Reactive Nitrogen Fluxes over Peatland in Response to the Atmospheric Burden of Intensive Agriculture

Monday, 15 December 2014: 10:50 AM
Christian Brummer1, Undine Richter1, Miriam Hurkuck1, Jean-Pierre Delorme1, Jeremy J. Smith1 and Werner Leo Kutsch2, (1)Johann Heinrich von Thünen Institute, Braunschweig, Germany, (2)ICOS Headoffice, Helsinki, Finland
During a 10-month field campaign, we used a total reactive atmospheric nitrogen (ΣNr) converter (TRANC) coupled to a fast-response chemiluminescence detector to measure ΣNr concentrations and fluxes between a peatland ecosystem and the atmosphere. Oxidized Nr species such as NOx, HONO, HNO2, aerosol NO3 and reduced Nr species such as NH3, aerosol NH4 were converted to NO with the total exchange flux being determined using the eddy-covariance technique. The field site was part of a natural park with a very small remaining protected zone of less than 2 km x 2 km. The park was surrounded by an area of intensive agricultural land use. Total Nr concentrations were mainly varying between 20 and 60 ppb with peak values of up to 120 ppb coinciding with the main fertilization periods on the neighboring agricultural land in early spring and fall. The trend in weekly averaged ΣNr concentrations from TRANC measurements was in good agreement with results from KAPS denuder filter systems when the latter were combined with the missing and apparently highly variable NOx contribution. Wind direction and land use in the closer vicinity clearly regulated whether total Nr concentrations were NH3 or NOx-dominated. Values of monthly averaged diurnal flux courses ranged between -40 and +20 ng N m-2 s-1 with the majority of fluxes showing net deposition of ΣNr to the land surface. The cumulative net exchange of ΣNr at the end of the observation period resulted in an uptake of the ecosystem of only ~1 kg N ha-1 with intermittent periods showing net ΣNr release. This is an indicator for an oversaturation of this N-limited ecosystem caused by agricultural practices such as livestock production and fertilization. Bog plants were temporarily not capable of taking up the surplus nitrogen from the atmosphere, which highlights the importance for a reformulation of protection guidelines for vulnerable ecosystems such as peatlands.