Comparative Study of Macroinvertebrates and Diatoms as Bioindicators of River Water Quality in Addis Ababa
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Date
2008-01
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Addis Ababauniversity
Abstract
A crucial element in planning water quality assessment, management and conservation programme
of a river is the selection of the biological indicators used to appraise biodiversity and
environmental conditions. The present study, therefore, aimed at comparing macroinvertebrates
and diatoms as bioindicators of river water quality in Addis Ababa. A total of 16 sampling stations
were selected along the course of Kebena River and Little and Big Akaki Rivers for qualitative
evaluation of physical habitats and collection of samples used for the determination of the
taxonomic composition and abundance of macroinvertebrates and diatoms. Riffle sites were chosen
for sampling to make the comparison among sites easier. Standard methods of sampling and
analysis of samples were employed throughout the study period. Biotic indices and multivariate
analytical methods, particularly dissimilarity index, clustering and indirect ordinations were used
for the analysis of the results. Macroinvertebrates diversity was extremely poor precluding
comparison among sampling stations. The highest and lowest macroinvertebrates taxa richness was
5 and 0 respectively. Surprisingly, only two macroinvertebrates taxa were found at the upstream
site of Kebena River, which had the least anthropogenic disturbance but with the least physical
habitat quality (40.6 %). But, the highest diatom tax richness (30 taxa) was observed at this site
followed by 17 taxa at the upstream of both Little Akaki and Big Akaki Rivers. The lowest diatom
taxa richness (4 taxa) was observed near the discharge point of Awash Tannery, where other
industries are also concentrated. Community loss index for diatom data was higher at sampling
sites receiving industrial effluent. All diatom biotic indices were indicative of responses to load of
pollution though it was not possible to select the index that could discriminate impacted sites from
reference site clearly with such cross-sectional study. Generally, the study depicted that the rivers
in Addis Ababa are highly affected by physical habitat degradation and pollution due to point and
non-point sources. Based on biotic indices and multivariate analysis results, diatoms are found to
be better than macroinvertebrates in indicating sources and degree of pollution as well as in
discriminating reference site from impacted sites of the study area. Hence, studies that consider
seasonal variations and all the factors that determine diatoms composition are recommended in
order to develop a refined diatom-based river water quality monitoring tool for the rivers in Addis
Ababa and other parts of the country. Furthermore, responsible authorities should take urgent
ameliorative measures to improve water quality of the rivers in the city.
Key words: macroinvertebrates; diatoms; bioindicator; water quality; monitoring; indices
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Keywords
macroinvertebrates; diatoms; bioindicator; water quality; monitoring; indices