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Use of Doubly-Labeled Water (${}^{3}\text{HH}^{18}\text{O}$) for Determination of H₂O Flux and CO₂ Production by a Mammal in a Humid Environment

Ronald D. Gettinger
Oecologia
Vol. 59, No. 1 (1983), pp. 54-57
Published by: Springer in cooperation with International Association for Ecology
Stable URL: http://www.jstor.org/stable/4217064
Page Count: 4
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Use of Doubly-Labeled Water (${}^{3}\text{HH}^{18}\text{O}$) for Determination of H₂O Flux and CO₂ Production by a Mammal in a Humid Environment
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Abstract

The accuracy of the doubly labeled water (${}^{3}\text{HH}^{18}\text{O}$) technique for estimating H₂O flux and CO₂ production in pocket gophers was evaluated in laboratory experiments. Experiments were conducted under conditions of elevated humidity in order to determine the influence of unlabeled H₂O vapor input on H₂O flux and CO₂ production rates which are determined from isotope turnover. High humidity is commonplace in burrows of many small mammals, including those of the pocket gopher, and theoretically could introduce substantial errors when determining these rates with isotopic procedures. Water influx that was estimated from tritium turnover was not significantly different from actual H₂O influx which was determined from feeding rates. Also, ${}^{3}\text{HH}^{18}\text{O}$ techniques yielded estimates of CO₂ production that were not significantly different from values determined from energy intake rates. Such close agreement was not anticipated. The unexpected accuracy probably results due to offsetting errors associated with (1) the influx of unlabeled H₂O vapor through the skin and lungs of labeled pocket gophers and (2) the effects of biological fractionation of isotopes in the body H₂O of labeled pocket gophers.

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