TY - JOUR
T1 - The mechanistic basis for storage-dependent age distributions of water discharged from an experimental hillslope
AU - Pangle, Luke A.
AU - Kim, Minseok
AU - Cardoso, Charlene
AU - Lora, Marco
AU - Meira Neto, Antonio A.
AU - Volkmann, Till H.M.
AU - Wang, Yadi
AU - Troch, Peter A.
AU - Harman, Ciaran J.
N1 - Funding Information:
We gratefully acknowledge support for this work provided by the National Science Foundation, awards EAR-1344552 and EAR-1344664, and by the Philecology Foundation. Minseok Kim acknowledges support provided through a CUAHSI Pathfinder Fellowship. Antonio Meira Neto acknowledges support from the Science Without Borders Program, from the CAPES Foundation, Brazil. We thank John Adams, Michael Sibayan, and Nate Abramson for outstanding management and technical support of research activities at UA-B2. Hydrologic and chemical data from this experiment are incorporated into an online database administered by the UA-Biosphere 2 staff. Data inquiries should be addressed to Peter A. Troch (Science Director at UA-Biosphere 2). Last, we thank four anonymous reviewers of the manuscript, whose comments proved very helpful for improving the organization and clarity of its content.
Publisher Copyright:
© 2017. American Geophysical Union. All Rights Reserved.
PY - 2017/4/1
Y1 - 2017/4/1
N2 - Distributions of water transit times (TTDs), and related storage-selection (SAS) distributions, are spatially integrated metrics of hydrological transport within landscapes. Recent works confirm that the form of TTDs and SAS distributions should be considered time variant—possibly depending, in predictable ways, on the dynamic storage of water within the landscape. We report on a 28 day periodic-steady-state-tracer experiment performed on a model hillslope contained within a 1 m3 sloping lysimeter. Using experimental data, we calibrate physically based, spatially distributed flow and transport models, and use the calibrated models to generate time-variable SAS distributions, which are subsequently compared to those directly observed from the actual experiment. The objective is to use the spatially distributed estimates of storage and flux from the model to characterize how temporal variation in water storage influences temporal variation in flow path configurations, and resulting SAS distributions. The simulated SAS distributions mimicked well the shape of observed distributions, once the model domain reflected the spatial heterogeneity of the lysimeter soil. The spatially distributed flux vectors illustrate how the magnitude and directionality of water flux changes as the water table surface rises and falls, yielding greater contributions of younger water when the water table surface rises nearer to the soil surface. The illustrated mechanism is compliant with conclusions drawn from other recent studies and supports the notion of an inverse-storage effect, whereby the probability of younger water exiting the system increases with storage. This mechanism may be prevalent in hillslopes and headwater catchments where discharge dynamics are controlled by vertical fluctuations in the water table surface of an unconfined aquifer.
AB - Distributions of water transit times (TTDs), and related storage-selection (SAS) distributions, are spatially integrated metrics of hydrological transport within landscapes. Recent works confirm that the form of TTDs and SAS distributions should be considered time variant—possibly depending, in predictable ways, on the dynamic storage of water within the landscape. We report on a 28 day periodic-steady-state-tracer experiment performed on a model hillslope contained within a 1 m3 sloping lysimeter. Using experimental data, we calibrate physically based, spatially distributed flow and transport models, and use the calibrated models to generate time-variable SAS distributions, which are subsequently compared to those directly observed from the actual experiment. The objective is to use the spatially distributed estimates of storage and flux from the model to characterize how temporal variation in water storage influences temporal variation in flow path configurations, and resulting SAS distributions. The simulated SAS distributions mimicked well the shape of observed distributions, once the model domain reflected the spatial heterogeneity of the lysimeter soil. The spatially distributed flux vectors illustrate how the magnitude and directionality of water flux changes as the water table surface rises and falls, yielding greater contributions of younger water when the water table surface rises nearer to the soil surface. The illustrated mechanism is compliant with conclusions drawn from other recent studies and supports the notion of an inverse-storage effect, whereby the probability of younger water exiting the system increases with storage. This mechanism may be prevalent in hillslopes and headwater catchments where discharge dynamics are controlled by vertical fluctuations in the water table surface of an unconfined aquifer.
KW - hillslope hydrology
KW - hydrological transport
KW - residence times
KW - storage-selection functions
KW - tracer hydrology
KW - transit times
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U2 - 10.1002/2016WR019901
DO - 10.1002/2016WR019901
M3 - Article
AN - SCOPUS:85017427287
SN - 0043-1397
VL - 53
SP - 2733
EP - 2754
JO - Water Resources Research
JF - Water Resources Research
IS - 4
ER -