Do Plants Grow Differently Around Leaky Weirs?

Abstract

Degraded river systems lead to problems beyond poor water quality. Alluvial pastures along degraded rivers lose their resilience against floods and droughts, and aquatic animals are deprived of their breeding grounds when tributaries dry up too quickly. Conventional strategies to repair degraded rivers are costly, driving landscape managers to seek better solutions. In-stream structures such as leaky weirs, rock gabions, and Beaver Dam Analogues are gaining popularity due to their immediate hydrological impacts and their use of cheap, natural materials. Some policy makers, however, distrust these nature-based solutions, as they believe such methods rest on claims unsubstantiated by research.

Our study, conducted from 2023 to 2024, explored leaky weirs. These low, in-stream structures are thought to facilitate wetland recovery by altering local hydrology, but their effects on riparian plants have not been studied. Our study aimed to determine whether plant communities differed between sites with leaky weirs compared to sites without leaky weirs. We found that plant did grow differently around leaky weirs; however, this difference was only seen within 50m of the riverbank. In treatment sites, the abundance and richness of wetland plants along the inner riparian zone was significantly higher than in control sites. However, we saw no significant differences in pasture and canopy compositions. From this, we conclude that leaky weirs may have a positive impact on plant communities; however, this effect is only local in the short term and must be further tested through manipulative studies.