Transforming meadows into free surface water wetlands: Impact of increased nitrate and carbon loading on greenhouse gas production
Summary, in English
In a laboratory study we investigated 1) the potential production of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) and 2) the effect of nitrate (NO3−) and anaerobic N2O development on CH4 production in sediment from a recently recreated free surface water wetland (FSWW) and in soil from an adjacent meadow. We designed an experiment where production of greenhouse gases was registered at the time of maximum net development of N2O. We made additions of biodegradable carbon (glucose) and/or NO3− to sediment and soil slurries and incubated them at four temperatures (4, 13, 20, 28 °C). Gas production from both substrates was positively correlated with temperature. We also found that the sediment produced more N2O than the soil. N2O production in sediment was NO3− limited, whereas in soil carbon availability was lower and only combined additions of NO3− and glucose supported increased N2O development. CH4 production was generally low and did not differ between soil and sediment. Nor did glucose addition increase CH4 rates. The results suggest that neither soil nor sediment environment did support development of methanogenic populations. There were no clear effects of NO3− on CH4 production. However, the highest records of CH4 were found in incubations with low N2O production, which indicates that N2O might be toxic to methanogens. In summary, our study showed that transforming meadows into FSWWs implies a risk of increased N2O emissions. This does not seem to be valid for CH4. However, since N2O is almost always produced wherever NO3− is denitrified, increased N2O production in wetlands leads to reduced rates in downstream environments. Hence, we conclude that when balancing NO3− retention and global warming aspects, we find no reason to discourage future creation or restoration of wetlands.