Steve Omondi Oduor

Phytoplankton community relationship to environmental variables in three Kenyan Rift Valley saline-alkaline lakes

Temporal changes in total alkalinity, ionic composition and nutrient concentrations were studied in the saline, alkaline endorheic Kenyan Rift Valley Lakes Bogoria, Nakuru and Elmentaita to understand the association of these variables with phytoplankton community structure. In total, 24 taxa were found, with L. Bogoria having the fewest species. Although the cyanobacterium Arthrospira fusiformis dominated the phytoplankton biomass, especially in L. Bogoria, other groups came into play especially during high water levels in L. Nakuru and L. Elmentaita. Cluster analysis based on species biomass resulted in four groups, characterised by 13 indicator taxa. Most of the variation in these groups appeared to be associated with hydrological stability and perhaps biological factors rather than water chemistry, which only explained 44% of the variance in taxa composition on the first four axes derived from redundancy analysis. Species numbers decreased with elevated conductivity and water temperature. Synechocystis sp. occurrence coincided with phosphorus, water temperature and conductivity increase, whereas the distributions of Arthrospira fusiformis and Arthrospira platensis were mainly influenced by both light attenuation and elevated nitrate concentrations. Increases in silica and ammonium and declines in conductivity, total phosphorus and water temperature enhanced diatom abundances. Not only do the results of the present study indicate the unexpectedly high variability of phytoplankton community composition and water chemistry in these three alkaline tropical lakes, but also the data assist our understanding of the factors influencing flamingo populations on these lakes, which are significant conservation reserves and tourist attractions.

Temporal trends of ion contents and nutrients in three Kenyan Rift Valley saline-alkaline lakes and their influence on phytoplankton biomass

This study, carried out between November 2003 and February 2005, aimed to investigate the temporal trends of conductivity, ions, nutrient concentrations and phytoplankton biomass expressed as chlorophyll a in the Kenyan Rift Valley saline-alkaline lakes namely Nakuru, Bogoria and Elmentaita. The influence of environmental variables on phytoplankton biomass has always been of much interest in understanding phytoplankton dynamics. Being shallow and endorheic, these lakes’ chemical, physical and biological properties were found to be strongly influenced by the hydrologic cycle within their catchment area. The lakes are characterised by high nutrient concentrations but with low Ntot: Ptot ratios. Significant differences between surface and near-bottom samples for water temperature, chlorophyll a and some nutrients were found in these lakes. A stepwise Discriminant Analysis with lakes as defined groups resulted in a significant model with SRP, nitrate-N, conductivity and light supply being of major importance. A significant correlation between specific conductivity and total alkalinity (Kendalls τ = 0.85, n = 132) was calculated. While L. Bogoria showed the least temporal variation in conductivity-(65-73 mS cm−1), larger variations were observed in L. Elmentaita (21-77 mS cm−1). Na+ and K+ form the main cations with Cl−, HCO3 − and CO3 2 being the major anions in all the three lakes. Flouride was detected in high quantities (mean values L. Bogoria 72 meq 1−1, L. Nakuru 17 meq 1−1 and L. Elmentaita 71 meq 1−1). A PCA followed by multiple regression analysis with chlorophyll a as dependent variable showed that nitrate-N, conductivity, phosphorus and light supply were the key variables influencing algal biomass in these lakes.

A detailed time series assessment of the diet of Lesser Flamingos: further explanation for their itinerant behaviour

We hypothesised that changes in nutritional composition and quality of the pelagic phytoplankton community influence the occurrence of Lesser Flamingo populations in two Kenyan saline–alkaline lakes, Nakuru and Bogoria. This was achieved by carrying out a detailed time series assessment of the phytoplankton community composition and nutritional components (carbohydrates, crude protein and lipids) from July 2008 to October 2009 on a weekly basis for each lake. Lesser Flamingos were estimated visually from the lake shore of the sampling sites. In Lake Nakuru, Lesser Flamingos had a significant positive relationship with lipids and Arthrospira biomass but a negative relationship with small cyanoprokaryotes. For Lake Bogoria, no significant differences were observed as the Arthrospira was available throughout the sampling period though the flamingo numbers still fluctuated. We concluded that the nutritional composition and quality of the phytoplankton community influence the temporal and spatial abundance of Lesser Flamingos although other factors such as the prevailing environmental conditions may take precedence.

Ecomorphological variability of Arthrospira fusiformis (Cyanoprokaryota) in African soda lakes

The filamentous spirally coiled cyanoprokaryote Arthrospira fusiformis is found in extremely high densities in tropical soda lakes acting as driving force of the food web. We studied pronounced temporal morphological changes of Arthrospira in Kenyan soda lakes, Nakuru and Bogoria, and identified underlying key factors. Cell (diameter and height) and filament (height of coil, coil diameter, and number) dimensions were measured from weekly samples collected over a period of 16 months. In both lakes, medium‐sized cells and large, widely coiled filaments prevailed most. Percentage of large, widely coiled filaments was promoted by elevated levels of soluble reactive phosphorus, wind speed, temperature and conductivity and the opposite for small filaments. Large, narrow‐coiled filaments were associated with an increase in mainly Arthrospira‐grazing zooplankton and cyanophage infections. Widely coiled spirals were promoted by increased turbulences. Based on fluorescence measurements, we found widely coiled filaments representing high vitality. From this study we were able to demonstrate for the first time morphological patterns of Arthrospira in nature. Arthrospira morphotypes are suitable for indicating the biological status in soda lakes as they are subjective and therefore reflective of what is happening in its habitat. Additionally, this outcome might be also of interest for commercial ′Spirulina′ farms in enhancing high‐quality production.

