Review of deposition monitoring methods

Deposition monitoring may generally serve at least one of the following purposes: (a) determining ecosystems at risk, (b) evaluating temporal and spatial trends, (c) developing numerical models, or (d) estimating deposition effects. In this paper, an overview of available knowledge about monitoring methods is given. Furthermore, it is tried to illustrate the (dis)agreement between results obtained using different methods. It might be concluded that throughfall, micro meteorological methods (supplemented/supported by inference) and watershed balance methods (S saturated systems) yield similar estimates of the annual mean total deposition of sulphur, within generally acceptable uncertainly limits (~ 30%). A larger uncertainty exists to estimate reduced or oxidized nitrogen and base cation fluxes. It is clear that for individual ecosystems deposition in general, and dry deposition in particular, can still not be quantified with sufficient accuracy. The various methods have different advantages and drawbacks and the choice of a certain method for estimation of the flux of a specific pollutant to a specific ecosystem may in many cases depend on the purpose of the study and on requirements on accuracy and costs.