Macrobenthic diversity and its bioindicator potential in urban reservoirs: A Sri Lanka case study

Abstract

Studies addressing the macrobenthic diversity and their potential as bioindicators in water quality assessment programs are sparse for Sri Lanka. The present study investigated the macrobenthic diversity in relation to water quality parameters in some urban reservoirs in the Western Province of Sri Lanka, assessing their potential as bio-indicators in water quality assessment programs. The six study reservoirs included the Ihalagama Tank, Peralanda Tank, Kesbewa Tank, Boralesgamuwa Tank, Bolgoda Lake and Beira Lake. The microbenthic fauna abundance at randomly selected locations (n = 9) in each reservoir and selected water quality parameters (temperature; pH; electrical conductivity; total dissolved solids; BOD₅; dissolved nitrates; total dissolved phosphate and alkalinity of the overlying water at each location were measured between July 2020 and January 2021, using standard data collection methods). The species richness (SR), species heterogeneity (H′) and species evenness (J) of the macrobenthic fauna in each reservoir were calculated, and the abundance and water quality data analysed using ANOVA and PCA as appropriate. A total of 13 macrobenthic taxa (Glyphidrilus sp., Limnodrilus socialis, Dero sp., Stratiomyd larva, Chironomid larva, Bellamya sp., Melanoides tuberculata, Gyraulus sp., Lymnaea sp., Paludomus sp., Thiara sp., Ancylus sp. and Mesostoma sp.) were observed from the six study reservoirs. The oligochaete tubificid worm L. socialis dominated the sediment samples, accounting for more than 94.7% of the total macrobenthic abundance, with the highest relative abundance of this species observed in Beira Lake (99.3%). The species richness of the macrobenthic community was highest in the Ihalagama and Kesbewa tanks (SR = 5), while it was the lowest in the Peralanda Tank (SR = 2). Since the benthic community was mainly dominated by L. socialis, the lowest species heterogeneity and species evenness values were observed in Beira Lake (H′ = 0.05; J = 0.03). The values of the water quality parameters among the study reservoirs varied, with Beira Lake exhibiting significantly high BOD₅, dissolved nitrate, and total dissolved phosphate values (p < .05) than the other reservoirs, indicating a higher degree of eutrophication. Furthermore, the SR, J and H′ values for the study reservoirs decreased with increasing BOD₅, dissolved nitrate and total dissolved phosphate levels. Thus, it was concluded that the abundance and diversity of macrobenthic fauna are primarily governed by water quality parameters. Furthermore, L. socialis can be used as a potential bioindicator organism in water quality assessment programs in urban reservoirs.