B24B-07
Continuous multi-plot measurements of CO2, CH4, N2O and H2O in a managed boreal forest – The importance of accounting for all greenhouse gases
Tuesday, 15 December 2015: 17:30
2004 (Moscone West)
Patrik Vestin1, Meelis Mölder1, Elin Sundqvist1, Margareta Hellström1, Anders Båth2, Irene Lehner2, Per Weslien3, Leif Klemedtsson3 and Anders Lindroth1,4, (1)Lund University, Department of Physical Geography and Ecosystem Science, Lund, Sweden, (2)Lund University, Centre for Environmental and Climate Research, Lund, Sweden, (3)University of Gothenburg, Department of Earth Sciences, Gothenburg, Sweden, (4)Lund University, Physical geography and Ecosystem science, Lund, Sweden
Abstract:
In order to assess the effects of different management practices on the exchange of greenhouse gases (GHG), it is desirable to perform repeated and parallel measurements on both experimental and control plots. Here we demonstrate how a system system combining eddy covariance and gradient techniques can be used to perform this assessment in a managed forest ecosystem.<span">The net effects of clear-cutting and stump harvesting on GHG fluxes were studied at the ICOS site Norunda, Sweden. Micrometeorological measurements (i.e., flux-gradient measurements in 3 m tall towers) allowed for quantification of CO2, CH4 and H2O fluxes (from May 2010) as well as N2O and H2O fluxes (from June 2011) at two stump harvested plots and two control plots. There was one wetter and one drier plot of each treatment. Air was continuously sampled at two heights in the towers and gas concentrations were analyzed for CH4, CO2, H2O (LGR DLT-100, Los Gatos Research) and N2O, H2O (QCL Mini Monitor, Aerodyne Research). Friction velocities and sensible heat fluxes were measured by sonic anemometers (Gill Windmaster, Gill Instruments Ltd). Automatic chamber measurements (CO2, CH4, H2O) were carried out in the adjacent forest stand and at the clear-cut during 2010.
<span">Average CO2 emissions for the first year ranged between 14.4–20.2 ton CO2 ha-1 yr-1. The clear-cut became waterlogged after harvest and a comparison of flux-gradient data and chamber data (from the adjacent forest stand) indicated a switch from a weak CH4 sink to a significant source at all plots. The CH4 emissions ranged between 0.8–4.5 ton CO2-eq. ha-1 yr-1. N2O emissions ranged between 0.4–2.6 ton CO2-eq. ha-1 yr-1. Enhanced N2O emission on the drier stump harvested plot was the only clear treatment effect on GHG fluxes that was observed. Mean CH4 and N2O emissions for the first year of measurements amounted up to 29% and 20% of the mean annual CO2 emissions, respectively. This highlights the importance of including all GHGs when assessing the climate impacts of different forest management options. Our results show that continuous multi-plot measurements of the main GHGs are possible also at sites where GHG fluxes are low, at a reasonable cost and with reduced plot inter-comparison uncertainties.
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