Articles | Volume 14, issue 24
Research article
21 Dec 2017
Research article |  | 21 Dec 2017

Nitrous oxide emissions from a peatbog after 13 years of experimental nitrogen deposition

Sarah R. Leeson, Peter E. Levy, Netty van Dijk, Julia Drewer, Sophie Robinson, Matthew R. Jones, John Kentisbeer, Ian Washbourne, Mark A. Sutton, and Lucy J. Sheppard

Abstract. Nitrogen deposition was experimentally increased on a Scottish peatbog over a period of 13 years (2002–2015). Nitrogen was applied in three forms, NH3 gas, NH4Cl solution, and NaNO3 solution, at rates ranging from 8 (ambient) to 64 kg N ha−1 yr−1, and higher near the NH3 fumigation source. An automated system was used to apply the nitrogen, such that the deposition was realistic in terms of rates and high frequency of deposition events. We measured the response of nitrous oxide (N2O) flux to the increased nitrogen input. Prior expectations, based on the IPCC default emission factor, were that 1 % of the added nitrogen would be emitted as N2O. In the plots treated with NH4+ and NO3 solution, no response was seen, and there was a tendency for N2O fluxes to be reduced by additional nitrogen, though this was not significant. Areas subjected to high NH3 emitted more N2O than expected, up to 8.5 % of the added nitrogen. Differences in the response are related to the impact of the nitrogen treatments on the vegetation. In the NH4+ and NO3 treatments, all the additional nitrogen is effectively immobilised in the vegetation and top 10 cm of peat. In the NH3 treatment, much of the vegetation was killed off by high doses of NH3, and the nitrogen was presumably more available to denitrifying bacteria. The design of the wet and dry experimental treatments meant that they differed in statistical power, and we are less likely to detect an effect of the NH4+ and NO3 treatments, though they avoid issues of pseudo-replication.

Short summary
Nitrogen deposition was experimentally increased on a Scottish peat bog over a period of 13 years (2002–2015), simulating pollution from agricultural and fossil-fuel sources. We measured emissions of the greenhouse gas, nitrous oxide (N2O), in response to the increased nitrogen input. In the plots treated with ammonium and nitrate solution, no response was seen. Areas subjected to high ammonia emitted more N2O than expected. Differences were related to impacts on the vegetation.
Final-revised paper