Supplemental tests of gas trapping device for N2 flux measurement

Abstract The gas trapping device method (GTD) is a relatively new method to measure N 2 flux from waters. However, the non-equilibrium diffusion error and the reliability of GTD method compared to other previously established N 2 flux measurement methods has not been evaluated. In this study, the diffusive error of GTD, coming from non-equilibrium N 2 partial pressure between the headspace inside the gas sample bottle and the air, was estimated using a sterilization experiment. Moreover, the GTD and MIMS methods were compared for measuring N 2 flux from water under similar conditions. The results showed that there were maximum diffusion errors of 2.99% in the sample bottles prefilled with pure Helium, while only 1.09–1.76% diffusion errors in bottles prefilled with other N 2 standard gas (15% or 75%), indicating minor non-equilibrium diffusion errors. N 2 fluxes from water measured by GTD and MIMS methods are quite similar under all three concentrations of nitrate (5.30, 10.55 and 17.25 mg L −1 ) and two levels of temperature (20 and 30 °C). Therefore, the GTD method offers a reliable alternative method to estimate N 2 flux rate in aquatic ecosystem.