THE APPLICATION OF THROUGHFALL MEASUREMENTS FOR ATMOSPHERIC DEPOSITION MONITORING

An overview of the technical requirements of throughfall, stemflow and precipitation measurements used for monitoring atmospheric deposition to Forests is presented. A mechanistic basis is presented to link thr oughfall fluxes to atmospheric deposition. For homogeneous forest stan ds with a closed canopy, the overall uncertainty in annual mean soil l oads can be as low as 10-15% if state-of-the-art measurement and analy tical techniques are used in combination with a sufficiently large num ber of replicate samplers. The uncertainly in atmospheric deposition e stimates, however, is estimated much larger, i.e. up to 30% for sulphu r and 40% for nitrogen and base cations. This is mainly attributed to (i) uncertainties associated with the estimation of canopy exchange, a nd (ii) dry deposition to the forest floor and understorey vegetation which is usually not addressed in throughfall studies. Additional rese arch on canopy exchange in relation to tree species, ecological settin g and pollution climate is recommended, pounds and base cations, and m ay serve as a basis for improvement of current canopy budget models. C opyright (C) 1996 Elsevier Science Ltd