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P. Yillia, N. Kreuzinger, J. Mathooko:
"The effect of in-stream activities on the Njoro River, Kenya. Part II: Microbial water quality";
Physics and Chemistry of the Earth, 33 (2008), 8-13; 729 - 737.

The influence of periodic in-stream activities of people and livestock on the microbial water quality of the Njoro River in Kenya was monitored at two disturbed pools (Turkana Flats and Njoro Bridge) at the middle reaches. A total of 96 sets of samples were obtained from the two pools in six weeks during dry weather (January-April) in 2006. On each sampling day, two trips were made before and during in-stream activities and on each trip, two sets of samples were collected upstream and downstream of activities. This schedule was repeated four times each for Wednesday, Saturday and Sunday. Samples were processed for heterotrophic plate count bacteria (HPC), total coliform (TC), presumptive Escherichia coli and presumptive Enterococci. Additional samples were analysed for total suspended solids (TSS), turbidity, BOD5 and ammonium-N. The microbial water quality deteriorated significant (p < 0.05) downstream during activities at both pools. A similar trend was observed with the chemical indicators (TSS, turbidity, BOD5 and ammonium-N). The two groups of indicators demonstrated high capacity for site segregation based on pollution levels. Pollution levels for specific days were not significantly different (p > 0.05). This was incompatible with the variability of in-stream activities with specific days. The pooled data was explained largely by three significant principal components - recent pollution (PC1), metabolic activity (PC2) and residual pollution (PC3). It was concluded that the empirical site parity/disparity in the levels of microbial and non-microbial indicators reflected the diurnal periodicity of in-stream activities and the concomitant pollution they caused. However, microbial source tracking studies are required to distinguish faecal sources. In the meantime, measures should be undertaken to regulate in-stream activities along the stream and minimize the movement of livestock in the catchment.

In-stream activities; Microbial water quality