Effects of Stream Sediment and Water Quality on Macro invertebrate Abundance and Diversity in Gilgel Gibe Watershed, Southwestern Ethiopia F Stream Sediment and Water Quality on Macro Invertebrate Abundance and Diversity in Gilgel Gibe Watershed, Southwestern Ethiopia

Abstract

Background: Freshwater ecosystems face intense anthropogenic pressure, threatening water quality and biodiversity. Benthic macroinvertebrates are key bioindicators of ecosystem health, yet their response to multiple stressors from water and sediment pollution in tropical watersheds remains poorly understood. Study on sediment and water quality is helpful for integrated water resource management. This study investigated the individual and combined effects of stream sediment and water quality on macroinvertebrate abundance and diversity in the Gilgel Gibe watershed, Southwestern Ethiopia, in 2024. Methods: A cross-sectional study was conducted from October to November 2024 across 30 sampling sites in the Gilgel Gibe watershed. Macroinvertebrates were sampled using a rectangular kicking net (15 × 25 × 40 cm) with a mesh size of 300 m and identified to the family level with a stereomicroscope and standard guides. Physicochemical water quality parameters were measured onsite and analyzed in the laboratory using standard methods. Sediment samples were collected and their physicochemical quality was analyzed. Diversity indices (Shannon Wiener, Simpson and Margalef) were calculated. Multivariate analysis; Canonical Correspondence Analysis were applied to examine relationships between sediment and water quality with macroinvertebrate assemblages. Variance Partitioning Analysis quantified the relative contributions of water and sediment quality variables to community variation. Results: A total of 3,370 macroinvertebrates belonging to 7 orders and 36 families were collected; dominated by Ephemeroptera (34.12%), Trichoptera (27.24%), and Odonata (13.73%). Collector-gatherers dominated functional feeding groups (26.47%). Principal Component Analysis explained 37.08% of environmental variation differentiating urban, semi urban and rural sites. Canonical correspondence Analysis showed Water pH, Water Electrical Conductivity, Water Turbidity, Water depth, Sediment Electrical Conductivity, Sediment Organic Carbon and Water width were significant variables which influence the macroinvertebrate assemblage. Water Electrical Conductivity, Water depth, Biological Oxygen Depth5, Sediment Electrical Conductivity, Water pH and Sediment Available Phosphorous were the significant factors which influence the diversity of macroinvertebrates. Variance Partitioning Analysis revealed shared water and sediment variables explained largest proportion of macroinvertebrates assemblage variation. Water quality explained more the assemblage variation than sediment quality. Conclusion: The study revealed that macroinvertebrate abundance and diversity regulated jointly by water and sediment quality, and their combined effect is larger than their individual inputs. The shared effects of water and sediment variables explained a notable portion of community variation; highlighting the need for integrated ecosystem assessment. Water exerted a stronger separate influence on the assemblage than sediment quality. Therefore, effective biomonitoring and conservation of such ecosystems need a concerted approach with a priority for water quality management within the framework of sediment quality.