Nitrous oxide fluxes of disturbed minerotrophic peatlands

Minerotrophic mires (fens) represent an important part of the Northern peatlands (5*10(5) km(2)) and act as one of the most important sinks for terrestrial bond carbon and nitrogen. We have tried to clear up the influence of different management practices on nitrous oxide fluxes of these ecosystems. For this purpose investigations were performed on representative sites of the highly disturbed (degraded), N rich fen sites in Northeast Germany (5*10(3) ha): Paulinenaue (Rhin-Havelluch/Brandenburg, shallow cultivated grassland), Heinrichswalde (Friedlander Grobe Wiese/Mecklenburg-Vorpommem, deeply cultivated grassland), Muncheberg (Gumnitz, partially drained alder swamp forest). The annual flux rates showed a broad range. Especially newly drained fen sites (up to 26,9 kg N2O-N*ha(-1*)a(-1)) and grassland with high amounts of mineral fertilizer (480 kg N ha(-1) a(-1), calcium ammonium nitrate) or cattle waste (371 kg N*ha(-1) as urine) represent significant sources of nitrous oxide (7,2-15,7 kg N2O-N*ha(-1*)a(-1)). Mowing and moderate N fertilization rates (two cuts and rates up to 120 kg N*ha(-1)) caused only a weak increase in nitrous oxide emission (1,2-5,4 kg N2O-N*ha(-1*a)a(-1)), Reflooding led to an additional strong reduction of nitrous oxide fluxes (0,1-0,8 kg N2O-N*ha(-1*)a(-1)). The considerable temporal and spatial variability of flux rates was obviously induced by complex interactions of many factors and processes like water table, management systems, weather (especially by frost periods), soil degradation, plant growth, C/N transformation, and matter output on the emission rates in fens. However, the disturbed fens represent a significant source of nitrous oxide in Germany. Fens only occupy approx. 5,4 % of Germans total agricultural area, but their overall flux rate of 6574 t N2O-N*a(-1) has a share of approx. 12,4 % in the total nitrous oxide emission from German agriculture.