Lake Bogoria
Lake Bogoria is a saline, alkaline lake that lies in a volcanic region in a half-graben basin south of Lake Baringo, Kenya, a little north of the equator. Lake Bogoria, like Lake Nakuru, Lake Elementeita, and Lake Magadi further south in the Rift Valley, and Lake Logipi to the north, is periodically home to one of the world's largest populations of lesser flamingos. The lake is a Ramsar site and Lake Bogoria National Reserve has been a protected National Reserve since November 29, 1973.
History
The lake was formerly named after Anglican missionary James Hannington who visited in 1885.Description
Lake Bogoria is located in Baringo County, about 120 km north of Nakuru city and 240 km north of Nairobi. It is in the Gregorian Rift Valley.It was once part of a larger freshwater lake, joined with the current Lake Baringo.
As shown on the satellite picture at the top of this page, it is divided in three lobes: a large center one and two smaller ones at the north and south extremities. The two narrower areas separating these lobes are shallow, tectonically controlled sills at Nyalibuch and Mwanassis.
There are contradictions regarding its altitude. Unesco's Ramsar gives. More precise — and more prudent —, give c. 990 m as of August 1977, but also indicate that the lake's level fluctuates seasonally by 50 to 100 cm; and that it can vary by several meters for short periods, having fluctuated between c. 988 and c. 996 m during the 20th century. Lake-shore terraces around the shoreline, made of coarse angular gravel and angular orthoconglomerates, mark higher lake levels from the Pleistocene and Holocene. They are visible on 45% of the present level, and some are about 9 m above the present shoreline.
In 1991 the maximum length is and its width ranges from to.
The drainage basin is. The lowest point of the drainage divide is at 999 m near Loboi village; when the level of the lake reaches that altitude, its waters flow northward in lake Baringo drainage basin.
In 1978 its maximum depth was recorded as or, and precise that this was in the largest sub-basin or lobe; and that the two smaller parts at the north and south extremities were deep at that time.
In 2003 its maximum depth is just over in an area of. This is relatively shallow, but nevertheless deeper — and therefore hydrologically more stable — than the other endorheic lakes in Kenya.
The Rift Valley lakes undergo regular changes in water levels mostly in response to precipitation, which is unreliable and unpredictable.
In this region, lake Bogoria is the only alkaline lake that has minimal lake water fluctuations, and is used as a refuge for flamigos and other animals when other relatively shallow lakes dry out.
Its surface is generally but this fluctuates, essentially according to the amount of rainfall. Most of the rain falls between April and November, and precipitation ranges average about 700 mm on the Loboi plain and 1200 mm on the adjacent highlands. But El Nino years bring increased rainfall and flooding of the lake shores. For example, in 2020 its area increased to about : 2020 was one of the hottest years on record, but despite depressed rainfall in the short-rains season it also saw a wetter than normal January and February because of the strong positive Indian Ocean Dipole index during that period, and enhanced rainfall during the long-rains season .
However, evaporation rate is above 2500 mm, thus inducing a water deficit and creating semi-arid conditions over most of the lower parts of the Bogoria basin.
Wetlands
Although the lake is in a semi-arid part of Kenya Rift Valley, it is surrounded by numerous and varied wetlands along its shorelines, along faults where hot, warm and cold springs have developed, and along rivers that run across the rift floor.Types of wetlands
Six major types of wetland have been defined around lake Bogoria:- proximal hot springs, with small streamlets, exposed ground, high water temperatures over 40 ◦C that reach up to 99 ◦C at vents, and microbial mats of bacteria and less common diatoms; These are associated with:
- * hot spring marshes, found downstream of the proximal hot springs and adjacent to spring streamlets, and dominated by thick clusters of short reeds, mainly Cyperus laevigatus, that stand through a water layer 2 cm high or less and with temperatures ranging between 30–40 ◦C;
- artesian blister wetlands associated with cool springs. The circular blister mounds are about 15 m diameter and 1 to 2 m high. They are formed by cool artesian springs that emerge at the surface, creating a sort of water blister of about 1m3. They are capped with an arched semi-permeable cover of short graminoids such as Cyperus laevigatus, Pycreus mundtii and Leersia hexandra. The edges of these 'blister mounds' are dominated by Leersia hexandra mixed with other grasses and sedges. Further around are some Sporobolus spicatus, and downslope of these mounds and of other water seeps are often found small patches of Typha and wet meadows plants.
