The benthic macro-invertebrate diversity in relation to water quality of a stream habitat at Dediyagala, Sri Lanka

Abstract

The streams collect sediment and other fine and particulate material from their watersheds and transport them downstream as fluvial material. Macro-benthos is the most important secondary producers in stream ecosystem and their diversity explains the water quality of a stream to a greater extent. The present study determines the water quality and macro-benthos diversity at five sites of the 180m stream stretch at Dediyagala for a period of three months from February to April in 2012. Random samples were collected using a Surber sampler for benthos, and a Ruttner sampler for water samples. Water discharge was significantly different from headwater (0.0198 m3 s -1 ) to downstream (0.0456 m3 s −1 ).Bottom substrate was non uniform according to Uniformity Coefficient analysis except at two sampling sites of cascade and riffle habitats. There was no significant site specific or time specific variations in water temperature, pH, biochemical oxygen demand (BOD3), total suspended solids (TSS), total dissolved solids (TDS), and orthophosphate concentration. Nitrate concentration, dissolved oxygen (DO) and organic matter content of lithophytes varied significantly among the sampling sites (P<0.05). Principal Component Analysis (PCA) showed that TDS and DO were the most important parameters for explaining the water quality of the stream stretch studied whereas BOD3 was important only for the downstream site. The most abundant families of benthic organisms in the stream were Hydropsychidae, Helicopsychidae, Leptophelibiidae and Psephenidae which belonged to the orders of Trichoptera, Ephemeroptera, and Coleoptera. A Significant positive correlation was observed between DO and Shannon-Wiener diversity index (R 2=0.815, P< 0.05). Family Biotic Index (FBI) ranged between 2.63 and 3.16 indicating that water quality was suitable for healthy growth of macro−invertebrates in the stream.