Plants in streams act as physical ecosystem engineers, both influencing and responding to hydrogeomorphic processes. Instream vegetation may also influence propagule dispersal and retention, shaping plant community dynamics. These plant/sediment processes can promote hydrogeomorphic complexity and biogeomorphic successional processes. It remains unclear, however, how aquatic plants influence these biotic and abiotic processes in degraded lowland streams.
In this study, we sampled sediment (≤5 cm) from eight streams at different locations across the stream, including within aquatic vegetation and unvegetated areas. We conducted a propagule bank trial to identify the abundance and diversity of plant propagules and analysed the sediment characteristics of the sediment samples.
A total of 8365 seedlings from 123 species were recorded. Aquatic plants retained 36% more propagules and 25% more species than unvegetated channel locations. Similar patterns were found for fine sediment and organic matter retention. Vegetation communities were different across sites but not sampling locations based on either plant species or wetland plant functional groupings.
This study provides evidence that aquatic plants retain more plant propagules and species, and more fine sediment than vegetation free channel locations. Given the myriad benefits of aquatic vegetation to stream biota and abiotic processes, improving aquatic vegetation in streams may be an important early step in restoring hydrogeomorphic complexity and the facilitation of biogeomorphic successional processes in degraded streams.