Beavers Clean the Soil

Without beaver dams, loss of nutrients from soil would increase, and pollutants from upstream erosion would afflict waterways.

Scientists at the University of Exeter looked into the beneficial functions that beaver dams perform for soil and rivers. Look how much one family of beavers can do:

The research, led by hydrologist Professor Richard Brazier, found that the work of a single family of beavers had removed high levels of sediment, nitrogen and phosphorus from the water that flowed through their 2.5 hectare enclosure.

The family of beavers, which have lived in fenced site at a secret location in West Devon since 2011, have 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.

One beaver dam can impound a lot of water, trapping sediments and reducing erosion. Photo by David Coppedge, Lundy Canyon.

Soil from upstream managed lands had leached nitrogen and phosphorus into runoff. This runoff, 70% of which came from soil, became trapped in the beaver ponds. The scientists found that the beaver ponds trapped 100 tonnes of sediment in their ponds. Without them, the pollutants would cause harm to fish and humans, because high concentrations of nitrogen and phosphorus need to be removed in water treatment plants. Professor Richard Brazier saw the good news from beavers after the bad news from humans:

Professor Brazier said: “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. 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.”

Beaver pond with beaver house reached by underwater entrance. Photo by David Coppedge, McGee Canyon.

Previously trapped for their fur, or killed as pests, the studies show that beaver play an important role in the world. Insects, fish, other mammals, birds and plants all benefit from the deep ponds impounded by these busy animals who make large dams and protected dens one branch at a time. They are best left alone to do what they instinctively know how to do.

The old IMAX film “Beavers” is a gem that deserves to be watched by families. How such medium-size rodents do what they do is really quite astonishing. Their fur, their noses, their teeth, their webbed feet, their tails—everything about them is just right for their job. Bringing Darwin into this story would be like blasting a vuvuzela during a Bach symphony.