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 CO 2 have provided the opportunity to make direct measurements of 14 CO2 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 (δ 13 C and 14 C) of CO 2 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 CO 2 from the chamber, 2) a period of CO 2 build-up caused by surface water evasion, and 3) a final period of CO 2 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 δ 13 C and 14 C values. These represent the first direct measurements of the isotopic signature of CO 2 lost by evasion from water surfaces.