Kenya Rift Research Articles

Structural Controls on the Geochemistry and Output of the Wells in the Olkaria Geothermal Field of the Kenyan Rift Valley

The Olkaria geothermal field is located in the Kenya Rift valley, about 120 km from Nairobi. Geothermal activity is widespread in this rift with 14 major geothermal prospects being identified. Structures in the Greater Olkaria volcanic complex include: the ring structure, the Ol’Njorowa gorge, the ENE-WSW Olkaria fault and N-S, NNE-SSW, NW-SE and WNW-ESE trending faults. The faults are more prominent in the East, Northeast and West Olkaria fields but are scarce in the Olkaria Domes area, possibly due to the thick pyroclastics cover. The NW-SE and WNW- ESE faults are thought to be the oldest and are associated with the development of the rift. The most prominent of these faults is the Gorge Farm fault, which bounds the geothermal fields in the northeastern part and extends to the Olkaria Domes area. The most recent structures are the N-S and the NNE-SSW faults. The geochemistry and output of the wells cut by these faults have a distinct characteristic that is the N-S, NW-SE and WNW-ESE faults are characterized by wells that have high Cl contents, temperatures and are good producers whereas the NE-SW faults, the Ring Structure and the Ol’Njorowa gorge appear to carry cool dilute waters with less chloride concentration and thus low performing wells. Though the impacts of these faults are apparent, there exists a gap in knowledge on how wide is the impact of these faults on the chemistry and performance of the wells. This paper therefore seeks to bridge this gap by analysis of the chemical trends of both old wells and newly drilled ones to evaluate the impacts of individual faults and then using buffering technique of ArcGis estimate how far and wide the influence of the faults is. The data was obtained after the sampling and analysis of discharge fluids of wells located on six profiles along the structures cutting through the field. Steam samples were collected with a stainless steel Webre separator connected between the wellhead and an atmospheric silencer on the discharging wells whereas the analysis was done in house in the KenGen geochemistry laboratory. The results indicates that Olkaria field has three categories of faults that control fluid flow that is the NW-SE trending faults that bring in high temperature and Cl rich waters, and the NE-SW trending Olkaria fracture tend to carry cool temperature waters that have led to decline in enthalpies of the wells it cuts through. The faults within the Ol Njorowa gorge act to carry cool, less mineralized water. Though initially, these effects were thought to be in shallow depths, an indication in OW-901 which is a deeper at 2200 m compared to 1600 m of OW-23 well that proves otherwise. This is, however, to be proved later as much deeper wells have been sited.

Middle–late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstätte from the Central Kenya Rift (East Africa)

AbstractThe Miocene epoch was a time of major change in the East African Rift System (EARS) as forest habitats were transformed into grasslands and hominids appeared in the landscape. Here we provide new sedimentological and palynological data on the middle–upper Miocene Ngorora Formation (Tugen Hills, Central Kenya Rift, EARS), together with clay mineral characterizations, mammal finds and a description of the Ngorora fish Lagerstätte. Furthermore, we introduce a revised age ofc. 13.3 Ma for the onset of the Ngorora Formation. The older part of the Ngorora Formation (c. 13.3–12 Ma) records low-energy settings of lakes, floodplains and palaeosols, and evidence of analcime indicates that lakes were alkaline. The palynomorph spectrum consists of tree pollen (Juniperus, Podocarpus), Euphorbiaceae pollen (Acalypha, Croton) and herbaceous pollen of Poaceae and Asteraceae, suggestive of wooded grasslands or grassy woodlands. Alkaline lakes, floodplains and palaeosols continue upsection (c. 12–9 Ma), but environmental fluctuations become more dynamic. Paucity of palynomorphs and the presence of an equid may point to progressively drier conditions. A total of about 500 articulated fish fossils were recovered from distinctive layers of almost all sections studied and represent different lineages of the Haplotilapiines (Pseudocrenilabrinae, Cichlidae). Some of the fish kills may be attributable to rapid water acidification and/or asphyxiation by episodic ash falls. Repeated instances of abrupt change in water depth in many sections are more likely to be due to synsedimentary tectonic activity of the Central Kenya Rift than to climatic variation. Overall, the preservation of the Ngorora fish Lagerstätte resulted from the interplay of tectonics, formation of alkaline lakes and explosive volcanism. As records of grasslands that pre-date late Miocene time are rare, our finding of middle Miocene (12–13 Ma) grassy savannah in the Central Kenya Rift is also relevant to models of human evolution in East Africa.

