Effect of a lowered water table on nitrous oxide fluxes from northern peatlands

NORTHERN peatlands contain 20–30% of the total organic nitrogen and carbon in the world's soils 1,2 , and thus they apparently have the potential to exert a significant influence on the global atmospheric budget of the greenhouse gases carbon dioxide, methane and nitrous oxide (N 2 O). In the drier, warmer summer conditions predicted at high latitudes by some climate models 3,4 as a result of greenhouse-gas forcing, northern peatlands would become drier, increasing the rate of mineralization of organic matter 1,5 and of the microbial processes that produce N 2 O. These regions might therefore be expected to exert a strong feedback on climate. But whereas methane emissions have been well studied 6,7 , little is known about the effect on N 2 O fluxes of changes in the level of peatland water tables. Here we present a comparison of present-day N 2 O fluxes from virgin peatlands in Finland with those from sites in the same regions that were drained by ditching 30 and 50 years ago. The lowered water table had no effect on N 2 O emissions from nutrient-poor peat but enhanced those from nutrient-rich peat. We estimate that equivalent drying caused by climate change would increase the total emissions of N 2 O from northern peatlands by 0.03–0.1 teragrams of nitrogen per year, which is just 0.3–1% of the present global annual emissions. Thus northern peatlands are unlikely to exert a significant climate feedback from N 2 O emissions.