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

Matthias Sprenger, Doerthe Tetzlaff*, Jim Buttle, Hjalmar Laudon, Chris Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticle

7 Citations (Scopus)
4 Downloads (Pure)

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 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 holds for neither the evaporation, transpiration, or recharge.

Original languageEnglish
Pages (from-to)3965-3981
Number of pages17
JournalHydrology and Earth System Sciences
Volume22
Issue number7
DOIs
Publication statusPublished - 20 Jul 2018

Keywords

  • TRANSIT-TIME DISTRIBUTIONS
  • BOREAL HEADWATER CATCHMENT
  • RESOLUTION ISOTOPE DATA
  • SOIL-WATER
  • STABLE-ISOTOPES
  • RESIDENCE TIMES
  • RUNOFF GENERATION
  • UNSATURATED ZONE
  • STORAGE DYNAMICS
  • TRACER

Cite this

Water ages in the critical zone of long-term experimental sites in northern latitudes. / Sprenger, Matthias; Tetzlaff, Doerthe; Buttle, Jim; Laudon, Hjalmar; Soulsby, Chris.

In: Hydrology and Earth System Sciences, Vol. 22, No. 7, 20.07.2018, p. 3965-3981.

Research output: Contribution to journalArticle

Sprenger, Matthias ; Tetzlaff, Doerthe ; Buttle, Jim ; Laudon, Hjalmar ; Soulsby, Chris. / Water ages in the critical zone of long-term experimental sites in northern latitudes. In: Hydrology and Earth System Sciences. 2018 ; Vol. 22, No. 7. pp. 3965-3981.
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note = "We thank Pernilla L{\"o}fvenius (SLU) for providing PET data for Krycklan (via SITES) and Carl Mitchell for snowmelt data in Dorset. We thank Pertti Ala-aho, Paolo Benettin, Sylvain Kuppel, Aaron A. Smith, and Hailong Wang for constructive discussions on the topic. The authors would like to acknowledge the support of the Maxwell computing cluster funded by the University of Aberdeen. The Krycklan component of the study was funded by the KAW Branch-Point project. We thank the European Research Council (ERC, project GA 335910 VeWa) for funding. We acknowledge support by the German Research Foundation (DFG) and the Open Access Publication Fund of Humboldt-Universit{\"a}t zu Berlin. We thank Todd Walter and two anonymous referees for their critical comments to improve the manuscript. Data availability. The underlaying research data are not publicly available in a repository, as they contain 70 GB. However, they can be requested from the authors",
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T1 - Water ages in the critical zone of long-term experimental sites in northern latitudes

AU - Sprenger, Matthias

AU - Tetzlaff, Doerthe

AU - Buttle, Jim

AU - Laudon, Hjalmar

AU - Soulsby, Chris

N1 - We thank Pernilla Löfvenius (SLU) for providing PET data for Krycklan (via SITES) and Carl Mitchell for snowmelt data in Dorset. We thank Pertti Ala-aho, Paolo Benettin, Sylvain Kuppel, Aaron A. Smith, and Hailong Wang for constructive discussions on the topic. The authors would like to acknowledge the support of the Maxwell computing cluster funded by the University of Aberdeen. The Krycklan component of the study was funded by the KAW Branch-Point project. We thank the European Research Council (ERC, project GA 335910 VeWa) for funding. We acknowledge support by the German Research Foundation (DFG) and the Open Access Publication Fund of Humboldt-Universität zu Berlin. We thank Todd Walter and two anonymous referees for their critical comments to improve the manuscript. Data availability. The underlaying research data are not publicly available in a repository, as they contain 70 GB. However, they can be requested from the authors

PY - 2018/7/20

Y1 - 2018/7/20

N2 - 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 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 holds for neither the evaporation, transpiration, or recharge.

AB - 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 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 holds for neither the evaporation, transpiration, or recharge.

KW - TRANSIT-TIME DISTRIBUTIONS

KW - BOREAL HEADWATER CATCHMENT

KW - RESOLUTION ISOTOPE DATA

KW - SOIL-WATER

KW - STABLE-ISOTOPES

KW - RESIDENCE TIMES

KW - RUNOFF GENERATION

KW - UNSATURATED ZONE

KW - STORAGE DYNAMICS

KW - TRACER

U2 - 10.5194/hess-22-3965-2018

DO - 10.5194/hess-22-3965-2018

M3 - Article

VL - 22

SP - 3965

EP - 3981

JO - Hydrology and Earth System Sciences

JF - Hydrology and Earth System Sciences

SN - 1027-5606

IS - 7

ER -