Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

Sprenger, Matthias; Volkmann, Till H. M.; Blume, Theresa; Weiler, Markus

doi:10.5194/hess-19-2617-2015

Cited by 99 publications

(134 citation statements)

References 79 publications

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“…However, model calibration using soil moisture and stable isotope data, as suggested by Sprenger et al (2015b), would supply the basis of an assessment of how different parameter sets impact the model performance and water age estimates. Such an approach would provide site-specific characterization of the soil physical properties and would likely improve simulations compared to the currently applied pedotransfer functions and measurements on soil cores.…”

Section: Limitations and Outlookmentioning

confidence: 99%

Water ages in the critical zone of long-term experimental sites in northern latitudes

Sprenger¹,

Tetzlaff

Buttle

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. As northern environments undergo intense changes due to a warming climate and altered land use practices, there is an urgent need for improved understanding of the impact of atmospheric forcing and vegetation on water storage and flux dynamics in the critical zone. We therefore assess the age dynamics of water stored in the upper 50 cm of soil, and in evaporation, transpiration, or recharge fluxes at four soil-vegetation units of podzolic soils in the northern latitudes with either heather or tree vegetation (Bruntland Burn in Scotland, Dorset in Canada, and Krycklan in Sweden). We derived the age dynamics with the physically based SWIS (Soil Water Isotope Simulator) model, which has been successfully used to simulate the hydrometric and isotopic dynamics in the upper 50 cm of soils at the study sites. The modelled subsurface was divided into interacting fast and slow flow domains. We tracked each day's infiltrated water through the critical zone and derived forward median travel times (which show how long the water takes to leave the soil via evaporation, transpiration, or recharge), and median water ages (to estimate the median age of water in soil storage or the evaporation, transpiration, and recharge fluxes). Resulting median travel times were time-variant, mainly governed by major recharge events during snowmelt in Dorset and Krycklan or during the wetter winter conditions in Bruntland Burn. Transpiration travel times were driven by the vegetation growth period with the longest travel times (200 days) for waters infiltrated in early dormancy and the shortest travel times during the vegetation period. However, long tails of the travel time distributions in evaporation and transpiration revealed that these fluxes comprised waters older than 100 days. At each study site, water ages of soil storage, evaporation, transpiration, and recharge were all inversely related to the storage volume of the critical zone: water ages generally decreased exponentially with increasing soil water storage. During wet periods, young soil waters were more likely to be evapotranspired and recharged than during drier periods. While the water in the slow flow domain showed longterm seasonal dynamics and generally old water ages, the water ages of the fast flow domain were generally younger and much flashier. Our results provide new insights into the mixing and transport processes of soil water in the upper layer of the critical zone, which is relevant for hydrological modelling at the plot to catchment scales as the common assumption of a well-mixed system in the subsurface holds for neither the evaporation, transpiration, or recharge.

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Section: Limitations and Outlookmentioning

confidence: 99%

Water ages in the critical zone of long-term experimental sites in northern latitudes

Sprenger¹,

Tetzlaff

Buttle

et al. 2018

Hydrol. Earth Syst. Sci.

View full text Add to dashboard Cite

show abstract

“…However, model calibration using soil moisture and stable isotope data as suggested by Sprenger et al (2015b), would supply the basis of an assessment of how different parameter sets impact the model performance and water age estimates. Such an approach would provide site specific characterization of the soil physical properties and would likely improve simulations 35 compared to the currently applied pedotransfer functions and measurements on soil cores.…”

Section: Limitations and Outlookmentioning

confidence: 99%

Water ages in the critical zone of long-term experimental sites in northern latitudes

