Impacts of the Chimney Tops 2 Wildfire on Soil and Stream Water Chemistry in the Great Smoky Mountains National Park

The 2016 Chimney Tops 2 wildfire in the Great Smoky Mountains National Park (GRSM) has given a unique opportunity to investigate the effects of wildfire in the eastern US, in a humid climate that rarely experiences wildfire. With ongoing water quality monitoring efforts in the GRSM and a 2010 soil study, pre-fire data were available for evaluation of the potential effects to water and soil chemistry. The acid-base status of soils and streams which govern transport, fate and effects of acidic pollutants were considered in this study. Soils from A/O and B horizons were compared based upon burn severity level, with categories of high burn, low/medium burn, unburned and reference. Collections began immediately after the fire and continued into 2019. A post-fire characterization was conducted for stream water and soil on chemical parameters that were also measured pre-fire. In burned soils, pH, percent base saturation, exchangeable base cations and nitrate were significantly lower than non-burned soils. Exchangeable acidity and Al were significantly greater in burned areas than non-burned areas. An increase in exchangeable Al coupled with a decrease in exchangeable base cations resulted in increased exchangeable acidity and decreased percent base saturation in burned soils. These soil impacts could affect the regrowth of sensitive plant species due to loss of available nutrient cations and increased Al. The water samples showed consistent decreases in pH, conductivity and acid neutralizing capacity (ANC) post-fire, at all sites, burned and reference. The most significant change in stream water was a decrease in ammonium in burned watersheds, however the decline in pH and ANC remains unexplained based on this study’s measured parameters. This study contributes valuable information noting the lack of post-fire export of sulfate and nitrate in streams, and generally aligns with the few studies published on responses of forest fires on soil and stream chemistry in humid, acidic environments. The relationships identified on the response of soil and stream chemical properties to burn severity will inform understanding of patterns and timing of revegetation and recovery of the ecosystem from wildfire as well as the role of wildfire in exacerbating effects of acid deposition.