People already know that beavers are keystone species whose activities shape landscapes in broadly beneficial ways. If such descriptions sound a bit abstract, though, consider the observations of scientists who followed the activities of a single beaver pair living in the British countryside.
In a study published in the journal Earth Surface Processes and Landforms, researchers led by hydrologist Richard Brazier of the University of Exeter describe their measurements of sediment composition and water quality in ponds built by the beavers, who were released in 2011 as part of a species reintroduction effort. Beavers were extirpated from the British Isles about 400 years ago.
The beavers’ enclosure, roughly the size of three (American) football fields and situated on a stream below a farm, originally contained one small pond. Since their arrival the beavers have built 12 more ponds. Their enclosure 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.
The situation isn’t quite that simple; Brazier’s team cautions that the long-term nutrient fluxes are not fully understood. Microbes living in the ponds emit carbon dioxide as they respire, and eventually the ponds will fill and dry out, causing some of that carbon to be released. Yet much of the carbon will stay locked up, and vegetation that eventually grows in the nutrient-rich sediments will store even more.
Carbon aside, the beavers’ wetlands also filtered out one ton of nitrogen, which becomes a pollutant when released at high concentrations into riversheds, and prevented that eroded soil from becoming lost. A 2009 report estimated that agricultural soil erosion in the United Kingdom annually costs £45 million — $60 million in U.S. dollars — in damage. Beavers might offset that, suggest Brazier and colleagues, adding yet another line to the flood-controlling, biodiversity-promoting, recreation-enhancing ledger of their services.
Given the accomplishments of just one pair observed by Brazier’s team, the landscape-scale possibilities are enormous. Beavers can “deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes,” write the researchers, “limiting negative downstream impact” of agricultural pollution. To put it another way: beavers could help clean up our messes. The same applies to the rest of Eurasia, where beavers were eradicated from much of their historical range, and also North America, where their populations are now perhaps one-tenth of pre-colonial levels.
Their reintroduction to the United Kingdom, however, has been controversial, with farmers upset by beavers blocking irrigation channels. In North America beavers are hunted and trapped, and frequently killed for cutting down trees or flooding roads. As impressive as beavers are at engineering ecosystems, an even greater feat of social engineering may be required for people to accept them.
Source: Puttock et al. “Sediment and Nutrient Storage in a Beaver Engineered Wetland. Earth Surface Processes and Landforms.” Earth Surface Processes and Landforms, 2018.
Image: Lois Elling / Flickr
