Partitioning Sources of Water Vapor Flux to the Atmosphere from a Subalpine Forest during Spring Snowmelt

Wednesday, 17 December 2014
Kristen Welsh Unwala1, William Chapple2, John M Frank3, Brent E Ewers4 and David G Williams2, (1)University of Idaho, Moscow, ID, United States, (2)University of Wyoming, Laramie, WY, United States, (3)U.S. Forest Service, Fort Collins, CO, United States, (4)University of Wyoming, Botany, Laramie, WY, United States
Partitioning evapotranspiration (ET) sources is key for understanding responses of terrestrial ecosystems and water budgets to disturbance. Vegetation heterogeneity, in addition to spatial and temporal variations of source contributions, makes prediction and modeling of these components complicated. Fine scale isotope (δ18O and δD) measurements of sources compared with water vapor isotope composition can provide a greater understanding of the potential temporal shifts of ET sources. In this study, we measured the stable isotope composition of δ18O and δD in water vapor at the vegetation surface using an isotope laser spectrometer while concurrently measuring the isotopic composition of terrestrial water sources, including snow, leaf, stem, soil, and surface water. As snow melt progressed and plant activity increased, we monitored how the isotopic composition of the terrestrial sources changed and compared these results with changes in isotopic composition of water vapor during the same period. This work was conducted in a subalpine watershed located in southeastern Wyoming during a six-week period in the early growing season. The goal of this research was to better understand how ET sources shift temporally during spring snowmelt.