Phosphorus limitation in some tropical African lakes

Two of three Kenyan lakes studied between November 1979 and October 1980 have very short ³³PO₄ turnover times, indicating a high phosphorus (P) demand throughout the year. The P turnover time in Lakes Oloidien and Sonachi is as rapid as in the most P deficient temperate zone lakes. The third lake, Lake Naivasha, has a lower overall P demand and a wide seasonal range, with lowest demand between November 1979 and February 1980 when a P deficiency was unlikely. On an annual basis the Lake Naivasha status is, however, not statistically different from that recorded during the summer in Lake Memphremagog, a generally P-limited temperate zone lake. Lake Naivasha and Lake Oloidien fit well to the line of best fit for the Dillon-Rigler relationship relating total phosphorus (TP) and chlorophyll a derived in temperate zone lakes. Thus, temperate zone models predicting aspects of lake behaviour on the basis of TP may also be applicable to these two tropical lakes. Saline lake Sonachi had not only a short P turnover time but also responded dramatically to the fertilization of enclosures with P. However, it does not fit the TP-chla or the total nitrogen-chla plots from the temperate zone. This suggests that, in this saline lake at least, much of the TP is unavailable to the algae, with some of it in a particulate form that is readily extracted with boiling water. The epilimnetic N:P ratios also characterize lakes Oloidien and Sonachi lakes as highly P deficient and lake Naivasha as more moderately P limited. A single set of measurements in Winam Gulf (Lake Victoria) also showed a rapid P turnover time and thus P limitation, but as in lake Sonachi much of the TP was in a non-algal particulate form. Occasional measurements in three other hypertrophic and saline lakes suggest them to be primarily light limited on the basis of their very high photosynthetic cover. These findings support the hypothesis of a primary P limitation for those lakes not light limited, and contradicts literature suggestions that nitrogen is the primary limiting element in tropical lakes.     

Succession of planktonic rotifer populations in some lakes of the Eastern Rift Valley,Kenya

The quantitative succession of the spring and summer rotifer plankton and its biomass in six lakes of the Eastern Rift Valley of Kenya is discussed. The lakes can be divided into two groups: the low conductivity slightly alkaline lakes Naivasha, Oloidien and the Winam Gulf of Lake Victoria; and the high conductivity, highly alkaline-saline lakes Nakuru, Elmenteita and Bogoria. The former three show a qualitatively rich, typical warmwater rotifer association dominated by Brachionids and Filinia. The saline soda lakes are dominated by several populations of Brachionus dimidiatus, which can reach enormous numbers. The taxonomy and biometry of this species was subjected to statistical analysis. Some interesting and rare species are described: Anuraeopsis coelata, Lepadella triptera f. deconincki, Trichocerca gracilis and T. mus.The chemical limnology of the lakes is discussed and compared with other soda lakes in Central Africa, Europe and North America.     

Changes of phytoplankton communities in Lakes Naivasha and Oloidien, examples of degradation and salinization of lakes in the Kenyan Rift Valley

Increasing degradation of the water quality, caused by overuse and salinization, leads to considerable changes of the phytoplankton composition in Kenyan Rift Valley lakes. Exemplarily, the phytoplankton communities and biomasses of deteriorating freshwater Lake Naivasha and salinizing Lake Oloidien were studied between 2001 and 2005, accompanied by physico-chemical measurements (pH, total phosphorus and nitrogen, alkalinity, conductivity). Over the last three decades, the ecology of these two water basins has been subjected to dramatic changes, caused by excessive use of water and catchment area by man. In L. Naivasha a shift in the dominance of coccoid cyanobacteria towards dominance of Chlorophyceae (Botryococcus terribilis) was observed. Lake Oloidien exhibited a shift in the dominance of coccoid Chlorophyceae towards dominance of cyanobacteria (Arthrospira fusiformis, Anabaenopsis elenkinii). Phytoplankton findings and chemical data demonstrate that L. Naivasha has developed towards a eutrophic freshwater lake while L. Oloidien has progressed towards a hypereutrophic alkaline-saline lake. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Padisak     

Trends in waterbird numbers in the southern Rift Valley of Kenya

Bennun, L. & Nasirwa, O. 2000. Trends in waterbird numbers in the southern Rift Valley of Kenya. Ostrich 71 (1 & 2): 220–226.

