¹National Museums of Kenya, Box 40658, Nairobi, Kenya
²Vrije Universiteit Brussels, Plant Science and Nature management, B-1050, Brussels, Belgium.

^*Corresponding author: E-mail: nmk@museums.or.ke or gatereg@yahoo.com

Abstract

  Diatom assemblages can serve as useful indicators of water quality. In order to determine changes in stream water quality in an urban environment, diversity of epilithic diatom communities on both natural and artificial substrates were sampled in Nairobi River, Kenya in September 2000. Sampling of water and diatoms was carried in almost equidistant sites along a 60 km stretch of Nairobi River. Environmental data was explored by a computer program Principal Correspondence Analysis (PCA) and stations subjectively split into three groups: (1) headwater (sites1-2); (2) mid-waters (sites 3-7); and lower reaches (sites 8-15). The response of diatoms to environmental gradients were summarised using Canonical Correspondence Analysis (CCA), direct-gradient method (ter Braak and Verdonschot, 1990) and analysed using ANOVA. Our results suggest that diatom assemblages can reflect major types of environmental gradients and therefore can be used as indicators of ecological conditions in streams and rivers. Diatom assemblages, in both natural and artificial substrates, grouped together in similar environmental conditions. Consequently, satisfactory information can be obtained by the use of natural or artificial substrates.