Relating pyrogenic carbon accumulation to modern and historic fire regimes: Using estimates of peak flow rate and USLE to predict erosion

Jacob Ridlinghafer and Luke McGuire2
Department of Hydrology and Atmospheric Sciences
The University of Arizona

Since the 1980s, wildfire frequency and severity have increased, which can threaten ecosystem function, personal property, and human lives. Wildfires also lead to increased runoff, erosion, and transport of pyrogenic carbon (PyC) a charred organic byproduct of fire, that can impact downstream water quality. In this study, we analyzed PyC within soils in the Pinaleño Mountains, Arizona to understand how the movement of PyC is influenced by wildfire regime. Historically, the sites experienced different frequencies and severities of wildfire (i.e. wildfire regime). Samples were collected to quantify PyC in soil pits on hillslopes, where we expect portions of landscape to erode. In contrast, samples collected in colluvial hollows were expected to temporarily accumulate sediment. In future work, we plan to use the Curve Number method to estimate peak flow rate and subsequently predict erosion on hillslopes, and The Universal Soil Loss Equation (USLE) to predict PyC loss in colluvial hollows. Results indicate that modern fire regimes characterized by low severity fires have greater PyC accumulation when compared with areas that have typically burned at higher severities. In comparison, PyC accumulation in moderate severity regimes is approximately 70 percent of that in lower severity regimes. At one site, PyC mass showed evidence of net erosion. These preliminary results indicate lower severity fire regimes retain more PyC. This research could be used to improve wildfire land management practices, such as identifying where to perform controlled burns to reduce burn severity, or where to focus reseeding and mulching to reduce erosion.

2Department of Geosciences, The University of Arizona

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