An Assessment of Some Physical, Chemical and Biological Characteristics of Nyanchwa - Riana River Flowing through Kisii Town in South West Kenya
Ogendi G. M., A. M., Getabu; J. M. Onchieku, J. M., Babu

Abstract
A study was conducted to assess the water quality of Nyanchwa-Riana River flowing through Kisii town during the period May 2013 to June 2014. Sampling stations were selected on a transect covering the upper and middle reaches of Nyanchwa stream. A further two sampling stations were added after the confluence on the Riana River downstream. The water quality parameters assessed were dissolved oxygen concentration, pH, conductivity, turbidity, chlorophyll-a, total and soluble phosphate and nitrate concentrations and coliform counts. Nutrient concentrations generally increased from the source of the Nyanchwa -Riana River towards the lower reaches of the river. Soluble nutrient concentrations exhibited the same trend. The total phosphorous to total nitrogen ratio of 1:3 varied from the Redfield ratio of 1:16 commonly found in natural habitats. Total coliform counts exceeded those recommended in the international water quality standards of less than 10 coliform cells/100ml of water and those of NEMA of nil100ml-1. Observations on the physical and chemical parameters showed levels stressful to aquatic life, with dissolved oxygen concentrations less than 5 mgL-1 in some sampling points. These findings are useful in the management of the water quality in the two streams and on the River Riana flowing through Kisii town.

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