A direct method to measure 14CO2 lost by evasion from surface waters

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 (CO2)-C-14 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 (delta C-13 and C-14) 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 delta C-13 and C-14 values. These represent the first direct measurements of the isotopic signature of CO2 lost by evasion from water surfaces.