Abstract:
Influence of stream characteristics on diversity and distribution of benthic algae were
studied at Gongawwa Ela during the period of September to November in 2016. Four sampling
sites were selected and the distance between two sampling sites was 1.5km. Substrate types were
categorized by sieve analysis and grain size distribution curves. Principle Component Analysis
(PCA) was performed to identify the most important stream characteristics that could potentially
influence on the growth of benthic algae. Physicochemical characteristics of water (nitrate, Total
Dissolved Solids, temperature, pH, and Dissolved Oxygen) and substrates (pH, phosphate and
nitrate) showed significant temporal variations. Conductivity and water velocity levels of the
substrate varied significantly among the sampling sites. Species richness of benthic algae (29
genera) showed significantly negative correlations with the level of phosphate content (R2=-
0.9592, P<0.05) and pH levels (R2=-0.999, P<0.05) of the substrate. Well graded substrate was
observed only at the most downstream site (site 3) while other sites showed poorly graded
substratum consisting over 90% of sand. The most abundant algal division was Bacillariophyta and
the abundance of Flagilaria sp., Pinnularia sp., Stigeoclonium sp., and Pediastrum sp. showed
significant temporal variation. Pinnularia sp., Synedra sp., Anabaena sp. and Navicula sp. were
possible indicators of the upstream characteristics. Meanwhile, Cosmarium sp., Pinnularia sp.,
Surirella sp., Tabellaria sp., Synedra sp., Closterium sp. and Navicula sp. were possible indicators
of the downstream characteristics. The PCA showed that the most important stream characteristics
were DO, conductivity, Total Suspended Solids, water pH, nitrate in water and water discharge,
while conductivity, nitrate, phosphate, % organic matter, pH, and % canopy cover were the types
of substrate characteristics.
