Isotope hydrology is a field of geochemistry and

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

that uses naturally occurring stable and radioactive isotopic techniques to evaluate the age and origins of surface and groundwater and the processes within the atmospheric

hydrologic cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly const ...

. Isotope hydrology applications are highly diverse, and used for informing water-use

policy Policy is a deliberate system of guidelines to guide decisions and achieve rational outcomes. A policy is a statement of intent and is implemented as a procedure or protocol. Policies are generally adopted by a governance body within an orga ...

map A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...

ping

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

s, conserving water supplies, assessing sources of water

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...

, and increasingly are used in eco-hydrology to study human impacts on all dimensions of the hydrological cycle and

ecosystem service Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. ...

Details

Water molecules carry unique isotopic "fingerprints", based in part on differing ratios of the

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

isotopes that constitute the water molecule. Isotopes are atoms of the same element that have a different number of

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...

s in their nuclei.

Air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

, freshwater and seawater contain mostly oxygen-16 ( ¹⁶O). Oxygen-18 (¹⁸O) occurs in approximately one oxygen atom in every five hundred and has a slightly higher mass than oxygen-16, as it has two extra neutrons. From a simple energy and bond breakage standpoint this results in a preference for evaporating the lighter ¹⁶O containing water and leaving more of the ¹⁸O water behind in the liquid state (called isotope fractionation). Thus

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...

tends to contain more ¹⁸O than rain and snow. Dissolved ions in surface and groundwater water also contain useful isotopes for hydrological investigations. Dissolved species like sulfate and nitrate contain differing ratios of 34-S to 32-S or 15-N to 14-N, and are often diagnostic of pollutant sources. Natural radioisotopes like tritium (3-H) and radiocarbon ( 14-C) are also used as natural clocks to determine the residence times of water in aquifers, rivers, and the oceans.

Applications

The most commonly used isotope application in hydrology uses hydrogen and oxygen isotopes to evaluate sources or age of water, ice or snow. Isotopes in ice cores help to reveal conditions of past climate. Higher average global temperature would provide more energy and thus an increase the atmospheric ¹⁸O content of rain or snow, so that lower than modern amounts of ¹⁸O in groundwater or ice layer imply the water or ice represents a period of cooler climatic eras or even

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

s. Another application involves the separation of

groundwater flow Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

and

baseflow Baseflow (also called drought flow, groundwater recession flow, low flow, low-water flow, low-water discharge and sustained or fair-weather runoff) is the portion of the streamflow that is sustained between precipitation events, fed to streams by d ...

from streamflow in the field of catchment hydrology (i.e. a method of

hydrograph A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs). It can als ...

separation). Since precipitation in each rain or snowfall event has a specific isotopic signature, and

subsurface In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedr ...

water can be identified by well sampling, the composite signature in the stream is an indicator the proportion of the streamflow comes from overland flow and what portion comes from

subsurface flow Subsurface flow, in hydrology, is the flow of water beneath earth's surface as part of the water cycle. In the water cycle, when precipitation falls on the earth's land, some of the water flows on the surface forming streams and rivers. The rema ...

. Stable isotopes in the water molecule are also useful in tracing the sources (or proportion of sources) of water that plants use.

Current use

The isotope hydrology program at the

International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 195 ...

works to aid developing states to create a detailed portrait of Earth's water resources. In

Ethiopia Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...

Libya Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...

Chad Chad (; ar, تشاد , ; french: Tchad, ), officially the Republic of Chad, '; ) is a landlocked country at the crossroads of North and Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic ...

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...

and

Sudan Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...

, the International Atomic Energy Agency used radioisotope techniques to help local water policy identify and conserve

fossil water Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vos ...

. The International Atomic Energy Agency maintains a publicly accessible global network and isotopic database for Earth's rainfall and rivers.

References

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External links

Isotope Hydrology at the IAEA
Water Hydrology Hydraulic engineering

Details

Applications

Current use

See also

References

External links