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Titel:
NH3 flux measurements at Schagerbrug and Oostvaardersplassen, the Dutch contribution to the GRAMINAE experiment
 
Auteur(s):
 
Gepubliceerd door: Publicatie datum:
ECN SF 1-7-2000
 
ECN publicatienummer: Publicatie type:
ECN-C--00-079 ECN rapport
 
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Samenvatting:
This report summarizes the results of the research at ECN on the exchangeof ammonia between the atmosphere and grasslands within the GRAMINAE framework. The term exchange is used because of the bi-directional nature of ammonia, that can be taken up (dry deposition) as well as released (emission) by this type of surface. The main objective was to investigate the net contribution to atmospheric ammonia provided by the exchange with grasslands in relation to meteorological parameters and the land use management (fertilization and/or grass cutting). Besides, a comparison was made between the ammonia exchange obtained over intensively managed grasslands (Schagerbrug) and semi-natural grasslands (Oostvaardersplassen). Ammonia concentration gradients above a grassland in an intensively managed agricultural region in the North West of the Netherlands (Schagerbrug) were determined in the period July 1998 to July 2000. Use was made of three annular denuders (AMANDA). From the vertical concentration gradients the surface- atmosphere exchange of ammonia was calculated using the aerodynamic gradient technique. Measurements of the ammonia exchange were also performed at a grassfield that is part of a major wetland reserve close to the IJssel lake (IJsselmeer), in the center of the Netherlands (Oostvaardersplassen), during the period June 1994-September 1995. At Schagerbrug, low net emissions or small depositions were measured during the winter months, with a net emission per month up to 5 kg NH3/ha in summer. The net annual emission was 23 kg N/ha, with manure application contributing for about 50% to this level. At the Oostvaardersplassen mainly deposition occurs, but large emissions were measured in autumn. these emissions were probably the result of horses and geese residing in this nature area. A resistance model that take into account plant physiological data like apoplast NH4" concentrations and pH was evaluated and applied to the measured exchange fluxes obtained at the site Schagerbrug. Results show a good agreement between field observations and model simulations, although some improvements have to be made during nighttime periods. 12 refs.


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