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Innovations
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Every Drop Tells a Story: A New Technique for Dating Water Lance Frazer Abstract
Knowing the age, or residence time, of water in an aquifer can help scientists assess the susceptibility of drinking water supplies to surface contamination, and can also help in calculating how heavily a groundwater source can be used, based on how quickly it replenishes itself. Robert Criss of Washington University in St. Louis, Missouri, has developed a mathematical equation that determines not only the age of very recent water supplies, but also the age of groundwater that has already migrated into a river and mixed with the surface runoff. Criss believes his formula gives an accurate interpretation of residence time in a groundwater system and incorporates the impact of more recent rainfall on the isotopic balance. According to Criss, plugging rainfall and other data into his equation yields a characteristic "fingerprint" of a water supply that very closely matches the general variation that can be measured in springs and rivers.
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