HR: 0800h
AN: H51D-1171    [Abstracts]
TI: Characterization of Dissolved Organic Carbon Flushing in Three Small Watersheds, Oregon USA
AU: * Hood, E
EM: eran.hood@uas.alaska.edu
AF: University of Alaska Southeast Environmental Science Program, 11120 Glacier Hwy, Juneau, AK 99801 United States
AU: Gooseff, M N
EM: michael.gooseff@usu.edu
AF: Colorado School of Mines Dept. of Geology and Geologic Engineering, 1516 Illinois Street , Golden, CO 80401 United States
AU: Johnson, S L
EM: sherrijohnson@fs.fed.us
AF: USFS PNW Research Station, 3200 SW Jefferson Way , Corvallis, OR 97331 United States
AB: The hydrologic and biogeochemical responses of forested watersheds to inputs of rainfall and snowmelt can be an indicator of internal watershed function. We are studying how the flushing of dissolved organic carbon (DOC) in response to storm events may be sensitive to DOC pools contributing to runoff. We assessed how the quantity and quality, both chemical and spectroscopic, of DOC changed in response to a six day storm event during the wet season of 2003 in three small ($<$1 km2) basins in the H.J. Andrews Experimental Forest, Oregon. The watersheds included one old-growth watershed (WS 2) and two previously logged watersheds (WS 1 and WS 10). Pre-storm concentrations of DOC ranged from 1.5 to 2.2 mg C L$^{-1}$ in the three watersheds and increased approximately three-fold on the ascending limb of the storm hydrograph. Initial and stormflow concentrations of DOC were both highest in the unharvested, old-growth watershed. The specific UV absorbance (SUVA, 254 nm) of DOC in the three watersheds increased with rising DOC concentrations during the storm suggesting that the DOC mobilized from catchment soils during storms is more aromatic than the DOC present during baseflow. The increase in UV absorbance ranged from 8 to 36% and was most pronounced in the catchments that had been previously harvested. Chromatographic fractionation of DOC similarly showed that there was a shift in the chemical character of DOC during the storm, with the percentage of DOC composed of non-humic material decreasing by 8-20% from pre-storm conditions and then rebounding after the conclusion of the storm. Fluorescence properties of DOC during the storm event suggest that there is not a pronounced shift in the relative proportion of streamwater DOC derived from terrestrial versus aquatic precursor material. Taken together, these results suggest that DOC characterization can be used as a decisive tool to investigate changing sources of DOC and water within forested watersheds. Further complementary work assessing within watershed DOC pools could improve upon biogeochemical and hydrologic interpretation of watershed functions.
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting