HR: 16:30h
AN: B24A-03 INVITED     [Abstracts]
TI: Dissolved Organic Matter in the Yukon River Basin
AU: * Aiken, G
EM: graiken@usgs.gov
AF: U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Striegl, R
EM: rstriegl@usgs.gov
AF: U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Schuster, P
EM: pschuste@usgs.gov
AF: U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AB: Source materials, watershed geochemistry, oxidative processes and hydrology exert strong influences on the nature and reactivity of dissolved organic matter (DOM) in aquatic systems. At present, a critical question in carbon cycling is how climate change could alter the fate and chemical nature of dissolved organic carbon (DOC) released from watersheds, particularly those underlain by permafrost, and transported to rivers, lakes, estuaries and coastal waters. The spatial and temporal variability of DOM in surface waters associated with the Yukon River are being studied to better define processes controlling DOM in this system. Like many northern ecosystems, the Yukon River Basin is experiencing melting permafrost, drying of upland soils and changing wetland environments. Study results indicate that the transport of DOM in the river and its major tributaries is strongly seasonally dependent. Specific ultraviolet absorbance (SUVA) data, an excellent indicator of aromatic carbon content of DOM, also indicate a large variation in the chemical nature of the organic matter transported by the river. Lowest DOC concentrations and SUVA values were observed for samples collected in the winter under low flow conditions and for tributaries dominated by ground water inputs. Greatest DOC concentrations and SUVA values were measured on samples collected during the spring on the leading part of the hydrograph. High SUVA values are indicative of greater amounts of organic material originating from higher plants that are present in upper soil horizons and wetlands of the watershed. Aquatic humic substances collected from the Yukon River during the snowmelt period were found to have low nitrogen contents and greater amounts of aromatic C relative to samples from other aquatic environments. Low N content and high aromaticity are indicative of humic substances evolved from higher plant sources with little alteration resulting from microbial degradation or soil interactions. In addition, 14C data indicate that the DOM in the river is comprised of recent C and suggests that, at this stage of permafrost melting, the C signal is dominated by young organic matter. Continued permafrost melting can be expected to result in significant changes in hydrologic flow paths and soil microbial processes in the Yukon River Basin watersheds that will alter both the amount and reactivity of DOM transported by the river.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
DE: 1030 Geochemical cycles (0330)
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting