Catchment Travel Times From Composite StorAge Selection Functions Representing the Superposition of Streamflow Generation Processes

Rodriguez, Nicolas; Klaus, Julian

doi:10.1029/2019wr024973

Cited by 46 publications

(73 citation statements)

References 98 publications

(218 reference statements)

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“…Recent numerical experiments on real or virtual hydrological systems (Danesh‐Yazdi, Klaus, Condon, & Maxwell, 2018; Kaandorp, de Louw, van der Velde, & Broers, 2018; Remondi et al, 2018; Yang, Heidbüchel, Musolff, Reinstorf, & Fleckenstein, 2018) showed that, even if SAS functions simplify the shapes of the age distributions compared with TTDs, they may not be described well by unimodal distributions. Rodriguez and Klaus (2019) used high frequency (i.e., sub‐daily) stable isotopes in precipitation and discharge over 2 years and found that the SAS function in a slate catchment with complex flow paths may contain several peaks consistent with experimentally identified discharge generation processes.…”

Section: Acknowledging the Multimodality Of Water Age Distributionsmentioning

confidence: 99%

“…This has made the detection of the entire shape of the TTDs more feasible than in the past. High‐frequency tracer observations can now constrain the left‐hand part of TTDs representing the short (e.g., hours to days) and intermediate (e.g., weeks) transport time scales (Rodriguez & Klaus, 2019), while long records of tracers can constrain the right‐hand tail of TTDs associated with long transport time scales (e.g., months to years, Rodriguez, Pfister, Zehe, & Klaus, 2019; Neal et al, 2011). Tracer time series that span several years at high resolution (von Freyberg, Studer, Rinderer, & Kirchner, 2018) will pave the way for the detailed investigation of water flow paths and their influence on TTDs.…”

Section: Acknowledging the Multimodality Of Water Age Distributionsmentioning

confidence: 99%

“…The unsteady TTDs p Q ( T , t ) can be obtained by solving a water balance equation for each water parcel [usually referred to as age master equation (Botter et al, 2011)]. Numerical solutions to the age master equation (Benettin & Bertuzzo, 2018; Harman, 2015; Rodriguez & Klaus, 2019; vander Velde et al, 2012; Visser et al, 2019) usually consider one control volume for the entire hydrological system and use the ‘age‐ranked storage’ S T ( T , t ) as state variable. S T represents the distribution of water volumes in storage, ranked by age.…”

Section: Simulations Of Tracer Concentrations Through Sas Functionsmentioning

confidence: 99%

“…The M functions λ m ( t ) are time‐varying weights summing to 1 to ensure mass conservation. In this study, we used constant weights, but they can be parameterised to change with various hydrological quantities such as precipitation intensities, storage, or storage variations (Rodriguez & Klaus, 2019). Each weight λ m ( t ) defines the relative volumetric contribution of the component Ω m ( y , t ) to the considered outflow [here discharge Q ( t )] at time t .…”

Section: Simulations Of Tracer Concentrations Through Sas Functionsmentioning

confidence: 99%

“…The TTD model (blue pdf) is a simplification of reality that works well for simulating (blue curve) a given tracer output measured in a discrete manner (red dots). Adapted from Rodriguez and Klaus (2019)…”

Section: Introductionmentioning

confidence: 99%

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Multimodal water age distributions and the challenge of complex hydrological landscapes

Rodriguez

Benettin

Klaus

2020

Hydrological Processes

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Travel time distributions (TTDs) are concise descriptions of transport processes in catchments based on water ages, and they are particularly efficient as lumped hydrological models to simulate tracers in outflows. Past studies have approximated catchment TTDs with unimodal probability distribution functions (pdf) and have successfully simulated tracers in outflows with those. However, intricate flow paths and contrasting water velocities observed in complex hydrological systems may generate multimodal age distributions. This study explores the occurrence of multimodal age distributions in hydrological systems and investigates the consequences of multimodality for tracer transport.Lumped models based on TTDs of varying complexity (unimodal and multimodal) are used to simulate tracers in the discharge of hydrological systems under well-known conditions. Specifically, we simulate tracer data from a controlled lysimeter irrigation experiment showing a multimodal response and we provide results from a virtual catchment-scale experiment testing the ability of a unimodal age distribution to simulate a known and more complex multimodal age system. Models are based on composite StorAge Selection functions, defined as weighted sums of pdfs, which allow a straightforward implementation of uni-or multi-modal age distributions while accounting for unsteady conditions. These two experiments show that simple unimodal models provide satisfactory simulations of a given tracer, but they fail in reproducing processes occurring at different temporal scales. Multimodal distributions, instead, can better capture the detailed dynamics embedded in the observations. We conclude that experimental knowledge of flow paths and the systematic use of data from multiple, independent tracers can be used to validate the assumption of water age unimodality. Multimodal age distributions are more likely to emerge in landscapes where the distributions of flow path lengths and/or water velocities are themselves multimodal. In general, age multimodality may not be particularly pronounced and detectable, unless comparable amounts of water with contrasting ages reach a given outflow. K E Y W O R D Shydrological tracer, lumped model, multimodal distribution, StorAge Selection function, travel time, water age distribution, water chemistry, water velocity

