| dc.description.abstract | Kisumu Bay is greatly impacted by pollution from anthropogenic activities around
Nyanza Gulf and from increasing levels of industrial and municipal waste discharges
\ from Kisumu City. This has resulted in significant changes; in the level of
eutrophication and the general ecology of the bay, impacting negatively on water
quality, biodiversity, fisheries and livelihoods. These changes need to be monitored
constantly for the effective environmental management of the gulf. The level of
eutrophication of the Kisumu Bay has, however, not been determined. This study
aimed at estimating the Trophic State Indices and Phytoplankton Quotients, 'as key
indicators of eutropbication, in Kisumu Bay, and to determine the level of
eutrophication of Kisumu Bay. Water quality measurements were conducted from
April 2009 to March 2010. Physico-chemical parameters including Secchi depth was
determined with a Secchi disc, turbidity,' temperature, conductivity, alkalinity and
dissolved oxygen concentration were measured in situ using a seabird multi-parameter
water quality probe, whereas nutrients levels (ammonia, nitrates, nitrite, total
nitrogen, soluble reactive phosphorus, total phosphorus and chlorophyll a) and
phytoplankton analyses were done by spectrophotometric and microscopic
techniques, respectively. There were significant spatial differences in the dissolved
oxygen concentrations (ANOVA, p< 0.01) within the bay. These differences were
highly pronounced at the Kisat, Maboko and Yacht Club stations which are associated
with sewage discharges from Kisumu City. Significant differences (ANOVA, p <
0.05) associated with discharges from Kisumu City and seasonal nutrient runoffs from
storm water were also observed in the spatial and temporal distribution of
phosphorous, ammonia, nitrates, nitrites and silicates within the bay. Significantly
higher (ANOVA, p<O.05) chlorophyll a concentrations were recorded during the dry
v
season when compared to the rainy season, probably as a result of higher turbidity
during the rainy season, which reduces light penetration into the water, and thereby
reducing the rates of phytoplankton production. Cyanophyceae was the most abundant
phytoplankton group contributing 5']010 of the total phytoplankton ;~unt, followed by
Chlorophyceae (28%), Desmidaceae (11%), Bacillariophyceae (4%) and
Euglenophyceae (1%). Among the Cyanophyceae, the most dominant species were
Microcystis spp,Chroococcusspp, Anabaena spp and Cylindrospermopsis spp,
Different phytoplankton distribution patterns were observed between the offshore
Maboko station and the inshore stations. The mean phytoplankton quotient for
Kisumu Bay was 4.1, whereas the Trophic State Index mean value was 145.3,
indicating that the bay is highly eutrophic. The study attributes this observation to
high nutrient loads from anthropogenic activities in the catchment area and industrial
and municipal waste discharges from Kisumu City, and recommends stricter
enforcement of the established policies on waste discharges from municipal and
industrial establishments. The study also recommends the institution of environmental
education and awareness creation targeting the catchment area and lake side
communities as a policy to abate pollution in the bay and Lake Victoria as a whole. | en_US |
