Forest fires that have burned thousands of acres near Durango over the last several years may be responsible for unlocking the mercury trapped beneath the soil in the San Juan National Forest and allowing it to wash into Vallecito Reservoir northeast of Durango, according to preliminary findings by a University of Colorado at Boulder engineering professor.
Vallecito is one of five reservoirs in the Four Corners region under fish consumption advisories due to elevated mercury levels in fish. The reservoir is used for recreational fishing, irrigation and water sports.
Professor Joseph Ryan in the department of civil, environmental and architectural engineering at CU-Boulder has been studying the issue of mercury mobility in southwestern Colorado with the Mountain Studies Institute in Silverton for the last one and a half years. Recently, he and his colleagues received a $690,000 grant from the National Science Foundation to expand on the work.
Coal-fired power plants in the Four Corners region are believed to be the primary source of mercury in La Plata and Montezuma counties. The mercury would be harmless if not for the sulfate-reducing bacteria beneath the soil that turns it into methylmercury, a toxic substance that is readily absorbed in the fatty tissues of organisms, according to Ryan.
When a large forest fire such as the 2002 Missionary Ridge Fire burns through an area containing mercury from atmospheric deposition, it appears to make matters worse by oxidizing sulfur molecules that bind the mercury in organic matter in the soil. This causes the mercury to be released and allows it to be more readily converted to methylmercury.
"We think the Missionary Ridge fire might have resulted in the fish consumption advisories for mercury that are now in effect at Vallecito Reservoir," Ryan said.
Ryan's initial research on the mercury problem was funded by university sources, including the CU-Boulder Outreach Committee, Undergraduate Research Opportunities Program and College of Engineering and Applied Science. The new grant will allow for more detailed studies, with $150,000 of the grant going directly to the Mountain Studies Institute.
Ryan will collaborate with Koren Nydick of the Mountain Studies Institute, George Aiken at the U.S. Geological Survey and Kathryn Nagy of the University of Illinois at Chicago. Students from CU-Boulder and Fort Lewis College will participate in the studies, which will include analyzing soil samples both before and after various prescribed burns planned in the area.
The project is one of several technical studies undertaken as part of the San Juan Collaboratory, a program established to facilitate research that serves the needs of rural southwestern Colorado and expand learning opportunities for Fort Lewis College students by creating a bridge with CU-Boulder.
For more information on the Colorado Fish Tissue study and fish consumption advisories, go to http://www.cdphe.state.co.us/wq/FishCon/index.html .