Effects of channel hydraulics and morphology on water-mediated dispersal in an alpine river

Water-mediated dispersal (hydrochory) connects spatially separated terrestrial and aquatic communities, facilitating the movement of reproductive materials and organisms through river networks. Anthropogenic pressures and climate change have altered these dynamics, potentially affecting biodiversity. Although dispersal distances and landing mechanisms are commonly attributed to interactions between channel flow, morphology, and particle properties, these relationships remain poorly investigated, especially in alpine rivers. We conducted field experiments in an 80-m-long channel of a braided river floodplain in Switzerland, releasing wooden cylinders as plant propagule mimics at three discharge rates. We used a 2D depth-averaged numerical model to quantify hydraulic variables and link them to measured particle travel distances and landing sites. We found that the number of floating particles decayed exponentially with distance, with decay rates primarily related to discharge. The deposition patterns were dictated by channel morphology rather than particle size, and the submergence of the river bed at low discharges strongly influenced the landing position. This study emphasizes the impact of small-scale channel heterogeneity on the dispersal of naturally buoyant materials. Our findings may help conservation and restoration measures, identify ecological flows and dispersal hotspots, especially in hydropower-impacted rivers.