Each January since 1991, volunteer teams have counted waterbirds at major wetlands in the southern Kenyan Rift Valley. There has been consistent coverage at Lakes Naivasha, Elmenteita, Nakuru and (since 1992) Bogoria. These lakes are shallow and, except for Bogoria, fluctuate greatly in extent; all but Naivasha are saline. Lake levels were moderately high in 1991–1993 but have been generally low since. Flamingo totals for the three saline lakes combined were more than one million from 1992–1994, but roughly halved each year since then. Greater Flamingos Phoenicopterus ruber made up between 0.7 and 4.1% of total flamingo numbers; other waterbirds made up between 2.7 and 10.2% of the overall total. Lakes Naivasha, Elmenteita and Nakuru together hold most of the non-flamingo waterbirds in the southern Rift; to compare trends for other species, we pooled totals for these sites. Significant, or near-significant, declines were evident for grebes, pelicans, cormorants, storks, gulls, rallids, kingfishers, terns and raptors. No group showed an overall increasing trend. At Dandora, a smaller site with stable water levels, these groups showed large annual fluctuations but no obvious declines. In most waterbird groups where numbers decreased, the probable cause was sustained low lake levels at Lake Nakuru; numbers at Lake Naivasha remained stable. Exceptions were rallids, kingfishers and raptors, where numbers steadily declined at Naivasha. There is a need to investigate local environmental causes of these changes for kingfishers and raptors, and to assess possible loss of breeding sites for rallids.     

Swamps,springs and diatoms: wetlands of the semi-arid Bogoria-Baringo Rift,Kenya

Lakes Bogoria and Baringo lie in a semi-arid part of the Kenya Rift Valley between 0° 15′–0° 30'N and 36° 02′–36° 05′E. Nevertheless, the area around these lakes contains numerous wetland systems that have been formed: along lake shorelines; along faults where hot, warm and cold springs have developed; and along river systems that cross the rift floor. Six major types of wetland are recognized: Proximal Hot Springs; Hot Spring Marshes; Blister Wetlands; Typha and Cyperus papyrus Swamps; Floodplain Marshes; Hypersaline Lake Littoral Wetlands; and Freshwater Lake Littoral Wetlands. These show significant variability in terms of geomorphic setting, water chemistry, temperature, plant communities and diatom floras. They are variously dominated by macrophytes, such as Cyperus laevigatus, Typha domingensis and Cyperus papyrus. In some cases macrophytes are absent. In hot spring settings and in hypersaline lake littoral zones bacterial mats are common. Although absent in some samples, diatoms occur in at least parts of all of the wetlands, varying in diversity, abundance and species composition. Canonical correspondence analysis indicates that diatom floras show a close relationship with pH, temperature, and specific conductivity, with other environmental variables such as Si and nitrate being of secondary importance. Common diatoms include: Anomoeoneis sphaerophora var. guntheri, Navicula tenella, N. cuspidata, and Nitzschia invisitata in hot springs, where diversity is generally low and abundance is variable. Other wetland types contain distinctive diatom floras that variously include: Fragilaria brevistriata, Gomphonema parvulum, Navicula tenelloides, Nitzschia communis, N. latens, N. sigma, Rhopalodia gibberula, and Stauroneis anceps.     

Bioturbation in matgrounds at Lake Bogoria in the Kenya Rift Valley: implications for interpreting the heterogeneous early Cambrian seafloor

Modern burrowing organisms feed on microbial organic matter in matgrounds near hot springs on the margins of Lake Bogoria, a saline alkaline lake in the Kenya Rift Valley. The burrowers produce a low-diversity trace assemblage similar to those produced by undermat miners during the Ediacaran–Cambrian transition. Despite obvious differences in body plans and phylogenetic affinities, these modern animals feed on microbes in similar ways to those inferred for primitive bilaterians. With increasing distance from hot-spring vents, outflow channels and adjacent matgrounds, the diversity and depth of the traces increase and mixgrounds become dominant. This modern extreme environment gives clues for interpreting the heterogeneous early Cambrian seafloor, with: (1) the restriction of ‘pre-agronomic revolution’ matground substrates; and (2) expansion of adjacent ‘post-agronomic revolution’ mixground areas.     

