Impact of altering the water table height of an acidic fen on N 2 O and NO fluxes and soil concentrations

Abstract

The impact of experimentally intensified summer drought and precipitation on N 2 O and NO turnover and fluxes was investigated in a minerotrophic fen over a 2‐year period. On three treatment plots, drought was induced for 6 and 10 weeks by means of roofs and drainage and decreased water table levels by 0.1–0.3 m compared with three nonmanipulated control plots. When averaged over the three treatment plots, both N 2 O and NO emission showed only little response to the drought. On the single plot scale, however, a clear impact of the treatment on N 2 O and NO fluxes could be identified. On the plot with the weakest water table reduction hardly any response could be observed, while on the plot with the greatest drainage effect, N 2 O and NO fluxes increased by 530% and 270%, respectively. Rewetting reduced NO emissions to background levels (0.05–0.15 μmol m −2 h −1 ), but heavily enhanced N 2 O emission (18–36 μmol m −2 h −1 ) for several days in the plots with largest water table reduction. These peaks contributed up to 40% to the cumulative N 2 O fluxes and were caused by rapid N 2 O production according to isotope abundance data. According to N 2 O concentrations and isotope abundance analysis N 2 O was mostly produced at depths between 0.3 and 0.5 m. During water table reduction net N 2 O production in 0.1 m depth steadily increased in the most effectively dried plot from 2 up to 44 pmol cm −3 day −1 . Rewetting immediately increased net N 2 O production in the topsoil of the drought plots, showing rates of 18–174 pmol cm −3 day −1 . This study demonstrates that drought and rewetting can temporarily increase N 2 O emission to levels that have to date only been reported from nutrient rich and degraded fens that have been drained for agricultural purposes.

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