Isotope hydrology
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Isotope hydrology is a field of hydrology that uses isotopic dating to estimate the age and origins of water and of movement within the hydrologic cycle. The techniques are used for water-use policy, mapping aquifers, conserving water supplies, and controlling pollution. It replaces or supplements past methods of measuring rain, river levels and other bodies of water over many decades.
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Water molecules carry unique fingerprints, based in part on differing proportions of the oxygen and hydrogen isotopes that constitute all water. Isotopes are forms of the same element that have variable numbers of neutrons in their nuclei.
Air, soil and water contain mostly oxygen 16 (O-16). Oxygen 18 (O-18) occurs in one oxygen atom in every five hundred and is a bit heavier than oxygen 16, it has two extra neutrons. From a simple energy standpoint this results in a preference for evaporating the lighter O-16 containing water and leaving more of the O-18 water behind in the liquid state. Thus seawater tends to be richer in O-18 and rain and snow relatively depleted in O-18. Higher average global temperature would provide more energy and thus an increase in atmospheric O-18 water. Lower than normal amounts of O-18 in groundwater or an ice layer would imply that the water or ice represents an evaporation origin during cooler climatic eras or even ice ages.
Carbon 14 dating is also used as part of isotope hydrology as all natural water contains dissolved carbon dioxide.
[edit] Current use
The isotope hydrology program at the International Atomic Energy Agency works to aid developing states (including 84 projects in more than 50 countries) and to create a detailed portrait of Earth's water resources.
In Ethiopia, Libya, Chad, Egypt and Sudan, the International Atomic Energy Agency used such techniques to help local water policy deal with fossil water.
An arsenic pollution crisis in Bangladesh that the World Health Organization calls the "largest mass poisoning of a population in history" has been investigated using this technique.
