HR: 10:20h
AN: H22B-01 INVITED     [Abstracts]
TI: Factors Affecting the Temporal Variation of DOC in Stream Water Across Storm Events: the Importance of Flushing, Timing of Delivery, and Production Rates
AU: * Hornberger, G M
EM: hornberger@virginia.edu
AF: University of Virginia, 411 Cabell Hall, Charlottesville, VA 22904
AU: Kaplan, L A
EM: lakaplan@stroudcenter.org
AF: Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311
AU: Newbold, J D
EM: newbold@stroudcenter.org
AF: Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311
AB: Questions related to transport of DOC from catchment soils to streams are vexed. Observed variation of DOC in streams over storm events may be due to "flushing" of DOC that builds up in unsaturated soils between events and also may be due to the timing of water delivery from riparian areas versus hillslopes. Furthermore, the rates at which DOC is produced in riparian and hillslope areas can have an impact on variation of DOC with discharge. Most reports of stream-water DOC variation across storm events in the literature show rapid initial increases in DOC on the rising limb of the hydrograph, an effect that can be attributed to flushing of a riparian zone. Graphs of concentration versus discharge (c-Q plots) typically show a clockwise looping pattern as DOC is flushed from the riparian zone and as lower-DOC hillslope water is delivered to the stream later in the event. In some instances simple mixing models appear to provide adequate descriptions of observed behavior and in other cases explicit consideration of hydrological flow paths appears to be necessary. We analyze data on discharge, DOC, and electrical conductivity for White Clay Creek in Southeastern Pennsylvania to examine how the various factors that affect temporal variability of DOC across storms manifest themselves in a Piedmont catchment of moderate topographic relief. Observations show behavior different from the norm. Although DOC increases on the rising limb of the hydrograph, elevated concentrations persist through the falling hydrograph - c-Q plots loop in the anticlockwise direction. DOC concentrations increase to a consistent maximum value of approximately 10 to 12 mg per liter and plateau there. Finally, a power-spectrum analysis indicates that variance of DOC does not fall off as a power of frequency as is typical for solutes in streams. These results indicate that simple mixing (flushing) models, including those that incorporate standard models of flow through soils, cannot capture the observed temporal variability.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005