Domitila Kyule^1,, Nicholas Outa², Jacob Iteba³, Erick Ogello², Jonathan Munguti¹, Kevin Obiero⁴, Elick Otachi⁵, Anastasia Muia⁵

The recent heavy rains in many parts of Kenya have changed several aspects of the Rift Valley lakes. Data collected before the rainfall events is therefore crucial for a better understanding of these systems hence the need for this paper. Two Rift Valley lakes in Kenya (Nakuru and Bogoria) were investigated between June 2008 and January 2009. The objective of the study was to investigate the dynamics and abundances of viruses, heterotrophic bacteria and phytoplankton biomass. Three sampling sites were selected in both Lakes. Temperature and conductivity were determined by probes in situ while Soluble Reactive Phosphorous (SRP) was determined using the ascorbic acid method. Dissolved Organic Carbon (DOC) was measured as non-purgeable organic carbon with a TOC-VCPH total organic carbon analyzer, while chl-a was extracted with acetone. Water samples for bacterio- virioplankton were fixed immediately after collection and enumeration of samples stained with SYBR Gold was done with epifluorescence microscopy. It was observed that conductivity was twice higher in Lake Bogoria than in Nakuru, and higher temperatures were recorded in the former than in the latter. DOC in Lake Nakuru was three times higher than that of Bogoria. Chl-a and SRP exhibited an antagonistic interrelationship. Virus abundances in Lake Nakuru ranged from 0.51-141.6 ×108 ml-1, among the highest observed in any natural aquatic system examined so far, and for Lake Bogoria the range was between 0.17-15.0 ×108 ml-1. The numbers of heterotrophic bacteria were one order of magnitude lower than that of viruses and virus to bacteria ratio (VBR) in both lakes. The study revealed that temperature and conductivity have effects on bacterial, viral numbers and phytoplankton, that cyanophages appear to play an important role in the dynamics of phytoplankton. Further, molecular and genetics studies could help to elucidate the interplay among microorganisms. Publishing this study now can provide valuable information for understanding the long-term dynamics of the microbial communities in these lakes and how they may be affected by changes in precipitation, which can inform conservation and management efforts in Kenya.

Bacterioplakton, viroplankton, saline lakes, lake Nakuru, lake Bogoria