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A DIRECT METHOD TO MEASURE 14CO2 LOST BY EVASION FROM SURFACE WATERS

M F Billett, M H Garnett, S L Hardie

Abstract


Recent methodological advances in the use of zeolite molecular sieves for measuring the isotopic signature of

CO2 have provided the opportunity to make direct measurements of 14CO2 in various field situations. We linked a portable

molecular sieve/pump/IRGA system to a floating chamber to demonstrate the potential of the method to quantify the isotopic

signature (d13C and 14C) of CO2 lost by evasion (outgassing) from surface waters. The system, which was tested on a peatland

stream in Scotland, involved 1) an initial period of scrubbing ambient CO2 from the chamber, 2) a period of CO2 build-up

caused by surface water evasion, and 3) a final period of CO2 collection by the molecular sieve cartridge. The field test at 2

different sites on the same drainage system suggested that the results were reproducible in terms of d13C and 14C values. These

represent the first direct measurements of the isotopic signature of CO2 lost by evasion from water surfaces.

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