Cenozoic extension in the Kenya Rift from low‐temperature thermochronology: Links to diachronous spatiotemporal evolution of rifting in East Africa

AbstractThe cooling history of rift shoulders and the subsidence history of rift basins are cornerstones for reconstructing the morphotectonic evolution of extensional geodynamic provinces, assessing their role in paleoenvironmental changes and evaluating the resource potential of their basin fills. Our apatite fission track and zircon (U‐Th)/He data from the Samburu Hills and the Elgeyo Escarpment in the northern and central sectors of the Kenya Rift indicate a broadly consistent thermal evolution of both regions. Results of thermal modeling support a three‐phased thermal history since the early Paleocene. The first phase (~65–50 Ma) was characterized by rapid cooling of the rift shoulders and may be coeval with faulting and sedimentation in the Anza Rift basin, now located in the subsurface of the Turkana depression and areas to the east in northern Kenya. In the second phase, very slow cooling or slight reheating occurred between ~45 and 15 Ma as a result of either stable surface conditions, very slow exhumation, or subsidence. The third phase comprised renewed rapid cooling starting at ~15 Ma. This final cooling represents the most recent stage of rifting, which followed widespread flood‐phonolite emplacement and has shaped the present‐day landscape through rift shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East African Rift System, extension appears to be diachronous, spatially disparate, and partly overlapping, likely driven by interactions between mantle‐driven processes and crustal heterogeneities, rather than the previously suggested north–south migrating influence of a mantle plume.

Influence of regional tectonics and pre-existing structures on the formation of elliptical calderas in the Kenyan Rift

Abstract Calderas are formed by the collapse of large magma reservoirs and are commonly elliptical in map view. The orientation of elliptical calderas is often used as an indicator of the local stress regime; but, in some rift settings, pre-existing structural trends may also influence the orientation. We investigated whether either of these two mechanisms controls the orientation of calderas in the Kenyan Rift. Satellite-based mapping was used to identify the rift border faults, intra-rift faults and orientation of the calderas to measure the stress orientations and pre-existing structural trends and to determine the extensional regime at each volcano. We found that extension in northern Kenya is orthogonal, whereas that in southern Kenya is oblique. Elliptical calderas in northern Kenya are orientated NW–SE, aligned with pre-existing structures and perpendicular to recent rift faults. In southern Kenya, the calderas are aligned NE–SW and lie oblique to recent rift faults, but are aligned with pre-existing structures. We conclude that, in oblique continental rifts, pre-existing structures control the development of elongated magma reservoirs. Our results highlight the structural control of magmatism at different crustal levels, where pre-existing structures control the storage and orientation of deeper magma reservoirs and the local stress regime controls intra-rift faulting and shallow magmatism. Supplementary material: Details of the Standard Deviation Ellipse function and statistical methods are available at http://www.geolsoc.org.uk/SUP18849 .

Animal movements in the Kenya Rift and evidence for the earliest ambush hunting by hominins

Animal movements in the Kenya Rift Valley today are influenced by a combination of topography and trace nutrient distribution. These patterns would have been the same in the past when hominins inhabited the area. We use this approach to create a landscape reconstruction of Olorgesailie, a key site in the East African Rift with abundant evidence of large-mammal butchery between ~1.2 and ~0.5 Ma BP. The site location in relation to limited animal routes through the area show that hominins were aware of animal movements and used the location for ambush hunting during the Lower to Middle Pleistocene. These features explain the importance of Olorgesailie as a preferred location of repeated hominin activity through multiple changes in climate and local environmental conditions, and provide insights into the cognitive and hunting abilities of Homo erectus while indicating that their activities at the site were aimed at hunting, rather than scavenging.

