Wildfires change dissolved organic carbon composition in boreal headwater streams

Boreal forests are one of the largest terrestrial carbon sinks which export large amounts of carbon annually into downstream waters as dissolved organic material (DOM). Once in water, DOM can be readily consumed and respired by microbes depending on its concentration and composition, thereby offsetting carbon sequestration on land. Increasing wildfire frequency associated with climate change has the potential to change the concentration and composition of DOM exported from land into receiving waters. We tested how wildfire changes the concentration and composition of DOM exported from boreal forests into boreal shield headwater streams in northwestern Ontario, Canada over a summer growing season. We compared the composition of DOM between catchments that were either burned in the last four years (n = 10) or had been undisturbed for at least 20 years (n = 10) using optical spectroscopy and ultra-high-resolution mass spectrometry. We found a 28% increase, on average, in dissolved organic carbon concentrations in burned streams by August. Burned streams had lower H:C and higher O:C, indicating less bioavailable DOM, likely because of black carbon from the burned catchments entering the streams. These results will inform forest management policy and improve carbon accounting in Canada to meet international obligations by providing novel results on carbon movement from terrestrial to aquatic systems in context of wildfires.

Primary Presenter: Erin Matula, Trent University (erinmatula@trentu.ca)

Authors:

Erin Matula, Trent University  (erinmatula@trentu.ca)

Erik Emilson, Natural Resources Canada  (erik.emilson@nrcan-rncan.gc.ca)

Emily Smenderovac, Natural Resources Canada  (emily.smenderovac@nrcan-rncan.gc.ca)

Jeremy Fonvielle, University of Cambridge  (jaf91@cam.ac.uk)

Dan Thompson, Natural Resources Canada  (daniel.thompson@nrcan-rncan.gc.ca)

Andrew Tanentzap, Trent University  (atanentzap@trentu.ca)