Abstract
Beavers are the archetypal keystone species, which can profoundly alter ecosystem structure and function through their ecosystem engineering activity, most notably the building of dams. This can have a major impact upon water resource management, flow regimes and water quality. Previous research has predominantly focused on the activities of North American beaver (Castor canadensis) located in very different environments, to the intensive lowland agricultural landscapes of the United Kingdom and elsewhere in Europe.Two Eurasian beavers (Castor fiber) were introduced to a wooded site, situated on a first order tributary, draining from intensively managed grassland. The site was monitored to understand impacts upon water storage, flow regimes and water quality. Results indicated that beaver activity, primarily via the creation of 13 dams, has increased water storage within the site (holding ca. 1000m3 in beaver ponds) and beavers were likely to have had a significant flow attenuation impact, as determined from peak discharges (mean 30±19% reduction), total discharges (mean 34±9% reduction) and peak rainfall to peak discharge lag times (mean 29±21% increase) during storm events. Event monitoring of water entering and leaving the site showed lower concentrations of suspended sediment, nitrogen and phosphate leaving the site (e.g. for suspended sediment; average entering site: 112±72mgl−1, average leaving site: 39±37mgl−1). Combined with attenuated flows, this resulted in lower diffuse pollutant loads in water downstream. Conversely, dissolved organic carbon concentrations and loads downstream were higher. These observed changes are argued to be directly attributable to beaver activity at the site which has created a diverse wetland environment, reducing downstream hydrological connectivity. Results have important implications for beaver reintroduction programs which may provide nature based solutions to the catchment-scale water resource management issues that are faced in agricultural landscapes.
Highlights
Beavers are widely referred to as ecosystem engineers (Hartman and Tornlov, 2006; Wright et al, 2002) as they modify river systems and surrounding riparian areas to create suitable habitat for themselves which subsequently benefits a wide range of other species
A pair of beavers was introduced to the site in 2011; since when, a significant change in ecosystem structure, most notably a three-order of magnitude increase in ponded surface water storage, has been recorded (Fig. 2)
The site has changed from a woodland site, with no permanent surface water storage, to a site dominated by 13 dam-pond structures, with dam lengths extending to 30 m (Fig. 1), covering a surface area of over 1500 m2
Summary
Beavers are widely referred to as ecosystem engineers (Hartman and Tornlov, 2006; Wright et al, 2002) as they modify river systems and surrounding riparian areas to create suitable habitat for themselves which subsequently benefits a wide range of other species. All of the aforementioned activities increase the structural heterogeneity of their environment (Rolauffs et al, 2001) having hydrological and geomorphological impacts, but creating a diverse range of habitats with significant (positive) biodiversity implications (Rosell et al, 2005). Stimulated by the EC Habitats Directive, reintroduction programs have seen the re-establishment of Eurasian beaver colonies across northwest Europe (de Visscher et al, 2014), including Scotland (Jones and Campbell-Palmer, 2014). In England, there is currently only one known wild population, subject to a rigorous five year monitoring program (Natural England, 2015)
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