A new study, undertaken by a team of University of Exeter researchers using captive Eurasian beavers (Castor fiber), has demonstrated the significant impact the animals have had on reducing the flow of tons of soil and nutrients from nearby fields into a local river system.
Led by University of Exeter’s Professor Richard Brazier, the 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 were introduced to a controlled 1.8 ha site in 2011.
“The animals built 13 dams, slowing the flow of water and creating a series of deep ponds along the course of what was once a small stream,” the scientists explained.
“We measured the amount of sediment suspended, phosphorus and nitrogen in water running into the site and then compared this to water as it ran out of the site having passed through the beavers’ ponds and dams.”
“We also measured the amount of sediment, phosphorus and nitrogen trapped by the dams in each of the ponds.”
The results showed the 13 beaver dams had trapped 101.53 tons of sediment, 70% of which was soil, which had eroded from ‘intensively managed grassland’ fields upstream.
Further investigation revealed that this sediment contained 15.9 tons of nitrogen and 0.91 tons of phosphorus, which are nutrients known to create problems for the wildlife in rivers and streams and which also need to be removed from human water supplies to meet drinking-quality standards.
“It is of serious concern that we observe such high rates of soil loss from agricultural land, which are well in excess of soil formation rates,” Professor Brazier said.
“However, we are heartened to discover that beaver dams can go a long way to mitigate this soil loss and also trap pollutants which lead to the degradation of our water bodies.”
“Were beaver dams to be commonplace in the landscape we would no doubt see these effects delivering multiple benefits across whole ecosystems, as they do elsewhere around the world.”
The findings were published online April 2 in the journal Earth Surface Processes and Landforms.
Alan Puttock et al. Sediment and Nutrient Storage in a Beaver Engineered Wetland. Earth Surface Processes and Landforms, published online April 2, 2018; doi: 10.1002/esp.4398