SPATIAL VARIATIONS IN SUMMER DISSOLVED ORGANIC CARBON CONCENTRATIONS, SOURCES, AND FLUXES ACROSS THE CANNING RIVER WATERSHED IN NORTHEASTERN ALASKA

In northeastern Alaska, rivers drain continuous permafrost watersheds that span from the mountains of the Brooks Range to the coast of the Beaufort Sea, resulting in vegetation, soil organic matter, and hydrologic gradients that can vary between catchments. We studied how these landscape gradients drive spatial variability in concentrations, sources, and fluxes of dissolved organic carbon (DOC) along the Canning River watershed. Water samples were collected from the Canning mainstem and contributing streams from late June to early August 2019-2023, downstream of (i) the Brooks Range headwaters, (ii) the Brooks Range foothills, and (iii) the coastal plain and river delta. We measured DOC concentrations and radiocarbon isotopic composition, and calculated DOC flux using discharge estimates from numerical modeling. River mainstem DOC concentration more than doubled and became younger from the mountains (0.48 mg C L^-1; 805 yBP) to the delta (1.4 mg C L^-1; 525 yBP). Stream DOC concentrations were highest within the coastal plain (12 mg C L^-1) and foothills (3.1 mg C L^-1) compared to the mountains (0.48 mg C L^-1). Despite making up ~1/3 of the watershed area, the coastal plain and foothills accounted for 42% and 37% of total DOC export. These two physiographic domains disproportionately influence the age and export of summer DOC from the Canning, with implications for coastal biogeochemical cycling and responses to Arctic warming. We hypothesize this is due to strong hydrologic coupling between streams and DOC produced from young, organic-rich, soils during the wet summer months.

Primary Presenter: Craig Connolly, Environmental Protection Agency, Office of Research and Development (connolly.craig@epa.gov)

Authors:

Craig Connolly, University of Texas at Austin, presently at U.S. EPA Atlantic Coastal Environmental Sciences Division  (connolly.craig@epa.gov)

Joshua Koch, U.S. Geological Survey Alaska Science Center  (jkoch@usgs.gov)

James McClelland, University of Chicago Marine Biological Laboratory  (jmcclelland@mbl.edu)

Michael Rawlins, University of Massachusetts, Amherst,  (rawlins@geo.umass.edu)

Marisa Repasch, University of New Mexico  (mrepasch@unm.edu)