HR: 0800h
AN: B11A-0065    [Abstracts]
TI: Characterization of Dissolved Organic Matter in Surface, Soil, and Ground Waters of a Small (10 ha) Catchment Using Stable Isotopes (C, N, S) and Chemical Methods
AU: * Frentress, J
EM: frentrej@onid.orst.edu
AF: Oregon State University, Department of Botany and Plant Pathology 2075 Cordley Hall, Corvallis, OR 97331,
AU: Lajtha, K
EM: lajthak@science.oregonstate.edu
AF: Oregon State University, Department of Botany and Plant Pathology 2075 Cordley Hall, Corvallis, OR 97331,
AU: Jones, J
EM: jonesj@science.oregonstate.edu
AF: Oregon State University, Department of Geosciences 104 Wilkinson, Corvallis, OR 97331,
AU: Kendall, C
EM: ckendall@usgs.gov
AF: United States Geological Survey, 345 Middlefield Rd MS 434, Menlo Park, CA 94025,
AB: In order to better understand sources of dissolved organic matter (DOM) in streams at the small watershed scale, we initiated a one-year investigation of the chemical and isotopic characteristics of DOM at the HJ Andrews Research Forest in Blue River, OR. These data will be used to test two mechanistic hypotheses to explain observed hysteresis patterns where dissolved organic carbon (DOC) concentrations in surface flow are greatest during the ascending limb of the hydrograph during storms and over the water year, with decreased DOC concentrations in surface flow during the descending limb of the hydrograph: Hypothesis 1) A flushing effect with no change in dominant flowpaths; Stream DOC concentrations directly reflect the DOC concentrations in the soil that are initially high and decrease during the event and throughout the water year due to the flushing of DOC. Hypothesis 2) A change in dominance from near-surface to subsurface hydrologic flowpaths during the event, with high-DOC sources in near-surface flowpaths dominating early and low-DOC sources in groundwater dominating later in the event. In order to address this ambiguity, the characterization of DOM using stable isotopes and other fingerprinting techniques (e.g. SUVA, C:N) was used to identify sources of organic matter to streams throughout an individual storm event and through the water year. If the first hypothesis (flushing effect) is correct, DOM in surface water should carry a similar fingerprint to the DOM in soil waters throughout the rain event and water year. If the second hypothesis (change in flowpaths) is correct, the fingerprint of DOM in the surface water should closely resemble that of soil water early in the event and change to reflect a mix of the two fingerprinted DOM sources – groundwater and soil water – later in the event. In addition to established chemical characterization methods like SUVA and C:N, a new technique of DOM isolation via solid-phase extraction using C-18 resin was used to isolate DOM in water samples from surface flow, soil water, and groundwater for C, N, and S isotopic analysis. The characterization of DOM from these water sources using stable isotopes, SUVA, and C:N ratios will be applied in an endmember mixing model and compared with a model using d18O to distinguish pre-event and event water.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0496 Water quality
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1830 Groundwater/surface water interaction
DE: 1895 Instruments and techniques: monitoring
SC: Biogeosciences [B]
MN: 2007 Fall Meeting