Relationship Between Water Quality Indicators And Benthic Macroinvertebrate Assemblages In The 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 zone conditions, consisting riparian assessment, benthic macroinvertebrate collection, and water quality sample collections for analysis for different parameters. PCA was performed on physico-chemical indicators and then BIO-ENV BEST to determine any significant relationship between physico-chemical and benthic macroinvertebrates. ANOSIM was employed to test the hypothesis for variations between the sampling sites in terms of physico-chemical parameters and riparian vegetation cover. Spearman rank correlation indicated that some water quality indicators area related to benthic macroinvertebrate assemblages while others did not respond. Elassoneuria(r=0.78), Ephemerella (r=0.75), Synclita (r=0.79), Macrobdella (r=0.90) and Actnonaias (r=0.91) were highly correlated with dissolved oxygen (ρ<0.05). Hexatoma was highly correlated with percentage canopy cover (r=0.83, ρ<0.01) at the nine sampling sites. However, Actnonaias was also highly correlated with DO (r=0.91, ρ<0.01). Macrobdella was negatively correlated (r=-0.85, ρ=0.002) to Temperature(T) and Total Nitrogen (TN). In general, macroinvertebrate communities were dominated by two orders, Ephemeroptera (32.3%) and Diptera (53.2%). The study revealed that the diversity and evenness from the most disturbed habitat (A and K1) were much less than in the site from the less disturbed habitat (KS, E and T2). ANOSIM test indicated a significant difference in sites in terms of physico-chemical parameters (R=392, p=0.1) while macroinvertebrates were not significant. BIO-ENV BEST indicated discharge, sulphate and phosphate to have had greatest influence on benthic macroinvertebrate assemblages (BEST p=0.515). In this way, we rejected our null hypothesis that water quality indicators have no relationship with benthic macroinvertebrate assemblages in the Kuywa River. This knowledge is important to the community, government and water resource managers as they plan in investing resources to rehabilitate the catchments with a view of improving the health of equatorial rivers.