Ecosystem-atmosphere gaseous exchange – Work package 4.1

The C exchanged by fluxes of CO₂ to and from the ecosystems and the atmosphere by biological processes is the quantitatively most important pathway for the C exchange, with well known anticipated consequences for the climate system (IPCC, 2001). Fluxes of CH₄, and the N-containing gases are quantitatively less important. However, these gases have particular significance for the climate system, as they have several-fold greater forcing effects on the climate than CO₂ and influences atmospheric chemistry, beside the fact that they contributes to the local, ecosystem, C and N balance. Fluxes of these gases are sensitive to climatic and environmental perturbations (Ambus and Robertson, 1999; Hungate et al., 1997).

The exchange of C gases (CO₂ and CH₄) and N gases (NO and N₂O) between the ecosystem and the atmosphere will be measured using static flux chambers. In each experimental plot a permanent chamber base of 70 cm × 70 cm will be installed at the start of the project. The bases will be left in the plots throughout the experiment and will be used as chamber bases for all flux measurements. CO₂ fluxes will be measured regularly at two-week intervals and on a diurnal basis in campaigns. The measurements will include net ecosystem CO₂ flux and respiration in transparent and opaque chambers, respectively, placed onto the bases. In the second to fourth treatment year, measurements will be done with particularly high frequency in order to detect treatment-induced changes in ecosystem C-fluxes and – balances during the three first years of treatments.

Methane, nitric oxide and nitrous oxide fluxes will be monitored on a campaign basis in the first to third treatment years during periods when significant fluxes are expected, e.g. during warm-up of the soil in wet spring, in connection with heavy rainfall events and in autumn after plant senescence. Methane and nitrous oxide will be measured by manual collection of gas samples and subsequent GC analysis, and NO will be measured on-line using a chemiluminescence detector.