Release of nitrous oxide and dinitrogen from a transition bog under drained and rewetted conditions due to denitrification: results from a [N-15]nitrate-bromide double-tracer study

摘要

Denitrification is well known being the most important nitrate-consuming process in water-logged peat soils, whereby the intermediate compound nitrous oxide (N2O) and the end product dinitrogen (N-2) are ultimately released. The present study was aimed at evaluating the release of these gases (due to denitrification) from a nutrient-poor transition bog ecosystem under drained and three differently rewetted conditions at the field scale using a N-15-tracer approach ([N-15]nitrate application, 30 kg N ha(-1)) and a common closed-chamber technique. The drained site is characterized by a constant water table (WT) of -30 cm (here referred to as D30), while rewetted sites represent a constant WT of -15 cm, a constant WT of 0 cm (i.e. waterlogged), and an initial WT of 0 cm (which decreased slightly during the experiment), respectively, (here referred to as R15, R0, and R0(d), respectively). The highest N2O emissions were observed at D30 (291 mu g N2O-N m(-2) h(-1)) as well as at R0(d) (665 mu g N2O-N m(-2) h(-1)). At the rewetted peat sites with a constant WT (i.e. R15 and R0), considerably lower N2O emissions were observed (maximal 37 mu g N2O-N m(-2) h(-1)). Concerning N-2 only at the initially water-logged peat site R0(d) considerable release rates (up to 3110 mu g N-2-N m(-2) h(-1)) were observed, while under drained conditions (D30) no N-2 emission and under rewetted conditions with a constant WT (R15 and R0) significantly lower N-2 release rates (maximal 668 mu g N-2-N m(-2) h(-1)) could be detected. In addition, it has been found that natural WT fluctuations at rewetted peat sites, in particular a rapid drop down of the WT, can induce high emission rates for both N2O and N-2.