An Application of Ephemeroptera, Plecoptera and Tricoptera (EPT) Index Method in Assessing Water Quality: A Case Study of River Kibisi, Mt. Elgon area, Kenya

Abstract

Mt. Elgon region is one of the most cherished water towers in Kenya. However, rivers arising from this water catchment have been heavily impacted by pollution due the degradation of the catchment as a result of human encroachment. Poor water quality has in turn negatively impacted on human health due to an increase of waterborne diseases that have proved to be fatal. These rivers are the main sources of drinking water, other domestic uses and animal watering. Despite the health problems caused by use of contaminated river water in the region, fast methods for water quality assessment are lacking and untested. Therefore, this study aimed at testing the Ephemeroptera, Plecoptera and Tricoptera (EPT) method in the assessment of water quality status of River Kibisi in Mt. Elgon area. The EPT method is a quick and reliable water quality assessment method that has successfully been applied in many temperate countries including South Africa. Study sites were selected on the basis of pollution levels that included an impacted (mildly polluted) site at the edge of the forest, (moderately polluted) site in the upland agricultural area and heavily polluted site in the lowland urban area. At each site both physical (water temperature, turbidity, transparency and TSS) and chemical (pH, dissolved oxygen, conductivity and TDS) characteristics were measured in situ using standard methods prior to the sampling of the benthic macro-invertebrates. The collection of the benthic macro-invertebrates was done using the Hess sampler of area 0.0284 m² and a mesh size of 100µm. Benthic macro-invertebrates and were preserved in 4% formaldehyde and transferred to the laboratory in Kisumu (KEMFRI) where they were sorted, enumerated and identified out for the orders Ephemeroptera, Plecoptera and Tricoptera. Count data was used for the computation of the EPT Index. Results obtained showed that the three sampling sites differed significantly in water quality status based of the physical and chemical analysis with Temperature with a mean 15.3±0.46, 17.9±0.67, 19.7±055; Turbidity had a mean 78.0±27.1, 112.0±40.9, 182.0±39.2; TSS had a mean of 13.1±1.86, 26.0±6.82, 44.8±8.62; Transparency had a mean 0.6±0.10, 0.6±0.11, 0.23±0.05. Conductivity similarly differed significantly with mean 134.9±7.03, 157.0±10.76 and 166.0±12.69; pH measuring an average of 7.7±0.07, 7.7±0.10 and 7.2±1.16; other parameters showed a similar trends. DO had a mean 7.5±0.59, 6.9±0.54, 5.0±0.62; TDS had a mean 257.8±21.7, 291.8± 348.0±22.7. at the forested, agricultural and urban sites respectively. Analysis of the EPT index correlated closely with the physical and chemical parameters (r² = 0.3503; p < 0.05 for pH; and r² = -0.5398; p < 0.05 for conductivity). It was concluded that the EPT index method can be a useful tool in the assessment of water quality for tropical rivers.