Abstract:
We assessed the relative performance of diatoms and macroinvertebrates to measure
municipal and industrial impacts on the ecological integrity of the three major rivers
flowing through Addis Ababa. Both community metric and multivariate statistical techniques were used to analyze the environmental variables and species data along the pollution
gradient. This study in the Addis Ababa urban area revealed that three biologically highly
stressed rivers are being impacted primarily by physical habitat degradation and both point
and nonpoint pollution. The macroinvertebrate composition was liable to severe physical
habitat and chemical water quality degradation. Consequently, macroinvertebrates were
less diverse and not found at all at the most polluted sites with very low dissolved oxygen
levels. Based on community metrics and multivariate analysis results, diatoms more
reliably indicated a gradient of pollution than macroinvertebrates. However, both organism
groups equally discriminated the two relatively unimpacted upstream sites from all other
impacted sites. As diatoms are immobile and ubiquitous (i.e., at least a few can be found
under almost any condition), they are good indicators of pollution levels among heavily
impacted sites where macroinvertebrates are completely absent or less diverse. Therefore,
diatoms are the powerful bioindicators for monitoring urban-impacted and seriously
stressed rivers and to examine pollution gradients and impacts of specific pollution sources.
