A preliminary macroinvertebrate Index of Biotic Integrity for bioassessment of the Kipkaren and Sosiani Rivers, Nzoia River basin, Kenya

Abstract

Management efforts for the Lake Victoria Basin have been hampered by a lack of clear standards against which to judge the degree of environmental degradation, highlighting the need for a multi-metric approach for this purpose. Indeed, management priorities for the Lake Victoria catchment must be based on reliable assessments of the biological integrity of the inflowing rivers that can potentially influence the ecological functioning of the lake. Accordingly, macroinvertebrate metrics were evaluated for their responsiveness to human impacts, utilizing Pearson’s correlations with physico-chemical parameters. The resultant 9 metrics that provided the best discrimination between physico-chemical samples, using the separation power of Mann–Whitney U and Kolmogorov–Smirnov tests (P < 0.05) from the 21 sampling sites utilized in this study were the: (i) abundances of Ephemeroptera, Plecoptera and Trichoptera; (ii) relative abundances of Diptera; (iii) Ephemeroptera, Plecoptera and Trichoptera:Diptera ratio; (iv) Oligochaeta, Mollusca, Hemiptera, Odonata and the proportions of tolerance taxa; (v) dominant taxa; and (vi) the relative proportions of invertebrates that fall into the gatherer and predator feeding groups, based on the variability they exhibited across the sampling sites. Using the inter-quartile ranges to establish the scoring criteria, the index was able to delineate impacted from less-impacted sites along the rivers, providing preliminary evidence of responses to changes in the ecosystem integrity exhibited by resident macroinvertebrate assemblages in both rivers.