Abstract:
Riparian land use has substantial effects on aquatic habitats and biological communities
resulting in a dramatic loss of natural riparian vegetation and affecting the physicochemical
properties of streams. The study investigates the relationships among indigenous riparian
plants and water quality in the upper Gilgel Gibe catchment in southwestern Ethiopia. The
floristic composition of the riparian vegetation and the water quality of streams were studied
at selected sites, ranging from first to third order streams. We quantified relationships between
disturbance level and both physicochemical characters and traits of riparian plant species
during two sampling periods (December 2013 and April 2014). Data were collected from a
priori designated three land use types (forest, plantation and agriculture) and ranked along
nine streams. Ranks were based on surrounding land use characteristics and deforestation
categories. We used analysis of variance (ANOVA) and the Tukey’s post-hoc test to conduct
pair-wise comparisons among different land use types. Both species richness and diversity
values of forest sites were significantly (p<0.001) higher than agricultural sites. Whereas,
stream water quality deterioration indicator gradient such as total suspended solid (TSS),
water turbidity, and orthophosphate were significantly (p<0.001) higher in agricultural sites
than forest sites. We identified species such as Croton macrostachyus, Ficus sur, Maytenus
arbutifolia, and Millettia ferruginea as indicator species of water quality (p<0.05). Our study
is the first assessment of the role of indigenous plant species as indicator of highland stream
water quality in the tropical area. The study contributes to the on-going discussion on the
assessment and monitoring of stream ecosystems and for following stream restoration projects
in tropical regions around the globe.
