Abstract:
Abundance-Biomass Comparison (ABC) approach is a graphical approach that compares the abundance and biomass of
organisms in order to predict the environmental stress level of an ecosystem. The present study was conducted in selected sites
located at non-rehabilitated and rehabilitated areas of the Diyawannawa wetland in Sri Lanka in the monsoonal and non-monsoonal
seasons. The ABC was performed on the macrobenthic mollusk species collected from the study sites. Eight species of macrobenthic
mollusks, namely, Bithynia tentaculata, Melanoides turbeculata, Melanoides turriculus, Thiara scabra, Lamellidens marginalis,
Pila globosa, Gyraulus saigonensis and Lymnaea stagnalis were recorded during the study period. Based on Principal Component
Analysis, B. tentaculata, and, P. globosa were identified as characteristic gastropod species that could be used to classify study sites
in the rehabilitated and non-rehabilitated areas of this tropical wetland system. In the monsoonal season, overlapping cumulative
percentage dominance of abundance and cumulative percentage dominance of biomass curves in sites A, B, and F indicated partially
disturbed environmental conditions. The site C of the non-rehabilitated area, showed a typical undisturbed condition and the sites
D and E of the rehabilitated area the cumulative percentage dominance of biomass curve was located above the abundance curve,
indicating disturbed environmental conditions in these sites during monsoonal season. During the non-monsoonal season in all the
sites except site F of the rehabilitated area, the cumulative percentage dominance of abundance curve was located above the biomass
curve, indicating undisturbed environmental conditions in these sites. In the site F, the cumulative percentage dominance of
abundance and the cumulative percentage dominance of biomass curves were crossing each other, indicating partially disturbed
environmental conditions at this site. The values of the W statistic, which ranged from 0.004 to 0.374 in the non-monsoonal season
and ranged from 0.1 to 0.2 in the monsoonal season, and pollution and water quality categorization by modified biotic index (MBI)
were in agreement with the results of the ABC approach.
