A new field approach for the collection of samples for aquatic 14CO2 analysis using headspace equilibration and molecular sieve traps: The super headspace method

Abstract

Carbon dioxide evasion from inland waters such as lakes, rivers and streams represents a significant component of the global carbon cycle, yet in many parts of the world, relatively little is known about its source. Radiocarbon dating of aquatic CO2 has the potential to provide new insights into C cycling in the terrestrial–aquatic–atmosphere continuum, and whilst a range of methods are available for the collection of samples for 14C analysis, they all have limitations or disadvantages (e.g. slow collection rates and potential non-equilibrium). These issues are further compounded in remote field sites. Here, we describe a new method for the field collection of CO2 samples from low-pH waters (pH < 7) for radiocarbon analysis, which involves a scaled-up version of the widely used headspace equilibration technique coupled with syringe injection of samples into molecular sieve traps for convenient and stable storage. We present the results of laboratory and field tests to verify this ‘super headspace method’ and discuss its advantages compared with existing techniques, particularly for sampling in remote locations. This includes its high portability, speed of use and absence of any special sample preservation requirements.