HR: 0800h
AN: B21C-0898    [Abstracts]
TI: Dissolved Organic Matter Controls on Terrestrial Carbon Sequestration and Export in Contrasting California Ecosystems
AU: * Sanderman, J
EM: jsandman@nature.berkeley.edu
AF: University of California, Berkeley EPSM - Ecosystem Sciences , 151 Hilgard Hall - MC3110, Berkeley, CA 94720
AU: Amundson, R
EM: earthy@nature.berkeley.edu
AF: University of California, Berkeley EPSM - Ecosystem Sciences , 151 Hilgard Hall - MC3110, Berkeley, CA 94720
AU: McColl, J G
EM: for\_soil@nature.berkeley.edu
AF: University of California, Berkeley EPSM - Ecosystem Sciences , 151 Hilgard Hall - MC3110, Berkeley, CA 94720
AB: Here we report results from the first year of a study characterizing dissolved organic carbon (DOC) fluxes within two first-order watersheds: (1) a humid coastal forest and (2) a semi-arid coastal prairie. Our goals are to quantify (1) the importance of DOC in redistributing C within the soil profile; (2) the magnitude of DOC losses relative to respiratory losses; and (3) seasonal changes in DOC export (both in magnitude and composition) from these upland soils to the local stream network. We are continuously monitoring hydrologic conditions and periodically collecting water samples for chemical analysis in order to construct detailed DOC budgets for these two watersheds. We are utilizing $^{13}$C, $^{14}$C and $^{13}$C NMR analyses on DOC and relevant soil C fractions to reveal numerous insights into information on the internal transformations of organic matter as it moves through the soil in and out of the aqueous phase. Analyzing both the solid and dissolved phase of C allows us to discern the sources and sinks of DOC as rainfall moves down through the soil and ultimately out into the stream network. Results thus far (for the 03/04 water year) show that, in the redwood stand, rainfall mobilized 450 kgC ha$^{-1}$ yr$^{-1}$ as DOC from the O horizons, but while only 80 kgC ha$^{-1}$ of that was leached below the A horizon and less than 10 kgC ha$^{-1}$ was exported to the stream. Laboratory leaching and sorption experiments support these data. DOC concentrations and stable C isotope composition both in soil and stream water samples exhibited pronounced seasonal trends, reflecting changes in DOC sources. Radiocarbon results for DOC and soil density fractions will also be presented. While the redwood site appears to retain DOC, the coastal prairie site is a large net exporter of DOC (stream flux = 24 kgC ha$^{-1}$ yr$^{-1}$), with concentrations and isotopic composition varying in a more complex matter with time and space that seems to correlate with the hydrologic flow path.
DE: 1836 Hydrologic budget (1655)
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting