Effect of anthropogenic activities on physico-chemical parameters and benthic macroinvertebrates of Mara river tributaries, Kenya

Abstract

The impact of anthropogenic activities within Bomet and Mulot towns on water quality of Amala and Nyangores tributaries of Mara River, Kenya was assessed using a combination of solid waste, physico-chemical parameters and benthic macroinvertebrates. Site characteristics and ongoing anthropogenic activities were observed and recorded, while solid waste was visually identified and categorized. Physico-chemical parameters were determined in situ while benthic macroinvertebrates were analyzed on sediment samples and classified using appropriate keys. Results indicated that all sites were disturbed by anthropogenic activities, except one that was relatively protected at the upper catchment spring draining into Nyangores tributary. Most (96.1%) solid waste encountered was recyclable, while polythene bags were dominant (48.9%). Significantly more solid waste was recorded along Amala than Nyangores tributary. Dissolved oxygen, conductivity, total suspended solids and total phosphorus levels varied significantly between sites, along Amala as well as Nyangores tributaries. Eight benthic macroinvertebrate taxa comprising 628 individuals were encountered in both tributaries, with Nyangores recording a significantly higher diversity than Amala tributary, as also confirmed by Shannon-Weiner diversity index. Dipterans were the most dominant taxa, contributing 81.9% and 70.9% of the total benthic macroinvertebrates encountered along Amala and Nyangores tributaries, respectively, while pollution sensitive taxa in the orders, Ephemeroptera and Plecoptera combined, accounted for less than 0.88% of the total benthic macroinvertebrate taxa in the two tributaries. These findings are indicative of perturbed systems whose severity seem to be driven by anthropogenic activities within and along the Mara River tributaries.