Spatial variability in water quality and macroinvertebrate assemblages across a disturbance gradient in the Mara River Basin, Kenya

Abstract

Across the Afrotropical ecosystems human activities are increasingly modifying natural flow regimes, nutrient and organic matter loading and processing in streams and rivers with implications on ecosystem structure and functioning. The Mara River Basin has undergone extensive land-use change, but influences of these changes on water quality and aquatic communities are not well understood. This study investigated changes in water quality and macroinvertebrate assemblages across a disturbance gradient arising from rural human activities in nineteen sites; grouped into three condition categories (reference undisturbed (n = 7), moderately disturbed (n = 6) and disturbed (n = 6)). Temperature, dissolved oxygen, total dissolved solids, pH and electrical conductivity were measured in situ at each sampling site, and samples collected for analysis of nutrients and total suspended solids. Sampled macroinvertebrates were identified mainly to family level for analysis of structural and functional composition. There were significant spatial variations in water quality variables across the disturbance gradient (p <0.05). Highest mean temperature and suspended solids were recorded at the disturbed sites and lowest at undisturbed sites. Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa dominated (70% in abundance) undisturbed sites while Diptera dominated (48% in abundance) at disturbed sites. Additionally, higher diversity and richness indices were recorded at undisturbed sites. Collectors were the dominant taxa at all sites with the abundance of shredders being highest at undisturbed sites. This study adds further evidence showing that land-use change from forestry to agriculture has a strong influence on the structural and functional composition of macroinvertebrates in Afrotropical streams.