Ecohydrologic considerations for modeling of stable water isotopes in a small intermittent watershed

Knighton, James; Saia, Sheila M.; Morris, C.; Archiblad, Josephine A.; Walter, M. Todd

doi:10.1002/hyp.11194

Cited by 48 publications

(65 citation statements)

References 62 publications

(141 reference statements)

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“…While it was shown that tracer-aided modelling using stable isotopes of water benefits from partitioning ET into a fractionating E flux and a non-fractionating T flux (Knighton et al, 2017), separate water age analyses for E and T have been considered only recently (Smith et al, 2018). However, our analyses showed 10 that the two different fluxes can have markedly different travel time dynamics (Figure 2), average travel time distributions (Figure 4), and water age dynamics (Figure 8).…”

Section: What Controls Travel Times and Water Ages In Evapotranspiratmentioning

confidence: 84%

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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Section: What Controls Travel Times and Water Ages In Evapotranspiratmentioning

confidence: 84%

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

Sprenger¹,

Tetzlaff²,

Buttle³

et al. 2018

Preprint

View full text Add to dashboard Cite

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“…SWAT simulations incorporated a temperature dependent threshold for transpiration with markedly different basal temperatures for EH and AB (Table ), yet our hydrologic model‐based predictions showed only a slight decrease in spring (March ‐ May) AET, and a slight increase in May and June peak discharge, generally agreeing with the direction of influence predicted by Ford and Vose (). A portion of spring runoff inducing events are caused by rapid melting of accumulated winter snowpack on saturated and often frozen soils (Knighton, Saia, et al, ), on which forest composition has limited influence.…”

Section: Resultsmentioning

confidence: 99%

Possible Increases in Flood Frequency Due to the Loss of Eastern Hemlock in the Northeastern United States: Observational Insights and Predicted Impacts

Knighton

Conneely

Walter

2019

Water Resources Research

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Trees exert a fundamental control on the hydrologic cycle, yet previous research is unclear about the nuanced relationship between forest cover and riverine flood frequency. In the Northeastern United States, warming air temperatures have resulted in a decline of Eastern Hemlock (EH), and subsequent increases in observed catchment water yield. We evaluated the possibility of EH loss leading to a changed flooding regime. We first investigated plant hydraulic regulation by root water uptake in EH and American Beech (AB; a candidate successional species) through stable isotope analysis of stream, soil water, and plant xylem water. EH xylem water showed evidence of deeper soil water uptake than AB during both wet and dry seasons, suggesting species succession may be an important mechanism for altering catchment “plant accessible water.” Next, we estimated catchment flood frequency with mechanistic hydrologic simulations for present conditions, and two hypothetical cases where all EH is succeeded by AB. The largest change to catchment extreme discharge after AB succession coincided with fall season tropical moisture export‐derived precipitation. We observed reduced sensitivity under future climatic forcing with an ensemble simulation of five localized constructed analogs downscaled general circulation models. Thus, the influence of forest composition on the flood regime may be most related to the temporal alignment of the synoptic‐scale processes that generate Atlantic Basin tropical cyclones and regional plant phenology of the Northeast United States. Our results provide a justification for using physically based hydrologic models incorporating plant hydraulic regulation when evaluating future flooding frequency.

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“…We simulated daily discharge, soil moisture, snowpack water equivalent, and groundwater storage with a modified version of JoFlo, the lumped model of Archibald et al (2014). This model has previously been applied to evaluate broad patterns of surface runoff (Knighton, Pleiss, et al, 2019) and forest cover change (Singh et al, 2019) across CONUS, as well as in catchment-scale studies of stable water isotope dynamics (Knighton et al, 2017) and nutrient transport (Georgakakos et al, 2018).…”

Section: Rwu Parameter Estimationmentioning

confidence: 99%

Understanding Catchment‐Scale Forest Root Water Uptake Strategies Across the Continental United States Through Inverse Ecohydrological Modeling

Knighton

Singh

Evaristo

2020

Geophysical Research Letters

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Trees influence the partitioning of water between catchment water yield and evapotranspiration through mediation of soil water via root water uptake (RWU). Recent research has estimated the depth of RWU for a variety of tree species at plot scales with measurements of stable isotopes in water and sap flux. Though informative, there are some challenges bridging the gap between plot‐ and catchment‐scale water fluxes. We estimated catchment‐scale tree RWU behavior for 139 forested catchments across the continental United States from continuous streamflow records with inverse ecohydrological modeling. Our catchment‐scale RWU estimates agreed well with existing plot‐scale research. Monoculture catchments dense with trees reliant on shallow soil water exhibited reduced transpiration losses compared to deep‐rooted and mixed‐species forests within the Budkyo framework. This research highlights the importance of representing plant characteristics that define RWU control of transpiration in land surface and earth systems models.

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Ecohydrologic considerations for modeling of stable water isotopes in a small intermittent watershed

Cited by 48 publications

References 62 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

Possible Increases in Flood Frequency Due to the Loss of Eastern Hemlock in the Northeastern United States: Observational Insights and Predicted Impacts

Understanding Catchment‐Scale Forest Root Water Uptake Strategies Across the Continental United States Through Inverse Ecohydrological Modeling

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