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. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
In the UK intensively managed grasslands, soil erosion rates of between 0.5 and 1.2 t ha-1 yr-1 have been reported (Bilotta et al, 2010; Gregory et al, 2015), and agricultural erosion rates can exceed 140 t ha-1 yr-1 (Chambers and Garwood, 2006)
In 2009, the cost of soil erosion in the UK was estimated at £45 million per annum, much of which was due to the off-site impacts associated with sediment and nutrient pollution (DEFRA, 2009)
It is further evident that beaver ponds change not just the hydrological regime of small channels, by slowing flow and enhancing water storage (Puttock et al, 2017), and create landscapes with depositional sediment regimes (Burchsted et al, 2010), as signified by the large sediment volumes recorded in this study
Summary
In the UK intensively managed grasslands, soil erosion rates of between 0.5 and 1.2 t ha-1 yr-1 have been reported (Bilotta et al, 2010; Gregory et al, 2015), and agricultural erosion rates can exceed 140 t ha-1 yr-1 (Chambers and Garwood, 2006). Beavers are often termed ecosystem engineers (Jones et al, 1994) They can extensively modify riparian and river systems to create habitats more suitable for habitation (McKinstry et al, 2001; Nyssen et al, 2011; Nummi and Holopainen, 2014). The most significant geomorphic impact of beavers results from their dam building ability and the consequent impoundment of large volumes of water and potentially associated sediment and nutrient accumulation in ponds (Naiman et al, 1988; Butler and Malanson, 2005; Hood and Bayley, 2008). In addition to increasing biodiversity (Law et al, 2017), it has been suggested that, due to their engineering activity, beavers could play a role in the management of river catchments (Puttock et al, 2017)
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