Soil Organic Carbon Quality in a Toposequence after the Gondola Fire using 13C NMR and MIR/PLSR.

In the Sierra Nevada, fire is a significant driver of ecosystem processes and services and biogeochemical cycling.  We have developed a collection of archived samples from before and after the Gondola Fire, and we have resampled this location 10-years post-burn to better understand the longer term impacts of wildfire on soil organic matter.  Soil samples were collected at an eroding hillslope and its downslope depositional area during the summer of 2013, 10 years after the wildfire to determine the long-term landscape effects on carbon cycling.  As depositional areas in eroding landscapes have the potential to serve as significant carbon sinks, it is crucial to understand the distribution of organic carbon fractions between these two landform positions.  Here we describe the differences between these fractions, and the long-term impact of the Gondola Fire using 13C NMR (nuclear magnetic resonance) calibration of mid-infrared spectroscopic (MIR) analyses with a partial least squares regression (PLSR).  These analyses divide the carbon into three fractions, particulate organic carbon (OC), humic OC, and resistant OC, which is consistent with charcoal.  These OC fractions can illustrate changes in soil physical and chemical properties after a fire, and the concentration and distribution of the charcoal fraction within a landscape can illustrate how carbon can become stabilized or lost on a landscape scale.