Interpretation of homogeneity in δ18O signatures of stream water in a nested sub-catchment system in north-east Scotland

S. M. Dunn, J. R. Bacon, C. Soulsby, D. Tetzlaff, M. I. Stutter, S. Waldron, I. A. Malcolm

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

The isotope hydrology of a set of nested sub-catchments in the north-east of Scotland has been studied to examine the mixing processes and residence times of water in the catchments. The measured delta O-18 in stream waters was found to be exceptionally uniform both temporally and spatially. Hydrochemical mixing analyses showed that groundwater contributes between 62 and 90% of the stream flow in all sub-catchments. Model analysis indicated that the delta O-18 in stream water is indicative of a highly mixed system in which near surface runoff appears to be mixed with groundwater, within the soil profile, before being released from the catchment. Small fluctuations in the stream water delta O-18 response are generated by a small proportion (<10%) of less-well mixed water in infiltration excess runoff during storm events. A comparative application of the model to a nearby catchment, which has a lower proportion of groundwater runoff, demonstrated contrasting behaviour, with significantly less mixing of waters occurring and a more distinct difference in the age of runoff generated by different flow paths. This highlighted that standard methods for characterization of mixing mechanisms are often insufficient and may not discriminate between systems that have retained quite distinct flow paths throughout catchment transit, and those which have been mixed at some stage. Model sensitivity analysis also indicated that the simulated mean residence time of water varies most strongly in response to different parameters compared with the delta O-18 response. This has implications for estimating water residence times from isotope data. Copyright (C) 2008 John Wiley & Sons, Ltd.

Original languageEnglish
Pages (from-to)4767-4782
Number of pages16
JournalHydrological Processes
Volume22
Issue number24
Early online date17 Jul 2008
DOIs
Publication statusPublished - 30 Nov 2008

Keywords

  • delta O-18
  • tracer
  • residence time
  • modelling
  • mixing
  • catchment
  • residence times
  • mesoscale catchments
  • surface-water
  • runoff processes
  • groundwater
  • model
  • transport
  • isotope
  • chemistry
  • pollution

Cite this

Interpretation of homogeneity in δ18O signatures of stream water in a nested sub-catchment system in north-east Scotland. / Dunn, S. M.; Bacon, J. R.; Soulsby, C.; Tetzlaff, D.; Stutter, M. I.; Waldron, S.; Malcolm, I. A.

In: Hydrological Processes, Vol. 22, No. 24, 30.11.2008, p. 4767-4782.

Research output: Contribution to journalArticle

Dunn, S. M. ; Bacon, J. R. ; Soulsby, C. ; Tetzlaff, D. ; Stutter, M. I. ; Waldron, S. ; Malcolm, I. A. / Interpretation of homogeneity in δ18O signatures of stream water in a nested sub-catchment system in north-east Scotland. In: Hydrological Processes. 2008 ; Vol. 22, No. 24. pp. 4767-4782.
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AB - The isotope hydrology of a set of nested sub-catchments in the north-east of Scotland has been studied to examine the mixing processes and residence times of water in the catchments. The measured delta O-18 in stream waters was found to be exceptionally uniform both temporally and spatially. Hydrochemical mixing analyses showed that groundwater contributes between 62 and 90% of the stream flow in all sub-catchments. Model analysis indicated that the delta O-18 in stream water is indicative of a highly mixed system in which near surface runoff appears to be mixed with groundwater, within the soil profile, before being released from the catchment. Small fluctuations in the stream water delta O-18 response are generated by a small proportion (<10%) of less-well mixed water in infiltration excess runoff during storm events. A comparative application of the model to a nearby catchment, which has a lower proportion of groundwater runoff, demonstrated contrasting behaviour, with significantly less mixing of waters occurring and a more distinct difference in the age of runoff generated by different flow paths. This highlighted that standard methods for characterization of mixing mechanisms are often insufficient and may not discriminate between systems that have retained quite distinct flow paths throughout catchment transit, and those which have been mixed at some stage. Model sensitivity analysis also indicated that the simulated mean residence time of water varies most strongly in response to different parameters compared with the delta O-18 response. This has implications for estimating water residence times from isotope data. Copyright (C) 2008 John Wiley & Sons, Ltd.

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