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Water Science: hydrological and biogeochemical modeling, BREN, Nov 19
Water supply depends on stream and plant interactions. Hydrologic analysis is discovering significant differences in our fresh water supply system.
BREN Research colloquia
Santa Barbara based colloquia by Bren faculty members are generally high-level talks about research in a particular area of environmental science and management.
Jeffrey McDonnell, Oregon State University
"The two water worlds paradox: Isotope evidence that trees and streams return different water pools to the hydrosphere
Richardson Chair, Watershed Science
Distinguished Professor of Hydrology
Oregon State University
Thursday, Nov. 19, 2009
12:30 - 1:30 p.m.
Bren Hall 1414
"The two water worlds paradox: Isotope evidence that trees and streams
return different water pools to the hydrosphere"
For more information: Bren.UCSB.edu
Hosted by Christina Tague
View complete list of currently scheduled Bren events
Ground Water Isn't All Alike!
Hydrologists invoke translatory (piston-like) flow to describe water movement in upland, humid watersheds from the soil surface to the stream. Water entering as precipitation displaces old water, pushing it deeper into soil and eventually the stream.
Within this paradigm, water at any soil depth is well mixed.
Plants passively take up water along a water-potential gradient and preferentially extract water at high water potentials, implying that plants extract the same water that eventually enters the stream.
Recent work with Renee Brooks at EPA Corvallis and colleagues at Oregon State U. focuses on water-isotope data from various pools collected throughout a small watershed at the HJ Andrews LTER site in western Oregon.
These data imply that tightly bound water retained in this soil and used by trees does not participate in translatory flow, mix with mobile water, or enter the stream.
Following rainless summers, initial fall rain events are locked into small pores with low matric potential until transpiration empties these pores during dry summers. Winter rainfall does not displace the tightly bound water.
Southern California Implications for Water Mixing in the Soil
Because transpiration and stormflow are out of phase in our Mediterranean climate, two water worlds exist where trees and streams return different water to the hydrosphere. For similar hydroclimate regimes, these findings have profound implications for hydrological and biogeochemical modeling, which assume complete mixing of water within soil.
Jeffrey J. McDonnell is Richardson Chair in Watershed Science and University Distinguished Professor of Hydrology at Oregon State University. He is a Fellow of the American Geophysical Union and a recipient of the Dalton Medal from the European Geophysical Union.
Edited by Carolyn Allen