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

Rebecca M Mckenzie,Kerry J Dinsmore,Mustafa Z Özel,Jacqueline F Hamilton,Y Sim Tang,Julia Drewer,Mark A Sutton,J Neil Cape,Netty Van Dijk,Ute Skiba,Margaret Anderson,Martin W Gallagher,Eiko Nemitz

doi:10.5194/bg-13-2353-2016

Rebecca M Mckenzie, Kerry J Dinsmore + Show 11 more

Open Access

https://doi.org/10.5194/bg-13-2353-2016

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Abstract

Abstract. Dissolved organic nitrogen (DON) contributes 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 the deposition and export of N, precipitation, stream and soil water samples were collected from an ombrotrophic peatland and analysed for DON over a 2-year period. In wet-only deposition DON contributed up to 10 % of the total dissolved nitrogen (TDN) and was the most dominant fraction in soil water (99 %) and stream water (75 %). NH4+ was the most dominate form of N in precipitation, with NO3− contributing the least to precipitation, soil water and stream water. Precipitation and stream DON were qualitatively analysed by a two-dimensional gas chromatograph coupled to a nitrogen chemiluminescence detector (GC × GC-NCD) after trapping onto C18 solid phase extraction (SPE) cartridges. Ten unique compounds were detected and five identified as pyrrole, benzonitrile, dodecylamine, N-nitrosodipropylamine and decylamine. Five compounds were present in both precipitation and stream samples: pyrrole, benzonitrile and three unidentified compounds. The SPE-extraction efficiency for DON was very low (11 %), but with improvements DON speciation could become a valuable tool to provide information on its sources and pathways and inform chemical transport models.

Highlights

The total deposition of N in the UK was estimated to be approximately 330 Gg in 2004, with wet and cloud deposition accounting for approximately 211 Gg (63.9 %), and the rest consisting of dry deposition (Fowler et al, 2009; Hertel et al, 2011).Wet deposition of the dissolved inorganic nitrogen (DIN) compounds ammonium (NH+4 ) and nitrate (NO−3 ) has been studied over many years (Violaki et al, 2010; Cape et al, 2011; Zhang et al, 2012)
dissolved organic nitrogen (DON) is an important source of nitrogen in precipitation and stream water and must not be ignored in measurements of atmospheric nitrogen deposition rates or stream-water nitrogen balances
The mean volume-weighted concentration of DON found in the precipitation over the total study period was 4.8 μmol N L−1, with a mean contribution of 9 % to total dissolved nitrogen (TDN)

Summary

Introduction

Wet deposition of the dissolved inorganic nitrogen (DIN) compounds ammonium (NH+4 ) and nitrate (NO−3 ) has been studied over many years (Violaki et al, 2010; Cape et al, 2011; Zhang et al, 2012). The former is produced by the dissolution of ammonia gas (NH3) and the scavenging of NH+4 aerosol, and the latter by the dissolution of nitric acid gas (HNO3) and the scavenging of NO−3 aerosol (Russell et al, 1998; Cornell et al, 2003; Tian et al, 2011). Studies have shown that DON can contribute 30–50 % of the wet deposition of watersoluble N (Neff et al, 2002; Cape et al, 2004, 2011; Zhang et al, 2008, 2012; Cornell, 2011)

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