DOC quality in boreal forest streams along a latitudinal gradient through interior Alaska

J.A. O'Donnell¹, E.S. Kane², J.B. Jones¹, G.R. Aiken³, and J.W. Harden⁴.¹Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, USA 99775, ²Forest Science Department, University of Alaska Fairbanks, Fairbanks, Alaska, USA 99775, ³United States Geological Survey, Boulder, Colorado, USA 80303 , ⁴United States Geological Survey, Menlo Park, California, USA 94025

In the boreal forest, terrestrial inputs of dissolved organic carbon (DOC) are a dominant source of organic matter to aquatic ecosystems. The fraction of DOC that is readily metabolized (labile DOC or LDOC) often varies among streams due to differences such as watershed hydrology and wetland extent. We examined LDOC and DOC quality in streams along a latitudinal gradient in interior Alaska on four dates between June and September 2005. LDOC was measured as the fraction of DOC lost over four-week incubation.

Stream DOC concentration and specific ultraviolet absorbance (SUVA), a measure of DOC aromaticity, varied among watershed types. Groundwater- and glacially-fed streams had low DOC concentrations (mean = 5 mgC L^-1) and SUVA (mean = 1.2 L mgC^-1 cm^-1), whereas streams draining watersheds with extensive wetlands had high DOC and SUVA (mean = 21 mgC L^-1 and 3.5 L mgC^-1 cm^-1, respectively). Stream temperature explained 24% of the variance in DOC concentration (p = 0.001), but was not a significant predictor of SUVA. LDOC averaged 24% across all streams and was negatively correlated with SUVA (p = 0.02). In addition to temperature, watershed topography and hydrology appear to be important controls on DOC in these streams.