Afrocymbella barkeri sp. nov. (Bacillariophyta), a common phytoplankton component of Lake Challa,a deep crater lake in East Africa

A new freshwater diatom, Afrocymbella barkeri Cocquyt & Ryken sp. nov., is described from Lake Challa, a deep and unproductive crater lake near Mt Kilimanjaro in equatorial East Africa, based on light and electron microscopic observations. This tropical diatom is a representative of the rather small genus Afrocymbella with only 12 known species and with a distribution restricted to the African Rift. Taxa belonging to this genus are heteropolar and characterized by dorsiventral valves curved along the pervalvar axis and the presence of small pseudosepta and septa on the open girdle bands. Afrocymbella barkeri was common only towards the end of the dry and windy season corresponding to northern hemisphere summer, when deep water-column mixing caused upwelling of nutrient-rich water from the hypolimnion. This taxon was observed free living in the water column during mixing, but the presence of a small apical pore field at the foot pole, along with some cells with mucilage stalks, suggests that its primary habitat probably involves attachment to a substrate.     

Standing crop densities and distribution of Spirulina and benthic diatoms in East African alkaline saline lakes

SUMMARY. The diversity of Eastern Rift Valley alkaline saline lakes is illustrated and their temporal fluctuations in ionic concentration are emphasized.
The standing crop densities of phytoplanktonic blue-green algae of the genus Spirulina and benthic diatoms were measured. Spirulina abundance was measured as dry mass density and the validity of the gravimatric estimates was checked by chlorophyll analysis and microscopic counting. Benthic diatom standing crops were assessed by chlorophyll determinations. Spirulina density is extremely variable in time and may fluctuate over more than an order of magnitude. High density blooms of Spirulina are not a common characteristic feature of these lakes. The causes of changes in Spirulina standing crop and the associated alterations in the structure of the primary producer community are discussed and three qualitative states which may occur are described.
Similar standing crops of benthic diatoms (mean 45 mg m⁻² of chlorophyll-α) were found at all lakes wherever the water depth was shallow enough to allow light penetration to the sediment surface.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

A photographic census of flamingos in the Rift Valley lakes of Tanzania

An aerial photographic census of flamingos ( Phoenicopterus minor and P. ruber) was conducted on 20 July 1994 on nine lakes in Tanzania: Lakes Natron, Manyara, Magadi (Ngorongoro), Burungi, Embagai, Eyasi, Lagarja, Masek, and Ambussel. This census, conducted concurrently with a survey in Kenya, documented the numbers and distribution of flamingos in the Rift Valley Lakes of East Africa. The total population size of flamingos in the Tanzanian lakes surveyed was |mF907,000. The largest concentrations in Tanzania were found in Lake Natron and Embagai Crater Lake. Although flamingos are known to breed in Lake Natron, no evidence of breeding was observed during the survey. The total estimate for the southern Kenya and northern Tanzania Rift Valley was |mF2·8 million. Trends in flamingo populations, survey methodology, and future monitoring needs are discussed.     

Inter-lake movements of the Lesser Flamingo Phoeniconaias minor and their conservation in the saline lakes of Kenya

Maina, J.G. 2000. Inter-lake movements of the Lesser Flamingo Phoeniconaias minor and their conservation in the saline lakes of Kenya. Ostrich 71 (1 & 2): 126.

The Lesser Flamingo Phoeniconaias minor is the only algivore in the saline lakes of Kenya occurring in spectacular assemblages that form the tourism base. The flamingos show unpredictable, spontaneous, “nomadic” movements between the saline lakes whose precipitating ecological factors were not well established. Food, conductivity, breeding, predation and fresh water availability were regarded as the primary factors in spite of their global coverage in explaining animal movements. Evidence is emerging that food, especially algal species composition, density, and lake levels are the primary driving factors for these inter-lake movements, with other factors being consequences of these. Algal species composition and lake levels are subject to limnological processes in the lakes, climatic conditions and human activities in the catchment of the saline lakes. Environmental degradation is now a critical factor influencing the limnology of these fragile ecosystems with far ranging consequences on lake levels, algal species composition and succession. These changes determine flamingo utilization patterns within and between the lakes. This calls for a review of the conservation status and management of the saline lakes, home to a few but highly specialised species.     

