| dc.description.abstract | Lake Naivasha being an endorheic basin, within an
intensive agricultural region requires continuous
assessment of basic factors controlling phytoplankton
productivity, because agricultural activities can
contribute to basic ecological changes. Such changes
include those attributed to eutrophication, which could
be detrimental to the well developed fishery in Lake
Naivasha.
Phytopiankton productivity was determined in thres
different ecological zones in Lake Naivasha, i.e.
littoral, open-water and a semi-enc1osed basin. Nearisothermal
conditions were observed in all the stations,
with a seasonal change of 3°C. The water was well
oxygenated with orthograde curves, however dissolved
oxygen stratification was well developed at Crescent
Island Lake. Secchi disc transperency, conductivity,
alkalinity, and nutrient concentrations were greatest
at Crescent Island Lake.
Phy topi ank ton biornass as chlorophyll a, showed
significant differences in concentration between
stations and over time, with ranges of 26.5-40.5, 20.6-
59.8 and 11.2-41.9 pg/1 at Safariland, Hippopoint and
Crescent Island Lake respectively. This could be
attributed to differences in species composition:
Closterium. Micrpcystis. Ceratium. and Melosira spp.were abundant at Main Lake stations, while Melosira spp.
dominated Crescent Island Lake.
Photosynthetic rates were maximal in sub-surface
waters (0.5-1.0 m depth) in all the stations,
coinciding with more than the 15 '/. level o"f incident
irradience measured as Secchi depth and PAR light
attenuation. Maximum gross photosynthesis (Gpmax) was
highest at Safari land between January and March 1990 and
Crescent Island Lake took there after. Crescent Island
Lake had the highest values of specific photosynthetic
rate (Pmax) than the other stations with higher
chlorophyll a concentration in January to March. | |
