title: Methane and nitrous oxide exchange over a managed hay meadow.
abstract: The methane (CH4) and nitrous oxide (N2O) exchange of a temperate mountain grassland near Neustift, Austria, was measured during 2010-2012 over a time period of 22 months using the eddy covariance method. Exchange rates of both compounds at the site were low, with 97% of all half-hourly CH4and N2O fluxes ranging between ±200 and ±50 ng m-2s-1, respectively. The meadow acted as a sink for both compounds during certain time periods, but was a clear source of CH4and N2O on an annual timescale. Therefore, both gases contributed to an increase of the global warming potential (GWP), effectively reducing the sink strength in terms of CO2equivalents of the investigated grassland site. In 2011, our best guess estimate showed a net greenhouse gas (GHG) sink of -32 g CO2equ. m-2yr-1for the meadow, whereby 55% of the CO2sink strength of -71 g CO2m-2yr-1was offset by CH4(N2O) emissions of 7 (32) g CO2equ. m-2yr-1. When all data were pooled, the ancillary parameters explained 27 (42)% of observed CH4(N2O) flux variability, and up to 62 (76)% on shorter timescales in-between management dates. In the case of N2O fluxes, we found the highest emissions at intermediate soil water contents and at soil temperatures close to 0 or above 14 °C. In comparison to CO2, H2O and energy fluxes, the interpretation of CH4and N2O exchange was challenging due to footprint heterogeneity regarding their sources and sinks, uncertainties regarding post-processing and quality control. Our results emphasize that CH4and N2O fluxes over supposedly well-aerated and moderately fertilized soils cannot be neglected when evaluating the GHG impact of temperate managed grasslands.
authors.affiliation: Institute of Ecology, University of Innsbruck, Austria.
authors.forename: L
authors.initials: L
authors.lastname: Hörtnagl
authors.affiliation: Institute of Ecology, University of Innsbruck, Austria ; European Academy of Bolzano, Bolzano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Wohlfahrt
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