Protein-Energy Malnutrition Still Exists in Kenya in the Twenty-First Century

Malnutrition among preschool children is an indicator of underdevelopment and is high in many developing communities. Malnutrition affects performance of children in the later adulthood life. Though determinants of malnutrition vary from region to region, the underlying cause for malnutrition is poverty. A cross-sectional study was conducted to identify prevalence and determinants of nutrition status of preschool children in the Rift Valley in Kenya. Mothers of these children were respondents who provided information on selected variables. Nutrition status was measured by weight-for-age, height-for-age and weight-for-height. General prevalence of malnutrition was still high in this population, with more males than females having poor nutrition status as measured by weight-for-age, height-for-age and weight-for-height. Risk factors for malnutrition in this population were age, sex, education level of the head of household, time taken by women on other household chores (especially collecting fuel wood), number of pregnancies a mother has had, income of the head of household and income from cash crop farming. Education level of household heads could improve nutrition through appreciating the role of good nutrition for child development and availing resources at the household level for adequate nutrition and health. The major determinants of malnutrition included time spent on household chores (30%), income (12%) and gender (10%).

Varying styles of magmatic strain accommodation across the East African Rift

AbstractObservations of active dike intrusions provide present day snapshots of the magmatic contribution to continental rifting. However, unravelling the contributions of upper crustal dikes over the timescale of continental rift evolution is a significant challenge. To address this issue, we analyzed the morphologies and alignments of >1500 volcanic cones to infer the distribution and trends of upper crustal dikes in various rift basins across the East African Rift (EAR). Cone lineament data reveal along‐axis variations in the distribution and geometries of dike intrusions as a result of changing tectonomagmatic conditions. In younger (<10 Ma) basins of the North Tanzanian Divergence, dikes are largely restricted to zones of rift‐oblique faulting between major rift segments, referred to here as transfer zones. Cone lineament trends are highly variable, resulting from the interplay between (1) the regional stress field, (2) local magma‐induced stress fields, and (3) stress rotations related to mechanical interactions between rift segments. We find similar cone lineament trends in transfer zones in the western branch of the EAR, such as the Virunga Province, Democratic Republic of the Congo. The distributions and orientations of upper crustal dikes in the eastern branch of the EAR vary during continental rift evolution. In early‐stage rifts (<10 Ma), upper crustal dikes play a limited role in accommodating extension, as they are confined to areas in and around transfer zones. In evolved rift basins (>10 Ma) in Ethiopia and the Kenya Rift, rift‐parallel dikes accommodate upper crustal extension along the full length of the basin.

English

Survey on the Utilization of Weather Information and Products for Selected Districts in Kenya

The introduced species fishery of Lake Naivasha, Kenya: ecological impact vs socio‐economic benefits

AbstractLake Naivasha is a shallow, freshwater lake in the eastern Rift Valley of Kenya. Its fish community now comprises only introduced species. Oreochromis spirulus niger was stocked in 1925 as a forage fish for the largemouth bass, Micropterus salmoides, introduced in 1929 for sport fishing. Further introductions of tilapiines followed for commercial exploitation. A gillnet fishery opened in 1959, and the annual species catch composition to 2000 was dominated by Oreochromis leucostictus. Following their accidental introduction, carp Cyprinus carpio appeared in catches in 2002; by 2010, it comprised >99% of landings by weight. Carp now provides a sustainable fishery in a lake heavily impacted by anthropogenic stressors, including water abstraction and nutrient enrichment. Oreochromis niloticus was reintroduced in 2011 to reinvigorate tilapia stocks following the collapse of its stocks in the 1990s and early 2000s, and the African catfish Clarias gariepinus is now captured in small but increasing numbers. The current status of the fishery, especially the predominance of carp, presents major management challenges; these are addressed by stakeholder engagement and co‐management. The introductions have artificially created a commercial fishery that provides substantial societal benefits in a semi‐arid region of a developing country with high poverty levels.

