The Impact of Modjo Tannery on Modjo River: Diatom-Based Water Quality Assessment
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Date
2005-06
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Addis Ababa University
Abstract
The present study aimed at assessing the impact of Modjo Tannery on Modjo River using diatoms as bioindicators. A total of 4 sampling sites were selected along the course of Modjo River for evaluation of physicochemical parameters and determination of the taxonomic composition and abundance of diatoms. Standard Method of sampling and analysis of samples were employed throughout the study period. Biotic indices and multivariate analytical methods, particularly Redundancy analyses were used for the analysis of the result. Most of the physico-chemical characteristics of the wastewater effluent were above the provisional discharge limit set out by the Ethiopian Environmental Protection Authority and world Health Organization. All physicochemical water quality parameters measured in samples from Modjo River except dissolved oxygen exhibited similar spatial variations with their levels declining consistently from their maxima at S2, the point of discharge of the tannery effluent, to those of the downstream sites. The lowest oxygen concentration of S2, which was far below the level capable of supporting aerobic heterotrophs, was significantly different from those of other sampling sites (p< 0.05) and coincided with the present highest levels of BOD5 and COD. Sites with relatively good water quality, S1 (reference site) and S4 (the most downstream site), were associated with such pollution-sensitive species of diatoms as Cocconeis placentula, Fragilaria crotonensis, Gomphonema angustatum and G. gracile, while sites with poor water quality, S2 and S3(below S2), supported an assemblage of such pollution-tolerant species as Fragilaria capucina, Gomphonema parvulum, Hantzschia amphioxys and Nitzschia palea, Species richness, diversity and abundance of diatoms differed significantly among the sampling sites, with their highest and lowest levels occurring at S1 and S2, respectively. RDA of the association of sampling sites, diatom species and physico-chemical water quality clearly separated the reference site (S1) from S2 and S3 in terms of water quality, which was also suggested by the physico-chemical and biological data recorded in the present study. The present results clearly show the detrimental impact of the tannery effluent on the ecological integrity of Modjo River. The water quality of Modjo River represents a serious threat to public health and aquatic and terrestrial life. The concerned government bodies including EEPA should, therefore, do their utmost to put an end to the ever-increasing degradation of the water quality of this ecologically and economically important river. Key words: bioindicators, diatoms, water quality, Modjo River, monitoring; RDA
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Keywords
Bioindicators, Diatoms, Water Quality, Modjo River, Monitoring, RDA