TY - JOUR
T1 - Seasonal and Topographic Variations in Ecohydrological Separation Within a Small, Temperate, Snow-Influenced Catchment
AU - Knighton, James
AU - Souter-Kline, Valessa
AU - Volkman, Till
AU - Troch, Peter A.
AU - Kim, Minseok
AU - Harman, Ciaran
AU - Morris, Chelsea
AU - Buchanan, Brian
AU - Walter, M. Todd
N1 - Funding Information:
This research was supported by a 2017 American Geophysical Union Horton Research grant and an IGERT Cross-Scale Biogeochemistry and Climate Small grant. We thank Scott Steinschneider (Cornell University) for statistical guidance. All hydrologic data is available within the CUAHSI HydroClient database under the project code CUISO. Source code for JoFlo is available at https://github.com/cran/EcoHydRology/blob/master/R/Lumped_VSA_model.R and within the R package EcohydRology (Fuka et al.,). Source code of the rSAS model is available at https://github.com/charman2/rsas website.
Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/8/1
Y1 - 2019/8/1
N2 - The hypothesis of ecohydrological separation (ES) proposes that the water contained in surface soils is not uniformly extracted by root water uptake nor uniformly displaced by infiltration. Rather vegetation selectively removes water held under tension, and water infiltrating wet soil will bypass much of the water-filled pore space. Methodological differences across previous studies have contributed to disagreement concerning the prevalence of ES. We measured stable isotopes of O and H in precipitation, snowpack, canopy throughfall, and stream water over a period of 18 months in a temperate catchment. At six locations across a wetness gradient, we sampled bulk soil water isotopes weekly and xylem water of Eastern hemlock and American beech stems seasonally. We used these observations in a soil column model including StorAge Selection functions to estimate the isotopic composition and ages of groundwater recharge and ET. Our findings suggest ES may exist with spatial and temporal heterogeneity. Root water uptake ages possibly vary between Eastern hemlock and American beech, suggesting functional strategies for water uptake may control the presence of ES. Newly infiltrated water bypassing the shallow soil was the most likely explanation for bulk soil isotopic measurements made at upslope locations during the winter and summer seasons, whereas rapid displacement of stored soil water by infiltrated waters was the most likely during the spring and fall seasons. Future research incorporating high temporal frequency soil and plant xylem water isotopic measurements applied to StorAge Selection functions may provide a useful framework for understanding rooting zone isotope dynamics.
AB - The hypothesis of ecohydrological separation (ES) proposes that the water contained in surface soils is not uniformly extracted by root water uptake nor uniformly displaced by infiltration. Rather vegetation selectively removes water held under tension, and water infiltrating wet soil will bypass much of the water-filled pore space. Methodological differences across previous studies have contributed to disagreement concerning the prevalence of ES. We measured stable isotopes of O and H in precipitation, snowpack, canopy throughfall, and stream water over a period of 18 months in a temperate catchment. At six locations across a wetness gradient, we sampled bulk soil water isotopes weekly and xylem water of Eastern hemlock and American beech stems seasonally. We used these observations in a soil column model including StorAge Selection functions to estimate the isotopic composition and ages of groundwater recharge and ET. Our findings suggest ES may exist with spatial and temporal heterogeneity. Root water uptake ages possibly vary between Eastern hemlock and American beech, suggesting functional strategies for water uptake may control the presence of ES. Newly infiltrated water bypassing the shallow soil was the most likely explanation for bulk soil isotopic measurements made at upslope locations during the winter and summer seasons, whereas rapid displacement of stored soil water by infiltrated waters was the most likely during the spring and fall seasons. Future research incorporating high temporal frequency soil and plant xylem water isotopic measurements applied to StorAge Selection functions may provide a useful framework for understanding rooting zone isotope dynamics.
KW - Markov Chain Monte Carlo
KW - SAS functions
KW - ecohydrological separation
KW - two water worlds hypothesis
KW - vadose zone
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U2 - 10.1029/2019WR025174
DO - 10.1029/2019WR025174
M3 - Article
AN - SCOPUS:85070102029
VL - 55
SP - 6417
EP - 6435
JO - Water Resources Research
JF - Water Resources Research
SN - 0043-1397
IS - 8
ER -