Environmental Drivers of Macrozoobenthos Structure Along a Discontinuous Tributary of the Oder River (North-Western Poland)

The Myśla River, a right-bank tributary of the Oder catchment, was the focus of our study on the impact of environmental parameters on macrozoobenthos diversity and composition. We surveyed 18 sites along the Myśla catchment, from upstream to the outlet, recording environmental features and sampling macrozoobenthos. The taxa composition (31 taxa) was dominated by insect larvae, particularly Diptera Chironomidae, with moderate contributions from mollusc families such as Sphaeriidae, Bithyniidae, and Planorbidae, which are primarily filter-feeders or grazers. Based on environmental affinities, the river was divided into three sections. Sites within lake areas and those with diverse sediment types exhibited the highest biodiversity. Conductivity, flow rate, nitrogen compound levels, dissolved oxygen, suspended particles, and current velocity most strongly influenced biodiversity, while substrate type shaped taxa composition. Lakes heavily disrupt the ecological continuity of the Myśla River, significantly altering natural ecological processes and causing deviations from the River Continuum Concept (RCC), whereas artificial structures exert only minor additional influence. We examined the applicability of the RCC by analyzing macrozoobenthos structure along the upstream-to-downstream gradient. This preliminary study contributes to ongoing regional research, highlighting the role of lakes in shaping the Myśla River ecosystem and assessing the relevance of RCC in unique river systems.