Tests of models of cloudwater deposition to forest canopies using artificial and living collectors

Cloud water deposition at a high-elevation site in the Vosges Mountains (France)

The importance of cloud water deposition fluxes to a high-elevation site in the Vosges Mountains (France) has been studied. An existing one-dimensional cloud water deposition model has been adapted to site conditions. The adaptation of the main parameters has been tested and is discussed. These tests illustrate the small influence of the surface area index (SAI) and the roughness length on cloud water deposition and the negligible contribution of sedimentation compared to impaction of cloud droplets. Model input data, including cloud water composition, liquid water content (LWC) and wind speed, have been collected over a 1-year period and are used to evaluate annual cloud deposition fluxes of major ions and trace metals. The calculations indicate that the hydrologic input by cloud water (55.5 mm year(-1)) is negligible compared to the input by rainwater (1265 mm year(-1)). However, due to the higher concentrations in cloud water, the deposition fluxes of cloud water represent 10-28% of the total wet deposition (rain + cloud deposition) for major ions and 50% or higher for trace elements.

Atmospheric input of elements to forest ecosystems: a method of estimation using artificial foliage placed above rain collectors

Usefulness of a method of artificial foliage was tested for estimation of total ionic inputs from the atmosphere to forest ecosystems, as well as of processes relevant to ionic fluxes through tree canopies: uptake, leaching, passive flow. The studies were performed in Norway spruce and European beech stands in Karkonosze Mountains (Poland), in 1995-97. Artificial leaves of increasing leaf area index: 0, 2, 6 and 12 m(2) m(-2 )were placed above standard rain collectors. It has been found that total atmospheric fluxes of H(+), NH(4)(+), Ca(2+), Mg(2+), Pb(2+), NO(3)(-) and SO(4)(2-) rose as surface area of the foliage increased. This was especially true for nitrate, sulphate and ammonium. No such relationship was found for K(+), Na(+), Zn(2+), Cd(2+), Cu(2+) and PO(4)(3-). The increase in anion fluxes exceeded that in neutralising cations (NH(4)(+), Na(+), K(+), Mg(2+), Ca(2+)) and led to progressive rainwater acidification with the increase in the foliage area. An analysis of net canopy exchange (atmospheric input-throughfall flux) has shown that SO(4)(2-), PO(4)(3-), Na(+), Ca(2+) and Cu(2+) flowed passively through the tree crowns; NH(4)(+), NO(3)(-), Zn(2+), Cd(2+) and occasionally Pb(2+) were efficiently absorbed, whereas K(+) was leached from the canopies. Beech was more effective in modifying ionic pool from the atmosphere than spruce. This related to H(+) (greater absorption) and Mg(2+) (greater leaching). It has been demonstrated that the results concerning trends in net canopy exchange and produced by the simple method of artificial foliage are comparable to more sophisticated techniques of the measurements. This proves the method to be useful.