloi National Park was designated a protected area under Kenyan law in 1973. The shoreline within the Park is approximately 90 km long and is characterized by several spits, muddy shorelines, some rocky shorelines, inlets, seasonal river mouths, and some lush growths of submerged and rooted macrophytes (e.g., Potamogeton pectinatus). Sibiloi Bay and Allia Bay are shallow regions near the Park’s headquarters that boast the largest submerged beds of rooted aquatic macrophytes of Lake Turkana proper. Another important wetland habitat in Sibiloi National Park is Koobi Fora, which lies directly east of North Island, midway between the southern and northern ends of Sibiloi National Park. The wetland areas of Sibiloi National Park, which are devoid of fishing activities other than some sports fishing and cases of poaching, support the highest fish biomass in Lake Turkana. Furthermore, experimental fishing within Sibiloi National Park produced individuals larger than those caught with the same fishing gear in highly fished areas, such as those surrounding Ferguson’s Gulf (Ojwang et al. 2007).
Other Protected Areas of the Lake
In 1978, UNESCO listed Mt Kulal and the southern lake area, including South Island, in its Biosphere Reserves Directory. In 1983, South Island was created as a national park in its own right, followed in 1985 by Central Island. At the south end of the lake, there are a crater lake and some small lakes that are hydraulically connected to the main lake. At Loiyangalani, on the southeastern shore, an oasis of potable springs and doum palms is the focal point for the largest human settlement on the eastern shores of the lake. Another oasis not far north is the water source for El Molo village on the lake. Similar spring-fed oases on the western lake shores at Eliye and Lobolo provide valuable sources of potable water to the local population. These springs are crucially important, as the main lake water itself is too high in fluoride for safe consumption (Avery 2010, 2012a, 2014).
Central Island is especially interesting as it includes three distinct lakes within the main lake, each with different salinities and each providing a distinct habitat for birds in particular, including lesser flamingos (Avery 2012b).
Lake Turkana Biodiversity
Phytoplankton diversity is relatively low in Lake Turkana . The phytoplankton community is dominated by the blue-green algae Microcystis aeruginosa and the green alga Botryococcus braunii. The total annual photosynthetic plankton primary production was estimated at ca. 2 kg O2/m2/year (Källqvist et al. 1988). The zooplankton community includes copepods, cladocerans, and protozoans, whose total production has been estimated at 216,000–540,000 tonnes dry weight per year (Hopson 1982). There are records of 50 species of benthic organisms, dominated by ostracods and insects, within the lake and Omo Delta (Cohen 1986).
Lake Turkana is home to at least 60 fish species (Froese and Pauly 2013), 12 of which are endemic. For the most part, the species found in Lake Turkana can be found elsewhere in Nilo-Sudan lake and river systems. The number of fish species in the lake is low when compared to other African lake and river ecosystems, except for Lake Albert, which has a similar fish composition and diversity. Many of the more diverse lake systems, which host hundreds of species dominated by cichlids, are older and deeper than Lake Turkana (Lowe-McConnell 1987). Endemic species of fish include small zooplanktivores (Brycinus minutus, Brycinus ferox) that form a unique mid-water scattering layer in the lake, a smaller and more pelagic species of Lates (L. longispinus) and cichlids (Haplochromis turkanae, Hemichromis exsul). Unlike in Lake Victoria and some other African Lakes, the Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) are native to Lake Turkana and in fact are the highest valued species in the lake’s commercial fishery.
Lake Turkana supports over 350 native and migratory bird species, making it an “Important Birdlife Area” (UNESCO 2014). The lake and Omo River, in particular, also host the world’s largest remaining population of Nile crocodile (Crocodylus niloticus) and contain protected breeding grounds for this species as well as for hippopotamus and several venomous snake species (UNESCO 2014). Mammals sighted in the park areas and their environs include Grevy’s (Equus grevyi) and Burchell’s zebra (Equus quagga burchellii), Grant’s gazelle (Nanger granti), beisa oryx (Oryx beisa), topi (Damaliscus korrigum), greater kudu (Tragelaphus strepsiceros), hippopotamus (Hippopotamus amphibious), lion (Panthera leo; IUCN Red List status – vulnerable), cheetah (Acinonyx jubatus, vulnerable), leopard (Panthera pardus), striped hyena (Hyaena hyaena), wild dog (Lycaon pictus, endangered), and silver-backed jackal (Canis mesomelas). There are also four species of endemic reptiles in the region, including three species of frogs (Bufo chappuisi, B. turkanae, and Phrynobatrachus zavattari) and the endemic Turkana mud turtle (Pelusios broadleyi, vulnerable).
Lake Turkana is abutted by Turkana County on its western side and Marsabit County on its eastern side, with some of the lake’s southernmost regions within Samburu County. The Turkana tribe dominates Turkana County, but minor tribes that have migrated to the lake from other regions are also present. Marsabit County has a more diverse group of tribes, including the Dassanech, the Gabra, the Rendille, the Samburu, the El Molo, and the Turkana (Kaijage and Nyagah 2010). Nearly 100,000 members of at least eight distinct indigenous ethnic groups are heavily reliant on flood-recessional farming along the Omo River (Richter et al. 2010), while about 250,000 people of various ethnicities are dependent on fishing within the lake basin.
