Transforming Meadows Into Free Surface Water Wetlands: Impact Of Increased Nitrate And Carbon Loading On Greenhouse Gas Production

摘要

In a laboratory study we investigated 1) the potential production of nitrous oxide (N_2O), methane (CH_4) and carbon dioxide (CO_2) and 2) the effect of nitrate (NO_3~-) and anaerobic N_2O development on CH_4 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 N_2O. We made additions of biodegradable carbon (glucose) and/or NO_3~- to sediment and soil slurries and incubated them at four temperatures (4,13, 20, 28 ℃). Gas production from both substrates was positively correlated with temperature. We also found that the sediment produced more N_2O than the soil. N_2O production in sediment was NO3 limited, whereas in soil carbon availability was lower and only combined additions of NO~-_3 and glucose supported increased N_2O development. CH_4 production was generally low and did not differ between soil and sediment. Nor did glucose addition increase CH_4 rates. The results suggest that neither soil nor sediment environment did support development of methanogenic populations. There were no clear effects of NO_3~- on CH_4 production. However, the highest records of CH_4 were found in incubations with low N_2O production, which indicates that N_2O might be toxic to methanogens. In summary, our study showed that transforming meadows into FSWWs implies a risk of increased N_2O emissions. This does not seem to be valid for CH_4. However, since N_2O is almost always produced wherever NO_3~- is denitrified, increased N_2O production in wetlands leads to reduced rates in downstream environments. Hence, we conclude that when balancing NO_3~- retention and global warming aspects, we find no reason to discourage future creation or restoration of wetlands.