Atmospheric inputs of nutrients and pollutants to uplands in north-east Scotland
The effects of vegetation size and architecture, in combination with elevation effects, on the amounts of atmospheric inputs of both nutrient and pollutant substances were studied by means of collecting precipitation both above and below tree and heather canopies. Use was made of 'filter' type gauges, designed to enhance interception deposition, in order to identify the main ionic substances associated with this deposition type. Results illustrate how effects of tree size and shape, as well as elevation, are tempered by local topographic and climatic factors. The total leaf area of the canopy is not necessarily an over-riding factor in determining amounts of atmospheric deposits caught by the canopy; canopy structure is seen to be equally as important. As well as a main two year field study, secondary experiments were carried out to test filter gauge design (both in the field and the laboratory). These included looking at elevation effects on interception deposition, and dry deposition estimates were made through washing of gauges and also by collection of precipitation on an event basis. Filter gauge design studies illustrated that gauge design has little effect on amounts of interception deposition collected; over the range of particle sizes and micrometeorological conditions encountered in the field, the differences in relative efficiencies of the different gauge types are of little consequence. At a site with a relatively unhindered fetch, interception deposition was seen to increase with elevation. Dry deposition was not considered to be a significant input at this site. Pb was studied as an exemplary heavy metal; it seems that Pb input is predominantly through rain (rather than being associated more with the 'filter' component of precipitation) suggesting long-range transport. Pb was found to accumulate within the organic horizons of the soil---the pathway through the ecosystem being predominantly adsorption onto plant surfaces from the rain, and then falling to the ground as litter.