RISK ASSESSMENT AND REMEDIATION OF SOIL AND AMENDMENT TRACE ELEMENTS
Title: Relating forest injury near Palmerton, PA to zinc contamination from smelting
Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 2010
Publication Date: February 1, 2011
Citation: Beyer, W.N., Krafft, C., Klassen, S., Green, C.E., Chaney, R.L. 2011. Relating forest injury near Palmerton, PA to zinc contamination from smelting. Environmental Toxicology and Chemistry. 61:376-388.
Interpretive Summary: The north side of Blue Mountain near Palmerton, PA, suffered severe zinc phytotoxicity due to deposition of smelter emissions over 90 years until 1980 when the smelter closed. Part of the mountainside was remediated and has grass, forb and shrub cover, but un-remediated mountainside soils remain nearly barren of plant cover. The present experiments were undertaken to examine additional effects of the historic soil contamination on plants in the parts of Blue Mountain which remained vegetated, soils past the center of the mountain toward the south, and soils more distant from the smelters. Locations were selected in specific soil series along the ridgetop from relatively uncontaminated to severely contaminated with zinc and other elements emitted by the smelter. Forest cover was evaluated at each site as well as total and plant available metals and nutrients with the intent to establish the relationship between measured soil zinc and reduction in forest plant cover. Canopy closure, the best overall metric of forest structure, was reduced to about half of the average reference value at 3000 mg/kg of zinc (144 mg/kg of Sr(NO3)2-extractable zinc). Seedling density was the most sensitive variable of the forest, decreasing from 9 per sq m at the reference sites to 2.6 per sq m at about 540 mg/kg of zinc (35 mg/kg of Sr(NO3)2-extractable zinc). Because the smelter emissions were alkaline, already zinc phytotoxic soils near the smelter have higher initial pH than soils further from the smelter, and the higher soil pH reduces the toxicity of accumulated soil zinc. However, natural acidic rainfall will continue to reduce soil pH, and increase the phytoavailability of soil zinc such that forest injury is expected to become more severe over time if no action is taken to remediate the toxicity of the metals in the Blue Mountain soils. The results relating soil zinc to reduction in forest cover provide information to make management decisions about remediation of the contaminated publicly owned soils near Palmerton.
The forest on Blue Mountain, near Lehigh Gap, has been injured by emissions from two historic zinc smelters in Palmerton, PA, located to the north at the base of the mountain. The uppermost soil and litter from sites along a transect just south of the ridgetop contained from 64 to 4400 mg/kg of zinc. We took measurements at 15 sampling sites; canopy cover, shrub and vine cover, and total species richness were negatively correlated with soil Zn concentrations, and herb cover, rock cover, and percent snags were positively correlated with soil Zn concentrations, the probable, principal cause of injury. Understanding how ecotoxicological injury is related to soil Zn concentrations helps us to quantify the extent of the injury on Blue Mountain as well as to generalize other sites. Canopy closure, the best overall metric of forest structure, was reduced to about half of the average reference value at 3000 mg/kg of Zn (144 mg/kg of Sr(NO3)2-extractable Zn). Seedling density was the most sensitive variable of the forest, decreasing from 9 per sq m at the reference sites to 2.6 per sq m at about 540 mg/kg of Zn (35 mg/kg of Sr(NO3)2-extractable Zn). Liming the strongly acid Hazelton soils at the sites would partially ameliorate the observed phytotoxicity. Phytotoxicity, desiccation from exposure, and a gypsy moth infestation combined to form a barren area on the ridgetop. Restoring this barren area to native forest would require protecting saplings from desiccating winds, as well as reducing phytotoxicity.