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

摘要

The impact of experimentally intensified summer drought and precipitation on NO 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 NO and NO emission showed only little response to the drought. On the single plot scale, however, a clear impact of the treatment on NO 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, NO and NO fluxes increased by 530% and 270%, respectively. Rewetting reduced NO emissions to background levels (0.05-0.15 omol mpo hp#), but heavily enhanced NO emission (18-36 omol mpo hp#) for several days in the plots with largest water table reduction. These peaks contributed up to 40% to the cumulative NO fluxes and were caused by rapid NO production according to isotope abundance data. According to NO concentrations and isotope abundance analysis NO was mostly produced at depths between 0.3 and 0.5 m. During water table reduction net NO production in 0.1 m depth steadily increased in the most effectively dried plot from 2 up to 44 pmol cmpd dayp#. Rewetting immediately increased net NO production in the topsoil of the drought plots, showing rates of 18-174 pmol cmpd dayp#. This study demonstrates that drought and rewetting can temporarily increase NO emission to levels that have to date only been reported from nutrient rich and degraded fens that have been drained for agricultural purposes.