Journal
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
Volume 118, Issue 17, Pages 10225-10242Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/jgrd.50701
Keywords
water isotopes; dewfall; nocturnal boundary layer; forest hydrology
Categories
Funding
- CIRES
- National Science Foundation [AGS-0955841, EAR-0910831]
- Los Alamos National Laboratory Directed Research and Development Project entitled Isotopic Tracer for Climate Relevant Secondary Organic Aerosol [20090425ER]
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [0955841] Funding Source: National Science Foundation
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The movement of moisture into, out-of, and within forest ecosystems is modulated by feedbacks that stem from processes which couple plants, soil, and the atmosphere. While an understanding of these processes has been gleaned from Eddy Covariance techniques, the reliability of the method suffers at night because of weak turbulence. During the summer of 2011, continuous profiles of the isotopic composition (i.e., delta O-18 and delta D) of water vapor and periodic measurements of soil, leaf, and precipitation pools were measured in an open-canopy ponderosa pine forest in central Colorado to study within-canopy nocturnal water cycling. The isotopic composition of the nocturnal water vapor varies significantly based on the relative contributions of the three major hydrological processes acting on the forest: dewfall, exchange of moisture between leaf waters and canopy vapor, and periodic mixing between the canopy and background air. Dewfall proved to be surprisingly common (similar to 30% of the nights) and detectable on both the surface and within the canopy through the isotopic measurements. While surface dew could be observed using leaf wetness and soil moisture sensors, dew in the foliage was only measurable through isotopic analysis of the vapor and often occurred even when no dew accumulated on the surface. Nocturnal moisture cycling plays a critical role in water availability in forest ecosystems through foliar absorption and transpiration, and assessing these dynamics, as done here, is necessary for fully characterizing the hydrological controls on terrestrial productivity.
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