Trace Metals in Organic Horizons of High Elevation Forested Soils in Maine.

Trace metals in mountain ecosystems of the northeastern United States have received considerable attention in recent years as researchers examine the effects of atmospheric deposition on the health and function of forests.  High elevation soils are particularly sensitive to changes in atmospheric chemistry due to higher deposition of pollutants by wet and dry deposition, interception of wet cloud moisture, the formation of rime ice, and the tenacity of highly organic soils to retain trace metals.   The purpose of this research project was to assess concentrations and spatial and temporal changes in trace metal concentrations on six mountains in Maine.  This was done by collecting soil samples from organic and mineral horizons along an elevational gradient, and analyzing the samples for various trace metals, including As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V and Zn.  The samples were analyzed for trends in metal concentration with elevation.  This data was also compared with data collected from the same sites 14 and 31 years ago to assess changes in metal concentration, and therefore atmospheric deposition, over time.  Analysis of mineral horizons shows an overall slight increase in trace metal concentration with increasing elevation, with a few exceptions.  Metal variability in organic horizons increased with increasing elevation.  The organic horizon data show that all mountains have zinc and lead concentrations that are at least a tenfold magnitude higher than concentrations collected 14 years ago, and at least twice as high as EPA limits.  Levels of cadmium, copper, and nickel also increased substantially since previous studies, but mercury levels decreased to below detection limits.