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Title The contribution of internal cycling to sulphur deposition below a Scots pine forest. Interim report.CEH Staff publications
Name(s) Cape, J N (Neil)
Sheppard, L.J. (Lucy)
Institute of Terrestrial Ecology
Physical Details 12pp.
Publication 1991
Subjects T07059h5; CEH staff publication;
Files CEH Staff copy
Abstract The overall objective of this study was described in the previous report (Cape, 1990). In brief, it is to quantify the contribution of canopy leaching to the deposition of sulphate below a forest canopy, and thereby to demonstrate the validity of using throughfall and stemflow measurements as estimates of total (wet and dry) deposition of sulphur to forests. The results from the field experiment are described in the previous report. and in a paper "in press" (Cape et at. 1991) which is attached as an Appendix. Two alternative interpretations were made: i) after the soil/canopy system reached equilibrium following soil application of the radioisotope the contribution of canopy leaching was negligible; ii) the soil/canopy system never reached equilibrium and canopy leaching was a major contributor to sulphate in throughfall. The first interpretation necessarily implies very rapid dry deposition of sulphur dioxide to the canopy, suggesting an important role for ammonia gas in enhancing dry deposition. If correct, then current estimates of the dry deposition of sulphur dioxide based on stomatal uptake (as used in regional modelling) are seriously in error. If the second interpretation is correct, then measurements below the canopy of sulphate in throughfall and stemflow cannot be simply used to estimate total sulphur deposition to forests. There was insufficient time resolution in the measurements made during the 1989 experiment to draw a firm conclusion. Moreover, as the experiment was conducted in summer, during the active growth phase, leaching might have been expected to be minimal as root-absorbed sulphate could be converted to protein and used in new foliage. The possibility of co-deposition is also enhanced in summer, as concentrations of sulphur dioxide are generally smaller than in winter, while concentrations of ammonia are generally greater. After establishing that accumulation of radio-labelled sulphur continued over winter (see below), it was decided to per
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