Transport and fate of dissolved organic carbon (DOC) in rivers are important aspects of the carbon cycle along the terrestrial to freshwater to marine continuum. Recent studies have quantified fluvial DOC export to the marine environment in many systems, but in-stream losses of DOC are poorly constrained. This study compared DOC yields (kg C/ha/season) in four large watersheds, 22 tributaries to those watersheds, and 5 additional main stem locations in Maine to gain insight on in-stream DOC losses. The season was 1 April to 15 November and streams were sampled during 2011 through 2013. Discrete, monthly, DOC data and continuous discharge data were used with LOADEST regression software to calculate seasonal DOC yields. There were no significant differences in the DOC yield of the tributaries and the larger watersheds, indicating little net in-stream loss. Wetland abundance, which is associated with higher DOC yield in this environment, did not consistently increase from tributaries to the larger watershed or longitudinally along the main stems. This geographic distribution of wetlands therefore indicates that it is unlikely that inputs of DOC from un-sampled tributaries compensated for losses from sampled tributaries. Specific UV absorbance at 254 nm (SUVA<sub>254</sub>) in tributaries and along the main stems suggested dominance by terrestrially-derived (allochthonous) DOC. We did not observe consistent changes in SUVA<sub>254</sub> among tributaries and the main stems or longitudinally along the main stems, suggesting little change in DOC source and that in-stream algal sources (autochthonous) in lower reaches did not compensate for losses of allochthonous DOC. Calculated DOC uptake velocities were among the slowest reported for temperate rivers. These findings suggest that in-stream losses of DOC are minimal and that the vast majority of DOC in major rivers in Maine is transported conservatively to the coastal ocean.

Evidence for conservative transport of dissolved organic carbon in major river basins in Maine

253rd National Meeting (2017)

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