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Isotope hydrology of the Allt a' Mharcaidh catchment, Cairngorms, Scotland: implications for hydrological pathways and residence times
Author(s) -
Soulsby C.,
Malcolm R.,
Helliwell R.,
Ferrier R. C.,
Jenkins A.
Publication year - 2000
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/(sici)1099-1085(200003)14:4<747::aid-hyp970>3.0.co;2-0
Subject(s) - drainage basin , hydrology (agriculture) , catchment hydrology , environmental science , residence time (fluid dynamics) , residence , geology , geography , cartography , geotechnical engineering , demography , sociology
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 δ 18 O=−7·69‰) exhibited strong seasonal variation in δ 18 O values over the study period, ranging from −2·47‰ in the summer to −20·93‰ in the winter months. As expected, such variation was substantially damped in stream waters, which had a mean and range of δ 18 O of −9·56‰ and −8·45 to −10·44‰, respectively. Despite this, oxygen‐18 proved a useful tracer and streamwater δ 18 O variations could be explained in terms of a two‐component mixing model, involving a seasonally variable δ 18 O signature in storm runoff, mixing with groundwater characterized by relatively stable δ 18 O levels. Variations in soil water δ 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 baseflows is consistent with effective mixing processes in shallow aquifers at the catchment scale. Examination of the seasonal variation in δ 18 O levels in various catchment waters provided a first 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 runoff and 2 and >5 years for shallow and deeper groundwater, respectively. These 18 O data sets provide further evidence that the influence of groundwater on the hydrology and hydrochemistry of upland catchments has been underestimated. Copyright © 2000 John Wiley & Sons, Ltd.