HR: 0830h
AN: H41D-1035    [PDF]
TI: Estimating catchment residence time using environmental tracers: modeling recharge and input uncertainty
AU: Weiler, M
EM: markus@2hydros.de
AF: Department of Forest Engineering, Oregon State University, 215 Peavy Hall, Corvallis, OR 97331 United States
AU: * McGuire, K J
EM: kevin.mcguire@orst.edu
AF: Department of Forest Engineering, Oregon State University, 215 Peavy Hall, Corvallis, OR 97331 United States
AU: Kendall, C
AF: US Geological Survey, Bldg. 15, McKelvey Building, Menlo Park, CA 94025 United States
AU: Welker, J
AF: Natural Resource Ecology Laboratory, Colorado State University, NESB, B250, Fort Collins, CO 80523 United States
AU: McDonnell, J J
AF: Department of Forest Engineering, Oregon State University, 215 Peavy Hall, Corvallis, OR 97331 United States
AB: The residence time of subsurface water in a catchment is an important control on stream water quality. The residence time reflects the various flow pathways, storage volumes, and chemical interaction times of water transported through the catchment to the stream. Residence time estimates therefore provide a primary description of the hydrological system and catchment sensitivity to anthropogenic inputs and land-use change. Residence time is estimated typically with environmental tracers (e.g., $^{18}$O and $^{2}$H) using simple lumped-parameter models that define the transfer of input (rainfall) to output (baseflow) tracer composition. However, the estimation of recharge and spatial input variability can introduce considerable uncertainty in modeled residence time distributions. This paper presents a new approach to modeling residence time that combines a transfer function model with a non-linear wetness index model to estimate catchment-average recharge. Using this model, the effects of input uncertainty are explored for several catchments in the H.J. Andrews Experimental Forest (basin scales range from 0.09-62 km$^{2}$). Our results show that these catchments produce heavy-tailed residence time distributions signifying a long memory to past inputs. Catchments with steeper and shorter hillslopes had distributions with more mass at short residence time indicating a contribution from rapid flow pathways. Uncertainty derived from measured spatial variability of tracer input affected the mean more than the shape of the residence time distribution. Thus, the mean residence time appears to be a robust estimator of the residence time distribution given input uncertainty.
DE: 1040 Isotopic composition/chemistry
DE: 1832 Groundwater transport
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting