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TitleTree-ring isotope geochemistry and air quality changes in northeastern Alberta
AuthorSavard, M M
SourceSociety of Environmental Toxicology and Chemistry North America 32nd Annual Meeting, abstract book; by SETAC; 2011.
Alt SeriesEarth Sciences Sector, Contribution Series 20110382
PublisherSociety of Environmental Toxicology and Chemistry North America
MeetingSETAC North America; Boston; US; November 13-17, 2011
File formatpdf
NTS74D; 83G; 83J
AreaFort McMurray; Pembina River
Lat/Long WENS-116.0000 -114.0000 55.0000 53.0000
Lat/Long WENS-112.0000 -110.0000 57.0000 56.0000
Subjectsgeochemistry; isotopic studies; oxygen isotopes; nitrogen; oil sands; coal; carbon isotopes; vegetation; tree rings
ProgramEcosystems Risk Mitigation, Environmental Geoscience
AbstractThis project uses C and N isotopes in tree rings to evaluate the effects of air quality changes on soil biogeochemical processes and photosynthetic functions of trees. Our approach involves combining tree-ring C and N stable isotope series with statistical modelling to distinguish the responses of trees due to natural (climatic) conditions from the ones potentially caused by emissions from the Athabasca oil-sand developments where truck fleets, oil upgraders, desulphurization and hydrogen plants, boilers, heaters and turbines have been emitting NOx and SOx since 1967. White spruce trees 165 years or older, were selected at 55 km from the heart of the development operations. The growth rings were dated and separated at a time resolution of 1 or 2 years for the 1880-2009 period. The average carbon isotope values of cellulose from the rings covering the 1880-1965 period show short-term variations mostly explained by regional climatic conditions, whereas the 1968-1995 series significantly departs from the pre-operation pattern. Most importantly, the nitrogen isotope series of treated wood shows an average decrease of 1.0 per mill during the 1970-2009 period. The statistical links between the variations of the regional drought index and the isotopic C and N responses during the pre-operation period allows to develop predictive climatic models. When we apply these models to predict the natural isotopic behaviour of the recent period, the measured isotopic trends of the operation period depart from the modelled curves. In contrast, using multiple regression analyses combining climatic conditions and air pollution proxies allows to reproduce the measured C and N isotopic curves (r2 of 0.67 and 0.44, respectively). The d13C isotope trends suggest that air contaminants emitted from oil-sands developments has lowered the stomatal conductance and water use efficiency of the studied trees. It also seems that the foliar system has been recovering since the reduction of SO2 emissions after 1995. Regarding the N isotopic series, our hypothesis is that the anthropogenic N input has increased the amount of N taken up by miccorhizal fungi which release light N for the host trees growing in non-saturated conditions. Importantly, our N isotopic measurements in tree rings seem to reflect the N saturation levels in soils impacted by anthropogenic emissions.