Greenhouse gas fluxes from drained peatland : Measurement techniques and management impacts

Sammanfattning: Agricultural use of drained peatlands has significant implications for national greenhouse gas (GHG) emission inventories. Once drained, peatlands emit large amounts of carbon dioxide (CO2), may become small methane (CH4) sinks and, with nitrogen fertilisation, may emit large quantities of nitrous oxide (N2O). Studies on the influence of set-aside cropland in reducing GHG emissions from peatlands are rare, measurement techniques for continuous long-term observations are costly and detection of small fluxes is critical. This thesis investigated management effects on GHG fluxes from a cropland (CL) and an adjacent set-aside (SA) grassland on peat. An affordable relaxed eddy accumulation (REA) system for measuring continuous fluxes of CO2, N2O, CH4, and water vapour (H2O) was designed and tested. A convenient method for optimising chamber flux measurement duration and number of concentrations was developed and tested against experimental data. The SA site showed higher annual CO2 emissions than the CL site (0.41 and 0.16 kg CO2 m-2 yr1 , respectively). Nitrous oxide and CH4 emissions had a minor influence on the climate effect at both sides. The REA system reliably measured GHG fluxes over complete growing seasons, based on a comparison of CO2 and H2O fluxes with an eddy covariance system. The chamber optimisation method yielded similar results to experimental data, and can be valuable in the planning phase of measurement campaigns. In conclusion, this thesis found no evidence that setting-aside agricultural land on peat reduced GHG emissions and emphasises the importance of affordable and reliable measuring equipment.