Episodes of environmental stability versus instability in Late Cenozoic lake records of Eastern Africa

Episodes of environmental stability and instability may be equally important for African hominin speciation, dispersal, and cultural innovation. Three examples of a change from stable to unstable environmental conditions are presented on three different time scales: (1) the Mid Holocene (MH) wet–dry transition in the Chew Bahir basin (Southern Ethiopian Rift; between 11 ka and 4 ka), (2) the MIS 5–4 transition in the Naivasha basin (Central Kenya Rift; between 160 ka and 50 ka), and (3) the Early Mid Pleistocene Transition (EMPT) in the Olorgesailie basin (Southern Kenya Rift; between 1.25 Ma and 0.4 Ma). A probabilistic age modeling technique is used to determine the timing of these transitions, taking into account possible abrupt changes in the sedimentation rate including episodes of no deposition (hiatuses). Interestingly, the stable-unstable conditions identified in the three records are always associated with an orbitally-induced decrease of insolation: the descending portion of the 800 kyr cycle during the EMPT, declining eccentricity after the 115 ka maximum at the MIS 5–4 transition, and after ∼10 ka. This observation contributes to an evidence-based discussion of the possible mechanisms causing the switching between environmental stability and instability in Eastern Africa at three different orbital time scales (10,000 to 1,000,000 years) during the Cenozoic. This in turn may lead to great insights into the environmental changes occurring at the same time as hominin speciation, brain expansion, dispersal out of Africa, and cultural innovations and may provide key evidence to build new hypotheses regarding the causes of early human evolution.

Effect of vegetation cover on millennial-scale landscape denudation rates in East Africa

The mechanisms by which climate and vegetation affect erosion rates over various time scales lie at the heart of understanding landscape response to climate change. Plot-scale field experiments show that increased vegetation cover slows erosion, implying that faster erosion should occur under low to moderate vegetation cover. However, demonstrating this concept over long time scales and across landscapes has proven to be difficult, especially in settings complicated by tectonic forcing and variable slopes. We investigate this problem by measuring cosmogenic 10 Be-derived catchment-mean denudation rates across a range of climate zones and hillslope gradients in the Kenya Rift, and by comparing our results with those published from the Rwenzori Mountains of Uganda. We find that denudation rates from sparsely vegetated parts of the Kenya Rift are up to 0.13 mm/yr, while those from humid and more densely vegetated parts of the Kenya Rift flanks and the Rwenzori Mountains reach a maximum of 0.08 mm/yr, despite higher median hillslope gradients. While differences in lithology and recent land-use changes likely affect the denudation rates and vegetation cover values in some of our studied catchments, hillslope gradient and vegetation cover appear to explain most of the variation in denudation rates across the study area. Our results support the idea that changing vegetation cover can contribute to complex erosional responses to climate or land-use change and that vegetation cover can play an important role in determining the steady-state slopes of mountain belts through its stabilizing effects on the land surface.

†Kenyaichthyidae fam. nov. and †Kenyaichthys gen. nov. - First Record of a Fossil Aplocheiloid Killifish (Teleostei, Cyprinodontiformes).

