Effect of a Summer Flood on Benthic Macroinvertebrates in a Medium-Sized, Temperate, Lowland River

Floods are naturally occurring extreme hydrological events that affect stream habitats and biota at multiple extents. Benthic macroinvertebrates (BM) widely used to assess ecological status in rivers, but their resistance resilience floods medium-sized, temperate, lowland rivers Europe have not been sufficiently studied. In this study, we quantified the effect of a moderate (5-year return period) yet long-lasting unpredictable flood occurred summer 2020 on BM community Jeziorka River central Poland. To better understand mechanisms by which studied affected community, also evaluated dynamics hydrological, hydraulic, channel morphology, water quality conditions across 1300 m long reach. Continuous level monitoring, depth surveying, discharge measurements. As well, in-situ lab-based measurements were carried out between March August 2020. communities sampled three times eight sites along reach, once before twice after flood. High flow velocities during resulted bed instability leading sand substrate movement caused streambed aggradation up 0.2 m. Dissolved oxygen ammonium-nitrogen major drivers structure. Taxa richness, abundance, BMWP-PL index declined significantly, whereas Shannon evenness Simpson diversity indices showed no significant change first post-flood sampling, as indicated Kruskal–Wallis Tukey tests. Non-metric multidimensional scaling (NMDS) analysis composition was significantly Seven weeks peak (August sampling), had fully recovered from disturbance. The results can serve approximation for relevant applications other low-gradient, temperate rivers.