Indicator Organisms of Environmental Conditions in a Lotic Water body in Sri Lanka
G.A.R.K. GAMLATH and M.J.S. WIJEYARATNE
The species diversity and abundance of benthic invertebrates and some environmental parameters including dissolved oxygen level, BOD5, COD, pH, temperature, salinity and turbidity of the Dutch canal in the Muthurajawela swamp in the west coast of Sri Lanka were monitored from December 1994 to June l995. Dissolved oxygen level ranged from 0.2 mg I-1 to 9.9 mg I-1. The pH, salinity and turbidity ranges were 6.0-7.4, 0 - 1.6 ppt and 2-35 ppm respectively. The ranges of the values for BOD5 and COD were 0.01-0.91 mg I-1 and 1.2 5.6 mg I-1 respectively.
The species diversity' was found to be low at low dissolved oxygen levels. The low abundance of the gastropod Melanoids turberculata and the three oligochaete species namely Nais raviensis, Dero zeylanica and Dero dorsalis was observed to be indicative of low dissolved oxygen levels while high abundance of gastropod, Neritina perottetiana indicated slight saline conditions less than I6 ppt. The high abundance of Nais raviensis, Dero zeylanica and Dero dorsalis was also indicative of slightly acidic pH conditions while low abundance of chironomid species indicated high turbidity.