Supplemental tests of gas trapping device for N-2 flux measurement

摘要

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 degrees C). Therefore, the GTD method offers a reliable alternative method to estimate N-2 flux rate in aquatic ecosystem. (C) 2016 Elsevier B.V. All rights reserved.