Equisetum and the cycling of mercury at Mount St. Helens: Plant-soil relations, 1980–1984

The Hg content ofEquisetum shoots at six stations near Mount St. Helens rose to a peak value in July 1982, 26 mo after the great eruption of May 1981. The July 1982 peak in plant Hg content was followed by a continual decline in plant tissue Hg at all six stations as measured in September 1982 and August 1984. During this 2 yr period, soil Hg levels declined at only three of the six stations, while remaining essentially unchanged at two stations and increasing nearly 20-fold at one station. Therefore, soil Hg behaved independently with respect to plant Hg at least at three of the six sites. This follow-up study at Mount St. Helens supports the notion of a major source of atmospheric mercury which is taken up directly by plants.