Elevation and land use as drivers of macroinvertebrate functional composition in Afromontane headwater streams

Abstract

Macroinvertebrates play a unique role in aquatic ecosystems by acting as processors of nutrients and organic energy from allochthonous and autochthonous sources. Within East Africa, and especially Kenya, anthropogenic influences on streams and rivers as a result of deforestation and the expansion of agricultural lands are pervasive. This study investigated land use v. altitudinal shifts in the functional composition of macroinvertebrates within the Mount Elgon catchment in western Kenya. A total of 20 sampling sites in 12 streams, 10 sites each within forested and agricultural areas, located in 3 elevation categories were sampled for physicochemical water parameters and macroinvertebrates. Significant (P<0.05) spatial variation was observed in total suspended solids, coarse particulate organic matter, temperature and electrical conductivity between forested and agricultural sites. Shredder biomass and abundance was higher in forested streams at higher elevations. There was a significant increase in the abundance (of shredders, predators, collector filterers and gatherers), taxon richness (of shredders, predators and scrapers) and biomass (of shredders, collector filterers and gatherers) of functional feeding groups with increasing elevation. Data of near-natural sites are urgently needed to disentangle altitude and land use influences on the diversity and composition of aquatic communities in high-elevation streams in the tropics.