ASSESSMENT OF THE ECOLOGICAL INTEGRITY OF LOWER SABAKI RIVER USING MACRO-BENTHIC INVERTEBRATES AS BIOLOGICAL INDICATORS

The present study was conducted at the lower reaches of the Athi-Galana-Sabaki River system that empties its water into the Indian Ocean. The objective of the study was to assess the ecological integrity of the lower Sabaki River using macro-benthic invertebrates as biological indicators. Macro-benthic invertebrate samples were collected monthly from December 2015 through February 2016 using a scoop net of 500µm mesh-size, at three selected sampling stations (St.-1-downstream station, St.-2 middle station and St.-3-uppermost station). Physico-chemical parameters were measured in-situ using digital meter sensor probes and water samples collected at each sampling station for nutrients analysis. The nutrients; phosphorus and nitrogen were analysed using the APHA-2012 standard methods and procedures. Species diversity, richness and evenness were calculated using Shannon-Wiener-diversity Hʹ, Margalef’s Dʹ and Pielou’s Jʹ Evenness indices, respectively. A total of 24,479 specimens belonging to 4 classes, 11 orders, 23 families and 23 species were sampled. Results showed higher species richness and evenness at St.-3 while St.-1 recorded the lowest richness and evenness. Shannon diversity index was <1 at all the sampling stations. Principal Component Analysis (PCA) results showed that two components; PC-1 and PC-2 explained 100% of the water quality variability in the sampled stations with pH, nitrites, nitrates and phosphates showing positive loadings in both PCs. Similar correlations between these parameters with species richness, diversity and evenness were also evident in the analysis with Pearson correlation. This study revealed that macro-benthic invertebrates could be used as potential indicators of the integrity of the lower Sabaki River, which was confirmed with the correlations with physico-chemical parameters. Key words: Sabaki River, Ecological integrity, Biological indicators, Macro-benthic inverterbrates