MACROINVERTEBRATE FUNCTIONAL AND STRUCTURAL RESPONSES TO HUMAN DISTURBANCE AND FLOW CESSATION IN AFROMONTANE-SAVANNAH RIVERS

Abstract

Freshwater ecosystems in the Afrotropics are increasingly threatened by human activities and disturbances, including agriculture, livestock grazing, water abstraction, and sand harvesting. These activities degrade habitat quality, alter flow regimes, and influence the composition and functioning of aquatic communities. This study assessed the structural and functional responses of macroinvertebrate communities to varying levels of human disturbance, flow permanence, and seasonality in the Wundanyi-Bura catchment, a representative Afromontane-savannah River system in southeastern Kenya. Macroinvertebrates were sampled from 18 study sites categorized by varying disturbance levels (low, moderate, high), flow duration type (permanent vs seasonal), and season (dry vs wet). Physical and chemical water quality parameters, habitat characteristics, and land-use patterns were also quantified. Functional composition was evaluated using Functional Feeding Groups (FFGs) and 14 biological traits comprising 52 ecological trait attributes. Results showed significant degradation in water and habitat quality with increased disturbance, particularly in the lower river reaches. Functional trait analyses revealed that disturbed and seasonal sites were dominated by resilient taxa such as burrowers, predators, and collector-gatherers, while less disturbed, permanent sites had higher proportions of sensitive taxa like shredders and scrapers. Flow variability and seasonality strongly influenced trait distributions and ecosystem attributes, including trophic dynamics, organic matter processing, and top-down control. Multivariate analyses (ANOSIM, NMDS, SIMPER) and trait-based approaches provided robust indicators of ecological integrity and disturbance gradients. This study underscores the value of integrating functional traits and FFG ratios in biomonitoring and river health assessment. It provides crucial baseline data for the Afrotropics, where biomonitoring frameworks are still underdeveloped, and highlights the need to consider both structural and functional metrics in the conservation, restoration, and management of freshwater ecosystems under increasing anthropogenic pressures.