Stable water isotopes

The stable water isotopes deuterium and oxygen-18 are natural tracers in the water cycle that can be used to determine the origin of water components and to track climatic changes.

On the basis of the stable isotopes deuterium (2H) and oxygen-18 (18O) it is possible to gauge the mean elevation of river catchments and to distinguish individual water components in groundwater (e.g. river water infiltrate and precipitation infiltrate) by the isotopic signature of precipitation, which varies according to region, elevation and season. Deuterium and oxygen-18 are also increasingly used throughout the world to detect climatically induced changes in the water cycle. The Global Climate Observing System GCOS Switzerland has used deuterium and oxygen-18 as official climate parameters since 2007. The International Atomic Energy Agency IAEA coordinates the isotopic measurements globally and manages the Global Network of Isotopes in Precipitation GNIP and the Global Network of Isotopes in Rivers GNIR.

Stable reference gauging network

In the National Groundwater Monitoring NAQUA ISOT module, isotope reference data has been collected since 1980 in precipitation (13 monitoring sites) and in watercourses (9 monitoring sites) for applied hydrological studies. In a pilot study, the 50 groundwater gauging stations in the NAQUA TREND module were analysed for deuterium and oxygen-18 from 2006 to 2013 to establish groundwater recharge dynamics and surface water/groundwater interactions.

Isotope_2H&18O_Karte_2015 — Deuterium and oxygen-18 in precipitation, watercourses and groundwater (2013), geographic area and groundwater regime in valley bottoms. Mean value per NAQUA monitoring site. Precipitation and watercourse monitoring sites of the ISOT module, groundwater monitoring sites of the TREND module.

Development over time variable

Regular seasonal fluctuations characterise the annual cycle of isotope values in precipitation. These are overlaid by longer-term developments of global climatic changes. In line with the general temperature trend, deuterium and oxygen-18 levels in precipitation increased at all precipitation gauging stations from the early 1980s until the beginning of this century. Between 2005 and 2015, deuterium and oxygen-18 levels in precipitation were temporarily stagnant, or declining; since then they have risen again. Deuterium and oxygen-18 levels were highest between 2008 and 2010 at most groundwater gauging stations at which measurements were taken in the Isotopes in Groundwater pilot study, which was conducted between 2006 and 2013.

Entwicklung 18O Niederschlag 1981-2020 — Development of oxygen-18 values in precipitation at selected gauging stations (1980 to 2022). Mean value per NAQUA gauging station and year.

Interpolated raster data (isoscapes)

Areal maps were produced using spatially interpolated data of the distribution of oxygen-18 and deuterium in precipitation for selected years. The multi-regression method with topography and monthly precipitation, and in combination with the residual interpolation by ordinary kriging was considered the most appropriate method. The model was developed using data in the period 2007 to 2020. Monthly raster maps in 500 m resolution have been determined for the years 2013 and 2020.

Basic information: Water isotopes (PDF, 223 kB, 31.10.2023)