Canopy interaction process

It is essential to differentiate between matter input in the open field and that beneath the forest canopy. The solute flux in stand precipitation consists of wet and dry deposition, and is modified by canopy interaction processes (Rasmussen 1990, UN-ECE 1998). 

Turning to exchange between the canopy and the underlying soil, sedimentation processes are of primary importance. This includes deposition via precipitation, whereby, as outlined above, organic chemicals can be transported dissolved in the water, associated with particles trapped in the precipitation, or sorbed to the surface of the water/ice. The chemical fluxes below the canopy are, however, much more difficult to estimate than the wet deposition to the canopy, due to the interactions between the precipitation and the canopy. When a raindrop hits a leaf, some of the chemical dissolved in the rain may sorb to the leaf, but on the other hand, chemical already present on the leaf may dissolve in the rain. Similarly, particles in a raindrop may be retained on the leaf surface (for instance by leaf hairs), or particles which had already accumulated on the leaf surface (for instance via dry deposition) may be... 

Having now outlined the different mass transfer processes in the soil-canopy-atmosphere system and briefly explored their interactions, the next section will examine two of the most important processes in more detail, namely dry deposition with aerosols and diffusive gaseous exchange. 

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