The effects of land use, temperature and water level fluctuations on the emission of nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) from organic soil cores in Iceland

Agricultural practices can affect soil microbial production and emission of the major greenhouse gases (GHG’s) nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4). The purpose of this study was to gain insight into the influence of temperature, water level and water level fluctuations on the GHG emission of soils representing the three major types of landuse in Iceland: undisturbed peatland, drained uncultivated peatland and hayfield on drained peatland. Twenty-four soil cores, from three different areas were set up in controlled laboratory conditions and subjected to varying temperatures and water table levels. Vegetation was removed on eighteen of the twentyfour soil cores. On six soil cores the vegetation was kept undisturbed to gain information on the GHG emission effect of vegetation. Gas samples were collected by a common methodology based on a static chamber technique for N2O and CH4 and a dynamic chamber method for CO2. The results show that landuse type significantly affects soil GHG’s production (P=0.000). Raised temperatures increased the emission of CO2 (P<0.001) and CH4 (P<0.001) significantly but not the emission of N2O (P=0.458). Water level fluctuations (WL), which were only conducted for the drained peatland and hayfield soil cores, had a strong influence on soil N2O emission. The N2O emission increased significantly (P=0.000) with water level fluctuations for both drained peatland soil cores and hayfield soil cores. However, the magnitude of the hayfield on drained peatland emission was 3-fold compared to drained soil cores. Water fluctuations increased the hayfield soil CO2 emission significantly (P=0.002), but no significant change was detected in the emission of the drained peatland soil cores (P=0.086) nor between the landuse groups (drained and hayfield) (P>0.005). No CH4 emission change was recorded with soil water fluctuations, which may be due to an insufficiently long incubation time. These studies show that draining of peatland increases emission of N2O and CO2 and decreases emission of CH4. Temperature had significant effect on the emission of CH4 and CO2 but not on N2O emission. Water level fluctuations significantly affected N2O production in both drained and hayfield soil cores but CO2 production was only significantly affected in the hayfield soil cores. Vegetation had significant effect on the production of N2O and CO2. Here, the highest emission calculated in CO2 equivalents was measured from the undrained peatland. The reason for this was the very high methane emission at the highest temperatures, 13°C and 18°C. However, if the results are evaluated for each temperature compared to average annual temperature in Iceland, the hayfield soil cores emitted most GHG’s. From the WL study the highest GHG emission was measured from the hayfield soils and secondly from the drained peatland soils.