( Beavers long known for their beneficia...)Beaver dams create healthy downstream ecosystems

Beavers, long known for their beneficial effects on the environment near their dams, are also critical to maintaining healthy ecosystems downstream. Researchers have found that ponds created by beaver dams raised downstream groundwater levels in the Colorado River valley, keeping soil water levels high and providing moisture to plants in the otherwise dry valley bottom. The results will be published 8 June in Water Resources Research, a journal of the American Geophysical Union.

Cherie Westbrook of Colorado State University and colleagues there and at the U.S. Geological Survey in Fort Collins, Colorado, conducted a three-year study in Rocky Mountain National Park, examining valley ecosystems downstream in the Colorado River. They noted that water diverted by beaver dams is forced out of the natural stream channel and spreads across and down the valley for hundreds of meters [yards]. In addition, dams built on the river changed the direction of groundwater flow in the valley. The changes caused water to infiltrate the river banks and flow underground toward the sides of the valley, instead of down the center of the valley.

The researchers suggest that the elevated moisture levels found in soil surrounding the dams would otherwise require water from a very large natural flood, which they estimate as the 200-year flood, to achieve the same expansive water availability to the valley bottom. Additionally, beaver dams built away from natural river channels further redirect water across the valley, enhancing the depth, extent, and duration of inundation associated with smaller floods; they also elevate the water table to sustain plant and animal life during the dry summer season.

"This study broadens the view of the importance of beaver in the valley bottoms beyond the upstream ponds," Westbrook said. "We found that upstream ponds were not the main hydrologic effect of the dams in the Colorado River valley. Instead, the beaver dams greatly enhanced
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Source:American Geophysical Union

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