Memory effects on greenhouse gas emissions (CO 2 , N 2 O and CH 4 ) following grassland restoration?

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