- Typha and Cyperus papyrus swamps, fed by a mix of surface streams, groundwater seeps or warm springs. Where water is shallow and ephemeral, these are dominated by tall Typha domingensis ; where water is permanent — usually in broad depressions —, the dominant vegetation is floating Cyperus papyrus;
- floodplain marshes, with seasonal flooding and populated by short grasses;
- hypersaline lake littoral wetlands, found on the lake shores: they are flooded, gently sloping, siliciclastic delta margins, often modified by flamingo nesting. Their pH is around 10, with an alkalinity ca. 1000 meq l−1. Hot springs may also feed into some of these sites. There are no macrophytes and few diatoms: cyanobacteria dominate ;
- freshwater lake littoral wetlands, forming narrow to extensive fringes around the relatively fresh water Lake Baringo, dominated by a variety of wetland vegetation.
Wetlands areas
In the south, two freshwater springs supply permanent streams. All three are used extrensively for drinking, as well as the water from some hot springs streams — some of these being substantially less salty than the lake water. Other streams, such as the Emsos to the south and the Parkirichai to the west, are ephemeral: they flow only after heavy rains.
; The Loboi Swamp
This swamp is to the north of the lake. It hugs the base of a horst block oriented north-south. According to radiocarbon datation, it was created only 700 years ago in a former floodplain environment — possibly as a consequence of faulting. In 1969, it spread over 6 km in length; but water was diverted from the Waseges river and by 2001 it was only 3.5 km long and about 0.5 km wide. At least three warm springs, and groundwater inputs, feed it. The Loboi river also contributes to it but that river periodically shifts its bed and that modifies its relative role regarding the swamp. This river is cool and only slightly alkaline. The springs have a similar chemistry but they are warmer, have a higher nitrate content, and are slightly acidic. The resulting waters of the Loboi Swamp are also slightly alkaline, and generally reflect the mixing of fluvial, spring and groundwater inflows.
Its areas of semi-permanent or seasonal standing water are dominated by Typha domingensis and also have some Leersia hexandra, Ipomoea aquatica, and other taxa. These areas surround a wetter area populated by near pure stands of Cyperus papyrus that are rooted or floating in water up to 1.5 m deep. Acacia scrub occurs on an adjacent horst block to the west, with grasses such as Sporobolus spicata on adjacent plains.
; The Kesubo floodplain marshes
These are also to the north of the lake, east of the Loboi swamp. They rest at the southern end of an extensive alluvial fan formed by the Sandai river. The Kesubo Floodplain Marshes are seasonally flooded and lie between the rift valley boundary faults, to the east, and a small horst block, to the west. The river waters are slightly alkaline, cool, and have a low total alkalinity. The marshes are similar in their general water chemistry, but are slightly acidic and have a distinctly lower NO3 content. Short grasses are the dominant vegetation type and cattle graze the area.
; The Campground Wetlands
These lie near the Lake Bogoria National Reserve entrance, to the south of the Loboi swamp, and at the limit dividing faulted volcanic uplands and colluvial-alluvial sediments. They contain several types of habitats. defined them as an 'Artesian Blister Wetland', and that wetland also includes slightly acidic, nitrate enriched, warm springs.
; The Loburu Delta
This is on the western shore of Lake Bogoria. It is composed of silts and gravels, and shows a variety of fluvial, deltaic, and beach settings. It has active hot springs that feed a series of marshes dominated by Cyperus laevigatus. The springs are alkaline, of the Na-HCO3 type, contain a lot of silica and nitrate, and the temperature near the vents is extremely hot. The areas immediately adjacent to the vents and in nearby streamlets commonly include microbial mats of Phormidium, Pseudanabaena, Spirulina, Synechococcus and Calothrix, but are devoid of macrophytes.
the Cyperus marshes, which have similar water chemistries, are dominated by short reeds less than 20 cm high. Temperatures range from about 32◦C to about 60◦C near the hot spring streamlets that cross the marshes. There are also algal and cyanobacterial mats. The lake shoreline at Loburu does not present many aquatic macrophytes. The lake brine is of Na-CO3-HCO3-Cl composition, with a pH range of 9.3–10.6. Some shallow marginal lagoons have salinities exceeding 100 g l−1. Temperature at the time of sampling ranged between 28 and 33 ◦C, but exceed 60 ◦C at sublacustrine hot spring vents. However, cyanobacteria — mainly Spirulina platensis — are abundant and support up to 2 million flamingoes.