Monitoring Wet Deposition in Forest - Quantitative and Qualitative Aspects : Monitoring Air Pollution and Forest Ecosystem Research. Proceedings of a Workshop

1989

S. 39-63

15 Abb., 2 Tab., 23 Lit. Ang.

Unselbständiges Werk

200047451

Since a substantial portion of the forest's wet deposition is acceptor dependent and because there are manyfold interactions of gases, particles and aqueous solutions or suspensions in the canopy, under forest cover a measurement separation of dry and wet deposition is not feasible. The large spatial and temporal variations of the acceptor dependent deposition are leading to the conclusion that the amount of deposition in forests can not be sufficiently estimated by using open area measurement results only. In order to quantify the site specific deposition of forested areas it is necessary to undertake long term measurements and sampling of bulk precipitation in area representative forest stands. Such monitoring should also include the precipitation deposition of airborne organic chemicals of anthropogenic origin. The more easily measured open area deposition however can serve as a very helpful data frame work. The enormous spatial variation of throughfall and drip necessitates a large number of measurement replications on the selected research plots. Normally at least 10-15 gauges should be installed per plot. As far as stemflow is concerned the spatial variation is in such a magnitude that in most deposition monitoring programmes only estimates are made. It is recommended to use the same gauges both for precipitation measurement and substance concentration. Gauges of funnel-type design consisting of laboratory quality polyethylene are commonly considered to be most effective. The traditional standard rain gauges are not suitable for sampling water for chemical analysis because they are not made of chemically inert material. As a general rule the sampling time interval should not exceed two weeks.