Скачать или смотреть Seminar: Kyounglim Kang

2025 Spring Seminar Series
Department of Soil, Water, and Climate at the University of Minnesota

Seminar: Kyounglim Kang | Wildfire produces crystalline iron and manganese phases atypical in surface soils: application of multi-model synchrotron x-ray imaging and spectroscopy techniques

Abstract: The burning of vegetation, litter, and topsoil during a wildfire results in the deposition of an ash layer on the land surface, characterized by high pyrogenic carbon content, enriched metal concentrations and alkaline properties. Despite its significance in post-fire soil biogeochemistry, the molecular-scale speciation and reactivity of wildfire ash-particularly, the fate of redox-sensitive elements like Fe and Mn have received little attention. In this study, we examined the speciation and reactivity of solid-phase Fe and manganese Mn in ash particles produced from Glass Fire (California, 2020) using (micro) X-ray Absorption Spectroscopy (XAS), Scanning Transmission X-ray Microscopy (STXM), and batch dissolution experiments. Our results demonstrated that wildfire transforms poorly-crystalline soil Fe(III) minerals (e.g., 2-line ferrihydrite) to more crystalline phases like hematite and maghemite. Additionally, the combustion of aboveground biomass and litter produced Mn(II,III) minerals including hausmannite (Mn 2+ Mn 3+ 2 O 4 ) and bixbyite (Mn 2 O 3 ). Notwithstanding the greater crystallinity and lower solubility associated with the Fe and Mn oxy(hydr)oxide phases identified in the ash samples, dissolution experiments showed greater mobilization of Fe and Mn from the ash samples than from unburned surface soil samples in the presence of pyoverdine, an analog for microbial and root exudates with high affinity for Fe and Mn. Interestingly, analyses of soil samples showed that Fe and Mn phases identified in the ash samples were largely absent from the landscape surface two years after the fire. Our result indicates that wildfire ash introduces crystalline Fe and Mn phases into surface soils that can shift the short-term biogeochemistry of post-fire soil systems and impact ecosystem recovery.