The extended National Waters Inventory of Scotland (NWIS) monitoring network in combination with an extensive, supplementary low flow sampling campaign was used to create isoscapes of surface water for management purposes at high spatial resolution (100 m grid) across Scotland. The δ2H isoscape shows a strong isotopic separation along a north-south and east-west topographic (mountainous to the north and west and lowlands to the east) and climatic (wetter west, drier east) gradients. Isotopes were enriched in the western domain and depleted in the east and central Highland domains. The surface water d-excess isoscape show more complex spatial variability mainly related to contrasting moisture sources (sub-tropical North Atlantic Ocean, the North Sea, Polar Continental, and the Arctic) as well as secondary evaporation processes. The two-year NWIS isotope record exhibited a significant seasonal evaporative effect on surface water isotopes that progresses from winter through to a maximum in autumn as indicated by Local Evaporation Lines (LELs). The surface water isoscapes can be efficiently reproduced with geographically weighted regression (GWR) models using gridded annual precipitation, remotely sensed actual evapotranspiration, land cover, soil wetness, catchment area, and mean elevation. The GWR models showed potential to assess isotopic changes under future climate and land use change.
Bibliographical noteThis paper was partly funded by the Rural & Environment Science & Analytical Services Division of the Scottish Government. CB acknowledges support from the University of Costa Rica Research Council (project 217-B4-239). CS, DT, RSM, GEH and CB participated under the University of Costa Rica Research Council funded Isotope Network for Tropical Ecosystem Studies (ISONet). RSM acknowledges the support from the International Atomic Energy Agency (grant CRP-19747). DT and CS acknowledge funding from the European Research Council ERC (project GA 335910 VEWA) and the Natural Environment Research Council NERC (project NE/K000268/1). We thank Dr. Sarah Dunn and the late Dr. Julian Dawson for their help and encouragement in the initiation of this project. We thank all who provided samples for the low flow spot sampling scheme. Comments from Mark Brewer and two anonymous Reviewers improved the quality of the final paper. All 100 m isoscape raster maps and isotope data are available for download.
- Geographically weighted regression models
- Stable isotopes