Groundwater isoscapes in a montane headwater catchment show dominance of well-mixed storage

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Abstract

We conducted an integrated groundwater – surface water monitoring programme in a 3.2 km2 experimental catchment in the Scottish Highlands by sampling all springs, seepages and wells in six, spatially extensive synoptic surveys over a two year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70 % glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples were
analysed for stable isotopes, Gran alkalinity and electrical conductivity (EC). Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well-mixed shallow, groundwater stores. Moreover, lc-excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and EC of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotope
composition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterised by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasises the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.
Original languageEnglish
Pages (from-to)3504-3519
Number of pages15
JournalHydrological Processes
Volume31
Issue number20
Early online date9 Aug 2017
DOIs
Publication statusPublished - 30 Sep 2017

Fingerprint

headwater
catchment
groundwater
alkalinity
seepage
electrical conductivity
recharge
outcrop
geology
antecedent conditions
valley
hillslope
schist
residence time
stable isotope
isotopic composition
persistence
tracer
isotope
surface water

Keywords

  • groundwater
  • stable isotopes
  • isoscapes
  • lc-excess

Cite this

Groundwater isoscapes in a montane headwater catchment show dominance of well-mixed storage. / Scheliga, Bernhard; Tetzlaff, Doerthe; Nuetzmann, Gunnar; Soulsby, Chris.

In: Hydrological Processes, Vol. 31, No. 20, 30.09.2017, p. 3504-3519.

Research output: Contribution to journalArticle

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abstract = "We conducted an integrated groundwater – surface water monitoring programme in a 3.2 km2 experimental catchment in the Scottish Highlands by sampling all springs, seepages and wells in six, spatially extensive synoptic surveys over a two year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70 {\%} glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples wereanalysed for stable isotopes, Gran alkalinity and electrical conductivity (EC). Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well-mixed shallow, groundwater stores. Moreover, lc-excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and EC of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotopecomposition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterised by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasises the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.",
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AU - Soulsby, Chris

N1 - Acknowledgements We would like to thank the European Research Council (ERC, project GA 335910 VeWa) for funding. We further thank Jonathan Dick for running the isotope analysis.

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N2 - We conducted an integrated groundwater – surface water monitoring programme in a 3.2 km2 experimental catchment in the Scottish Highlands by sampling all springs, seepages and wells in six, spatially extensive synoptic surveys over a two year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70 % glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples wereanalysed for stable isotopes, Gran alkalinity and electrical conductivity (EC). Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well-mixed shallow, groundwater stores. Moreover, lc-excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and EC of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotopecomposition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterised by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasises the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.

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