Skip to main content

Tracers in Fresh Water

Tracers in Fresh Water

A tracer as used in hydrology is a substance in water that can be used for tracking water movement. Tracers primarily are used to determine the direction and rate of water movement. Knowledge of the rate at which groundwater flows can be useful, for example, in calculating the rate of contaminant movement in an aquifer . Knowledge of the rate at which river-water flows can be used to estimate the timing of floodwater movement in rivers.

Tracers also can be used to determine groundwater age. This estimate, in conjunction with knowledge of the direction of groundwater movement, can facilitate determination of the rate of movement.

Examples of Tracers

Hydrologists make use of both environmental tracers (natural or humanmade compounds present in the environment) and purposely introduced tracers (such as dyes or chloride that are injected into water).

Introduced Tracers.

Introduced tracers, such as dyes or chloride, are used to determine the direction and rate at which groundwater moves, the rate at which river-water flows, and mixing characteristics. Hydrologists can inject a tracer into a well (the injection well), and monitor nearby wells for the arrival of the tracer. Arrival of the tracer at a nearby well indicates movement of groundwater from the injection well toward that well, and thus allows determination of direction and rate of groundwater flow. In rivers, measurement of the rate at which a river carries an introduced tracer allows the river's flow rate to be calculated.

Oxygen Isotopes.

Isotopes of oxygen in water molecules are used to determine the source of groundwater and the direction of groundwater movement. The technique is based on the observation that proportions of heavy and light oxygen isotopes in water molecules often are distinct for water from different sources. For this technique to work, the different sources must have distinct isotopic signatures (a distinctive chemical composition), and all the potential sources must be characterized. To determine the direction of groundwater movement, hydrologists can map the movement of water from sources to observation points.

For example, in an agricultural area where irrigation water is derived from rivers, the groundwater underneath this area may contain a mixture of water that originated as precipitation and as irrigation water. By knowing the proportions of heavy and light oxygen isotopes in precipitation and in irrigation water, hydrologists can calculate how much of the groundwater originated from each of these two sources.

Tritium.

Tritium frequently is used as a tracer in groundwater studies. Tritium (3H) is a radioactive isotope of hydrogen. It has both natural and human-made sources. Large quantities of tritium were produced as a result of atmospheric testing of nuclear bombs beginning in the early 1950s. This so-called "bomb tritium" is present in groundwater that entered aquifers after the early 1950s. Thus, the presence of large concentrations of tritium in groundwater indicates the presence of "modern water," that is, water that entered the aquifer after the early 1950s. This information can often be used to determine the direction and rate of groundwater movement.

see also Groundwater, Age of; Isotopes: Applications in Natural Waters; Radionuclides in the Ocean; Tracers of Ocean-Water Masses.

Stephen R. Hinkle

Bibliography

Clark, Ian, and Peter Fritz. Environmental Isotopes in Hydrogeology. Boca Raton, FL: Lewis Publishers, 1997.

Cook, Peter, and Andrew Herczeg, eds. Environmental Tracers in Subsurface Hydrology. Boston, MA: Kluwer Academic Publishers, 2000.

Rantz, S. E. et al. Measurement and Computation of Streamflow. U.S. Geological Survey Water-Supply Paper 2175, 1982.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Tracers in Fresh Water." Water:Science and Issues. . Encyclopedia.com. 14 Dec. 2018 <https://www.encyclopedia.com>.

"Tracers in Fresh Water." Water:Science and Issues. . Encyclopedia.com. (December 14, 2018). https://www.encyclopedia.com/science/news-wires-white-papers-and-books/tracers-fresh-water

"Tracers in Fresh Water." Water:Science and Issues. . Retrieved December 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/news-wires-white-papers-and-books/tracers-fresh-water

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.