HR: 17:45h
AN: H44C-07    [Abstracts]
TI: Linking Soil Moisture, Micro-climate, and Transpiration in a Headwater Catchment
AU: * Barnard, H R
EM: Holly.Barnard@oregonstate.edu
AF: Oregon State University, Department of Forest Engineering, Corvallis, OR 97331, United States
AU: * Barnard, H R
EM: Holly.Barnard@oregonstate.edu
AF: Oregon State University, Department of Forest Science, Corvallis, OR 97331, United States
AU: Brooks, J
EM: Brooks.ReneeJ@epa.gov
AF: U.S. EPA/NHEERL Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, United States
AU: Kayler, Z
EM: Zachary.Kayler@oregonstate.edu
AF: Oregon State University, Department of Forest Science, Corvallis, OR 97331, United States
AU: Sulzman, E W
EM: Elizabeth.Sulzman@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, Corvallis, OR 97331, United States
AU: Phillips, C L
EM: Claire.Phillips@oregonstate.edu
AF: Oregon State University, Department of Forest Science, Corvallis, OR 97331, United States
AU: McDonnell, J J
EM: Jeff.McDonnell@orst.edu
AF: Oregon State University, Department of Forest Engineering, Corvallis, OR 97331, United States
AU: Bond, B J
EM: Barbara.Bond@oregonstate.edu
AF: Oregon State University, Department of Forest Science, Corvallis, OR 97331, United States
AB: Evapotranspiration is a major determinant of streamflow in forested basins. However, the role topography plays in forest water relations is poorly understood. To date, many hydrological models use only a single value for transpiration across a catchment. Quantifying the variation in forest water use with regards to slope position is central to understanding controls on water quantity and quality in hydro-ecological models and is critical to predicting the hydrologic impacts of various forestry operations. We measured transpiration, soil moisture, and foliar pre-dawn water potential in 4 plots across a ridge to ridge transect throughout the summers of 2005 and 2006 in a headwater catchment in western Oregon. Additionally, we measured deuterium and ¹⁸O of xylem water and soil water to track changes in the depth of transpiration source water throughout the summers. From May through October 2006, daily average transpiration in upslope plots was approximately 40% greater than that of valley bottom plots (1.0 mm day^-1 vs. 0.6 mm day^-1, respectively). Minimum pre-dawn water potential values ranged from -0.8 to -1.3 MPA in late August with north-facing plots having the lowest values. Stable isotope data indicates that transpiration rates remained higher longer in the growing season in plots where trees were able to access water deeper in the soil profile. Preliminary data suggest that topographic gradients influencing soil depth, soil moisture retention, and micro-climate result in large variation in forest water use over very small distances.
DE: 1804 Catchment
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1852 Plant uptake
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2007 Fall Meeting