THE INFLUENCE OF THE DIEL CLIMATIC CYCLE ON THE DEPTH-TIME DISTRIBUTION OF PHYTOPLANKTON AND PHOTOSYNTHESIS IN A SHALLOW EQUATORIAL LAKE (LAKE BARINGO, KENYA)

Lake Baringo is a shallow equatorial lake. This paper reports a diel s tudy of the depth-time distribution of phytoplankton and photosynthesi s at one location in Lake Baringo on 10 March 1989. The water column s hows a pattern of diurnal stratification probably accentuated by the h igh turbidity of the water and therefore rapid attenuation of solar en ergy. This stratified pattern breaks down at night due to atmospheric cooling and the regular onset of winds in the early evening. The phyto plankton is dominated by Microcystis aeruginosa with some associated e piphytes. It concentrates in the narrow euphotic zone during the diurn al period of stratification due to buoyancy of the Microcystis; evenin g breakdown of the thermocline results in the phytoplankton being mixe d throughout the water column. A series of measurements of photosynthe sis throughout the diurnal period gives an areal rate of 3.8 g O-2 m(- 2) d(-1). The relationship between this value and the level of fish ex ploitation in Lake Baringo is discussed. The diel cycle in Lake Baring o is interpreted as dominating over any seasonal limnological cycle in the lake.