HR: 0800h
AN: H11C-0645    [Abstracts]
TI: Nitrate Variability in Hydrological Flowpaths for a Mid-Appalachian Forested Catchment Following a Large-Scale Defoliation
AU: * Riscassi, A L
EM: alr8m@virginia.edu
AF: Department of Environmental Sciences University of Virginia, Clark Hall 291 McCormick Rd, Charlottesville, VA 22904, United States
AU: Scanlon, T M
EM: tms2v@virginia.edu
AF: Department of Environmental Sciences University of Virginia, Clark Hall 291 McCormick Rd, Charlottesville, VA 22904, United States
AB: Nitrogen (N) leakage from forested watersheds due to disturbance is a well-documented, but not well understood process that contributes to the degradation of receiving waters through eutrophication. Several studies have shown that large scale defoliation events in small forested watersheds in the Eastern U.S. cause immediate and dramatic increases in N flux to streams. Recovery times can differ dramatically depending upon location. Reasons for these differences are not well understood, however, because N transport and transformation processes are difficult to track over these long recovery timescales. This research focuses on a large-scale gypsy moth defoliation event that impacted Shenandoah National Park (SNP) in the late 1980s to early 1990s. Water chemistry and discharge have been monitored at a number of catchments within SNP over the timeframe since the defoliation. Recovery of these systems to pre-defoliation N levels has been observed to be unusually slow, lasting over a decade. Availability of high-frequency (i.e. hourly) stream chemistry and discharge data during storm events throughout the period of recovery allows us to investigate short- and long-term mechanisms for N "leaks" from forested watersheds. Through geochemical hydrograph separation techniques, we can determine how nitrate concentrations vary between event, soil, and groundwater during and in the years following a disturbance. Analyses focus on Paine Run, a 12.4 km2 catchment where over 50 storms have been characterized since the 1990-1992 defoliation. Standard geochemical hydrograph separation is performed using conservative tracers to determine the relative flow contributions from the three flow components for each measurement time step. Computed discharge components, along with measured steam nitrate concentrations (NO3 -) at each time-step, were used to solve for the relative concentration of NO3 - in each of the hydrologic zones for storms by solving the over-determined set of mixing model equations. This approach reveals how nitrogen moves through the catchment system and provides insight into the mechanisms that contribute to the observed long-term elevated nitrate levels.
DE: 1804 Catchment
DE: 1805 Computational hydrology
DE: 1817 Extreme events
SC: Hydrology [H]
MN: 2007 Fall Meeting