Impacts of artificial barriers on the connectivity and dispersal of vascular macrophytes in rivers: A critical review

Abstract

1. Macrophytes play important functional roles in river ecosystems, providing habitat and food, as well as influencing flow, water chemistry, and sediment dynamics.They also represent an important component of river biodiversity.2. Artificial river barriers have the potential to disrupt macrophyte dispersal, and compromise their distribution and persistence, but little information is available compared to barrier impacts on fish and macroinvertebrates. Here, we review the mechanisms supporting dispersal of river macrophytes in rivers and evaluate the nature of barrier impacts on macrophytes.3. Hydrochory (dispersal of propagules by water) is the principal mechanism of downstream dispersal, while zoochory (dispersal of propagules by animals) is likely to be the most important vector of upstream dispersal and inter-catchment transport.4. Most studies have focused on the impact of large structures such as dams, and the findings indicate the impact is highly context dependent. Slow-flowing habitats upstream of dams can act as traps to drifting propagules and thereby interrupt hydrochory. However, the consequences of interrupted hydrochory for downstream populations are unclear. River regulation can result in lower macrophyte diversity, although the lentic habitats associated with reservoirs can also favour an increase in the abundance and richness of macrophyte communities. 5. Instream barriers are unlikely to affect zoochory by birds directly, but barriers are well known to restrict fish movements, so there is considerable potential for barriers to disrupt zoochory by fish, although no empirical study has specifically examined this possibility.6. There is a paucity of studies examining the impacts of low-head barriers on macrophyte dispersal. Given the influence of macrophytes on river processes, we call for further research into barrier impacts on macrophyte population dynamics in order to gain a better understanding of the consequences of river fragmentation for fluvial communities and ecosystem functioning. K E Y W O R D Saquatic plant, dams, hydrochory, river regulation, zoochory

Selective effects of small barriers on river‐resident fish

“…Overall, our results support the idea that barrier impacts need to be viewed beyond their effects on migratory fish (Ogbeibu & Oribhabor, 2002;Fuller et al, 2015;Jones et al, 2020b), by showing their potential for causing far-reaching impacts on river-resident fish too (Weibel & Peter, 2013). Given the abundance of small barriers in rivers worldwide (Jones et al, 2019;Belletti et al, 2020), it is important to evaluate their more subtle effects to fully understand the extent and consequences of river fragmentation.…”

Rewilding watersheds: using nature’s algorithms to fix our broken rivers

“…2 provides an example of the restoration of a river's natural flow and sediment regime through dam removal, describing the consequences for key ecosystem functions in headwater, main channel and floodplain habitats. Rewilding outcomes by restoration of flows and habitat connectivity could include increased viability of river-edge egg-laying insects in hydropeaking headwater reaches (secondary production; Palmer and Ruhi 2019), improved dispersal of macrophyte propagules in the main channel, promoting primary production (Jones et al 2020), as well as deposition and transport of organic matter into floodplains (decomposition; Langhans and Tockner 2006). Similarly, biotic components in river ecosystems show spatio-temporally varying responses to the restoration of the flow regime.…”

The Importance of Catchments to Mine-pit Lakes: Implications for Closure

“…There was no true riparian vegetation recorded in any of the catchments, although fringing emergent taxa such as rushes were present around Stockton and Black Diamond A (both < 20% of the lake edge) and Lake Kepwari (a few patches). The presence of fringing vegetation in Lake Kepwari was likely due to entry of propagules during the river breach in 2011 and later flow-through trial (see Jones et al 2020).…”