The composition, transport, and fate of soil organic matter and pyrogenic carbon after prescribed burning

Abstract:

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 described, the alterations in SOM with prescribed burning need further investigation. This work aims to understand alterations in SOM under differing prescribed burn regimes (1- , 3-, 5-, and 10-year fire return intervals) through the use of advanced spectroscopic and spectrometric techniques (nuclear magnetic resonance (NMR) spectroscopy and time of flight secondary ion mass spectrometry) available through the Environmental and Molecular Sciences Laboratory (EMSL). In addition to shifts in bulk SOM composition, alterations in leaching and hydrologic regimes post-fire can cause alterations in the organic matter that is transported from terrestrial to aquatic systems. To better understand how prescribed burning impacts organic matter (OM) in aquatic systems, OM will be extracted from bulk soils with water. This extractable OM will be analyzed using ¹H NMR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry at EMSL to understand differences in dissolved OM quality under different burn regimes. We expect sites with more frequent burn intervals to have larger pools of pyrogenic carbon (PyC) in both the bulk soil and leached OM. We also expect for the longer burn intervals to have greater overall OM leaching and less PyC. Previous work has shown the significance of burn severity as a control on the quality of OM leached from soil under controlled laboratory burning, however this has yet to be investigated in field settings across different burn intervals. 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 the management of soil for carbon sequestration and water quality.