Effects of Zinc Smelter Emissions and Fire on a Chestnut-Oak Woodland

Abstract

Zinc ores have been smelted in Palmerton, Pennsylvania, since 1898. Within 2 km of the primary smelter, up to 8% Zn, 1500 ppm Cd, 1200 ppm Cu and 1100 ppm Pb by weight were found at the surface of the A1 soil horizon. Washed, oven—dried foliage of trees located near the smelters contained up to 4,500 ppm Zn and 70 ppm Cd by weight. The Lehigh Gap area of Blue Mountain near the smelters is sparsely vegetated or completely barren over an area of about 485 ha. Forests in burned and unburned areas were sampled for density and cover of trees, shrub, and herb species. Sassafras albidum and Nyssa sylvatica are the most common tree species in the burned, severely denuded areas; Arenaria patula is the most common herb. Very few tree seedlings are found near the smelters. Species which normally invade burned areas, including Populus tremuloides, Betula populifolia, Comptonia peregrina, and Pteridium aquilinum, are rare or absent at Lehigh Gap. Inhibition of seed germination and/or seedling growth by high levels of soil Zn is probably preventing establishment of these invader species. Quercus rubra and Pinus strobus seedlings planted in pots of high Zn soil collected near the smelters produced much less root and shoot growth than normal. Minimum toxic foliar levels for Q. rubra are approximately 250 ppm Zn and between 5 and 30 ppm Cd. Arenaria patula tolerated 100 ppm Zn in sand culture and a foliar content of 13,000 ppm Zn, and is probably a zinc—tolerant ecotype. Solution concentrations of up to 100 ppm Zn and 10 ppm Cd did not affect seed germination of Q. rubra, B. populifolia, and P. tremuloides, but at these metal concentrations the radicle fails to elongate. Radicle elongation occurs, but is significantly reduced, at > 1 ppm Zn or > 5 ppm Cd in solution culture. Saturation extracts of soils collected 1—5 km from the smelter contained 40—1.6 ppm Zn and 1.0—0.02 ppm Cd; thus only the Zn content of soils within 5 km of the smelter appears high enough to stunt root growth. The combined stresses of high soil—zinc levels plus fire appear to be the primary cause of the vegetation damage at Lehigh Gap. Either stress alone would have caused much less damage. Erosion and desiccation are important secondary factors preventing revegetation of the barren areas.