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Title Controlled fumigation of a Scots Pine forest with ammonia. Final report.CEH Staff publications
Name(s) Cape, J N (Neil)
Sheppard, L.J. (Lucy)
Binnie, J (Jillian)
Institute of Terrestrial Ecology
Physical Details 21pp.
Publication 1995
Subjects T07059h5; CEH staff publication;
Files CEH Staff copy
Abstract 1. Wet deposition in throughfall below forest canopies often contains more sulphate than in rain. Most of this 'excess' sulphur is thought to arise from dry deposition of sulphur dioxide on the foliage, from where it is washed by rain, but quantitative estimates based on existing models are not reliable. 2. Part of the uncertainty is a lack of knowledge of the interaction between ammonia and sulphur dioxide on plant canopies. Ammonia can neutralise the acidity formed when sulphur dioxide dissolves in water, thereby promoting the uptake of sulphur dioxide by wetted canopies. 3. In order to investigate by direct experiment the interaction between ammonia and sulphur dioxide in a forest, a sector of Devilla Forest in Fife was exposed to controlled fumigation with gaseous ammonia at concentrations within the range observed in polluted regions. The release of ammonia gas was controlled to be in direct proportion to wind speed, to produce a uniform distribution of the gas to the north-east of the release point. 4. In 1993 ammonia was released over an 8 month period, but only when the forest canopy was dry. There was a very large increase in ammonium ions in throughfall in the fumigated area, which declined monotonically away from the point of release. There was a significant, but less pronounced, increase in the deposition of sulphate ions in throughfall, following a similar pattern. 5. In 1994 ammonia was released in dry conditions, when the results were similar to those the previous year. For the last month of the experiment, ammonia release was permitted regardless of the wetness of the forest canopy. Under these conditions there was a very large increase in the amounts of ammonium and sulphate ions deposited in throughfall, and these amounts were highly correlated with each other. The rate of deposition of sulphur dioxide was estimated to occur almost as fast as the gas could be transported to the forest surface. 6. The implications of these experiments for model
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