Organic-Horizon Lead, Copper, and Zinc Contents of Mid-Atlantic Forest Soils, 1978–2004
2010
Johnson, A. H. | Richter, S. L.
Organic soil horizona were important sinks for atmospherically delivered Pb, Cu, and Zn throughout the latter part of the 20th century. By measuring the organic matter content and the concentrations and amounts of Pb, Cu, and Zn at 28 sites that had not been disturbed by fire or human activity between 1978 and 2004, we repeated a previous study of forest floor metal content in West Virginia, Maryland, Pennsylvania, New Jersey, New York, and Connecticut. Organic matter mass increased (P < 0.05) at many sites, but when all sites are pooled, there was not a statistically significant change. Lead concentration and mass in the forest floor decreased (P < 0.05) at nearly all sites, with median changes of −65 and −57%, respectively. The decrease in Pb amount was significantly correlated with O horizon thickness, suggesting that as litter, largely free of Pb, was added at the surface, the Pb added to the forest floor during the 20th century was migrating downward into the mineral soil. In 2004, Cu and Zn concentrations and amounts were dramatically lower at sites near point sources that had ceased operating in the 1970s or 1980s, and they decreased (P < 0.05) across the region. By 2004, nearly all of the sites had forest floor Pb, Cu, and Zn concentrations well below the levels associated with adverse effects on microbial respiration, suggesting that these metals are not altering forest floor decomposition or nutrient cycling rates.
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