The effects of the Eurasian beaver (Castor fiber) on hydrology and nutrient dynamics in UK headwater streams (UCL, University of Stirling, Wildfowl and Wetlands Trust)

Abstract

The Eurasian beaver (Castor fiber) is the first mammal to be reintroduced to the UK, gaining native status in Scotland in 2016, and gaining legal protection on 1 May 2019. Beavers are habitat engineers known to substantially alter river hydrology and nutrient cycling. Beaver dams slow water and route it through a variety of flow pathways causing increased surface water storage and, in some cases, the potential to change surface-groundwater exchanges with implications for local water table elevations on adjacent floodplains. Other effects may include reduced downstream peak discharge, and increased base flows.

The importance of these processes at larger spatial scales (e.g. catchment scale) is largely not understood. The coupling of hydrological conditions present in beaver ponds with biogeochemical activity means ponds are hotspots for nutrient cycling. Significant denitrification, methane release and landscape-scale carbon storage are reported. We suggest that these effects result from reduced flow velocities which cause carbon and nutrient-rich fine sediment to be trapped, enhancing microbial activity, and giving rise to reduced chemical conditions in sediments.

The proposal is to:
1) Gather hydrological field data sufficient to construct physically-based and spatially distributed numerical models to better understand hydrological processes at a range of scales
2) Investigate the potential of a flow device to address the perceived problematic effects of beaver ponds on agriculture
3) Investigate sediment characteristics in ponds along a gradient of ages.

Policy Impact

1) Assess the impact of beaver dams on hydrological processes which impact humans – especially in terms of natural flood risk management and effects on local groundwater levels.
2) Assess the potential for an industry standard mitigation measure to resolve conflicts between the presence of beaver dams and agriculture close to small streams and ditches.