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.
Highlights
Wetlands are unique ecosystems that share characteristics of terrestrial and aquatic ecosystems
The highest sediment conductivity was recorded from site F of the rehabilitated area and significantly lower percentage sand content was recorded at Site C of the nonrehabilitated area (Table 2)
The present study indicated significant spatial variations of silt and clay contents and sediment conductivity in the monsoonal season in Diyawannawa wetland
Summary
Wetlands are unique ecosystems that share characteristics of terrestrial and aquatic ecosystems. Wetland structure and associated functions are always influenced by the adjacent terrestrial and aquatic ecosystems. The wetlands are continuously adjusting and changing their structure and function to successfully withstand the environmental influences of adjacent ecosystems. Erosion, landslides, biomass removal, introduction of the alien invasive species, temperature and salinity fluctuations, accumulation of heavy metals and domestic solid wastes are some of natural and anthropogenic stresses/disturbances occurring in wetland ecosystems (Keddy 2010; Zhang and Ma 2011; Means et al 2017). Most wetland ecosystems are often exposed to a variety of natural and anthropogenic disturbances, and the effects of these perturbations are non-quantifiable
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