Residual Metals in Prescribed Fire Pile Burn Soils at Jasper Ridge Biological Preserve ('Oochamin 'Ooyakma)

Fire has been and will continue to be an important process in California landscapes and communities. Prescribed fire is playing an increasing role in maintaining fire regimes and developing sustainable management practices that protect ecosystems and communities alike. Fire has inherent risks, including to public health, the most well studied being the impacts from smoke. Additional and important impacts may arise from ash and soils that can be inhaled by fire professionals or lofted by winds and transported to nearby communities. My thesis examines the residue of soil-borne metals after prescribed burns to evaluate ecosystem and human health impacts. Chromium, Ni, Mn, and Fe were measured in ash and soil from pile burns in oak woodlands and chaparral at Jasper Ridge Biological Preserve ('Oochamin 'Ooyakma) (JRBP('O'O)), CA. Manganese was the only element measured that had an increased concentration following pile burning from the input of vegetation ash. Both water extractable and bioavailable concentrations (through inhalation) were measured in wind-dispersible fraction (< 53 μm). Chromium and Fe had decreased solubility, after pile burning, likely from minerology changes and high pH, while Mn and Ni had mixed responses. Prescribed fire pile burn samples were compared with wildfire samples from the 2020 Hennessey Fire (a part of the LNU Lightning Complex) in the North Coast Range, CA. Wildfire samples had significantly higher levels of naturally occurring metals than the JRBP('O'O) pile burns. Additionally, high levels of Cr(VI), a potent carcinogen, were in wildfire ash and soils, but absent in pile burn soils. Pile burning is thus an effective way to decrease fuel loads while minimizing risks from trace metals especially when near communities or on mafic geologies.