Evaluation of a Closed Tunnel for Field-Scale Measurements of Nitrous Oxide Fluxes from an Unfertilized Grassland Soil
- Klaus Schäfer *a,
- Jürgen Böttcherb,
- Daniel Weymannc,
- Carolin von der Heideb and
- Wilhelmus H. M. Duijnisveldd
- a Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Dep. Atmospheric Environmental Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany
b Leibniz Univ. of Hannover, Institute of Soil Science, Herrenhäuserstr. 2, 30419 Hannover, Germany
c Forschungszentrum Jülich GmbH, Agrosphere Institute (IBG-3), 52425 Jülich, Germany
d Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany. Assigned to Associate Editor Jan Willem van Groenigen
Emissions of the major greenhouse gas N2O from soils are characterized by huge spatial variability. An upscaling based on conventional small-scale chamber measurements is thus questionable and may involve a considerable amount of uncertainty. In this feasibility study, we evaluated the applicability of a large, closed tunnel for field-scale measurements of N2O fluxes from an unfertilized grassland soil. The tunnel, coupled to an open-path Fourier transform infrared spectrometer, covered 500 m2. During a 2-yr campaign, concurrent closed-chamber measurements (area of 0.045 m2) were performed at the tunnel plot. The tunnel system enabled high-density and precise N2O concentration measurements under dry, stable, nocturnal atmospheric conditions, but higher wind speeds and rain limited its application. To calculate an unbiased, predeployment N2O flux from the increase of N2O concentrations during tunnel deployment, we propose a novel approach based on inverse modeling (IMQ0). We show that IMQ0 is appropriate for the specific non–steady state tunnel setup. Compared with conventional models, which were developed for gas flux calculation from concentration gradients measured in vented closed chambers, IMQ0 is most accurate. Whereas N2O fluxes obtained from the tunnel measurements were generally small and at a typical background level, the chamber measurements revealed high spatial and temporal variability of N2O emissions, including slight N2O uptake and precipitation-triggered emission peaks. The cumulative N2O fluxes of both methods differed by one order of magnitude and were smaller for the tunnel measurements. We argue that the chambers were occasionally susceptible to detection of hotspots and hot moments of N2O emission. However, these emissions were evidently not representative for the field scale. Compared with available greenhouse gas measurement techniques, we conclude that the tunnel may serve as a gap-filling method between small-scale chamber and ecosystem-level micrometeorological techniques, particularly during stable nocturnal conditions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2012. . Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.