The extant Cyprinodontiformes (killifishes) with their two suborders Cyprinodontoidei and Aplocheiloidei represent a diverse and well-studied group of fishes. However, their fossil record is comparatively sparse and has so far yielded members of the Cyprinodontoidei only. Here we report on cyprinodontiform fossils from the upper Miocene Lukeino Formation in the Tugen Hills of the Central Rift Valley of Kenya, which represent the first fossil record of an aplocheiloid killifish. A total of 169 specimens - mostly extraordinarily well preserved - and a sample of ten extant cyprinodontiform species were studied on the basis of morphometrics, meristics and osteology. A phylogenetic analysis using PAUP was also conducted for the fossils. Both the osteological data and the phylogenetic analysis provide strong evidence for the assignment of the fossils to the Aplocheiloidei, and justify the definition of the new family †Kenyaichthyidae, the new genus †Kenyaichthys and the new species †K. kipkechi sp. nov. The phylogenetic analysis unexpectedly places †Kenyaichthys gen. nov. in a sister relationship to the Rivulidae (a purely Neotropical group), a probable explanation might be lack of available synapomorphies for the Rivulidae, Nothobranchiidae and Aplocheilidae. The specimens of †K. kipkechi sp. nov. show several polymorphic characters and large overlap in meristic traits, which justifies their interpretation as a species flock in statu nascendi. Patterns of variation in neural and haemal spine dimensions in the caudal vertebrae of †Kenyaichthys gen. nov. and the extant species studied indicate that some previously suggested synapomorphies of the Cyprinodontoidei and Aplocheiloidei need to be revised.

Streptomyces alkaliphilus sp. nov., isolated from sediments of Lake Elmenteita in the Kenyan Rift Valley.

A novel strain, designated No. 7(T), was isolated from a sediment sample collected from the alkaline, saline Lake Elmenteita located in the Kenyan Rift Valley. The optimal growth for the strain was found to be at temperature 30-35 °C, at pH 8.0-12.0 in the presence of 7.0-10.0 % (w/v) NaCl. The strain was observed to form a light green beige abundant aerial mycelium on Horikoshi 1 agar and to have morphological and chemotaxonomic characteristics typical of members of the genus Streptomyces. The peptidoglycan was found to contain LL-diaminopimelic acid as the diamino acid, with no diagnostic sugars identified. The predominant menaquinone was identified as MK-9(H6). The main polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and an unknown phospholipid. Cellular fatty acids were found to consist of saturated branched-chain acids with iso-C(15:0), anteiso-C(15:0), iso-C(16:0) and anteiso-C(17:0) acids predominating. The type strain had a genomic DNA G+C content of 72.8 mol% and formed a distinct phyletic line within the genus Streptomyces. Based on the chemotaxonomic results, 16S rRNA gene sequence analysis and the low DNA-DNA hybridization value with the type strain of Streptomyces calidiresistens, it is proposed that strain No. 7(T) (= DSM 42118 = CECT 8549) represents a novel species, Streptomyces alkaliphilus. The INSDC accession number for the 16S rRNA gene sequence of strain No. 7(T) is KF976730.

Molecular evolution of a central region containing B cell epitopes in the gene encoding the p67 sporozoite antigen within a field population of Theileria parva.

Protective immunity induced by the infective sporozoite stage of Theileria parva indicates a potential role for antibodies directed against conserved serologically reactive regions of the major sporozoite surface antigen p67 in vaccination to control the parasite. We have examined the allelic variation and determined the extent of B cell epitope polymorphism of the gene encoding p67 among field isolates originating from cattle exposed to infected ticks in the Marula area of the rift valley in central Kenya where the African cape buffalo (Syncerus caffer) and cattle co-graze. In the first of two closely juxtaposed epitope sequences in the central region of the p67 protein, an in-frame deletion of a seven-amino acid segment results in a truncation that was observed in parasites derived from cattle that co-grazed with buffalo. In contrast, the variation in the second epitope was primarily due to nonsynonymous substitutions, resulting in relatively low overall amino acid conservation in this segment of the protein. We also observed polymorphism in the region of the protein adjacent to the two defined epitopes, but this was not sufficient to provide statistically significant evidence for positive selection. The data indicates that B cell epitopes previously identified within the p67 gene are polymorphic within the Marula field isolates. Given the complete sequence identity of the p67 gene in all previously characterized T. parva isolates that are transmissible between cattle by ticks, the diversity observed in p67 from the Marula isolates in combination with the clinical reaction of the infected cattle is consistent with them originating from ticks that had acquired T. parva from buffalo.

