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| Titel |
Pollution and Climate Effects on Tree-Ring Nitrogen Isotopes |
| VerfasserIn |
M. M. Savard, C. Bégin, J. Marion, A. Smirnoff |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024484
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| Zusammenfassung |
| BACKGROUND
Monitoring of nitrous oxide concentration only started during the last 30 years in North
America, but anthropogenic atmospheric nitrogen has been significantly emitted over the last
150 years. Can geochemical characteristics of tree rings be used to infer past changes in the
nitrogen cycle of temperate regions? To address this question we use nitrogen stable
isotopes in 125 years-long ring series from beech specimens (Fagus grandifolia) of the
Georgian Bay Islands National Park (eastern Ontario), and pine (Pinus strobus)
and beech trees of the Arboretum Morgan near Montreal (western Quebec). To
evaluate the reliability of the N stable isotopes in wood treated for removal of soluble
materials, we tested both tree species from the Montreal area. The reproducibility
from tree to tree was excellent for both pine and beech trees, the isotopic trends
were strongly concordant, and they were not influenced by the heartwood-sapwood
transition zone. The coherence of changes of the isotopic series observed for the two
species suggests that their tree-ring N isotopic values can serve as environmental
indicator.
RESULTS AND INTERPRETATION
In Montreal and Georgian Bay, the N isotopes show strong and similar parallel agreement
(Gleichlaufigkeit test) with the climatic parameters. So in fact, the short-term isotopic
fluctuations correlate directly with summer precipitation and inversely with summer and
spring temperature. A long-term decreasing isotope trend in Montreal indicates progressive
changes in soil chemistry after 1951. A pedochemical change is also inferred for the
Georgian Bay site on the basis of a positive N isotopic trend initiated after 1971. At both
sites, the long-term δ15N series correlate with a proxy for NOx emissions (Pearson
correlation), and carbon-isotope ring series suggest that the same trees have been impacted
by phytotoxic pollutants (Savard et al., 2009a). We propose that the contrasted
long-term nitrogen-isotope changes of Montreal and Georgian Bay reflect deposition of
NOx emissions from cars and coal-power plants, with higher proportions from coal
burning in Georgian Bay (Savard et al., 2009b). This interpretation is conceivable
because recent monitoring indicates that coal-power plant NOx emissions play an
important role in the annual N budget in Ontario, but they are negligible on the Quebec
side.
CONCLUSION
Interpretations of long tree-ring N isotopic series in terms of effects generated
by airborne N-species have been previously advocated. Here we further propose
that the contrasted isotopic trends obtained for wood samples from two regions
reflect different regional anthropogenic N deposition combined with variations
of climatic conditions. This research suggests that nitrogen tree-ring series may
record both regional climatic conditions and anthropogenic perturbations of the N
cycle.
REFERENCES
Savard, M.M., Bégin,C., Marion, J., Aznar, J.-C., Smirnoff, A., 2009a. Changes of Air
Quality in an urban region as inferred from tree-ring width and stable isotopes.
Chapter 9 in “Relating Atmospheric Source Apportionment to Vegetation Effects:
Establishing Cause Effect Relationships” (A. Legge ed.). Elsevier, Amsterdam; doi:
10.1016/S1474-8177(08)00209x.
Savard, M.M., Bégin, C., Smirnoff, A., Marion, J., Rioux-Paquette, E., 2009b. Tree-ring
nitrogen isotopes reflect climatic effects and anthropogenic NOx emissions. Env. Sci. Tech
(doi: 10.1021/es802437k). |
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