Influence of Stream Characteristics on Diversity and Distribution of Benthic Algae in Gongawwa Ela in Kottawa Rain forest, Galle, Sri Lanka

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.