A new report of hydrology study at the HJ Andrews Experimental Forest LTER profoundly changes our view of the movement of water through mountain soil and into streams.
Several years of diligent study of the isotopic composition of precipitation, soil water, and streamflow within Watershed 10 at the Andrews Forest reveal that early wet season precipitation becomes tightly bound within the dry, end-of-summer soil. Water from later fall and winter precipitation washes by this sequestered water without mixing and eventually contributes to streamflow. The sequestered water exits the watershed via transpiration in subsequent dry seasons.
This work by Renee Brooks (EPA), graduate student Holly Barnard (OSU), and Jeff McDonald (OSU), substantially modifies a century of hydrologic theory that in a climate system like the Andrews Forest rain and snowmelt enter the soil, mix with soil water, and displace it downslope and eventually into the stream. These new findings suggest that soil contains two semi-independent water reservoirs: tightly-held water that is accessed by plants and loosely-held water that supplies streamflow.
Ecohydrologic separation of water between trees and streams in a Mediterranean climate. 2010. J. Renée Brooks, Holly R. Barnard, Rob Coulombe & Jeffrey J. McDonnell. Nature Geoscience. 3, 100 - 104 (2010). http://www.nature.com/ngeo/journal/v3/n2/full/ngeo722.html