TRANSPORT AND RETENTION OF PLANT COARSE POM IN A TROPICAL 2ND ORDER STREAM, THE NJORO RIVER, KENYA.

M.P.S. Leichtfried¹, G.O. Morara², and J.M. Mathooko². ¹Department Biological Station Lunz, Inst.of Limnology, Austrian Academy of Sciences, Seehof 4, A - 3293 Lunz/See, Austria, ²University Egerton, Zoology Dept., POB 536, Njoro, Kenya

Transport and retention of CPOM in the Njoro River was studied from May to September 1999. Experimental and natural leaf litter transport and retention on 2 different sites and the influence of human activities was studied. Leaves of 3 tree species (Dombeya goetzenii, Syzygium cordatum, Grewia forbesii) were used. Leaves of Dombeya g. moved over longest distance, 10 - 113 m in the reach with more retention structures (RSR) and 60 - 127 m in the reach with less retention structures (RSS). The leaf travel distances (1/k) for Dombeya g. were 48 (±18) m in the RSR and 90 (±9) m in the RSS (n=6). The leaf retention coefficients (-k) for Szyzygium c. are 0.0149 (±0.0022) in RSS and 0.0484 (±0.0202) in RSR, for Dombeya g. 0.0106 (±0.0180) in RSS and 0.0391 (±0.0154) in RSR. About 40 % of each leaf species travelled beyond the 50 m mark in the RSS. In the RSR, 95 % of the leaves were retained within the reach. Rock outcrops and debris dams retained the greatest number of leaves. In 3 sites with different anthropogenic disturbances is a significant inverse relationship between CPOM retained and the intensity of anthropogenic disturbances.