Conservation Status and Management
Lake Turkana is a shared transboundary resource by Kenya and Ethiopia. The region is rich in natural resources and hosts unique endemic species. Even though parts of the lake and lower Omo Delta have been zoned as an international biosphere reserve, the protected areas are facing immense threat from anthropogenic activities. In spite of the apparent threats, there is no management plan in place to guide resource use in the region. Recent efforts toward the development of wildlife management and fisheries management plans by Kenya Wildlife Services (KWS), National Museums of Kenya (NMK), and the State Department of Fisheries, Kenya, are initiatives worth fast tracking. Otherwise the prevailing scenario of uncoordinated Lake Turkana resources management will ultimately compromise ecosystem services with drastic negative implications for development, poverty alleviation, and adaptation toward anticipated long-term environmental changes.
The natural resources and human populations within the Omo Delta, which is an “oasis” in the region, could benefit tremendously if it was considered for designation as a Ramsar site. Other management efforts to consider include the establishment of a Lake Turkana-Omo Delta Transboundary Resource Management Committee, with members drawn from focal point ministries in Kenya and Ethiopia. Conservation and utilization of the World Heritage archaeological sites are needed to recognize and safeguard the region’s cultural heritage and to create development opportunities.
Threats and Future Challenges
A minimum environmental flow and an artificial 10-day flood have been proposed for Gibe III, but it is unknown whether a flood of this duration and size will be sufficient to sustain the ecological functioning of the lake (Avery 2012a). Although a reduction in flooding is touted as a benefit by some (e.g., Asnake et al. 2009), the resultant dampening of Lake Turkana’s water level fluctuations is of great ecological concern, given the importance of intra-annual fluctuations in controlling fish productivity in African lakes (e.g., Kolding and van Zweiten 2012). The amplitude of the controlled lake level fluctuations, assuming the environmental floods proposed by Asnake et al. (2009) are implemented, will be 400 mm less than the amplitude of the lake’s natural fluctuations.
Associated with the Gibe dams are thousands of hectares of sugar cane and cotton plantations and their irrigation infrastructure. Currently 150,000 ha are being developed along the Omo River as part of the Kuraz Sugar Project (see Fig. 5), whose planting began in February 2013 (Ethiopian Sugar Corporation 2014). The Ethiopian government plans to increase sugar production within Ethiopia from 300,000 t in 2009/2010 to 2.25 million tons by mid-2015 (Ethiopian Sugar Corporation 2014). Additional land concessions have been awarded, mainly for cotton production. A total of 445,000 ha commercial agricultural development is planned, of which 135,285 ha has been excised from two national parks (Omo and Mago) and one wildlife reserve (Tama) (Avery 2012a, 2013, 2014).
The Kuraz sugar scheme will alone abstract at least 30 % of the Omo River’s flow (ibid.). With the development of other irrigation schemes, the abstraction can only increase, which means the inflow to the lake will diminish. If there is 33.5 % reduction in the lake’s Omo River inflow, the lake will drop 13 m, and its volume will reduce to 59 % of its otherwise sustainable volume (ibid.). If there is 52 % reduction in Omo inflow, the lake will fall 22 m, and over half the lake’s volume will be lost (ibid.). A drop of as little as 10 m in lake level would reduce the lake’s size from 7,560 to 5,900 km2 and the lake’s volume from 238 to 170 km3 (Avery 2012a). Changes in the lake’s water levels will also lead to changes in the shape of the lake’s shorelines, which will be the most prominent in the wetland areas shown in Fig. 1 (Omo Delta, Ferguson’s Gulf, Allia Bay of Sibiloi National Park, and at the Turkwel and Kerio Deltas; Avery 2010, 2012a, 2014; Velpuri and Senay 2012). Changes in the annual volume and patterns of water inflow from the Omo River will impact a variety of important parameters in Lake Turkana, including turbidity, salinity, productivity, and habitat availability. These changes will interact to influence the feeding, breeding, movement, and ultimately the population levels of fishes in the lake and therefore the lake’s fishery. The Gibe Dams and irrigation schemes under construction will also have impacts beyond water inflow changes. For example, eutrophication caused by increased nutrient loads from fertilization of upstream crops or changes in turbidity due to deforestation along the Omo River will also alter the Lake Turkana ecosystem.
In addition to local development projects, the impacts of global climate change on the Lake Turkana ecosystems are projected to increase in severity. The ecosystem, which is already known for its historical environmental vicissitudes, will progressively experience even more extreme changes as a result of global climate change (e.g., Bishaw 2012). Greater efforts are therefore needed to forecast hydrodynamic and ecological responses to climate change in Lake Turkana. It is also important to understand and to strengthen local adaptation not only to improve local conditions but to avoid destabilization of the region occasioned by resource use conflicts.
In addition, the Lake Turkana region, which has historically been ignored by investors, has rapidly gained interest recently. This is attributed to the discovery of oil in the area and the ongoing exploration, which covers nearly the entire lake basin. The oil discovery is seen by many as the ultimate solution to the perennial resource use conflicts, poverty, and famine in the region. However with recent tumbling oil prices (in late 2014 and early 2015), the expected bonanza may be long delayed. Plus, if experiences from other part of Africa are anything to go by, then the usual “oil resource curse” may be unavoidable, i.e., a scenario where African countries with oil are ironically among the most economically troubled, undemocratic, and most conflict prone. Other socioeconomic activities that are usually associated with oil discovery and exploitation are also likely to have negative impacts on human well-being and biodiversity in the region.
The Lake Turkana region has also been earmarked for the development of one of the largest wind power farms in the region. The project when completed is expected to generate 310 MW. Other development activities in the area include the construction of the Lamu Port-South Sudan-Ethiopia Transport Corridor (LAPSSET), which will cut across the Lake Turkana area. These activities are not well planned and mitigated as per the requirements of Environmental Impact Assessments and will have enormous negative impacts on the resources of the region as well as potentially compromising the various ecosystem services that are currently enjoyed by the local communities and the region as a whole.
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