Ecological engineering and aquatic connectivity: a new perspective from beaver‐modified wetlands

Abstract

Summary Habitat fragmentation and wetland loss due to anthropogenic causes are usually attributed to physical modifications of the environment; however, the loss of key species can compound these impacts and further reduce the connectivity of aquatic ecosystems. Ecosystem engineers can play a critical role in modifying aquatic systems by altering the bed of ponds and streams, increasing water coverage and influencing biogeochemical processes within and adjacent to freshwater habitats. However, there is a paucity of research on how these organisms enhance connectivity among aquatic habitats, especially in otherwise isolated wetland systems. In this study, we collected field data at natural and agriculturally impacted sites to quantify physical alterations to otherwise isolated, morainal wetlands modified by beavers, and to determine how these modifications might enhance connectivity. For finer‐scale analysis, we collected and modelled bathymetric data for 16 wetlands, eight of which were occupied by beavers and eight abandoned by beavers. We demonstrated that beavers actively increase the volume‐to‐surface area ratio of wetlands by almost 50% and that their digging of foraging channels increases average wetland perimeters by over 575%. Some channels were 200–300 m long, which enhanced the interface between the riparian zone and upland forests. A coarse estimate of soil displacement due to the digging of channels by beavers exceeded 22 300 m3 within the total 13 km2 natural area. Additional measures of wetland depth, basin complexity and basin circularity revealed other dramatic differences between wetlands with beavers and those without in both natural and agricultural landscapes. Exclusion or removal of beavers could limit ecosystem processes and resilience, especially in areas with otherwise isolated aquatic habitats and limited connectivity. Conversely, reintroduction of such an ecosystem engineer into areas targeted for restoration could result in significant increase in habitat heterogeneity and connectivity.

Sediment and nutrient storage in a beaver engineered wetland

“…Another study (focusing on C. canadensis ), by Butler and Malanson (1995) suggests a lower, but still noteworthy value of 0.4 m 3 per burrow (Butler and Malanson, 1995). Similarly, in a study of C. canadensis in 16 US wetlands, it was found that the contribution of sediment from beaver canals to rivers was significant (Hood and Larson, 2014). The authors show that, over a 13 km 2 area in the Miquelon Lake Provincial Park, Canada, an estimated 22 315 m 3 of sediment was released into the watercourse.…”

“…It has been shown that there will be some sediment sourced from beaver building activity and within site erosion (Lamsodis and Ulevičius, 2012; de Visscher et al ., 2014; Hood and Larson, 2014). Sediment partitioning or source determination was not undertaken as part of this study.…”

Rapid surface-water volume estimations in beaver ponds

“…This is because the bathymetric curve proved resilient to fluctuations in "elevation" inherent to the impounded land surface. Also, the dams, intricate canals and holes that beavers create in the areas they inhabit (Hood and Larson, 2015) do not warp the shape of the bathymetric curve enough that a power function becomes inappropriate to sufficiently describe it. However, it appears that volume estimations are more resilient to aberrations in the bathymetric curve than are area estimates.…”

Impact of river channelization and riverfront development on fluvial habitat: evidence from Gomti River, a tributary of Ganges, India

“…The dominance of channel engineering and associated loss of river ecosystems and river processes has been widely discussed in the literature (Downs and Gregory 2014;Palmer et al 2014;Hood and Larson 2015;Peipoch et al 2015;Everard et al 2018;Wohl 2018). The river engineers involved in water resources development projects often cite the need of providing increasing water demands to growing population, whereas river ecologists argue about the needs of the riverine ecosystem in wake of unsustainable water abstractions (Downs and Gregory 2014).…”