Climate drivers of diatom distribution in shallow subarctic lakes

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Bacterial Diversity in the Haloalkaline Lake Elmenteita, Kenya

Lake Elmenteita is one of the alkaline saline lakes within the Kenyan Rift valley. The lake is situated on the floor of the Kenyan Rift Valley at 1,776?m above sea level and has no direct outlet. The microbial diversity of the lake was investigated using a culture-independent approach. Five different sampling points were selected randomly within the lake. Wet sediments and water samples were collected from each sampling point. In addition, dry mud cake was collected from three points where the lake had dried. DNA was extracted from the samples and the 16S rRNA genes amplified using universal primers for Bacteria. Thirteen clone libraries were constructed using the PCR amplified 16S rRNA genes. A total of 1,663 clones were picked. Representative clones were selected using ARDRA technique for sequencing. 655 partial and non-chimeric clone sequences indicated the presence of 37 orders in the Domain Bacteria. Cyanobacteria were the most abundant clones in terms of numbers whereas members of the phylum Firmicutes group were the second in terms of numbers but the most diverse in terms of genera represented. All clones affiliated to the class Betaproteobacteria originated from DNA obtained from the water samples. Analysis using BLAST showed that 93.1% of the sequenced clones had similarity values below 98% to both cultured and as yet uncultured bacteria, resulting in 596 phylotypes. Therefore, it can be concluded that Lake Elmenteita harbours phylogenetically diverse groups of bacteria involved in complex metabolic interactions within the Lake??s ecosystem.     

<Emphasis Type="Italic">Rhodobaca barguzinensis</Emphasis> sp. nov., a new alkaliphilic purple nonsulfur bacterium isolated from a soda lake of the Barguzin Valley (Buryat Republic,Eastern Siberia)

A novel strain, alga-05, of alkaliphilic purple nonsulfur bacteria was isolated from sediments of a small saline (60 g/l) soda lake near Lake Algin (Barguzin Valley, Buryat Republic, Russia). These bacteria contain bacteriochlorophyll a and carotenoids of the alternative spirilloxanthin group with predominating demethylspheroidenone. They are facultative anaerobes; their photosynthetic structures are of the vesicular type and arranged along the cell periphery. Growth of this strain is possible in a salinity range of 5–80 g/l NaCl, with an optimum at 20 g/l NaCl. Best growth occurred at 20–35°C. Analysis of the 16S rRNA gene sequences demonstrated that the studied isolate is closely related to the alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis (99% similarity) isolated from soda lakes of the African Rift Zone. According to the results of DNA-DNA hybridization, strain alga-05 has a 52% similarity with the type species of the genus Rhodobaca. On the basis of the obtained genotypic data and some phenotypic properties (dwelling in a hypersaline soda lake of Siberia, moderate halophily, ability to grow at relatively low temperatures, etc.), the isolated strain of purple bacteria was described as a new species of the genus Rhodobaca, Rca. barguzinensis sp. nov.     

Microzooplankton feeding behaviour: grazing on the microbial and the classical food web of African soda lakes

We investigated the feeding behaviour of the dominant microzooplankton of saline lakes in the East African Rift Valley. A set of grazing experiments revealed high ingestion rates of the two euryhaline rotifers Brachionus dimidiatus and Brachionus plicatilis and of the large-sized omnivorous ciliates Frontonia sp. and Condylostoma magnum reflecting the unique nature of tropical saline systems. The size spectrum of ingested particles was broad and even included filamentous cyanobacteria such as the commonly dominating Arthrospira fusiformis. Feeding selectivity on cyanobacteria, however, was rather low showing higher values for cryptomonads and small ciliates. Bacterial biomass was favoured by the presence of grazers, as small bacterivorous predators were reduced at an average of 13.9%, showing the cascading effect of large zooplankton on the food web structure. Overall, based on this first-time study of the microzooplankton feeding behaviour in East African soda lakes, a strong structuring effect of rotifers and large ciliates on microbial plankton communities is assumed, especially in times of high consumer biomass.     

