Mercury in Vegetation
...wood that included 5-10 years of recent growth. Organic and surface mineral soil (0-25 cm) were collected at three points about 1m from each tree and oriented 120, 240 and 360 degrees. All samples were taken to the lab and frozen. Once thawed a subsample was removed and dried at 65 degrees Celsius to determine moisture content. Mineral soils were analyzed for loss of ignition by ashing at 450 degrees Celsius for 12 hours. Mercury was determined by double amalgamation cold vapor atomic fluorescence spectroscopy. It was discovered that Hg in plant tissue is derived directly from the atmosphere and not the soil. Hg concentrations in woody tissue and foliage differed by area. Mercury concentrations in the Minneapolis-St. Paul area were higher than those in the remote forested areas to the north. Concentrations of Hg in organic and surface mineral soils differed by area but not soil texture. Mercury levels in two-year old needles were twice those in one-year old needles. The results obtained in this experiment are supported by similar research studies and the researchers did an excellent job interpreting their data. Although mercury emissions generally disperse widely in the atmosphere before being deposited to the earth’s surface, a fraction of the Hg is removed near the source. Foliar Hg exchange has been shown to be dependent on the atmospheric Hg concentration, duration and rate of uptake and the length of period of stomatal uptake. This accounts for the higher deposition of Hg in the woody tissue, foliage and soils in the urban study sites. Even though concentrations of Hg in organic and surface mineral soils didn’t vary in this experiment, many researchers have observed the relationship between Hg and dissolved organic carbons. Litterfall is a source of dissolved organic carbons and an important link in the cycling of Hg in forest ecosystems because it can be enriched by dry depositon of pollutants....