Bidirectional ammonia exchange above a mixed coniferous forest

Johan Neirynck, R Ceulemans

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    Two canopy compensation point models were used to study the bidirectional exchange of ammonia over a mixed coniferous forest subjected to high nitrogen deposition. The models were tested for 16 time series, average fluxes of which ranged between -270 and +1 ngm-2s-1. The static model consisted of a bidirectional stomatal flux and a unidirectional cuticular flux component. The dynamic model also allowed for desorption of ammonia from the leaf surface and took into account ammonia fluxes from precedent periods. The apoplastic ammonium/hydrogen ion ratio (Γ), which was derived to estimate the stomatal compensation point (Χs), amounted to 3300 in spring and 1375 during the summer/autumn. Empirical descriptions for cuticular resistances (Rw) in the static model, developed as a function of micrometeorological conditions and codeposition effects, failed to reproduce the measured fluxes. A better match with measurements was obtained using the dynamic model, which succeeded in simulating net-emission during the daytime.

    Original languageEnglish
    JournalEnvironmental Pollution
    Issue number3
    Pages (from-to)424-438
    Number of pages15
    Publication statusPublished - 2008

    Thematic list

    • Environment

    EWI Biomedical sciences

    • B002-biophysics


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