Relationship between riparian vegetation cover and macroinvertebrate assemblages in Kuywa River, Kenya

Abstract

The Kuywa River watershed has undergone riparian vegetation planting since 2006 in order to improve the river health. The planted riparian buffer zone vegetation was to improve channel stability, promote biodiversity, and improve water quality. Studies undertaken elsewhere have investigated how environmental factors affect ecosystem processes and functionalities but fail to show how water quality indicators influence the structure of the benthic macroinvertebrates. However, this study investigated the relationship between water quality indicators and benthic macroinvertebrate assemblages in the Kuywa River. Nine sites were assessed of different riparian vegetation cover and benthic macroinvertebrates were collected. Spatial characteristics were obtained by averaging four rounds of field sampling. Descriptive statistics employed included Richness Index (S), Abundance Index (N), Margalef Richness (d), Shannon Index (H), Simpson diversity (λ) and Pielou. BrayCurtis similarity measure and Multi-dimensional Scaling (MDS) were applied. To test the hypothesis, whether variations between the sites are significant, ANOSIM analysis was applied. Further, the effect of planted riparian zone vegetation was tested by the percentage of EPT. The study classified the study sites into 'Excellent', 'Good', and 'Poor'. Three genus were found to be positively correlated (p<0.01) with canopy cover and two negatively correlated. On the site richness, KG, K1 and T2 were found to have the highest family richness (15, 14, 14 respectfully) and A (8) the least. Our study found a significant difference between sites in terms of macroinvertebrate assemblages (R=0.94, p<0.01). For the sensitive species, K2, T2 and KM (14, 13, 11, respectfully) had the highest richness in terms of species, families and abundance. Site A had the lowest intolerant species (8). ANOSIM hypothesis testing indicated variations between sites were statistically different (R=0.94, p<0.1). SIMPROF test indicated that the MDS clusters generated for the nine sites were statistically significant (Pi=3.215, p=0.001). Our study concluded that the loss of large woody debris provided by riparian vegetation reduces substrate for feeding, attachment, and cover; causes loss of sediment and organic material storage; reduces energy dissipation; alters flow hydraulics and therefore distribution of habitats; reduces bank stability and community function. The land use above the site has a considerable influence on the river health. For management and restoration actions to be effective, we must diagnose cause as well as assess harm, which requires an improved understanding of the mechanisms through which land use impacts stream ecosystems. This knowledge is important to the community and water resource managers as it will yield information on effect of planted riparian zone vegetation on protecting the river health which may lead to the replication of the same project in other watersheds.