BEAVER DAMS CAN IMPROVE WATER QUALITY FOR WILD SWIMMERS AND ANGLERS

Beaver dams function as traps which delay the distribution of pollutants, improving the quality of downstream water, new research led by the University of Stirling has shown.

Scientists say the findings underline the beneficial effects beavers can have on fresh water where people enjoy outdoor pursuits such as wild swimming and angling.

Beavers were hunted to extinction in Britain 400 years ago but in the early 2000s, amid high level discussions among conservation organisations about reintroduction, there were unauthorised releases in Perthshire, before a formal multi-agency trial programme of reintroduction involving experts at the University of Stirling began in 2009 in Argyll.

Stirling’s scientists in the Faculty of Natural Sciences have researched the impact of the large semi-aquatic mammals on Scotland for more than 20 years.

A new paper published this week has revealed the results of analysis of water samples collected from a stream engineered by beavers at Bamff Estate over a two-year period.

By sampling above and below beaver dams, and at the inflow and outflow of beaver ponds throughout the seasons, scientists determined how these structures, which function as a barrier to flow, affect water quality downstream.

They discovered that the dams and ponds can trap and delay diffuse pollution created by soil erosion and livestock waste, reducing pollutant peaks by 95%. Analysis of samples show that there was a reduction in the transport and concentration of E. coli bacteria, a microbial pollutant that can cause illness.

Professor Nigel Willby, who co-authored the study, said: “Microbial pollution is likely to increase in the future due to enhanced pressures on water, food, and waste management systems so there is an urgent demand for sustainable solutions for prevention and remediation.

“In rural areas soil erosion and livestock waste are the main contributors to this issue, affecting the quality of aquatic habitats and the benefits we derive from water, including things like wild swimming and angling.

“When beavers engineer a stream, they build dams which creates barriers to flow resulting in the accumulation of water as a series of ponds – some surprisingly large. We found that these ponds can act as a trap for microbial pollutants and silt, especially when muddy or polluted waters enters a pond from upstream, reducing pollutant peaks by 95% and strongly delaying their movement which should be to the benefit of downstream systems.

“Our work adds weight to the already compelling evidence of the beneficial effects of beaver ponds in the landscape – for biodiversity, for flood risk reduction and other aspects of water quality. If we want to realise these benefits rather than robbing ourselves of them, we must find better ways to accommodate beavers in our landscapes

rather than continually removing their dams.”

Researcher Hannah White, who led the study, added: “Showing that beaver dams can help with diffuse pollution by slowing the flow of water in streams which then allows settlement and containment of pollutants adds a new option for tackling this issue in areas where beavers and their habitats are allowed to thrive.

“Scotland has an ambitious vision to be a future leader in sustainable and regenerative farming – if we want to realise that vision, we have to recognise the benefits that beaver-created wetlands can bring for nature and the environment.”

The impact of beaver dams on distribution of waterborne Escherichia coli and turbidity in an agricultural landscape was published in the journal Science of the Total Environment and was funded by the NERC Hydroscape project.

Sophie Ramsay, a member of the Ramsay family that own Bamff Estate, said: “We are delighted to see yet another vital piece of research from the University of Stirling, providing evidence from Bamff on the positive impacts of beavers. This study confirms that beavers can be not just compatible with farming but can play a significant role in the mitigation of downstream agricultural pollution.”