WASHINGTON, Dec. 5 (Xinhua) -- Forest fires can restructure the food webs of nearby lakes, resulting in greater mercury accumulation in trout and other top-level fish, according to a study published on Tuesday.

    Writing in Proceedings of National Academy of Sciences, researchers of Canada's University of Alberta found that fish from lakes affected by forest fires are higher in mercury than unaffected lakes.

    Lead author Erin Kelly and colleagues examined a mountain lake (Moab Lake, Jasper National Park, Alberta, Canada) affected by a July-August 2000 fire and found that mercury in rainbow trout and other large fish species was up to five times higher than before the fire.

    While a short-term discharge of mercury from the burned area to the lake was partially responsible, the primary contributor was a restructuring of the food web.

    The nutrient influx from the burned area increased lake productivity, which altered the fish's diet. Post-fire, trout began to eat smaller fish rather than invertebrates. This feeding change added another layer to the food web, causing fish at the top of the web to ingest more mercury than before the fire.

    As the occurrence of forest fires may increase due to both climate change and use of prescribed fires to counteract years of fire suppression, mercury contamination could become more widespread, the researchers said.