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Bedrock vadose zone storage dynamics under extreme drought: consequences for plant water availability, recharge, and runoff
  • +11
  • W. Jesse Hahm,
  • David N Dralle,
  • Maryn Sanders,
  • Alexander B Bryk,
  • Kristen Elizabeth Fauria,
  • Mong-Han Huang,
  • Berit Hudson-Rasmussen,
  • Mariel D Nelson,
  • Michelle A Pedrazas,
  • Logan Marcos Schmidt,
  • John Whiting,
  • William E Dietrich,
  • Daniella Rempe,
  • Maryn Sanders
W. Jesse Hahm
Simon Fraser University, Simon Fraser University

Corresponding Author:[email protected]

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David N Dralle
Pacific Southwest Research Station, United States Forest Service, Pacific Southwest Research Station, United States Forest Service
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Maryn Sanders
Caltech
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Alexander B Bryk
UC Berkeley, UC Berkeley
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Kristen Elizabeth Fauria
University of California, Berkeley, University of California, Berkeley
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Mong-Han Huang
University of Maryland, College Park, University of Maryland, College Park
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Berit Hudson-Rasmussen
University of Maryland, College Park, University of Maryland, College Park
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Mariel D Nelson
University of Texas at Austin, University of Texas at Austin
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Michelle A Pedrazas
University of Texas at Austin, University of Texas at Austin
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Logan Marcos Schmidt
University of Texas Institute for Geophysics, University of Texas Institute for Geophysics
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John Whiting
USDA Forest Service Pacific Southwest Research Station, USDA Forest Service Pacific Southwest Research Station
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William E Dietrich
Universith of California Berkeley, Universith of California Berkeley
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Daniella Rempe
University of Texas at Austinn, University of Texas at Austinn
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Maryn Sanders
University of Oregon
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Abstract

Bedrock vadose zone water storage (i.e., rock moisture) dynamics are sparsely observed but potentially key to understanding drought responses. Exploiting a borehole network at a Mediterranean blue oak savanna site-Rancho Venada-we document how water storage capacity in a deeply weathered bedrock profile regulates woody plant water availability and groundwater recharge. The site is in the Northern California Coast Range within steeply dipping turbidites. In a wet year (water year 2019; 647 mm of precipitation), rock moisture was quickly replenished to a characteristic storage capacity, recharging groundwater that emerged at springs to generate streamflow. In the subsequent rainless summer growing season, rock moisture was depleted by about 93 mm. In two drought years that followed (212 and 121 mm of precipitation) the total amount of rock moisture gained each winter was about 54 and 20 mm, respectively, and declines were observed exceeding these amounts, resulting in progressively lower rock moisture content. Oaks, which are rooted into bedrock, demonstrated signs of water stress in drought, including reduced transpiration rates and extremely low water potentials. In the 2020-2021 drought, precipitation did not exceed storage capacity, resulting in variable belowground water storage, increased plant water stress, and no recharge or runoff. Rock moisture deficits (rather than soil moisture deficits) explain these responses.
Apr 2022Published in Water Resources Research volume 58 issue 4. 10.1029/2021WR031781