Schlüsselwörter
(Englisch)
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reactive nitrogen; nitrogen cycling; greenhouse gases; flux monitoring; deposition; emission; thermal converter
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Forschungsprogramme
(Englisch)
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COST-Action ES0804 - Advancing the integrated monitoring of trace gas exchange between biosphere and atmosphere
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Kurzbeschreibung
(Englisch)
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Terrestrial ecosystems represent important sinks and sources of atmospheric greenhouse gases. Within recent and ongo-ing projects, a network of flux monitoring stations for greenhouse gases over various ecosystems in Europe has been es-tablished. Because nitrogen availability is one of the key limiting factors for the productivity of ecosystems, the joint moni-toring of the nitrogen exchange is essential at such stations. The aim of this project is the field evaluation of a novel con-verter for monitoring the net exchange of total reactive nitrogen (TorN). For this purpose we will carry out eddy covariance flux measurements with the TorN converter at the Swiss NitroEurope grassland site Oensingen over a period of several months. The already installed flux systems at the site will provide the unique opportunity to compare the TorN flux with parallel measurements of the main individual reactive nitrogen fluxes, namely NH3, NO, NO2, and HNO3. The managed grassland field will also provide significant temporal variability of the contribution of the different compounds, so that the TorN flux by the converter can be validated under a large range of different TorN composition situations. Based on the result we will be able to assess the applicability of the TorN eddy covariance system for long-term monitoring of the reac-tive nitrogen exchange at greenhouse flux monitoring sites. It will be an essential complement to interpret the observed greenhouse gas exchange at those sites with respect to global change and management effects.
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Partner und Internationale Organisationen
(Englisch)
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CH, DE, DK, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, NL, NO, PL, SE, UK
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Abstract
(Englisch)
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Terrestrial ecosystems represent important sinks and sources of atmospheric greenhouse gases (GHG). Within recent and ongoing projects, a network of flux monitoring stations for CO2 over various ecosystems in Europe has been established and extensions to include the other GHG are going on. Because nitrogen availability is one of the key limiting factors for the productivity of ecosystems, it also has a strong influence on the GHG exchange. The joint monitoring of the nitrogen exchange is therefore essential for the interpretation of the GHG budget at these monitoring stations. However, the exchange of nitrogen with the atmosphere includes various reactive nitrogen compounds (a.o. nitric oxide, nitrogen dioxide, ammonia, nitric acid, particulate ammonium and nitrate) and the individual measurement of all of them is very difficult in practice. In the present project, we therefore evaluated a novel converter system for monitoring the net exchange of total reactive nitrogen (Nr) by the eddy covariance method (EC). The total Nr converter (TRANC) thermally converts all reduced and oxygenated reactive nitrogen compounds to NO, which can then be analyzed by a single NO analyzer. The performed measurements and data evaluation showed that the TRANC system has a fast response time (ca. 0.3 s) and was able to detect deposition and emission fluxes of oxidized and reduced Nr gases by the EC method. The conversion efficiency for the major gaseous Nr compounds were found to be close to 100%. For particulate mineral N, also quantitative but more uncertain conversion efficiencies were observed. The performance of the TRANC system was tested and validated in the field at an intensively managed grassland site. The total Nr concentrations and fluxes in the field experiment agreed reasonably well with results of simultaneous measurements for individual compounds (dynamic chamber fluxes of NO and NO2; gradient and EC fluxes for NH3). While during growing phases, the total Nr flux was dominated by NO2 deposition, very large emission of NH3 was detected after slurry application on the field. Due to sensor separation effects and the low measurement height of 1.2 m, a moderate high-frequency damping loss of 20-25% for the EC flux with the TRANC had to be taken into account. This effect will be significantly lower for increased measurement heights commonly used above taller vegetation. For smaller fluxes, a considerable scatter (noise) was observed mainly due to the strongly varying concentrations of anthropogenic NOx compounds at the field site. These conditions impeded the determination of the flux detection limit for the TRANC system that needs to be done at a more remote site. It can be concluded that the TRANC based eddy covariance system is a reliable tool for permanent measurements of the net reactive nitrogen exchange between ecosystem and atmosphere at a relatively low maintenance and reasonable cost level allowing short-term and long-term applications.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C09.0028
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