Biologic Markers of Air-Pollution Stress and Damage in Forests (1989) / Chapter Skim
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Human Perturbation of C, N, and S Biogeochemical Cycles: Historical Studies with Stable Isotopes
Human Perturbation of C, N, and S Biogeochemical Cycles: Historical Studies with Stable Isotopes
Pages 143-156
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From page 143... ...
Examples include carbon isotope changes in tree rings due to local pollution effects or as a result of global changes in atmospheric CO: concentrations. Initial sulfur and nitrogen isotope studies suggest larger, more easily detectable changes of 2-7O/oo in precipitation and lake cores.
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From page 144... ...
To cite well-known examples of these processes, kinetically-controlled reactions such as photosynthesis favor concentration of light carbon in plants, while CO2 in the atmosphere is depleted in the heavy carbon isotope during equilibrium exchange with bicarbonate dissolved in the ocean. These kinds of fractionations introduce signals into the natural environment that are present as background isotopic distributions.
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From page 145... ...
and it is now recognized that environmental variables other than the isotopic composition of CO2 can significantly influence tree ring isotopic compositions
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Relationship of ~ values to amounts of heavy and light stble isotopes for carbon, nitrogen and sulfur isotopes. Source: Reproduced, with permission, from the Annual Review of Ecology Systematics Vol.
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Inc. from Carbon isotope measurements in baseline air, forest canopy air, and plants 1982.
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distance (~3. The foundry was closed from 1929-1949 when tree isotopic compositions are similar.
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SIGNAL-TO-NOISE The very extensive carbon isotope studies with tree rings have tackled a difficult problem in that the total atmospheric Ab signal is small at about 1°/oo and there is significant physiological noise that is often of this same magnitude or larger. The signal-to-noise ratio may be more promising for nitrogen and sulfur isotopes, where studies related to tree age and atmospheric pollution are just beginning.
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From page 150... ...
. Middle: 61SN of Big Moose Lake sediments, Adirondack Mountains, New York.
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Because tree rings and lake cores can be expected to integrate isotopic compositions of input N direct study of recent records may be the best way to evaluate whether anthropogenic N differs significantly in 815N from natural background N
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The strong isotopic signals seen in lake cores, however, suggest that development of new methods of analyzing trace amounts of tree sulfur for 83 S may prove very worthwhile. CONCLUSIONS Stable isotope changes in trees that are caused by specific air pollutants have been investigated in only a handful of studies.
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1983. Carbon isotope measurements in baseline air, forest canopy air, and plants.
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1 9SX. Sulfate fertilization and changes in sulfur stable isotopic compositions of lake sediments.
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1985. Distribution and isotopic composition of sulfur in lake sediments of northern Ontario.
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1978. Stable sulfur isotope analysis of SO2 pollution impact on vegetation.
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