Landscapes

Geology of the Conservancy

The formation of the Great Rift Valley profoundly affected the drainage of East Africa resulting in the formation of a chain of lakes: Turkana, Baringo, Bogoria, Nakuru, Elmenteita, Naivasha, Magadi, Natron and Tanganyika. Some of these lakes are long, narrow and deep, while others are wide and shallow. The lakes are located in areas with high evaporation rates but with low rainfall. Three of these lakes are fresh water while the rest are alkaline. Eruptions in the area of fluid lava with a low viscosity have resulted in the formation of Rhyolites while Basaltic rocks have been formed by a lava with a higher viscosity that has not flowed over such large distances.

These basaltic rocks are basic and contain relatively low amounts of silica (less than 45%) while Rhyolites are acidic rocks and hence rich in silica (greater than 45%). The parent rock of both types contains high levels of Sodium resulting in the soda lakes of the Rift Valley. Also visible are Trachyte rocks which have intermediate character. The high levels of chlorides in Lake Elmenteita are indicative of a closed lake system with high evaporation rates and hot springs fed by a geothermal aquifer. These fault movements were succeeded by trachytes and phonolites which were later covered by thin layers of lake sediments. Grid faulting followed this and resulted in minor vulcanicity in the area which has led to the formation of several large craters and in one area, there can be seen, the evidence of a very young lava flow that forms the “Ututu” or Bad Lands. Lava tubes are also a feature of this area. Research also shows there to be large lacustrine sediments that include thick diatomite from middle Pleistocene age at Kariandusi and Soysambu.

Soils of the Elmenteita Watershed and Basin

Soils found in the Elmenteita basin can be classified into five main types. These include the soils found on the hills and minor scarps, those found in the more mountainous areas and on the major scarps, soils developed in volcanic highlands and on volcanic plains and lastly those on the undifferentiated areas of the uplands.

Hills and minor scarps (H)

Mountains and major scarps (M)

Soils developed on sediments mainly from volcanic ashes

Volcanic plains (Pv)

Uplands undifferentiated levels (Ux)

Climate and the Hydrological Cycle

Elmenteita, the springs and streams provide the water supply to the originate the highland areas of Kenya, within the forested belts of the Mau Escarpment and the mountain ranges of the Central Rift. At Elmenteita, there is a dynamic relationship between the processes of precipitation, interception, through-flow, overland flow groundwater recharge which defines the interaction between vegetation cover and the hydrological cycle. In areas where ground surfaces are exposed from grazing and desertification, run-off is increased; this increase results in a smaller base flow and accelerated soil erosion, producing higher sediment yields that affect water quality as they are washed down into the lakes. The interaction between these processes also results in the eventual decline in groundwater pools.

Past Climatic Conditions

Between 20 and 12,000 years ago, the vegetation in the Elmenteita region was dominated by open grasslands and arid conditions. Later, between 17 and 15,000 years ago, a moderately wetter climate developed, which resulted in a slight increase in both montane and lowland forest vegetation in the region.

In the last 30,000 years, research has indicated unusually low lake levels, which suggests the existence of a prolonged period of aridity and low temperatures. The existence of a period of aridity and low temperatures is also supported by research which indicates a reduced forest distribution and increased grasslands in the region. In the Central Rift Valley, a trend towards warmer and wetter conditions around 12,500 BP was recorded, which coincided with glaciation at higher altitudes. As a result, Lake Elmenteita has experience low and intermittent lake water levels since that time.

Present Climatic Conditions

Several weather stations are located in the Elmenteita area; however, only two of those stations – Soysambu and Dundori – have reliable and continuous rainfall data from 1958 to present. Nevertheless, continuous temperature data is not available for Elmenteita area.The floor of the Central Rift Valley is currently mildly warm and dry, while the escarpments to the East and West are often cool and wet. Both rainfall and temperature typically correlate closely with altitude; yet, in the Central Rift Valley, this correlation is altered slightly due to the rain-shadow cast by the mountains located to the east. In this precise location, temperature decreases with altitude at a rate much faster than the rate at which precipitation increases; thus, Soysambu Conservancy is often hot, dusty and dry.

Elmenteita and part of its catchment area are classified in the agroclimatic zone VI-6 which is characteristically humid to arid with dry woodland vegetation. The remaining sections of the Central Rift are classified agroclimatic zone III-5 which is characterised by humid conditions with dry forest and woodland vegetation. In the region, the mean annual temperatures range from 12 degrees in the warm, humid upper catchment areas to 18 degrees in the hot, dry lowlands. Basin evaporation rates are high at above 1400mm/year. In the fringing highlands of the upper catchment, mean rainfall was reported at around 1066mm between1959-1985, whereas the mean was recorded at 733mm/year between1958-1987. Rainfall in the area tends to be modal, with two peaks in April and August. The average annual rainfall for Soysambu is about 790mm, with two peaks in April (average 107mm) and November (average 71mm).

