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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-141
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-141
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Jun 2020

Submitted as: research article | 09 Jun 2020

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This preprint is currently under review for the journal BG.

Memory effects on greenhouse gas emissions (CO2, N2O and CH4) following grassland restoration?

Lutz Merbold1,2, Charlotte Decock3, Werner Eugster1, Kathrin Fuchs4, Benjamin Wolf4, Nina Buchmann1, and Lukas Hörtnagl1 Lutz Merbold et al.
  • 1Department of Environmental Systems Science, Institute of Agricultural Sciences, Grassland Sciences Group, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland
  • 2Mazingira Centre, International Livestock Research Institute (ILRI), Old Naivasha Road, PO Box 30709, 00100 Nairobi, Kenya
  • 3Department of Environmental Systems Science, Institute of Agricultural Sciences, Sustainable Agro-ecosystem Group, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland, now at: Department of Natural Resources Management and Environmental Sciences, California State University, San Luis Obispo, California, USA
  • 4Institute for Meteorology and Climate Research (IMK-IFU), Karlsruhe Institute of Technology (KIT), Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, German

Abstract. A five-year greenhouse gas (GHG) exchange study of the three major gas species (CO2, CH4 and N2O) from an intensively managed permanent grassland in Switzerland is presented. Measurements comprise two years (2010/2011) of manual static chamber measurements of CH4 and N2O, five years of continuous eddy covariance (EC) measurements (CO2/H2O – 2010–2014) and three years (2012–2014) of EC measurement of CH4 and N2O. Intensive grassland management included both regular and sporadic management activities. Regular management practices encompassed mowing (3–5 cuts per year) with subsequent organic fertilizer amendments and occasional grazing whereas sporadic management activities comprised grazing or similar activities. The primary objective of our measurements was to compare pre-ploughing to post-ploughing GHG exchange and to identify potential memory effects of such a substantial disturbance on GHG exchange and carbon (C) and nitrogen (N) budgets. In order to include measurements carried with different observation techniques, we tested two different measurement techniques jointly in 2013, namely the manual static chamber approach and the eddy covariance technique, to quantify the GHG exchange from the observed grassland site. Our results showed that there were no memory effects on N2O and CH4 emissions after ploughing, whereas the CO2 uptake of the site considerably increased when compared to post-restoration years. In detail, we observed large losses of CO2 and N2O during the year of restoration. In contrast, the grassland acted as a carbon sink under usual management, i.e. the time periods (2010–2011 and 2013–2014). Enhanced emissions/emission peaks of N2O (defined as exceeding background emissions < 0.21 ± 0.55 nmol m−2s−1 (SE = 0.02) for at least two sequential days and the seven-day moving average exceeding background emissions) were observed for almost seven continuous months after restoration as well following organic fertilizer applications during all. Net ecosystem exchange of CO2 (NEECO2) showed a common pattern of increased uptake of CO2 in spring and reduced uptake in late fall. NEECO2 dropped to zero and became positive after each harvest event. Methane (CH4) exchange in contrast to N2O showed minor net uptake of methane seen by the static chambers and small net release of methane seen by the eddy covariance method. Overall, CH4 exchange was of negligible importance for both, the GHG budget as well as for the carbon budget of the site. Our results stress the inclusion of grassland restoration events when providing cumulative sums of C sequestration and/or global warming potentials (GWPs). Consequently, this study further highlights the need for continuous long-term GHG exchange observations as well as the implementation of our findings into biogeochemical process models to track potential GHG mitigation objectives as well as to predict future GHG emission scenarios reliably.

Lutz Merbold et al.

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Short summary
Our study investigated the exchange of the three major greenhouse gases (GHG) over a temperate grassland prior and post restoration through tillage in Central Switzerland. Our results show that irregular management events, such as tillage, have considerable effects on GHG emissions in the year of tillage, while leading to enhanced carbon uptake and similar nitrogen losses via nitrous oxide in the years following tillage as observed prior to tillage.
Our study investigated the exchange of the three major greenhouse gases (GHG) over a temperate...
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