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Title: In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport

Abstract

Nocturnal increases in water potential ( ) and water content (WC) in the upper soil profile are often attributed to root water efflux into the soil, a process termed hydraulic lift or hydraulic redistribution (HR). We have previously reported HR values up to ~0.29 mm day-1 in the upper soil for a seasonally dry old-growth ponderosa pine site. However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the diurnal patterns in WC, confounding efforts to determine the actual magnitude of HR. In this study, we estimated liquid (Jl) and vapor (Jv) soil water fluxes and their impacts on quantifying HR in situ by applying existing data sets of , WC, temperature (T) and soil physical properties to soil water transport equations. Under moist conditions, Jl between layers was estimated to be larger than necessary to account for measured nocturnal increases in WC of upper soil layers. However, as soil drying progressed unsaturated hydraulic conductivity declined rapidly such that Jl was irrelevant (< 2E-06 cm hr-1 at 0-60 cm depths) to total water flux by early August. In surface soil at depths above 15 cm, large T fluctuations can impact Jv leading tomore » uncertainty concerning the role, if any, of HR in nocturnal WC dynamics. Vapor flux was estimated to be the highest at the shallowest depths measured (20 - 30 cm) where it could contribute up to 40% of hourly increases in nocturnal soil moisture depending on thermal conditions. While both HR and net soil water flux between adjacent layers contribute to WC in the 15-65 cm soil layer, HR was the dominant process and accounted for at least 80% of the diurnal increases in WC. While the absolute magnitude of HR is not easily quantified, total diurnal fluctuations in upper soil water content can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total ecosystem water flux.« less

Authors:
 [1];  [2];  [3];  [4]
  1. ORNL
  2. U.S. Environmental Protection Agency, Corvallis, OR
  3. Oregon State University, Corvallis
  4. USDA Forest Service
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1018958
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Oecologia
Additional Journal Information:
Journal Volume: 166; Journal Issue: 4; Journal ID: ISSN 0029--8549
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; DRYING; ECOSYSTEMS; ELEVATORS; FLUCTUATIONS; HYDRAULIC CONDUCTIVITY; HYDRAULICS; MOISTURE; PHYSICAL PROPERTIES; PINES; SOILS; TRANSPORT; WATER

Citation Formats

Warren, Jeffrey, Brooks, J Renee, Dragila, Maria, and Meinzer, Rick. In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport. United States: N. p., 2011. Web. doi:10.1007/s00442-011-1953-9.
Warren, Jeffrey, Brooks, J Renee, Dragila, Maria, & Meinzer, Rick. In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport. United States. doi:10.1007/s00442-011-1953-9.
Warren, Jeffrey, Brooks, J Renee, Dragila, Maria, and Meinzer, Rick. Sat . "In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport". United States. doi:10.1007/s00442-011-1953-9.
@article{osti_1018958,
title = {In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport},
author = {Warren, Jeffrey and Brooks, J Renee and Dragila, Maria and Meinzer, Rick},
abstractNote = {Nocturnal increases in water potential ( ) and water content (WC) in the upper soil profile are often attributed to root water efflux into the soil, a process termed hydraulic lift or hydraulic redistribution (HR). We have previously reported HR values up to ~0.29 mm day-1 in the upper soil for a seasonally dry old-growth ponderosa pine site. However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the diurnal patterns in WC, confounding efforts to determine the actual magnitude of HR. In this study, we estimated liquid (Jl) and vapor (Jv) soil water fluxes and their impacts on quantifying HR in situ by applying existing data sets of , WC, temperature (T) and soil physical properties to soil water transport equations. Under moist conditions, Jl between layers was estimated to be larger than necessary to account for measured nocturnal increases in WC of upper soil layers. However, as soil drying progressed unsaturated hydraulic conductivity declined rapidly such that Jl was irrelevant (< 2E-06 cm hr-1 at 0-60 cm depths) to total water flux by early August. In surface soil at depths above 15 cm, large T fluctuations can impact Jv leading to uncertainty concerning the role, if any, of HR in nocturnal WC dynamics. Vapor flux was estimated to be the highest at the shallowest depths measured (20 - 30 cm) where it could contribute up to 40% of hourly increases in nocturnal soil moisture depending on thermal conditions. While both HR and net soil water flux between adjacent layers contribute to WC in the 15-65 cm soil layer, HR was the dominant process and accounted for at least 80% of the diurnal increases in WC. While the absolute magnitude of HR is not easily quantified, total diurnal fluctuations in upper soil water content can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total ecosystem water flux.},
doi = {10.1007/s00442-011-1953-9},
journal = {Oecologia},
issn = {0029--8549},
number = 4,
volume = 166,
place = {United States},
year = {2011},
month = {1}
}