RAPID: Fire Effects on Soil and Aquatic Organic Matter in a Southern Appalachian Hardwood Forest.

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The effects of forest fires are often thought of in terms acreage of trees lost or impacts on wildlife. But fires can also have an important influence the amount, kinds, and transport of organic matter that is in forest soil, with potentially large ramifications for forest productivity. However, studying the effects of wildfire is very difficult due to the rapid post-fire changes to the environment and often the lack of robust pre-fire data in locations that have recently burned. This project will take advantage of data on soil organic carbon collected prior to and immediately after the recent fire in the Great Smokey Mountains National Park to examine immediate post-fire effects on organic carbon cycling across the terrestrial-aquatic interface. The fire burned two sites with the park that are part of the National Ecological Observatory Network so it will be possible to couple a detailed pre-fire assessment of soil carbon with post-fire changes in the same locations. In doing so, this project will fill in gaps in our understanding of how fire affects forest ecosystems in the Eastern United States.Fire introduces a spectrum of thermally-altered carbon (C) such as black C (condensed-aromatic residue produced from incomplete combustion of organic matter), poly-aromatic hydrocarbons (PAHs), and low molecular weight organic acids (LMWOA) to terrestrial, atmospheric, and aquatic systems. This thermally-altered material can have important effects on quantity and quality of soil organic matter (SOM) as well as terrestrial and aquatic ecosystem function. The effects of fire on soil stocks and quality of dissolved organic matter (DOM) are poorly understood, however many streams have higher DOM concentrations post-fire, suggesting that soil concentrations of DOM increase and are mobile within the soil profile. Several pathways are available to this highly labile, hydrophilic DOC, including: (1) efficient transport to a stream where it may become an important source of carbon to aquatic organisms; and (2) efficient transport to deeper parts of the soil profile where naked mineral surfaces dominate and the sorptive capacity is highest and therefore this material can be sequestered as deep soil carbon. The partitioning of DOC between these pathways has important implications for predicting the impacts of fire on ecosystem function and services including, drinking water quality and soil carbon sequestration. The process of post-fire incorporation of these solid residues can be quite rapid but remains poorly understood. This work represents one of the first studies to examine the immediate post-fire dynamics of both particulate and dissolved classes of thermally-altered C in adjoining soils and aquatic systems.