Water-table changes and nutritional status affect trace gas emissions from laboratory columns of peatland soils

Peatlands potentially play a significant role in the global emission of three trace gases: carbon dioxide; methane; and nitrous oxide. We investigated the effect of a relatively small lowering of the water-table (10 cm) on the emission of these gases using repacked, root-free peat columns in the laboratory with peat from a nutrient-rich (eutrophic) site and a more nutrient-poor (mesotrophic) site, respectively. At a static high water-table (at the peat surface) high rates of anaerobic CO2 production were found, which were reflected in high (> 1.18) molar ratios of CO2 and CH4. A static water-table of 10 cm below soil surface led to equal (eutrophic soil) or lower CO2 emission (mesotrophic soil) compared with the high static water-table. However, at a regularly changing water-table (between 0 and 10 cm below the peat surface), CO2 emission at a low water-table was 1.5 (mesotrophic soil) to 3 times (eutrophic soil) higher than at a high-water table. Maximum rates of CO2 emission from the eutrophic soil exceeded those from the mesotrophic soil, except at a static high water-table. Methane emission was about one order of magnitude lower at a low static water-table compared with the static high water-table. There was no clear effect of the nutritional status of the peat on maximum methane emission in the various water-table treatments. The nutritional status of the peat had a profound influence on the effect of water-table lowering on N2O emission: nitrous oxide emission from the eutrophic soil was strongly increased at a low water-table, whereas there was no detectable N2O emission from the mesotrophic soil. Despite a clear effect of the water-table treatments on both trace gas emissions and on redox potentials in the soil, no significant correlation between these variables was found in either soil type.