Iron (oxyhydr)oxide Crystallinity and Redox Conditions as a Function of Permafrost Thaw in Abisko, Sweden04/15/2020
Increasing temperatures in the arctic can cause permafrost thaw that radically changes hydrological and redox conditions in the soil. Redox sensitive minerals like iron (Fe) oxides can precipitate or dissolve in response to redox changes. Fe oxides control the cycling of nutrients such as phosphorus (P), a limiting nutrient in arctic soils, by adsorption. The effects of progressing permafrost thaw and resulting changing hydrology on redox conditions and Fe oxide crystallinity in arctic environments are still unknown. To investigate these complex interactions, an in situ incubation experiment was conducted along a permafrost gradient in arctic soils in Abisko, Sweden. Permafrost thaw in Abisko results in ground collapse and surface ponding. Mesh bags were filled with Fe rich sediments and buried in the top soil along a permafrost gradient for either one or eight weeks. Redox conditions were measured continuously along the gradient and incubated materials were analyzed with x-ray absorption spectroscopy (XAFS) for changes in Fe oxide crystallinity. Changes in total Fe and P concentration were determined by sequential extractions of the incubated material. Preliminary results show a change from oxic to anoxic conditions as permafrost thaw progresses and surface ponding occurs. XAFS show a shift toward ferrihydrite, a poorly crystalline Fe oxide, in the soils with surface ponding after eight weeks. Ferrihydrite has a high capacity for P sorption and might limit the bioavailability of this critical nutrient in thawing arctic soils and potentially limit plant growth and microbial activity.