Sediment and nutrient storage in a beaver-engineered wetland

  • Beaver ponds were shown to hold large volumes of sediment and associated nutrients.
  • The beavers’ enclosure, roughly the size of three (American) football fields and situated on a stream below a farm, originally contained one small pond… and is now a wetland mosaic regulated by dams and canals, and the ponds are slowly filling with sediment — 101 tons of it to date, estimate Brazier’s team.
  • Some of that sediment was generated by the beavers’ own digging. The vast majority, though, is eroded soil from the adjacent farmland. Altogether the sediments contain 16 tons of carbon — representing, were every last ounce of it sequestered permanently, the average yearly carbon emissions of six British citizens.

Puttock et al. “Sediment and Nutrient Storage in a Beaver Engineered Wetland. Earth Surface Processes and Landforms.” Earth Surface Processes and Landforms, 2018.

AND see this article about this study: The tremendous benefits provided by just one beaver family Anthropocene Magazine May 30 2018

Abstract

Beavers, primarily through the building of dams, can deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes. Research is required to understand the implications and possible benefits of widespread beaver reintroduction across Europe. This study surveyed sediment depth, extent and carbon/nitrogen content in a sequence of beaver pond and dam structures in South West England, where a pair of Eurasian beavers (Castor fiber) were introduced to a controlled 1.8 ha site in 2011. Results showed that the 13 beaver ponds subsequently created hold a total of 101.53 ± 16.24 t of sediment, equating to a normalised average of 71.40 ± 39.65 kg m2. The ponds also hold 15.90 ± 2.50 t of carbon and 0.91 ± 0.15 t of nitrogen within the accumulated pond sediment.

The size of beaver pond appeared to be the main control over sediment storage, with larger ponds holding a greater mass of sediment per unit area. Furthermore, position within the site appeared to play a role with the upper‐middle ponds, nearest to the intensively‐farmed headwaters of the catchment, holding a greater amount of sediment. Carbon and nitrogen concentrations in ponds showed no clear trends, but were significantly higher than in stream bed sediment upstream of the site.

We estimate that >70% of sediment in the ponds is sourced from the intensively managed grassland catchment upstream, with the remainder from in situ redistribution by beaver activity. While further research is required into the long‐term storage and nutrient cycling within beaver ponds, results indicate that beaver ponds may help to mitigate the negative off‐site impacts of accelerated soil erosion and diffuse pollution from agriculturally dominated landscapes such as the intensively managed grassland in this study.

….Conclusion

Results presented in this paper illustrate that beavers can exert a significant impact upon sediment and nutrient storage. Beaver ponds were shown to hold large volumes of sediment and associated nutrients. Results also suggest that, whilst pond age and deposition in a dam–pond sequence may play a role in sediment and nutrient storage, the clearest control was pond size, with larger ponds holding more sediment per unit area.

Unlike most previous work, this study focused on a site located within an intensively managed grassland landscape. It was inferred that the majority of sediment trapped in the ponds originated from erosion in the upstream intensively managed grassland catchment, therefore, beaver dams mitigated the loss of this sediment downstream. While further understanding of the long‐term stability of sediment and nutrient storage in beaver ponds is now required, findings presented in this study have important implications for understanding the role beavers may play as part of catchment management strategies.