Variation in the extent of ecohydrologic separation in mixed conifer forest
Abstract
It is now widely accepted that water used for tree transpiration can be separate from water that supplies groundwater and streamflow. Broad evidence of such ecohydrologic separation forms the basis for the "two water worlds hypothesis" that challenges commonly held notions of how water moves through terrestrial ecosystems. Isotopic evidence supports that trees take up water from tightly bound soil pore spaces that often is not fully mixed with loosely bound water that eventually flows to groundwater and streams. Conditions that promote ecohydrologic separation and reduce complete mixing of loosely bound and tightly bound water in soil likely vary across soil types and complex topography in forested catchments. We examined the isotopic signature of water in three tree species, bulk soil, loosely bound soil water collected from soil lysimeters, and stream water at three different hillslopes in a mixed confer forest in southeastern Wyoming. Hillslopes differed in aspect and topographic position with corresponding differences in surface energy balance, snowmelt timing, and duration of soil moisture during the dry summer. We expect the magnitude of hydrologic separation would differ across the three hillslopes because of the these different physical conditions. One species sampled, lodgepole pine (Pinus contorta), is "isohydric"; stomatal conductance is regulated such that leaf water potential declines to a relatively high set point value during daily transpiration. The other two species, Engelmann spruce (Picea engelmannia) and sub-alpine fir (Abies laziocarpa) are "anisohydric", in that they allow daily minimum values of leaf water potential to vary and drop to values below that sustained by lodgepole pine. We predicted that ecohydrologic separation would be expressed to a greater degree on comparatively dry hillslopes and in species with anisohydric stomatal regulation. Quantifying and understanding such patterns of ecohydrological separation is important for predicting watershed hydrologic and biogeochemical responses to climate variability and change.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H13L1578B
- Keywords:
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- 0740 Snowmelt;
- CRYOSPHEREDE: 1621 Cryospheric change;
- GLOBAL CHANGEDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1817 Extreme events;
- HYDROLOGY