The effects of riparian land use on water quality and fish species composition in the headwater streams of Tana, Athi and Ewaso Ngiro Rivers within Central Kenya

Abstract

Land use changes on riparian zones of streams have profound impacts on water quality and fish diversity. Sampling took place in 17 streams and in two da ms along the streams in central Kenya and Nairobi which join up to form the three major rivers Tana, Athi and Ewaso ngiro. The physico - chemical parameters which contribute to the quality of water studied were temperature, dissolved oxygen, turbidity, flow rate, depth and width, conductivity and nutrients (Phosphates and Nitrates). Land use patterns included National park, ranches, built - up areas, flower farms, vegetable gardening areas and natural vegetation. Temperatures ranged from 13.4 °C to 22.4 °C and dissolved oxygen concentration ranged between 4.47 mg/l to 1.76 mg/l. Turbidity varied according to soil types and activities in the areas surrounding the streams. Kinania stream on Athi river had the highest conductivity of 71 μ s and high nutrient concentrations, being in a vegetable gardening area. Most other streams had low nutrient concentrations. Fish species obtained were Poecilia reticulata , Garra dembeensis , Chiloglanis brevibarbis , Barbus sp., Clarias gariepinus Amphiliu s uranoscopus , Labeo cylindricus , Oreochromis sp., Neobola fluviatilis and Mormyrus sp. The genus Barbus had more diversity than any other fish. Clarias gariepinus was the biggest fish and was found in lower parts of Athi river and in more turbid steam wat ers. Most of the fishes were small in total length (TL).The head water streams were dominated with species like Garra, Amphilius , and Neobola sp. At Hippo point dam on Ewaso ngiro, Labeo cylindricus was the largest fish obtained while at Karen on Athi rive r, Micropterus salmoides was the largest fish. The head water stream fishes were indicators of high water quality