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May 11th, 2009

Reducing “rock snot” in Boulder Creek

Matthew Miller, Diane McKnight, James Cullis, and colleagues have discovered that higher flow rates in Boulder Creek appear to cause a decrease in the amount of "rock snot" clinging to the rocks. Rock snot, a form of algae called Didymosphenia geminata or "didymo" for short, is native to the area. But something has caused the didymo to bloom out of control in parts of the local stream system, prompting researchers to label it a nuisance growth.

"If there's some, that's OK," said McKnight. "But if it covers the stream bed with thick mats from side to side it becomes a problem. The didymo chokes out natural algae in the stream and destroys the habitat for insects on which the fish feed."

The team's findings suggest that controlled flow releases from reservoirs during the summer could be used to limit the impact of this nuisance species in streams in the Colorado Front Range. Flows below Barker Reservoir near Nederland that are above 200 cubic feet per second--similar to those experienced last year once the reservoir started to spill in late June--appear to be sufficient to control the didymo. Such flows can make rocks move in the stream bed and destabilize the mats. Cullis is developing a two-dimensional model to predict how much water flow it would take to create movement in the stream bed at specific points in the creek.

The team worked with two projects managed by INSTAAR: the Niwot Ridge Long-Term Ecological Research Site and Boulder Creek Critical Zone Observatory. The team's research was published in Hydrobiologia, an international journal of aquatic sciences. Local radio station KUNC interviewed both McKnight and Cullis as part of a ~4-minute segment on didymo.

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