| dc.description.abstract | The sources of water for cities include Rivers and streams, lakes and reservoirs. The
capacities of these sources to meet these demands are however challenged by sedimentation and
enrichment of lakes and reservoirs by plant nutrients. There are various environmental impacts of
dam construction on River channels. This has necessitated studies on the limnology and
management of lakes and reservoirs especially Thika dam.
During this study, various samples were collected to measure the vanous attributes of
physico - chemical parameters, aquatic plant nutrients, chlorophyll a, zooplankton and fish. The
samples were collected from the influent Rivers, the transitional zone and open water zone, which
are the major zones of a reservoir. They then were analysed using various standard methods to
describe the limnology of Thika reservoir.
The results revealed that Thika dam is a cold-water reservoir that exhibits thermal, gaseous
and chemical stratification, with longitudinal and vertical patterns of distribution of physicochemical
and biological properties. The water is well oxygenated (surface value of 8.71 ± 0.29
mg/I.) with even higher values during the wet cold periods.
The hypolimnion is cold and anoxic. The influent nutrient levels are low but the transitional zones have magnified level of both nitrogen and phosphorus, which are attenuated with depth and
towards the dam wall. Chlorophyll a levels are high near the dam. wall (10.24 ± 2.02) and were
positively correlated with nutrients. Thermocyclops spp. dominated zooplankton group with its
distribution skewed towards the influent zone. Individuals of O-;'"iochromis niloticus were most
abundant individuals collected during the fishing exercise and their growth condition factor was
greater than one. It was shown that Thika reservoir is a mesotrophic reservoir and integrated
management interventions are required to maintain its capacity to supply water to Nairobi | en |
