ABSTRACT
‘Environmental isotopes’ are those isotopes that are widespread in nature and are part of the hydrological and/or geological cycle. This chapter describes the use of oxygen, hydrogen, carbon, nitrogen and sulphur isotopes. The selection is based on the fact that these isotopes are the ones most frequently studied in catchments, and very applicable for the study of catchments where the storage time of water is relatively short. Northern catchments such as in Scandinavia often are characterised by rather rugged topography, and well-defined catchment boundaries. River discharges have strong seasonal variations with snow melt as the main flood event. Rather thin unconsolidated glacial sediments, mostly tills, cover the lithified bedrock. In isotopic hydrograph separation the streamwater is normally separated into flows of new water (event water) and old water. Old water is water that was already in the catchment before the runoff event.
