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TitleCombined tree-ring carbon and nitrogen isotopes to infer atmospheric deposition in northeastern Alberta
AuthorSavard, M MORCID logo; Bégin, C; Marion, J
SourceAGU Fall meeting 2013, abstracts; B42A-08, 2013 p. 1
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130253
PublisherAmerican Geophysical Union
MeetingAGU Fall meeting 2013; San Francisco; US; December 9-13, 2013
Mediaon-line; digital
File formathtml
Areanortheastern Alberta; Fort McMurray; Edmonton
Subjectsgeochronology; environmental geology; dendrochronology; vegetation; carbon isotopes; isotopes; stable isotope studies; isotope ratios; climatic fluctuations; climate; Lower Athabasca Oil Sands; Air quality
ProgramEnvironmental Geoscience Coal & Oil Resources Environmental Sustainability
AbstractMonitoring atmospheric emissions from industrial centers in North America is significantly younger than the emitting activities themselves. Attention should be placed on SOx and NOx emissions as they have been increasing over the last 15 years in western Canada. In Northeastern Alberta in particular, two distinct diffuse pollution contexts deserve attention: the Lower Athabasca Oil Sands (OS) district (north of Fort McMurray), and the coal fired power plant (CFPP) area (west of Edmonton). The NOx and SO2 emissions started in 1967 and 1956, but the direct air quality monitoring has been initiated in 1997 and 1985, in these respective contexts. In an attempt to address the gap in emission and deposition monitoring, we explored the d13C and d15N patterns of spruce trees (Picea glauca and Picea mariana) growing in four stands in the OS district and one stand, in the CFPP area. Tree-ring series collected from these five sites all covering the 1880-2010 period were analyzed and their d13C and d15N values examined along with the climatic parameters and SOx and NOx emission proxies. For two stands in the OS district where soil drainage was poor d15N series did not vary significantly, but the intermediate and long-term d13C and d15N trends inversely correlate in the three other studied stands. For these three sites statistical analyses for the pre-operation calibration periods (1910-1961 and 1900-1951) allowed developing transfer functions and predicting the natural d13C and d15N responses to climatic conditions for the operation periods. The measured series all depart from the modeled natural trends, depicting anomalies. Interestingly, the anomalies in the two regions can be nicely reproduced by multiple-regression models combining local climatic parameters with acidifying emissions. Notwithstanding the significant inverse correlations between the d13C and d15N series for the three well drained sites and their link to acidifying emissions, it is too early to invoke a coupled response of these indicators to the modification of a single physiological process under pollution stress. A preliminary interpretation is that the concomitant inputs of NOx and SOx to the studied sites generated several effects, in the foliar and root systems, possibly lower stomatal conductance and increased ectomycorrhizal activities, respectively. The approach combining long tree-ring d13C-d15N series with statistical modeling tested here in two distinct diffuse pollution contexts permits to select objective criteria for interpreting anthropogenic impacts on local air-soil-plant C and N cycles.
Summary(Plain Language Summary, not published)
Major deposition in forests of nitrogen (N) and (S) emitted by human activities may lead to acidification and degradation of the terrestrial and aquatic ecosystems. This environmental issue is of concern in north-eastern Alberta where S- and N-bearing emissions have been reported to increase for the last 15 years. For two of the major sources of emissions in this region, oil sands extraction and coal fired power generation that started in 1967 and 1956, respectively, the emissions have been monitored only since 1997 and 1985. The lack of information in the early period of these operations does not allow to estimate the impact of the current emissions or the potential effects if the industrial activities were to intensify. This study has allowed to: propose tree-ring isotope ratios as monitoring tool to compensate for the lack of historical data; better understand the man-made perturbations of the S and N cycles; and describe changes in the biogeochemical processes of exposed forests.

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