Hydrodynamics of the Hyporheic Zone as a Determinant of Habitat Conditions and Growth of Water Crowfoots (Ranunculus Sp.)

The morphology of river channels, hydraulic conditions, and associated fluvial processes exert a strong influence on the development of aquatic organisms. This study aimed to evaluate the effects of filtration flux and hydraulic gradient within the hyporheic zone on habitat suitability of the growth of water crowfoot (Ranunculus section Batrachium, Plantae) patches in lowland rivers of the temperate zone. Conditions governing water exchange in the hyporheic zone were quantified based on empirical data collected between 2017 and 2019 at 41 study sites. Newly developed instruments – a gradientometer and a filtrometer – designed by one of the authors, were employed during field measurements. At most surveyed sites, hyporheic zones occupied by water crowfoots were characterised by dominant groundwater upwelling. Moreover, filtration flux in unvegetated sections of the riverbed was observed to be five times higher than in areas covered by water crowfoots. These findings support the hypothesis that groundwater upwelling in the hyporheic zone may primarily influence the establishment and growth of water crowfoot patches. However, further development of this vegetation can act as physical barriers that trap sediments, significantly reducing the filtration stream. Consequently, identifying the hydrodynamic properties of river sections colonised by these macrophytes is critical for developing and implementing natural river management strategies and for conserving the ecosystems they support.