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Nitrous oxide emissions from managed grassland: a comparison of eddy covariance and static chamber measurements

Jones, S.K.; Famulari, D.; Di Marco, C.F.; Nemitz, E.; Skiba, U.M.; Rees, R.M.; Sutton, M.A.. 2011 Nitrous oxide emissions from managed grassland: a comparison of eddy covariance and static chamber measurements. Atmospheric Measurement Techniques Discussions, 4 (1). 1079-1112. 10.5194/amtd-4-1079-2011

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Abstract/Summary

Managed grasslands are known to be an important source of N2O with estimated global losses of 2.5 Tg N2O-N yr−1. Chambers are the most widely used method to measure N2O fluxes, but also micrometeorological methods have successfully been applied. In this paper we present a comparison of N2O fluxes measured by non-steady state chambers and eddy covariance (EC) (using an ultra-sonic anemometer coupled with a tunable diode laser) methods from an intensively grazed and fertilised grassland site in South East Scotland. The measurements were taken after fertilisation events in 2003, 2007 and 2008. In four out of six comparison periods a short-lived increase of N2O emissions after mineral N application was observed, returning to background level within 2–6 days. Highest fluxes were measured by both methods in July 2007 with maximum values of 1300 ng N2O-N m−2 s−1 (EC) and 651 ng N2O-N m−2 s−1 (chamber method). Frequently, negative fluxes above the detection limit were observed in all comparison periods by EC, while with chambers negative fluxes were always below detection limit. Despite observed negative fluxes, median and average fluxes over each period were always positive. Over all 6 comparison periods 69% of N2O fluxes measured by EC at the time of chamber closure were within the range of the chamber measurements. Differences between N2O fluxes calculated from chamber measurements and EC over the same measurement period were never significant. Overall, N2O fluxes measured by EC during the time of chamber closure were smaller compared to those measured by chambers, however this was the case in only 3 out of 6 comparison periods. This inconsistency observed on the same experimental field at different times can partly be explained by the fact that the different techniques integrate fluxes over different spatial scales. Large fluxes measured by chambers may have represented local hotspots, which made a small contribution to the flux derived by the EC method which integrates fluxes over a larger area. The spatial variability from chamber measurements was high as shown by a coefficient of variation of up to 139%. No diurnal pattern of N2O fluxes was observed, possibly due to the small diurnal variations of soil temperature. Calculations of cumulative fluxes showed that different integration methods can introduce a large bias in the estimation of cumulative fluxes and therefore emission factors.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.5194/amtd-4-1079-2011
Programmes: CEH Topics & Objectives 2009 - 2012 > Biogeochemistry
CEH Sections: Billett (to 30 Nov 2013)
ISSN: 1867-8610
Additional Information. Not used in RCUK Gateway to Research.: Open Access article - click on the Official URL link for full text
Additional Keywords: N2O, eddy covariance, fluxes, emission factors
NORA Subject Terms: Meteorology and Climatology
Agriculture and Soil Science
Atmospheric Sciences
Date made live: 11 Nov 2011 15:50
URI: http://nora.nerc.ac.uk/id/eprint/15847

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