DOI: 10.36347/sajb.2016.v04i11.003

Pages: 975-985

The water quality of Nyabarongo River was assessed between January and December 2013 using selected physicochemical factors, bacteriological factors in combination with macroinvertebrate composition and diversity indices using standards techniques of water analysis and biological methods. Three sampling sites were chosen Kabirikarhaba, Cabwine-Mwami, and Ceshero. Suspended sediment concentration was high at the site of Cabwine-Mwami (1.08 ± 0.62 mg/L) in the habited area and less at the site of Kabirikarhaba (0.67 ± 0.23 mg/L) in the forest area. But it was low moderate at the site of Ceshero (0.68 ± 0.54 mg/L). Most nutrient concentrations were highest at the agricultural sites. Fecal bacteria were recorded in sampling water such as Escherichia coli and Klesbiella. Invertebrate taxa richness, biotic index, and the number of unique invertebrate species indicated moderate stress at the agricultural site and severe stress at the habituated area of site Cabwine-Mwami. At the agricultural site, declines in taxa richness within intolerant groups were partially offset by increases within tolerant groups. Analysis of seasonal patterns suggested detritus was the most important food source for invertebrates in the forested stream. Dominant macroinvertebrate groups shifted from Ephemeroptera at the forested site, to Chironomidae at the agricultural site, and Oligochaeta at the habited area. Physico-chemical parameters measured at the three sites did not seem sufficient to account for all of the observed differences in the invertebrate communities, suggesting some unmeasured toxicity.