A Direct Method to Measure14CO2Lost by Evasion from Surface Waters

Abstract

Recent methodological advances in the use of zeolite molecular sieves for measuring the isotopic signature of CO2have provided the opportunity to make direct measurements of14CO2 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 (δ13C and14C) of CO2lost 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 CO2from the chamber, 2) a period of CO2build-up caused by surface water evasion, and 3) a final period of CO2collection 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 δ13C and14C values. These represent the first direct measurements of the isotopic signature of CO2lost by evasion from water surfaces.