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TECHNICAL REPORTS

Atmospheric Pollutants and Trace Gases

Effects of Smelter Sulfur Dioxide Emissions

A Spatiotemporal Perspective Using Carbon Isotopes in Tree Rings

^a Natural Resources Canada, Geological Survey of Canada, 880 Chemin Ste-Foy, Bureau 840, QC, Canada G1S 2L2
^b INRS-ETE, 880 Chemin Ste-Foy, Bureau 840, B.P. 7500, Sainte-Foy, QC, Canada G1V 4C7

^* Corresponding author (msavard{at}nrcan.gc.ca).

Received for publication October 7, 2002. We wanted to test the hypothesis that forest exposure to phytotoxic gases indirectly affects their carbon uptake. We estimated that the reduction of photosynthesis may have reached 20 to 30% at a site located 9 km (test site) from the Horne copper smelter in Rouyn–Noranda, which is a point source of SO₂. Twenty-one spruce trees older than 100 yr were selected from seven sites at various distances from the smelter to evaluate conditions prior to and during the periods of smelter operation. The carbon isotope results obtained from spruce tree rings at our test site reveal an unprecedented and abrupt shift of +4 after the onset of smelter operations. This large and permanent shift exceeds natural variations in regional pre-smelter series or in the series at a remote control site. All trees up to 116 km downwind from the smelter show ¹³C positive shifts following the onset of operations. There is also a clear inverse relationship between the amplitude of the first-order trends and distance from the smelter. Those ¹³C trends indicate that trees exposed to high levels of SO₂ decrease their level of CO₂ uptake through activation of stomatal closure. This is strongly supported by the significant departure of the Rouyn–Noranda trends from those measured for trees from non-industrialized areas of the Northern Hemisphere, or calculated using global atmospheric conditions. Considering the large number of SO₂ point sources in North America, our results imply that CO₂ uptake by the boreal forest in the vicinity of these sources may be lower than previously thought.

Abbreviations: DINAMITE, Dendrogeochemical Investigation of Natural and Anthropogenic Metals in the Environment • VPDB, international standard used for reporting the relative abundances of ¹³C via the delta notation • VPDB, is a carbonate provided by IAEA in Vienna (V) as a replacement of the former international standard Peedee Belemnite (PDB)

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