Isotopes & Chemical Tracers Used in Hydrology

Periodic Table

The aim of this site is to present information on elements regularly found in groundwaters and which can be used as geochemical tracers and applied in arid and semi-arid zone hydrological and hydrogeological studies. On this site both chemical and isotopic tracers used primarily in groundwater studies are introduced. Dissolved gases are also used as tracers of age and past temperatures.

Periodic Table

Information of each tracer is organized in a standard format as follows

Basic information

  • Elemental geochemistry
  • Main source of the element
  • Isotopic geochemistry

Measurement techniques

  • Element/dissolved species measurement
  • Isotope measurement


  • Chemical tracer
  • Reference to case studies


Elements and their isotopes which are considered (so far) are:

The major elements found in waters

  • Cl, N, S, Na, K, Ca, Mg

Minor and trace elements

  • Br, B, F, I, Li, Sr, Ba, Si, Al, Mn, Cr, Mo, U

The isotopes of water

  • O, H

Dissolved gases

In the basic information section, the general geochemical properties of each element are presented together with its main sources and information on its isotopes. Measurement techniques section gives brief information on analyzing major and trace ions and isotopes. The application section focuses on their utilizations in groundwater and surface water and how the inert and reactive tracers can reveal information about recharge, discharge,age and flow systems. For each element, a few references are given and it is possible to access further information on case studies elsewhere on the G-WADI site. The convention of trace element or species divided by major ion is recommended and used in this site thus Br/Cl, with Cl being the reference element.

How Isotopic Analysis is Done