HR: 0800h
AN: B11A-0051    [Abstracts]
TI: Seasonal Variability in Dissolved Organic Matter Quantity and Composition from the Yukon River Basin
AU: * Spencer, R G
EM: rgspencer@ucdavis.edu
AF: University of California, Davis, Department of Land, Air & Water Resources, Veihmeyer Hall, One Shields Avenue, Davis, CA 95616, United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: United States Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AU: Wickland, K P
EM: kpwick@usgs.gov
AF: United States Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AU: Striegl, R G
EM: rstriegl@usgs.gov
AF: United States Geological Survey, Denver Federal Center, Lakewood, CO 80225, United States
AU: Hernes, P J
EM: pjhernes@ucdavis.edu
AF: University of California, Davis, Department of Land, Air & Water Resources, Veihmeyer Hall, One Shields Avenue, Davis, CA 95616, United States
AB: The Yukon River basin (YRB) is one of the largest in North America draining an area of 855 x 10³ km² in northwestern Canada and central Alaska and is a major source of terrigenous organic matter to the eastern Bering Sea and Arctic Ocean. The Yukon is also a relatively pristine catchment draining a vast area of taiga that is exceptionally susceptible to climatic change. Dissolved organic matter (DOM) plays a fundamental role in ecosystem biogeochemistry and is ubiquitous in aquatic systems. Samples were collected over a five year period from 2001 to 2005 from a number of locations and at different points in the hydrologic regime throughout the YRB. Sample locations represented different locations on the mainstream of the Yukon River, as well as tributaries ranging from organic rich black waters draining permafrost impacted watersheds to those dominated by glacial melt waters and groundwater. Dissolved organic carbon (DOC) concentrations were observed to vary greatly from 1.5 to 26.1 mgCL^-1 depending on source waters and time of year. Specific UV absorbance at 254 nm (SUVA) was also determined and ranged from to 1.3 to 4 highlighting the range in dissolved aromatic carbon content from different sources within the YRB. The hydrophobic acid (HPOA) fraction of the DOM was isolated from samples by XAD-8 resin adsorption for further investigation of DOM composition. The HPOA fraction represented 32 to 57 % of the total DOC for the range of samples studied. SUVA values from the HPOA fraction were higher than the unfractionated water samples (2.5 to 4.4) indicating a higher aromatic content for the HPOA fractions relative to the unfractionated DOM. However, the HPOA SUVA showed a good correlation to the unfractionated water samples SUVA (r² = 0.84, p<0.01). Dissolved lignin phenols were measured on the HPOA fraction in order to trace vascular plant derived material. The ratios of different lignin phenols (e.g. syringyl to vanillyl; S:V and cinnamyl to vanillyl; C:V) can be used to distinguish between angiosperms and gymnosperms and woody and non-woody vascular plant materials, respectively. In addition, acid to aldehyde ratios of vanillyl and syringyl phenols can indicate the degree of oxidation and have been shown to increase with increased microbial and fungal breakdown. Lignin phenol concentrations varied between 6.7 to 50.5 ug L^-1 dependent on source waters and time of year of sampling. The lowest concentrations of dissolved lignin were typically observed in samples taken from under ice prior to the spring melt and in groundwater dominated samples. Most YRB C:V and S:V signatures were consistent with a mixture of traditionally defined angiosperm non-wood tissues and gymnosperm wood sources. Lignin phenol concentrations were also observed to correlate to SUVA on the HPOA fractions (r² = 0.71, p<0.01) and the whole water samples (r² = 0.73, p<0.01). To further investigate the sources of DOM in the YRB a number of distinct endmember plant and litter materials were leached for between 194 to 336 hours. The contributions of these source materials using lignin phenol biomarkers of the different leached materials are shown and the potential for sourcing DOM of different origins highlighted.
DE: 0420 Biomolecular and chemical tracers
DE: 0428 Carbon cycling (4806)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 1055 Organic and biogenic geochemistry
DE: 1637 Regional climate change
SC: Biogeosciences [B]
MN: 2007 Fall Meeting