Drainage

The Central Rift Valley forms an important catchment for the drainage from the two forest stands on both margins of the rift.The Nyandarua Mountains to the East (3960m) and the Mau Escarpment to the West (300m) each drain into one of the three central rift lakes: Nakuru, Elmenteita and Naivasha. Due to its shallowness, Elmenteita fluctuates greatly not only in water level but also in alkalinity and thus can only at times support fish.

The lake is now a shallow, small, saline lake that is fed by inflows from the rivers Mbaruk, Chamuka and Meroroni. Historically, the main water source is the Meroroni River: initially flowing parallel to the other rivers and then abruptly changing direction to flow in a south-eastern direction along an extremely straight line.This is due to Rift Valley faulting. In recent years, inflow from the Meroroni River has decreased significantly as a result of increased upstream water withdrawal. There is also some inflow from hot springs located on the south- eastern part of the lake while subsurface flows from Lake Naivasha also add to water levels.

Lake Elmenteita Waters

Lake Elmenteita is a hypertrophic, saline lake of low water clarity. Saline lakes are usually shallow and their waters do not stratify vertically.The lack of vertical stratification means that they undergo large fluctuations in lake volume and surface area, as well as salinity levels. However, as a saline lake, the water is alkali carbonate meaning it is rich in sodium hydrogen carbonate chloride (NaHCO3Cl)); thus, it is considered an area of high biomass and productivity.This high biomass and productivity allows Lake Elmenteita to serve as a home and a feeding area to Lesser Flamingos and the breeding area for the Great White Pelicans. Lake Elmenteita does indeed support a migratory population of flamingos which varies according to lake levels and salinity. The fluctuations in lake volume and salinity of Lake Elmenteita have been linked to flamingo population crashes; research shows that these crashes have been associated with periods of extreme salinity.The saline conditions in Lake Elmenteita also leads to the high productivity of its major phytoplankton species; the cyanobacterium ‘Spirulina’ Arthrosporia fusiformis, which also serves as the only food source of the Lesser Flamingo.

Saline lakes have few species types, but contain large numbers of microorganisms. Most of the physical processes taking place in the lakes are controlled by wind- induced currents. Major water inflows of saline lakes are via ground water flow.These factors ultimately mean that environmental impact on ground water is much higher in saline lakes than fresh water lakes. The high nutrient content in saline lakes is important for the ecological processes occurring within the water column. Nutrient level changes will in turn result in changes in the species complement and population structure. Groundwater quality is the sum of all natural and anthropogenic influences.The processes that may result in addition of nutrients into ground water systems may be physical, geochemical, or biochemical. Some examples of ground water contamination sources are un- sewered domestic sanitation such as pit latrines, disposal of industrial waste, cultivation using agrochemicals, and mining activities.

Vegetation of the Conservancy

The vegetation on the estate can broadly be classified in two groups:

Vegetation Specific to Lake Elmenteita

Around the lake itself, vegetation contains one of the few remaining stands of protected riverine forest. The yellow fever trees (Acacia xanthophloea) are the main feature of the riverine areas. They are found in fairly dense stands on the major rivers feeding into lake Elmenteita. The forest is important in maintaining water quality flowing into the lake.

The lake perimeter is surrounded by short, salt tolerant grass, including Sporobolus, spicatus while swamps cover part of the south eastern section of the lake, comprised mainly of Typha and Cyperus papyrus. The Cyperus species is widespread over the northern section and other parts of the lake. Most of the lake’s shoreline is open and muddy, with rocky outcrops on the Eastern and Western sides. There are no macrophytes and little emergent vegetation in most sections except for the above mentioned Typha beds near the inflow of the hot springs at the southeast corner.

Vegetation Beyond the Lake Perimeter

Euphorbia candelabrum are scattered and mainly located on kopjes overlooking the lake and in the rocky areas to the south. It could be the largest remaining stand in Kenya Acacia woodlands also extend around the mouths of rivers. The area contains high diversity of tree, vine and plant species. Acacia xanthophloea is the sole tree species in this semi-arid area, where the soils consist of dominantly alkaline volcanic and lacustrine deposits and water salinity can be very high. The understory here is dominated by climbers: Senecio petitiunus, Commicarpus pedunculosus, Ipomea cairica, Achyranthes aspera and Hypoestes verticillaris.

The acacia trees in areas of the conservancy (particularly on the western shores of Lake Elmenteita) are under threat of destruction by the growing giraffe population.

Further beyond the lake, the vegetation is dominated by open savannah grasslands. This part of the ecosystem sustains large numbers of grazers including cattle which are the primary income from Delamere Estates. Main grass types are Chloris Gayana, Themeda trianda, Cynodon Dactylon Pinesetum Nizianumand Pinesetum Catabais. Dry bushland covers parts of the eastern and most of the southern and western sides of the lake, which is composed of Rhus natalensis, Sesbania sesban, Lantana trifolia and Vernonia spp.