Critical loads of sulfur and nitrogen and modeled effects of deposition reduction for forested ecosystems of Great Smoky Mountains National Park

Great Smoky Mountains National Park's forested ecosystems are highly vulnerable to sulfur (S) and nitrogen (N) deposition, which can harm vegetation and aquatic life. Research reveals that current deposition levels exceed critical thresholds at three of four studied sites when using protective chemical criteria like aluminum to base cations (Al:Bc) = 0.1 or no decrease in base saturation. Modeling shows that even drastic reductions—48% for S and 56% for nitrate (NO₃⁻)—fail to meet critical thresholds for acid neutralizing capacity (ANC) or prevent soil acidification. Only a 90% reduction in both S and NO₃⁻ deposition achieves ANC = 100 μeq L⁻¹ at one site, underscoring the severity of N saturation in upper sites. The study emphasizes the need for stringent chemical criteria to protect sensitive ecosystems when setting deposition reduction targets.

Pardo, L. H., Duarte, N., Van Miegroet, H., Fisher, L. S., & Robin-Abbott, M. J. (2018). Critical loads of sulfur and nitrogen and modeled effects of deposition reduction for forested ecosystems of Great Smoky Mountains National Park (, Ed.). U.S. Department of Agriculture, Forest Service, Northern Research Station. https://doi.org/10.2737/nrs-gtr-180