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Section: Acknowledging the Multimodality Of Water Age Distributionsmentioning

confidence: 99%

Section: Acknowledging the Multimodality Of Water Age Distributionsmentioning

confidence: 99%

Section: Simulations Of Tracer Concentrations Through Sas Functionsmentioning

confidence: 99%

Section: Simulations Of Tracer Concentrations Through Sas Functionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multimodal water age distributions and the challenge of complex hydrological landscapes

Rodriguez

Benettin

Klaus

2020

Hydrological Processes

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Transpiration patterns and water use strategies of beech and oak trees along a hillslope

et al. 2021

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The role of landscape topography in mediating subsurface water availability and ultimately tree transpiration is still poorly understood. To assess how hillslope position affects tree water use, we coupled sap velocity with xylem isotope measurements in a temperate beech-oak forest along a hillslope transect in Luxembourg. We generally observed greater sap velocities at the upslope locations in trees from average-sized trees, suggesting the presence of more suited growing conditions. We found a lower difference in sap velocity among hillslope positions for larger trees, likely due to the exploitation of deeper and more persistent water sources and the larger canopy light interception. Beech trees exploited a shallower and seasonally less persistent water source than oak trees, due to the shallower root system than oak trees. The different water exploitation strategy could also explain the stronger stomatal sensitivity of beech to vapour pressure deficit compared to oak trees. Xylem isotopic composition was seasonally variable at all locations, mainly reflecting the contribution of variable soil water sources and suggesting that groundwater did not contribute, or only marginally contributed, to tree transpiration. Overall, our results suggest that trees along the hillslope mainly rely on water stored in the unsaturated zone and that seasonally shallow groundwater table may not necessarily subsidize water uptake for species that do not tolerate anoxic conditions. Contrary to previous studies, at our site, we did not find higher sap velocity downslope as the subsurface hillslope structure promotes vertical water flux over lateral redistribution in the vadose zone.

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Sapwood and heartwood are not isolated compartments: Consequences for isotope ecohydrology

et al. 2022

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In most tree species, xylem consists of two different functional parts: sapwood and heartwood. While sapwood, as the flowpath for sap, has received more attention in isotope studies assessing water sources accessed by trees (e.g. soil water from different depths, groundwater, stream water or a mixture of these), much remains unknown about heartwood and the possible water exchange between the two functional parts. We investigated four tree species (Fagus sylvatica, Quercus petraea, Pseudotsuga menziesii and Picea abies) characterised by different xylem anatomy and timing of physiological activity to evaluate the degree of differentiation in isotopic composition of water between sapwood and heartwood on a biweekly time scale.We found that the sapwood and heartwood of all species displayed a concurrent variation in their isotopic composition throughout the growing season and on a daynight scale suggesting that the two are not isolated compartments. While the two functional parts display a consistent difference in isotopic composition in conifers, they are characterised by more similar values in broadleaved species in broadleaved species, suggesting a higher degree of water exchange. Furthermore, we have also observed a progressive change in the isotopic composition in broadleaved species with sampling depth rather than functional parts of xylem. Our study highlights the value of accounting for radial isotopic variation, which might potentially lead to uncertainties concerning the origin of the extracted water for water uptake studies.

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Catchment Travel Times From Composite StorAge Selection Functions Representing the Superposition of Streamflow Generation Processes

Cited by 46 publications

References 98 publications

Multimodal water age distributions and the challenge of complex hydrological landscapes

Multimodal water age distributions and the challenge of complex hydrological landscapes

Transpiration patterns and water use strategies of beech and oak trees along a hillslope

Sapwood and heartwood are not isolated compartments: Consequences for isotope ecohydrology

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