Characteristics of soil organic matter and pyrogenic carbon in soils and leachate after prescribed burning

Prescribed burning has exponentially increased in the United States over the past five years due to growing research into its use for land management and recent changes in legislation. While the impacts of wildfire on soil organic matter (SOM) composition have been well characterized, the alterations in SOM with prescribed burning need further investigation. This work aims to understand alterations in SOM in managed pine plantations under differing prescribed burn intervals (1- , 3-, 5-, and 10-year fire return intervals) and stand ages (1, 8, 33, 34, and 90 year old stands) through the use of advanced spectroscopic and spectrometric techniques (nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS)) available through the Environmental Molecular Sciences Laboratory (EMSL). In addition to shifts in bulk SOM composition, alterations in hydrologic regimes post-fire can cause alterations in the organic matter (OM) that is transported from terrestrial to aquatic systems. To better understand how prescribed burning impacts mobility of SOM, laboratory simulated leaching experiments were conducted, and extracted OM was analyzed using 1H NMR spectroscopy and FTICR-MS. Additionally, soil particle surfaces were characterized by ToF-SIMS. These results will improve our understanding of differences in dissolved OM quality under different burn regimes and forest stand management histories. We expect sites with more frequent fire return intervals to have larger pools of pyrogenic carbon (PyC) in both the bulk soil and leached OM. We also expect that sites with closed canopies will have higher OM concentration and lower PyC leaching. Understanding the role of prescribed burning in controlling SOM composition and fate as it is transported through a soil and to adjoining aquatic systems is critical for more accurate accounting of soil carbon stocks that inform Earth system models.