Collaborative Research: RAPID: Mechanisms and fate of fire-induced carbonate formation in a cold desert ecosystem

Drylands have always been linked with wildfires, but climate change and shifts in vegetation have altered the fire regime and carbon balance of these sensitive ecosystems. Wildfires consume vegetation, releasing stored organic carbon as carbon dioxide (CO2), a greenhouse gas. Recently, however, the accumulation of salts in the form of soil carbonates (i.e., inorganic carbon) have been observed after dryland wildfires. The mechanisms of fire-induced carbonate accumulation (FICA) and its importance to long-term carbon storage remain unknown. This research begins to address a gap in our knowledge about the origin, fate, and impact of fire-induced soil carbonates as wildfire activity is at its historic highest levels in drylands. Here, researchers characterize the environmental controls on fire-induced carbonate accumulation using a prescribed rangeland fire slated for September 2023 in an already intensively instrumented catchment of the US Department of Agriculture’s Northwest Watershed Research Center (NWRC) and Critical Zone Observatory (CZO). The research is part of an interdisciplinary group of researchers and land managers collaborating to enhance understanding of wildland fires to create greater regional impact. This research will characterize the abiotic factors contributing to fire-induced carbonate accumulation (FICA) using an experimental fire in September 2023, located within the cold desert, sagebrush steppe ecosystem characteristic of southern Idaho and the surrounding region. A combination of factors including soil pH, calcium availability, soil carbon dioxide (CO2) concentration, and extracellular enzymatic activity appear to lead to FICA, but the exact mechanisms involved, and the source and fate of this carbon remain unresolved. Uncommon in rangeland wildfire studies, the project will 1) collect soil samples just before the fire, and contrast these with post-fire conditions to facilitate future investigation of controls on FICA, and 2) measure soil CO2, moisture, and temperature conditions before, during, and for 9 months after the fire – a unique and perishable dataset, and something that has never been done to study the mechanisms driving carbonate formation caused by fires. Sample collection and sensor measurements will be stratified across north- and south-facing aspects, and burn severity treatments (i.e., vegetation types) to understand landscape controls on FICA. Soil samples are also considered perishable and will be archived for future investigation beyond initial pH, EC, and carbonate determination. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.