The import and export of organic nitrogen species at a Scottish ombrotrophic peatland

Abstract

Abstract. Dissolved organic nitrogen (DON) can contribute significantly to the overall nitrogen budget, but is not routinely measured in precipitation or stream water. In order to investigate the contribution of DON to deposition and export of N, precipitation, stream and soil water samples were collected from an ombrotrophic peatland and analysed for DON Over a two year period. In wet only deposition DON contributed up to 10% of the total dissolved nitrogen (TDN), 99% in soil water, and 75% in stream water. No correlations were observed between DIN and DON in precipitation stream water or soil water. DIN is an important source of nutrients and in ombrotrophic peatlands, is only deposited via precipitation. Too much nitrogen to a sensitive ecosystem can result in problems with the way in which it is processed, such as an increase in the export of N via nearby water bodies. It is therefore important to monitor N deposition and export. Precipitation DIN showed a loose seasonal pattern, with peak concentrations occurring between January and June, while DON concentrations tended to be lower in the winter months. Stream water DON and NH4+ showed no obvious seasonal pattern but NO3- showed larger concentrations in cooler months and the smallest during warmer months, with the exception of June and July 2010, when concentrations were high. Precipitation and stream DON was qualitatively analysed using GC × GC-NCD. Ten unique compounds were detected, of which only five could be identified: pyrrole, benzonitrile, dodecylamine, N-nitrosodipropylamine and decylamine. Five compounds were present in both precipitation and stream samples: pyrrole, benzonitrile and three unidentified compounds. A more detailed DON speciation may be used to identify sources and pathways of DON.