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A comparison of methods to estimate canopy exchange at the Speulder forest

Een vergelijking van methoden ter bepaling van canopy exchange in het Speulderbos

Synopsis

Differences observed between atmospheric deposition and throughfall fluxes in forests are often assumed to be the result of canopy exchange processes. To obtain more insight on these processes and to quantify them, several field experiments were performed at the Speulder forest research site. Relevant information was obtained by i) measuring open-field precipitation and throughfall fluxes with different time resolutions, using two canopy exchange models, ii) comparing deposition estimates from surface wash experiments using real and artificial twigs, respectively, and iii) comparing throughfall deposition estimates with estimates from micrometeorological techniques and inferential modelling. Specific information on canopy leaching of soil-derived sulphur was provided by a S-35 nutrition experiment. Sulphur was found to behave conservative within the canopy, with SO2 uptake more or less balancing leaching of soil- derived SO42-. Moreover, no significant canopy exchange was found for Na+ and Cl-. For reduced nitrogen and base cations, differences observed between atmospheric deposition and throughfall fluxes could almost completely be explained by canopy exchange. However, for closing the gap between the throughfall flux of NO3- and the deposition flux of NOy, additional research is necessary.
 

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