Browsing by Author "Muthuri, Francis M."

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    The Physico-chemical Conditions of Turkwel Gorge Reservoir, a New Man Made Lake in Northern Kenya
    (1999) Kotut, Kiplagat; Njuguna, Stephen; Muthuri, Francis M.; Krienitz, L.
    Variations in some physical, chemical, and nutrient conditions were investigated at Turkwel Gorge Reservoir and its inflowing river, Suam between 1994 and 1995. Seasonal changes in inflow volume had the greatest impact on the reservoir and river conditions investigated. A wide fluctuation in inflow volume combined with a regulated outflow independent of season resulted in a draw down of over 10 m in each year. Flood inflows during the wet season resulted in the lowest values of Secchi depth (range, 0.09-2.16 m), electrical conductivity (EC, range = 140-200 mS cm -1) and total alkalinity (TA, range = 75-111 mg 1-1) while the highest values were measured during the dry season. A functional relation between EC and TA (TA = 0.529 mg p1 EC: R ~ = 0.876) suggests a predominance of carbonates among the anions. Vertical profiles of temperature and dissolved oxygen (DO) revealed that the reservoir is monomictic with a wide variation in the depth of the daily mixed layer. High values of pH (range = 6.7-8.9) and DO (range = 4.9-9.2 mg V) were associated with periods of peak phytoplankton photosynthesis while the lowest values followed reservoir mixing. Peak total nitrogen (TN, range = 119-526 pg ki) and total phosphorus (TP, range = 8.9-71.6 pg 1-1) levels during the wet season resulted from increased river loading. Values of dissolved reactive silica (DRS, range = 0.41-9.77 mg kl) showed a wet season decline which was related to diatom depletion during the wet season. Annual reservoir areal loading rates of 27.38, 10.90 and 408.5 mg m -2 were computed for TN, TP and DRS respectively based on estimates of inflowing fiver loads in 1994. At the inflowing river Suam, low levels of EC (range =107-210 pS cm 1) and TA (range = 62-125 mg 1 -I) occurred during the wet season while the highest levels occurred shortly before the river dried up. The first flood water at the resumption of river inflow in March was characterized by very low levels of DO (range = 1.8-8.2 mg 11) and high levels of TN (range = 205-3354 pg 1 <) and TP (102-1259 pg 1-1). River pH (6.9-7.7) and DRS (range = 9.01-19.93 mg 1 -l) varied irregularly throughout the year.
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    Temporal changes in phytoplankton structure and composition at the Turkwel Gorge Reservoir, Kenya
    (Kluwer Academic Publishers, 1998) Kotut, Kiplagat; Krienitz, L.; Muthuri, Francis M.
    Temporal changes in phytoplankton chlorophyll a, composition, diversity, biomass (density and fresh weight) and primary production were investigated at the Turkwel Gorge Reservoir (Kenya) over a two year period (1994 and 1995). The phytoplankton properties investigated revealed a seasonal pattern that was very distinct in 1994 and muted in 1995. The wet season was characterized by higher levels of chlorophyll a, biomass and primary production and a lower diversity. A prominent seasonality in 1994 was found to be the result of a higher river inflow volume as compared to 1995. Chlorophyll a changes showed some positive correlation to changes in total nitrogen and total phosphorus. Diversity changes were inversely correlated to changes in total counts (R = −0.84 and −0.96 for 1994 and 1995 respectively). Individual species density changes varied from a distinct seasonal pattern to a nearly uniform density. While the diatom Achnanthes dominated the wet season in 1994, coccoid blue green algae were dominant during most of 1995. Throughout the study period, most biomass was due to the diatoms but with a lower percentage of total biomass in 1995 (40%) as compared to 1994 (88%). The wet season biomass in each year was dominated by the diatoms. Dominance of the intervening period changed irregularly between diatoms, dinoflagellates, green algae and blue green algae. The range of variation in chlorophyll a, total biomass and primary production were; 4.9 to 36.8 µg l-1, 440.14 to 11172.70 mg m-3 and 1.85 to 9.67 g O2 m-2 d-1 in 1994 and 4.9 to 11.5 µg l-1, 486.46 to 1351.39 mg l-1 and 3.08 to 5.41 g O2 m-2 d-1 in 1995 in the same order.