Effects of water quality on the diversity, abundance and distribution of benthic macro invertebrates along the shores of Lake Victoria in Homa-bay county Kenya

Abstract

Human-induced landscape alterations adversely affect habitat structure and functions in freshwater ecosystems, as well as the flow regime in the Lake Victoria basin. The massive discharge of wastewaters and other pollutants from the surrounding basin do interfere with ecological balance in parts of the lake thereby causing adverse impact on benthic macro-invertebrates especially along the lake shores. The overall objective of this study was to investigate the impact of water quality on the diversity, abundance and distribution of benthic macro-invertebrates along the Lake Victoria shores in Homa-Bay County, Kenya. Specific objectives were to: analyse the physico-chemical parameters of water quality, determine the diversity of benthic macro-invertebrate species, analyse the abundance and distribution of benthic macro-invertebrate species, and determine the impact of selected physico-chemical parameters on diversity, abundance and distribution of benthic macro invertebrate species along the shores of Lake Victoria, Homa-Bay County. The study adopted quasi experimental research design. Stratified random sampling was used to collect samples along Oluch-Kimira River Mouth, Homa Bay sewage discharge point and Mbita beach east of the course way at monthly intervals from September 2019 to February 2020. Samples of benthic macro invertebrate were collected using sweep net and grab sampler, preserved and laboratory identified using stereoscope, while water samples were collected using Van Dorn water sampler and nutrient analyses done using APHA (2017) standard methods at KMFRI. Physico-chemical parameters were measured in situ using YSI meter and Secchi disc for light intensity. Data was analysed using descriptive statistics, Shannon-Weiner Index, one way ANOVA, Turkey HSD post hoc and Canonical correspondence analysis (CCA). The study established that there was significant difference in diversity (F (2, 15) = 12.49, p= 0.001) and abundance and distribution of benthic macro invertebrate species (F (2, 15) = 14.41, p< 0.05) along the shores of Lake Victoria. Oluch-Kimira river mouth and Homa Bay sewage discharge point recorded significantly lower DO levels (4.0±0.46 to 6.2±0.19 MgL-1) compared to Mbita beach east of the course way (5.6±0.23 to 7.7±0.17 MgL-1), high nutrient load concentration, turbidity (317.47 NTU) and electrical conductivity (147.86 µScm¯¹) along Oluch Kimira river mouth, high dissolved oxygen concentration along Mbita beach east of the course way, and lower dissolved oxygen concentration along with high pH (8.47) at Homa Bay sewage discharge point. Benthic macro invertebrate diversity was relatively high along Mbita beach east of the course way with cloeon simile, Agrion splendens, Anodonta cygnea, Baetis and Caenis moesta being the most dominant species, whereas along Homa Bay sewage discharge point Spaniodoma sp, Sphaerium sp, Tubifex tubifex, Anodonta cygnea, Polycentropus and Naids were most dominant, and along Oluch Kimira river mouth, Anadonta cygnea, Tubifex tubifex, Melanoides tuberculata, Caenis moesta, and Sphaerium sp were dominant. The study concludes that changes in selected physico-chemical parameters and nutrient loads concentration along the shores of Lake Victoria influence the diversity, abundance and distribution of benthic macro invertebrates. The study provides baseline data for evaluating the trends in water quality and related changes in benthic-macro invertebrates and aquatic biodiversity along Lake Victoria shores in Homa Bay County, Kenya.