Isotope hydrology of the Allt a' Mharcaidh catchment, Cairngorms, Scotland: implications for hydrological pathways and residence times
✍ Scribed by C. Soulsby; R. Malcolm; R. Helliwell; R. C. Ferrier; A. Jenkins
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 300 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0885-6087
No coin nor oath required. For personal study only.
✦ Synopsis
The hydrology of oxygen-18 ( 18 O) isotopes was monitored between 1995 and 1998 in the Allt a' Mharcaidh catchment in the Cairngorm Mountains, Scotland. Precipitation (mean d 18 O À7 . 69%) exhibited strong seasonal variation in d 18 O values over the study period, ranging from À2 . 47% in the summer to À20 . 93% in the winter months. As expected, such variation was substantially damped in stream waters, which had a mean and range of d 18 O of À9 . 56% and À8 . 45 to À10 . 44%, respectively. Despite this, oxygen-18 proved a useful tracer and streamwater d 18 O variations could be explained in terms of a two-component mixing model, involving a seasonally variable d 18 O signature in storm runo, mixing with groundwater characterized by relatively stable d 18 O levels. Variations in soil water d 18 O implied the routing of depleted spring snowmelt and enriched summer rainfall into streamwaters, probably by near-surface hydrological pathways in peaty soils. The relatively stable isotope composition of base¯ows is consistent with eective mixing processes in shallow aquifers at the catchment scale. Examination of the seasonal variation in d 18 O levels in various catchment waters provided a ®rst approximation of mean residence times in the major hydrological stores. Preliminary estimates are 0 . 2±0 . 8 years for near-surface soil water that contributes to storm runo and 2 and 45 years for shallow and deeper groundwater, respectively. These 18 O data sets provide further evidence that the in¯uence of groundwater on the hydrology and hydrochemistry of upland catchments has been underestimated.