LICHENS AS MONITORS OF POLLUTANT ELEMENTS AT PERMANENT SITES IN MARYLAND AND VIRGINIA

Concentrations of sulfur, nitrogen, and seven metal elements are reported for the lichen Flavoparmelia baltimorensis from three monitoring stations in Maryland and Virginia. At Plummers Island, Maryland, 15 km from the center of Washington, D. C, lichens have been collected for nearly 100 years. The other two stations, Bear Island, Maryland (21 km) and Stony Man Mountain, Virginia (120 km), were established in the 1970's by Mason Hale to help document changes in ambient air quality in the Washington, D.C area. Concentrations of cadmium, chromium, nickel, zinc, and lead were consistently highest at Plummers Island and lowest at Stony Man Mountain; concentrations of the other four elements (nitrogen, sulfur, aluminum, and copper) were also consistently higher at Plummers Island than at Stony Man Mountain. Recent collections, in 1988 and 1992, revealed marked reductions in the concentration of all nine elements except aluminum al all three stations, providing limited, but encouraging, signs of improved air quality in the region.