Leveraging Long-Term, Multiscale Data to Understand Increased Carbon Release in an Alaskan Boreal Fen Complex

Since 2005, the Alaska Peatland Experiment (APEX) has maintained experimentally manipulated water table levels in a rich fen to investigate how these key carbon sinks will function in an uncertain climatic future. This fen, located in an area of discontinuous permafrost, is representative of similar fens across interior Alaska, where they are considered significant carbon sinks and are projected to become more common on the landscape as climate and permafrost systems shift. Leveraging nearly twenty years of chamber and tower carbon-dioxide and methane flux data, as well as nearly a decade of both multispectral and SAR satellite data,[2] we present an improved understanding of trends in trace gas fluxes in the context of a changing water table. We evaluate potential new functional patterns for rich fens, and endeavor to create time-series maps of total carbon flux using satellite systems. While water table position and carbon flux mapping via remote sensing platforms have been successful in other peatland systems, best practices for rich fens have not yet been established. Using the impressive temporal resolution of the APEX site, we compare a suite of historically successful multispectral and SAR indices to identify and implement carbon flux mapping across the site. Sentinel-1 SAR been used to successfully map variability in Water Table position with nearly 60% accuracy. Our research has found significant changes in the carbon flux of the fen, particularly within the last 10 years. Not only has the system overall become wetter, but the fen has begun to serve as a net source of carbon to the atmosphere, rather than a sink. [EK5] This change is largely due to increases in total methane production, as ecosystem respiration does not significantly change across both flooded conditions and water treatments. In the wettest years, when the water table remains above the soil surface for much of the growing season, CH4 accounts for nearly 8% of total carbon flux, more than four times that of the driest years. By considering both environmental and carbon flux trends across the entire data set, we are better able to understand and document the long-term changes in rich fen carbon fluxes and spatially [7] scale this understanding to the growing extent of this expansive ecosystem in interior Alaska.