Evaluation of the water and sediment quality of a lotic water-body in the western coastal region of Sri Lanka using Rapid Bioassessment Protocol II (RBP II) of benthic macroinvertebrates

The biotic indices used in Rapid Bioassessment Protocol II (RBP II) developed by United States Environmental Protection Agency was used to assess the feasibility of using benthic macroinvertebates as bio-indicators for monitoring water and sediment quality in Ja-Ela stream, which is a lotic water body in the western coastal region of Sri Lanka.  Five study sites to cover the entire length of the stream, which are in five different fringing land uses (undisturbed site, agricultural site, industrial discharge receiving site, densely populated urban site and a site close to the mouth of the stream) were sampled  for water and sediment quality parameters and benthic macroinvertebrates from April to October 2015. Shannon-Weiner diversity index (H`), Hilsenhoff Family Biotic index (FBI), Taxa richness (TRI), and Ehemeroptera, Plecoptera and Trichoptera (EPT) index were calculated for each site. Results indicated significant spatial variations in BOD 5 , COD, visibility, nitrate concentration and total phosphorus concentrations in the water, and total organic carbon content and particle size distribution in sediments. The highest mean values for H' (2.38), TR (13.6) and EPT (6.2) were recorded from the undisturbed site. Significantly higher FBI values are recorded from the industrial discharge receiving site (6.97) and the urban site (6.81), indicating that they are the most polluted sites with higher degree of organic pollution than other sites. These biotic index values showed significant correlations with sediment and water quality characteristics of the study sites (R 2 >0.5, p