- Mercury Mobilization Due to Fire (Prescribed Burning) – Boundary Waters Canoe Wilderness Area, Superior National Forest
Mercury is a leading environmental contaminant that has been identified in both populated regions and remote wilderness areas. Mercury is of particular concern because it biomagnifies up the food chain in aquatic ecosystems. Although the cycling of mercury through forested and aquatic systems has been studied, little is known about the cycling of mercury in response to wildland or prescribed fires. This issue is important because prescribed burns are a useful tool in fuels management.
This study is determining if additional transport and deposition of mercury is caused by fire. The hypothesis is that prescribed fires will affect mercury cycling by increasing the mobilization and transportation in burned watersheds. The additional mercury loading would likely lead to an increase in fish mercury concentrations.
Mercury contamination in Minnesota and other Great Lake States is of special concern. Fish consumption advisories are already in effect due to the elevated mercury levels in these regions. Within Minnesota, the highest mercury levels are found in the interior lakes of the northeast including the Superior National Forest and in the Boundary Waters Canoe Area Wilderness (BWCAW). Due to the major blowdown event of July 1999, an aggressive prescribed burning was developed by the Superior National Forest for the BWCAW. Our research is utilizing their prescribed burning program to compare undeveloped lakes in both burned (treatment lakes) and unburned (control lakes) watersheds. Mercury cycling is evaluated by measuring total-mercury, methyl-mercury (bioaccumulative form of mercury) and other important ions in precipitation, throughfall, soil, lake water and in 1+ year fish (perch) both pre-burn and post-burn to assess sources of mercury and determine if changes in sources alters the concentration of mercury in fish.
If prescribed fire enhances the watershed transport and bioaccumulation of mercury in fish, other fuel reduction techniques and / or post-fire management should be considered. This is especially relevant in sensitive regions such as the boreal region where high levels of mercury in fish is already a concern.
Superior National Forest
University of Minnesota
United States Geological Survey