Sprenger¹,

Tetzlaff²,

Buttle³

et al. 2018

Preprint

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Abstract. As northern environments undergo intense respond due to a warming climate and altered land use practices, there is an urgent need for improved understanding of the impact of atmospheric forcing and vegetation on water storage and flux dynamics in the critical zone. We therefore assess the age dynamics of water stored in the upper 50 15 cm of soil, and in evaporation, transpiration or recharge fluxes at four soil-vegetation units of podzolic soils in the northern latitudes with either heather or tree vegetation (Bruntland Burn in Scotland, Dorset in Canada, and Krycklan in Sweden). We derived the age dynamics with the physically based SWIS (Soil Water Isotope Simulator) model, which has been successfully used to simulate the hydrometric and isotopic dynamics in the upper 50 cm of soils at the study sites. The modelled subsurface was divided into interacting fast and slow flow domains. We tracked each day's 20 infiltrated water through the critical zone and derived forward median travel times (which show how long the water takes to leave the soil via evaporation, transpiration or recharge), and median water ages (to estimate the median age of water in soil storage or the evaporation, transpiration and recharge fluxes). Resulting median travel times were time-variant, mainly governed by major recharge events during snow melt in Dorset and Krycklan or during the wetter winter conditions in Bruntland Burn. Transpiration travel times were driven by the vegetation growth period with 25 longest travel times (200 days) for waters infiltrated in early dormancy and shortest travel times during the vegetation period. However, long tails of the travel time distributions in evaporation and transpiration revealed that these fluxes comprised waters older than 100 days. At each study site, water ages of soil storage, evaporation, transpiration and recharge were all inversely related to the storage volume of the critical zone: water ages generally decreased exponentially with increasing soil water storage. During wet periods, young soil waters were more likely to be 30 evapotranspired and recharged than during drier periods. While the water in the slow flow domain showed long-term seasonal dynamics and generally old water ages, the water ages of the fast flow domain were generally younger and much flashier. Our results provide new insights into the mixing and transport processes of soil water in the upper layer of the critical zone, which is relevant for hydrological modelling at the plot to catchment scales as the common assumption of a well-mixed system in the subsurface neither holds for the evaporation, transpiration nor recharge. 35Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2018-144 Manuscript under review for journal Hydrol. Earth Syst. Sci. Discussion started: 27 March 2018 c Author(s) 2018. CC BY 4.0 License. 2 IntroductionWater ages are useful metrics to assess hydrological processes as they reveal interactions between storage and fluxes of water in a hydrological system (Hrachowitz et al.,...

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“…Brunner et al (2012), for instance, examined the performance of a one-dimensional (1-D) unsaturated zone flow model when water table measurements were supplemented by evapotranspiration and soil moisture observations. Sprenger et al (2015) assessed the performance of three inverse modeling strategies based on the use of soil moisture and porewater isotope concentration data for a 1-D unsaturated flow and transport model. Kampf and Burges (2007) obtained encouraging results for a 2-D Richards equation flow model using integrated (subsurface outflow) and internal (piezometric water level and volumetric water content) measurements from a hillslope-scale experiment.…”

Section: Introductionmentioning

confidence: 99%

Multiresponse modeling of variably saturated flow and isotope tracer transport for a hillslope experiment at the Landscape Evolution Observatory

Scudeler

Pangle

Pasetto

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. This paper explores the challenges of model parameterization and process representation when simulating multiple hydrologic responses from a highly controlled unsaturated flow and transport experiment with a physically based model. The experiment, conducted at the Landscape Evolution Observatory (LEO), involved alternate injections of water and deuterium-enriched water into an initially very dry hillslope. The multivariate observations included point measures of water content and tracer concentration in the soil, total storage within the hillslope, and integrated fluxes of water and tracer through the seepage face. The simulations were performed with a three-dimensional finite element model that solves the Richards and advection-dispersion equations. Integrated flow, integrated transport, distributed flow, and distributed transport responses were successively analyzed, with parameterization choices at each step supported by standard model performance metrics. In the first steps of our analysis, where seepage face flow, water storage, and average concentration at the seepage face were the target responses, an adequate match between measured and simulated variables was obtained using a simple parameterization consistent with that from a prior flow-only experiment at LEO. When passing to the distributed responses, it was necessary to introduce complexity to additional soil hydraulic parameters to obtain an adequate match for the pointscale flow response. This also improved the match against point measures of tracer concentration, although model performance here was considerably poorer. This suggests that still greater complexity is needed in the model parameterization, or that there may be gaps in process representation for simulating solute transport phenomena in very dry soils.

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Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

Cited by 99 publications

References 79 publications

Water ages in the critical zone of long-term experimental sites in northern latitudes

Water ages in the critical zone of long-term experimental sites in northern latitudes

Water ages in the critical zone of long-term experimental sites in northern latitudes

Multiresponse modeling of variably saturated flow and isotope tracer transport for a hillslope experiment at the Landscape Evolution Observatory

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