Response of soil and streamwater of watersheds in the Great Smoky Mountains National Park to fire disturbance.

Abstract:

A watershed monitoring program was established in the Great Smoky Mountain National Park (GRSM) in the early 1990s to assess effects of atmospheric deposition and long-term changes in atmospheric deposition on soils and stream water quality. Starting on 28 November 2016 a wildfire started within the Park and expanded into the city of Gatlinburg, burning an area of 72.6 km² (roughly 44.4 km² within GRSM). The region had been under an extreme drought (D4). The burned area largely occurred in the West Prong of the Pigeon River in the GRSM, a watershed that has been monitored for stream water chemistry bimonthly at three stations since 1993 and at lesser intervals at an additional 15 sites. Soil chemistry has also been previously characterized in the burned watershed. There have been few comprehensive studies of the biogeochemical response of forest watershed in the eastern U.S. to fire. Given the elevated pools of soil nitrogen and sulfur due historical atmospheric deposition and the inherently low base saturation, we envision a complex response after fire. It is likely that there will be increases in soil mineralization, nitrification and nitrate leaching following fire disturbance, but also the enhanced supply of base cations from ash should serve to increase the low soil base saturation and neutralize acid inputs. The degree to which nitrate or base cation release dominate should influence the acid-base response and the mobilization/immobilization of sulfate, phosphorus, aluminum and other trace metals, and this interplay will likely vary in space and time. Observations from stream chemistry from immediately after the fire and long-term model simulations of watershed recovery from fire disturbance will be presented. As fire will likely become more common in forest watersheds in the Southeast under a changing climate, it will be useful to understand how recovery from acid deposition progresses under this new regime.