Assessment of Water Quality Status of River Kibisi, Kenya using the Ephemeroptera, Plecoptera and Trichoptera (EPT) Index

Abstract

Mt. Elgon region is one of the major water towers in Kenya. However, rivers arising from it are highly polluted due to human encroachment that has led to degradation of river water quality. The poor water quality of rivers in the region could be fatal because of water pollution that results in waterborne diseases that affect area residents. Many bio-assessment indices that include Water Quality (WQI), South Africa Scoring Index (SASS.S), Biotic Indicator Based Assessment (BIBA), Integrity Biotic Index (IBI) among others have been useful in assessment of water quality of lotic systems the world over. The application of the Ephemeroptera, Plecopera Trichoptera (EPT) index which has been widely used in the temperate countries would be a useful pollution indicator in this study because results obtained would be precise and reliable. This study aimed at testing the Ephemeroptera, Plecoptera and Trichoptera (EPT) index in the assessment of water quality status of River Kibisi in Mt. Elgon area. Study sites were selected on the basis of pollution levels that included mildly polluted site I at the edge of the forest, moderately polluted site II in the upland agricultural area and heavily polluted site III in the lowland urban area. At each site both physical (water temperature, turbidity, transparency and Total Suspended Solutes) and chemical (pH, dissolved oxygen, conductivity and Total Dissolved Solutes) characteristics were measured in situ using standard methods. The collection of the benthic macro-invertebrates was done using the Hess sampler of area 0.0284 m2 and a mesh size of 100~m. Benthic macro-invertebrates collected were preserved in 4% formaldehyde and transferred to the laboratory where they were sorted, enumerated and identified out for the orders Ephemeroptera, Plecoptera and Trichoptera. Count data was used for the computation of the EPT index. The abundances of collected benthic macro-invertebrates and the physicochemical parameters were compared using Kruskall Wallis H test. Pearson Rank Correlation (r2) test was used to assess the correlation between benthic macro-invertebrate abundance and the physico-chemical parameters. Results showed that water temperature increased significantly 15.3 ± 0.46, 17.9 ± 0.67, 19.7 ± 055 at sites I, II and III respectively; water turbidity did not vary significantly 78.0 ± 27.1, 112.0 ± 40.9, 182.0 ± 39.2 at sites I, II and III respectively; total suspended solutes differed significantly 13.1 ± l.86, 26.0 ± 6.82, 44.8 ± 8.62 at sites I, II and III respectively; transparency differed significantly 0.6 ± 0.10, 0.6 ± 0.11, 0.23 ± 0.05 at sites I, II and III respectively. Results also showed that conductivity did not differ significantly 134.9 ± 7.03, 157.0 ± 10.76, 166.0 ± 12.69 at sites I, II and III respectively; pH results did not differ significantly among sites 7.7 ± 0.07, 7.7 ± 0.10 and 7.2 ± 1.16 at sites I, II and III respectively; dissolved oxygen decreased significantly 7.5 ± 0.59, 6.9 ± 0.54, 5.0 ± 0.62 at sites I, II and III respectively and mean total dissolved solutes varied significantly 257.8 ± 21.7, 291.8 ± 348.0 ± 22.7 at sites I, II and III respectively. Analysis of the EPT index correlated closely with the physical and chemical parameters (r = 0.3503; P < 0.05 for pH; and r = -0.5398; P < 0.05 for conductivity). From the results it can be concluded that the EPT richness index is biotic tool that can be applied in the assessment of water quality of rivers in the tropical world.