A new diatom (Bacillariophyceae) genus with two new species from New Mexico,USA

A new diatom (Bacillariophyceae) genus and two new species are described from the arid region of the North American southwest. The new genus, Playaensis, and new species, P. circumfimbria and P. furtiva, are distinguished by frustule morphology and autecology. Playaensis possesses unique, narrowly lunate longitudinal ribs bordering the raphe and spathulate spines, but their evolutionary relationship to known genera is unclear. In Payton Lake, New Mexico, P. circumfimbria and P. furtiva are rare in the diatom community, and their geographic and geological extent are not known, but they may be restricted to alkaline, slightly saline lakes of the region.     

Microbiology of Lonar Lake and other soda lakes

Soda lakes are saline and alkaline ecosystems that are believed to have existed throughout the geological record of Earth. They are widely distributed across the globe, but are highly abundant in terrestrial biomes such as deserts and steppes and in geologically interesting regions such as the East African Rift valley. The unusual geochemistry of these lakes supports the growth of an impressive array of microorganisms that are of ecological and economic importance. Haloalkaliphilic Bacteria and Archaea belonging to all major trophic groups have been described from many soda lakes, including lakes with exceptionally high levels of heavy metals. Lonar Lake is a soda lake that is centered at an unusual meteorite impact structure in the Deccan basalts in India and its key physicochemical and microbiological characteristics are highlighted in this article. The occurrence of diverse functional groups of microbes, such as methanogens, methanotrophs, phototrophs, denitrifiers, sulfur oxidizers, sulfate reducers and syntrophs in soda lakes, suggests that these habitats harbor complex microbial food webs that (a) interconnect various biological cycles via redox coupling and (b) impact on the production and consumption of greenhouse gases. Soda lake microorganisms harbor several biotechnologically relevant enzymes and biomolecules (for example, cellulases, amylases, ectoine) and there is the need to augment bioprospecting efforts in soda lake environments with new integrated approaches. Importantly, some saline and alkaline lake ecosystems around the world need to be protected from anthropogenic pressures that threaten their long-term existence.     

Phytoplankton community structure and succession in the water column of Lake Naivasha,Kenya: a shallow tropical lake

Lake Naivasha is a shallow freshwater lake in the Rift Valley of Kenya. Since the 1980s, when the lake showed a seasonal shift between diatom and cyanobacterial dominance it has become moderately eutrophic. Its algal assemblage is now dominated by a persistent Aulacoseira italica population both numerically and in terms of contribution to overall primary production. Algal and cyanobacterial counts were used to derive Simpson's diversity, succession rate and total community succession, focusing on the 10 most numerically abundant taxa. 170 species were identified, 43 of which were in common with the 143 found in 1979–80, before the increase in trophic state. Most diatoms are indicators of moderate to high nutrient conditions. There is little horizontal or vertical variation in successional processes throughout the lake and although the absolute abundance of cells varies widely, proportional composition is relatively stable. In Crescent Island lagoon, the only regularly stratified site, hypolimnetic succession rates are lower than those in the epilimnion. Overall, community composition is controlled by mixing (and hence light regime) and nutrient availability. With `endless summer' conditions and full mixing, there is a successional pattern of `muted seasonality' adapted to physical instability and environmental stability.     

The virus's tooth: cyanophages affect an African flamingo population in a bottom-up cascade

Trophic cascade effects occur when a food web is disrupted by loss or significant reduction of one or more of its members. In East African Rift Valley lakes, the Lesser Flamingo is on top of a short food chain. At irregular intervals, the dominance of their most important food source, the cyanobacterium Arthrospira fusiformis, is interrupted. Bacteriophages are known as potentially controlling photoautotrophic bacterioplankton. In Lake Nakuru (Kenya), we found the highest abundance of suspended viruses ever recorded in a natural aquatic system. We document that cyanophage infection and the related breakdown of A. fusiformis biomass led to a dramatic reduction in flamingo abundance. This documents that virus infection at the very base of a food chain can affect, in a bottom-up cascade, the distribution of end consumers. We anticipate this as an important example for virus-mediated cascading effects, potentially occurring also in various other aquatic food webs.