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.