Volcanic volumes associated with the Kenya Rift: recognition and correction of preservation biases

Abstract New eruptive volume estimates have been calculated for the Kenyan segment of the East African Rift. Since the initial publications of volume estimates for the Kenyan Rift, numerous age dates have been obtained for the region allowing for temporal analysis of eruptive volumes. Additionally, more recent available datasets allow for the independent testing of map-derived volumes. Newly calculated volumes from available seismic data indicate a total volume of c. 310 000 km 3 , which is significantly more than map-derived volumes found here or published previously. It is suggested that the map-based estimates are likely affected by biases against recognizing small volume events in the older record. Such events have been, however, the main driver of erupted volume over the last 5 Ma. A simple ratio-adjustment technique was developed to counter these biases and results in convergence of the volume estimates from the two independent datasets examined. Supplementary material: Volume calculations and classifications are available at http://www.geolsoc.org.uk/SUP18800 .

Evaluation of In Vivo Toxicity of Dichloromethane: Methanolic Leaf Extracts of Prosopis juliflora in Female Wistar Albino Rats

Prosopis juliflora (Mathenge) is an exotic, evergreen leguminous lant found in the dry Coastal, Rift Valley and Northern parts of Kenya. It is tolerant to extreme environmental conditions, rated among top 100 most invasive species worldwide. The species leaf extracts is used in folk cure to various ailments and have promising pharmacological properties however; information on their toxicity in animals and human is insufficient. The study assessed phytochemical composition of P. juliflora leaf extracts, effects on body weights, organ weights, hematological parameters, liver function markers and histopathology in major organs of Wistar albino rats. Acute toxicity test was carried out at 2000 mg/kg body weight followed by a 28 days sub chronic toxicity study at 100, 350 and 1000 mg/kg body weight extracts dosages. The control animals were administered with normal saline. Animals were monitored for physical and behavioral changes including death. They were fasted overnight on 28th day and sacrificed on anesthesia on 29th day. Blood was collected by cardiac puncture. Hematological and liver functions tests were done. Tissue sample of selected organs were processed for histopathology. Data from control and treated animals groups were analyzed by ANOVA and Dunnett’s test. Phytochemicals confirmed included alkaloids, flavonoids, phenols, tannins, terpenoids and saponnins but no cardiac glycosides. Median lethal dose was estimated at above 2000 mg/kg body weight. Dose related transient toxicity symptoms included wheezing, decreased activity, and pilo erection. No significant toxicity effects on hematological parameters were noticed except in mean platelets volume. Similarly, no significant adverse effects occurred in liver function tests except at 1000 mg/kg body weight dosage. No significant adverse changes in plasma proteins, body weights and absolute organ weights were observed except in kidneys and spleen. Histological examination of sample tissues showed mild effects in spleen and kidneys but no adverse pathology in other organ tissues.

Violent place-making: How Kenya's post-election violence transforms a workers' settlement at Lake Naivasha

Violent events significantly influence the identity of places. Post-conflict areas evoke specific meanings and emotions, and the narratives of violent events have profound effects on the individual and collective interpretations of the venues of violence. This paper addresses the interdependent relationship between violence and place, considering the structural and multi-scalar conditions of a relational and discursive making of places. By linking them with an empirically grounded analysis of the materialisation of violence, we follow Gearóid Ó Tuathail's (2010) call for a more grounded study of place-specific causes for violent conflict. We focus on an empirical example – the post-election violence in Kenya 2007/08 – and look into one of its venues, a poor and heterogeneous workers' settlement at Lake Naivasha in Kenya's Rift Valley. Considering the specific socio-political setting in Kenya, we first examine the factors that explain why the violence broke out at that place in particular. We combine an exploration of the structural conditions that determined the violence, and which still regulate social life at present, with a presentation of the individual accounts of people directly or indirectly involved in the violence in Naivasha. We then investigate how the experience of violence has influenced the imaginations of the place, and whether these localised imprints of violence in Naivasha continue to regulate social and spatial (re)organisation after the events themselves. The study reveals that politically instigated societal divides continue to exist, and that memories of the violence induce intensified processes of segregation in the surveyed settlement during times of political uncertainty.

