These cute furry rodents almost went extinct in the 19th century, but conservation efforts have proven successful and right now, the world has a solid beaver population. But a new study conducted by Canadian researchers found that this increase in population also has some unforeseen consequences: beaver damming generates climate-changing methane emissions.

Beavers have a slight contribution to global warming, by encouraing methane emissions. Image via am980.

First of all, it has to be said that this is not a significant contribution to global warming or climate change. The analysis concluded that beaver activities contributed up to 0.80 teragrams (or 800 million kilograms) of methane to the atmosphere each year. Just so you can get an idea, the total methane emissions in the US alone come at about 700 billion kilograms in 2009 – so beavers can’t really be held accountable for such a tiny amount. It’s not really significant, especially since it can be considered as part of the natural, background emissions.

The fur trade of the sixteenth to nineteenth centuries nearly led to the extinction of beaver populations worldwide. However, after conservation efforts were amplified and the overall fur trade declined significantly, both North American (Castor canadensis) and Eurasian (Castor fiber) beavers populations grew. The North American beaver has also been introduced to Eurasia and South America. But these beaver populations have done more than just chew wood and build damns – they have created conditions for methane generation.

Colin J. Whitfield of the University of Saskatchewan in Canada led a study about the effect that the growth in beaver numbers in Eurasia and the Americas could be having on methane emissions. Beavers usually build these dams to create small, open air ponds, usually under 1,5 meters deep. In these shallow ponds carbon builds up in the oxygen-poor bottoms and generates methane, which is a potent greenhouse gas. According to Whitfield, it has long been known that release of methane from beaver ponds to the atmosphere is more intense than for other types of wetlands, so he set out to quantify just how much methane is emitted.

He and his team found that beavers have dammed up in excess of 42,000 square kilometres of aquatic pond areas, which are bordered with over 200,000 kilometres of shoreline habitat. In this process, they have generated 800 million kilograms of methane.

“The dynamic nature of beaver-mediated methane emissions in recent years may portend the potential for future changes in this component of the global methane budget. Continued range expansion, coupled with changes in population and pond densities, may dramatically increase the amount of water impounded by the beaver,” says Whitfield. “This, in combination with anticipated increases in surface water temperatures, and likely effects on rates of methanogenesis, suggests that the contribution of beaver activity to global methane emissions may continue to grow.”

Journal Reference:  Whitfield, C.J., Baulch, H.M., Chun, K.P., Westbrook, C.J. Beaver-mediated methane emission: The effects of population growth in Eurasia and the Americas, AMBIO. DOI 10.1007/s13280-014-0575-y

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