Throughfall

Aim supply data for quantifying deposition to the ground surface and understorey vegetation in tree stands By measuring throughfall the input to the ground under the forest canopy can be determined, although additional input is found in litterfall (subprogram LF). Comparison with open field measurements makes it possible to assess canopy interception and internal cycling of nutrients. Once a month 10-12 plastic bottles with funnels along a 200 m straight line in a representative stand are emptied.   Variables normal year Cl-, SO4-, NO3-, NH4+, Ca2+, Mg2+, Na+, K+, pH and water volume. and water volume, i.e. the same as precipitation chemistry programme campaign year additionally: heavy metals and mercury For further information see IVL.

	Rain and mist is intercepted by the tree canopy, where some evaporates, some is absorbed by the foliage and still some trickles through - throughfall - and reaches the ground. Some substances, mainly nitrogen compounds, are greedily absorbed by the canopy. The evergreen spruce intercepts considerably more precipitation than pine and deciduous trees.
	The throughfall is captured in plastic bottles swept in aluminum foil as protection against algal growth.