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Grad student seminar: Exploring post-wildfire water quality: Photodegradation of pyrogenic carbon

Thursday, April 30, 2020, 12:30PM - 1:30PM


Jessie Egan


Virtual meeting

Nearly 80% of the United States’ freshwater originates in forested landscapes at risk of wildfires, which influence both the terrestrial landscape and hydrologic regime by introducing a heterogeneous spectrum of thermally altered carbon compounds, known as pyrogenic carbon (PyC). Given the projected increase in both wildfire frequency and intensity, understanding the coupling of hydrologic transport and chemical fractionation that wildfires impose on water sources is critical. New research has begun to show that PyC can be quite mobile and reactive with turnover time of decades or years in soils rather than previously assumed millennia timescales, emphasizing the importance of dissolved PyC (DPyC) translocation from soils to rivers. While riverine PyC transport has been identified as a key component of the global PyC cycle, the extent to which photodegradation contributes to both short-term and long-term DPyC chemical fraction has yet to be resolved. We investigate the role of photodegradation as a major driver altering aquatic PyC physical and chemical properties. Artificial PyC was created by burning organic matter at various temperatures to isolate distinct portions of the PyC spectrum. The organic matter, including leaves and soils, was collected from Great Smoky Mountain National Park where ongoing research was being conducted following the 2016 Chimney Tops 2 wildfire. Each temperature range of the PyC spectrum was separately leached, filtered, and the dissolved fraction was placed outside and exposed to natural sunlight for various exposure times ranging from zero to 28 days. This photodegradation experiment took place in Boulder, Colorado during the summer months to maximize daily sun exposure. Photochemistry was confirmed by monitoring the photochemical formation of hydrogen peroxide via fluorescence spectroscopy. The dissolved organic matter was characterized using excitation-emission matrix (EEM) fluorescence spectroscopy and total organic carbon analysis. By isolating distinct portions of the PyC spectrum, we will better be able to anticipate the fate of PyC in watersheds effected by wildfires.