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

Abstract

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 (N₂) 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 ¹⁵N-tracer approach ([¹⁵N]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 µg N₂O–N m⁻² h⁻¹) as well as at R0_d (665 µg 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 µg N₂O–N m⁻² h⁻¹). Concerning N₂ only at the initially water-logged peat site R0_d considerable release rates (up to 3110 µg N₂–N m⁻² h⁻¹) were observed, while under drained conditions (D30) no N₂ emission and under rewetted conditions with a constant WT (R15 and R0) significantly lower N₂ release rates (maximal 668 µg N₂–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 N₂.

Keywords:

• denitrification
• dinitrogen
• nitrogen-15
• nitrous oxide
• peat soil
• rewetting
• stable isotope tracer techniques

Acknowledgements

We would like to thank both reviewers for the very helpful comments and discussions. Furthermore, we would like to thank the German Science Foundation (DFG) for funding the present study. In addition, our special thanks go to Mr B. Apelt (Helmholtz Centre for Environmental Research – UFZ, Department of Soil Physics) for the GC analyses and Mrs S. Bösel (Martin-Luther-University Halle-Wittenberg, Institute of Agricultural and Nutritional Sciences) for ¹⁵N₂ analysis with a Delta V Advantage IRMS.

Disclosure statement

No potential conflict of interest was reported by the authors.