CHANGES IN MINERAL-SOIL ORGANIC MATERIAL POST WILDFIRE IN A ZERO ORDER BASIN

Abstract

Carbon sequestered in soils generally exceeds that in living flora. Therefore understanding carbon dynamics and storage is critical to developing a better understanding of the global carbon balance and flux. The relationship between carbon character and the mineral-organic moieties controls short and long-term carbon cycling. Wildfire returns the above-ground carbon to the subsurface, whereby it supplies essential nutrients or remains energetically unfavorable to microbial respiration. The response of the soil post-wildfire was investigated in this study. Soil samples from nested pits were collected in a zero-order basin located within the Jemez River Basin Critical Zone Observatory, NM USA, with a >50 year fire-free history, before and after a natural fire. Sampling included 2011 samples (pre-fire), 2013 (directly post-fire), and 2015 (post-fire) at nearly identical locations and depths to compare wildfire effects on soil composition, carbon character with depth, and mineral-soil organic matter (SOM) interaction. Mineral-SOM interaction was characterized by transmission Fourier transform infrared (FTIR) spectroscopy, an essential tool for providing insight into SOM composition with the ability to observe small changes in organic complexes, especially SOM-mineral functional groups. FTIR spectroscopy exploits the response from infrared (IR) radiation active molecules in the mid-IR range (600-4000 𝑐𝑚 −1 ). An absorbance of an IR active molecule is observed as energy transferred via vibrations, rotations, and bending of the molecule. This study will augment quantitative data collected on the pyrogenic carbon (PyC) (Pohlmann et al., separate study) to elucidate connections between OM-mineral interactions, short and long-term carbon storage (as biochar) and wildfire. By comparing the SOM character as a function of time, depth, and in response to a natural but significant perturbation, a better understanding can be developed on how mineral-OM interactions change when subjected to wildfire.