Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions

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Abstract

We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. “pre-event” water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as “isostats,” not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.
Original languageEnglish
Pages (from-to)969-985
Number of pages17
JournalWater Resources Research
Volume50
Issue number2
Early online date6 Feb 2014
DOIs
Publication statusPublished - Feb 2014

Keywords

  • rainfall-runoff
  • isotopes
  • transit times
  • peat
  • riparian zone
  • hydropedology
  • connectivity
  • soils

Cite this

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title = "Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions",
abstract = "We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10{\%}. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40{\%}. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. “pre-event” water typically accounts for >80{\%} of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as “isostats,” not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.",
keywords = "rainfall-runoff, isotopes, transit times, peat, riparian zone, hydropedology, connectivity, soils",
author = "Doerthe Tetzlaff and Christian Birkel and Dick, {Jonathan James} and Josie Geris and Christopher Soulsby",
year = "2014",
month = "2",
doi = "10.1002/2013WR014147",
language = "English",
volume = "50",
pages = "969--985",
journal = "Water Resources Research",
issn = "0043-1397",
publisher = "American Geophysical Union",
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TY - JOUR

T1 - Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions

AU - Tetzlaff, Doerthe

AU - Birkel, Christian

AU - Dick, Jonathan James

AU - Geris, Josie

AU - Soulsby, Christopher

PY - 2014/2

Y1 - 2014/2

N2 - We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. “pre-event” water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as “isostats,” not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.

AB - We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. “pre-event” water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as “isostats,” not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.

KW - rainfall-runoff

KW - isotopes

KW - transit times

KW - peat

KW - riparian zone

KW - hydropedology

KW - connectivity

KW - soils

U2 - 10.1002/2013WR014147

DO - 10.1002/2013WR014147

M3 - Article

VL - 50

SP - 969

EP - 985

JO - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 2

ER -