Impact of Silverado Fire on soil carbon

The Earth’s soil contains three times more carbon than our atmosphere. Small differences in how soil carbon is stored and released can impact the carbon cycling and accuracy of climate change models. One fraction of soil carbon, pyrogenic carbon (PyC) is produced from partial combustion of soil organic matter (SOM). It is more resistant to microbial decomposition, and its longer residence in the soil provides greater potential for carbon sequestration. We sought to understand to understand the effect of a wildfire event on PyC deposits, using nitrogen and carbon isotopes as a proxy due to the effect of fractionation on isotopes caused by changes in organic matter during combustion. We hypothesized that after the occurrence of a wildfire, there will be a higher δ15N ratio (δ = delta notation) in the burned soil relative to unburned locations and that the δ13C ratio will remain constant and that total carbon (C) and total nitrogen (N) of the burned sites will be lower than in unburned sites. We collected soil samples at five sites within Limestone Canyon Preserve, an area affected by the 2020 California Silverado Fire. The results showed significant variability in δ15N and δ13C as well as total C and total N between the sites but did not support the original hypothesis. Due to variations in nitrogen cycling processes, the fractionation during combustion did not overwhelm isotopic signals of N cycle processes, which highlights the importance of establishing location-based control samples when measuring δ15N as an indicator of PyC.