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.