Sudden flamingo deaths in Kenyan Rift Valley lakes

The East African Rift Valley Lakes Bogoria and Nakuru sometimes host around 75% of the world population of lesser flamingos Phoeniconaias minor. In this area, mysterious flamingo die-offs have occupied researchers for four decades. Recently, cyanobacterial toxins came into the fore as a possible explanation for mass mortalities because the main food source of lesser flamingos is the cyanobacterium Arthrospira fusiformis. We took weekly samples from July 2008 to November 2009 from Lakes Nakuru and Bogoria and analyzed them by high performance liquid chromatography for microcystins. Monthly, samples were cross-checked using protein phosphatase inhibition assays with lower detection limits and additionally screened for polar toxins. During our study period, three flamingo die-offs occurred at L. Bogoria and we were able to analyze tissues of 20 carcasses collected at the shoreline. No cyanotoxins were detected either in plankton samples or in flamingo tissues. Accordingly, other reasons such as food composition or bird diseases played a key role in the observed flamingo die-offs.

Bacteria with industrial potential from Lake Nakuru, Kenya

Bacteria with industrial potential in Lake Nakuru were isolated and characterised over six months in 2010. The enzymatic activities of 30 isolates towards various macromolecules were investigated by testing their ability to degrade starch, cellulose, casein and lipid substrates. Fifteen isolates exhibited an ability to degrade macromolecules, with some able to hydrolyse two or more macromolecules, including 8 degrading starch, 6 proteins, 5 cellulose and 5 lipids. The genomic DNA of the LNS08, LNC09, LNC11 and LNC06 isolates, which showed the highest potential to degrade macromolecules, were analysed and their identity closely related to the known bacteria Nesterenkonia lacusekhoensis (LNS08), Bacillus agaradhaerens (LNC06) and Bacillus sp. accession no. AB043860.1 (LNC09 and LNC11). Nesterenkonia lacusekhoensis can be used as a lipid degrader, B. agaradhaerens can be used in the degradation of proteins and Bacillus sp. accession no. AB043860.1 has potential for the production of sugars from starch and cellulose. Lake Nakuru is thus a rich source of alkaliphilic bacteria that can be used in industry.

Simulation of constructed wetland treatment in wastewater polishing using PREWet model

Abstract To minimize the negative impact of wastewater when disposed into water bodies, proper treatment before its disposal is vital. Different wastewater treatment scenarios can be tested using predictive and analytical models. A screening-level, analytical model known as the PREWet model was calibrated and validated. The model assumes steady-state conditions and one-dimensional longitudinally varying concentration. The model was calibrated on a pilot-scale wetland and used to predict treatment through a constructed wetland. Performance of the calibrated model was statistically evaluated for its predictive ability by simulating the wastewater treatment through a constructed wetland. Different constituents were modelled which include: total phosphorous (TP), total coliform (TC), biochemical oxygen demand (BOD) and total suspended solids (TSS). The model coefficients were estimated using field and laboratory studies. Sensitivity analysis indicated that detention time of wastewater in constructed wetland w...

Soda Lakes of the East African Rift System: The Past, the Present and the Future

The soda lakes of the East African Rift System are unique water bodies whose formation, topography and locational settings have conferred upon them endorheic basin features with arid to semiarid climatic conditions. These features, together with the geological characteristics of their catchments, have favoured the development of saline alkaline properties that make them peculiar and important from a number of perspectives. Most of these lakes have extreme environmental characteristics shown by high ionic contents of their water, high temperature conditions and eutrophic states. This enables them to support growth of few tolerant species of extremophilic Cyanobacteria and other microbes. Some of these lakes such as the Lakes Nakuru and Bogoria are highly productive, yielding some of the highest primary production rates in the world. This high productivity supports hundreds of thousands to, sometimes, millions of Lesser Flamingos in these two lakes. These lakes, however, are highly vulnerable to climate changes and environmental degradation associated with human activities due to their unique environmental conditions. This paper explores some of these unique features, the threats to their existence, the challenges to their conservation and potential strategies to protect them.

Trophic state and nutrient limitation in Lake Baringo, Kenya

The trophic state of Lake Baringo and factors that could be limiting the development of algal biomass in it were investigated during one wet/dry hydrological cycle in 2014–2015. Water samples were analysed for dissolved inorganic nutrients, including , and , total phosphorus and Chlorophyll a. Light attenuation was estimated using Secchi depth. The trophic state was determined using Carlson trophic state indices (CTSI). Deviations in CTSI, nutrient ratios and ambient nutrient concentrations were used to identify factors limiting phytoplankton growth. The mean values measured for Secchi depth, nitrate, total phosphorus and Chlorophyll a showed significant seasonal variation (p < 0.05). Based on the Carlson trophic state index, the results show that Lake Baringo is eutrophic. However, the lake is also experiencing phosphorus limitation and poor light penetration, because of high turbidity, which is more pronounced during the wet season.