Removal of terrestrial dissolved organic carbon in aquatic ecosystems of a temperate river network.

Monday, 14 December 2015: 15:25
2006 (Moscone West)
Wilfred M Wollheim1, Robert James Stewart1, George Aiken2, Kenna D Butler3, Nat Morse1 and Joseph Salisbury4, (1)University of New Hampshire, Department of Natural Resources and Environment, and Institute for the Study of Earth, Oceans and Space (EOS), Durham, NH, United States, (2)USGS, Boulder, United States, (3)USGS Colorado Water Science Center Boulder, Boulder, CO, United States, (4)University of New Hampshire, Durham, NH, United States
Surface waters play an important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the net removal of terrestrial DOC in aquatic systems is poorly constrained. We used a combination of spatially distributed sampling of three DOC fractions, nitrate, and chloride in streams of different size throughout a river network and modeling to quantify the net removal of terrestrial DOC relative to other constituents during a summer base flow period. The approach was applied to the 400 km2 Ipswich River watershed, MA, USA. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal of DOC occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change. Model fits were improved using the different DOC fractions than when using bulk DOC, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.