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 language | English |
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Pages (from-to) | 4767-4782 |
Number of pages | 16 |
Journal | Hydrological Processes |
Volume | 22 |
Issue number | 24 |
Early online date | 17 Jul 2008 |
DOIs | |
Publication status | Published - 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