ASSESSMENT OF BENTHIC MACROINVERTEBRATES AS BIOINDICATORS OF WATER QUALITY IN RIVER NAKA, CHUKA, THARAKA-NITHI, KENYA

Abstract

Freshwater ecosystems worldwide have been progressively deteriorating leading to a decrease in aquatic biodiversity. Conventionally, evaluation of water quality uses single physical-chemical parameters which may be insufficient to fully assess the quality of freshwaters. This study used bio-indicators to assess water quality of River Naka in Tharaka-Nithi County, Kenya. Fluvial ecosystems support rich and diverse assemblages, making them vulnerable to possible alterations in the habitat. The study assessed the diversity and abundance of benthic macroinvertebrate communities and their use as bioindicators of water quality. Grab sampling was used to collect water samples, a kick sampler and D-frame aquatic net was used to collect 121 benthic macroinvertebrates from three selected sites and determined using EPT Index (Ephemeroptera, Plecoptera and Trichoptera group). The data obtained was used to determine the index of the sampling sites. Physico-chemical factors were analyzed in-situ (temperature, turbidity and pH) and in the laboratory(nitrates and phosphates). The highest EPT index values (28) at the upstream corresponded to good water quality, while the slightly low values (21) at the midstream indicated moderate water quality and the lowest values (15) recorded at the downstream showed fair water quality. The downstream water quality parameters exceeded World Health Organization limits, posing a health risk to water consumers. Continuous bio-assessment of rivers based on EPT biotic indicators should be conducted on a regular basis to establish a long-term profile of water quality state and ecological integrity of rivers.