HR: 14:41h
AN: OS43B-04    [Abstracts]
TI: Dissolved Organic Carbon Export by the Yukon River
AU: * Aiken, G
EM: graiken@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Striegl, R
EM: rstriegl@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Dornblaser, M
EM: mmdornbl@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Raymond, P
EM: peter.raymond@yale.edu
AF: Yale University, School of Forestry and Environmental Studies, New Haven, CT 06511 United States
AU: Wickland, K
EM: kpwick@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AB: Spatial and temporal variability of dissolved organic carbon (DOC) in surface waters associated with the Yukon River are being studied to better define processes controlling DOC in this system and to examine the effects of warmer temperatures on C export from large permafrost dominated watersheds. The Yukon River Basin is experiencing melting permafrost, drying of upland soils and changing wetland environments. Results from the Yukon River at Pilot Station (YRP) indicate that DOC concentration and specific ultraviolet absorbance at 254 nm, an indicator of DOC aromaticity, were strongly seasonal. Values were greatest during the spring flood (May 1-June 30), suggesting a high contribution of minimally altered terrestrial plant material; intermediate during summer through autumn (July 1-October 31); and lowest during winter low flow (November 1-April 30). DOC collected downstream of YRP during summer 2003 was primarily of recent terrestrial plant origin. We applied the USGS LOADEST program to daily stream flow and DOC measurements to calculate water and DOC flux at YRP during 1978-80 and 2001-03. Annual water discharge averaged 193 ± 24 km³ a^-1 during 1978-80 and 212 ± 21 km³ a^-1 during 2001-03. Based on the seasonality of water discharge and DOC concentration and chemistry, fluxes were divided into spring flood, summer through autumn and winter flow periods. Linear regressions of C flux versus total water discharge were calculated for each flow period and the 1978-80 and 2001-03 results were compared by Analysis of Covariance. DOC export decreased from ~ 0.88 Tg C /100 km³ water in 1978-80 to ~ 0.53 Tg C / 100 km³ water in 2001-03, during summer through autumn. Summer through autumn coincides with high soil biological activity and a possible basin-wide increase in the depth and duration of the soil active layer over the past several decades. There was no significant difference in DOC flux during winter when river discharge is dominated by groundwater or during the spring flood when DOC is efficiently flushed from the watershed with little or no biogeochemical alteration. Reduced summer through autumn DOC export from the Yukon River basin contrasts with observations of increased DOC concentrations in rivers in northern Europe and contradicts suggestions that rising temperatures in northern latitudes might result in a significant increase in the flux of DOC to the marine system.
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1055 Organic and biogenic geochemistry
DE: 4806 Carbon cycling (0428)
DE: 4825 Geochemistry
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005