The role of turbidity on picoplankton organic carbon synthesis and growth rates in Lake Baringo ,Kenya

Abstract

Wind induced turbidity in Lake Baringo impacts negatively on picoplankton biomass and growth rates. This study investigated the impact of turbidity on picoplankton organic carbon synthesis and growth rates at low (northern), moderate (central) and high sediments disturbance (southern) zones in Lake Baringo. The investigation-followed simple completely randomised design and analysis of variance. Turbidity was measured in the field by a portable turbid meter. Van Dorn was used for field water sample collection. Composite samples of picoplankton from each of the sampling sites were incubated in 3 glass bottles. 100 ml of water were filtered through nuclepore filters using a suction pump to remove predators. Acrdidine orange was used to stain the nuclepore filters. Picoplankton cells were counted under epiflourescence microscope using the frequency of dividing cells technique. Results of this study have shown that picoplankton abundance was strongly and positively related to particulate organic matter (R2 = 0.89; P5 0.004) and dissolved organic carbon (R2 = 0.88; Pfi 0.005) in all the three zones. Specific picoplankton organic carbon synthesis was positively related to the turbidity at the southern (R2 = 0.46; Ps 0.14) and central zones (RZ= 0.47; P$0.l3) but lowest positive relation was observed at the northem zone (R2=0.23, P5033). Picoplankton loss estimates showed strong association with turbidity at the southem (R2=0.503, Ps 0.11) and northen-1 (R2=0.509, P5 0.11) zones, but weak association in the Central zone (R2 I 0.38; P§ 0.19). ln the Southern zone the picoplankton specific growth rates were weakly related to the lake’s water turbidity (R2=0.32, P$ 0.24) while in both northem and central zones there was no link. Picoplankton specific growth rates were strongly and positively related to biological oxygen demand (R2 = 0.56; Pg 0.04) in all the zones. Particulate organic carbon and dissolved organic carbon were strongly and positively related (R2 = 0.99; PS 0.05) in all the zones. These results reassert the phenomenon of energy storage by organic carbon in lake ecosystems. The frequency of dividing cells technique shows that picoplankton organic carbon synthesis, growth rates and the cell division phase of the cell cycle are physiological processes impacted upon and functionally dependent on turbidity. Rainfall influenced these processes with low effects during the dry season (December 2003- March 2004) and high effects during the wet seasons (June 2003-July 2003) in the central, northern and southem zones in ascending order of magnitude. This information is useful for policy appraisal and the management of Lake Baringo fisheries and other freshwater lakes ecosystems with a similar problem of sediments deposits.