Ethnobotanical Survey of Selected Medicinal Plants Used By the Ogiek Communities in Kenya against Microbial Infections

The role played by traditional medicine based on the use of medicinal plants for health purposes is significant both in growing and developed economies. Although the use of medicinal plants is already considerably documented across the globe, their increased use has only been noted in the recent past. In the African context, however, the dosage of such plants together with their pharmacological observations is yet to be well documented. In this paper, an attempt is made at documenting such knowledge with respect to traditional medicine among the Ogiek for future generations and to serve as a repository for further scientific studies on traditional medicine. The study was carried out involving the Ogiek community who live in the Mau forests in the central Rift Valley of Kenya where they still depend largely on hunting and gathering. A total of 20 traditional healers aged between 50 and 70 years were interviewed by use of a questionnaire. It was evident from the 32 plant families collected that the majority are used in treating malaria (21.88%), pneumonia (21.88%), stomachache (21.88%), and tonic related diseases (21.88%). Other remedies used fewer plant families. It is therefore recommended that follow up studies pertaining to these plants be carried out for validation of their efficacy by in vitro and in vivo studies. It is also recommended that further studies on hygienic administration of these drugs be carried out. Conservation of the endangered plant species involving conventional methods should be encouraged. There should be clear policies regarding traditional medical practices in Kenya and elsewhere in East Africa.

Belliella kenyensis sp. nov., isolated from an alkaline lake.

A red-pigmented, Gram-reaction-negative, aerobic bacterial strain, designated No.164(T), was isolated from sediment sample from the alkaline Lake Elmenteita located in the Kenyan Rift Valley. Results of 16S rRNA gene sequence analysis indicated that the isolate represented a member of the genus Belliella, with the highest sequence similarity (97 %) to Belliella pelovolcani DSM 46698(T). Optimal growth temperature was 30-35 °C, at pH 7.0-12.0 in the presence of 0-4 % (w/v) NaCl. Flexirubins were absent. The respiratory menaquinone (MK-7), predominant cellular fatty acids (iso-C15 : 0, anteiso-C15 : 0 and a mixture of C16 : 1ω7c and/or iso-C15 : 0 2-OH) and DNA G+C content (38.1 mol%) of strain No.164(T) were consistent with those of other members of the genus Belliella. The polar lipids consisted of phosphatidylethanolamine, eight unspecified lipids and one unspecified phospholipid. Several phenotypic characteristics can be used to differentiate this isolate from those of other species of the genus Belliella. The results of polyphasic analyses presented in this study indicated that this isolate should be classified as representing a novel species of the genus Belliella. The name Belliella kenyensis sp. nov. is therefore proposed; the type strain is strain No.164(T) ( = DSM 46651(T) = CECT 8551(T)).

English

The dairy industry in Kenya is an important source of livelihood among the smallholder farmers who supply over 70% of the total milk. However, there is a growing concern on rising costs of milk production among farmers. The study assessed profit efficiency of smallholder dairying in the Rift Valley and Central Provinces of Kenya using stochastic frontier analysis for estimating farm level profit efficiency and identifying the specific determinants of efficiency. The results showed that the farmers are fairly profit efficient with an average of about 68%. Cost of fodder produced on farm significantly improved profit efficiency among farmers. However dairy profit efficiency can be enhanced if fodder production is embraced, as well as other supplemental feed technologies that are commensurate with local conditions. Institutional policy reforms on smallholder dairying will help protect the industry and its sustainability for smallholders. Key words: Dairy, profit efficiency, stochastic frontier, smallholder farmer.