Reconstructing environmental change using stable isotopes delta-nitrogen-15 and delta-carbon-13) and metal contents of tree-rings

This thesis evaluates stable isotopes (nitrogen and carbon) and elemental compositions of tree-rings as environmental monitors. This was initiated with a local study to examine the temporal record of tree-ring delta 15N values from oak stands that underwent large-scale tree-clearing and land-use change at different times. Trees from the perimeter of each stand record a marked 1.5-2.5‰ increase in the delta15N values of their tree-rings synchronous with the tree-clearing and land-use change. This indicates that changes in forest ecosystem nitrogen cycling, whether due to climate, land-use or other environmental changes can be faithfully monitored with nitrogen isotopic compositions of tree-rings.;Stable isotope analysis of tree rings was extended to a regional study of whether anthropogenic pollution is recorded in carbon and nitrogen cycles in forested ecosystems. Tree-ring delta13C values and delta 15N values in oak and birch from sites across Ontario and New Brunswick are correlated at both remote and urban-proximal sites, with delta 15N values decreasing since 1945 and converging on 1‰ at urban-proximal sites and decreasing but not converging on a single delta15N value in remote sites. These results are consistent with increasing anthropogenic influence on carbon and nitrogen cycles since 1945 and indicate that tree-ring nitrogen and carbon isotopic compositions record the regional extent of pollution.;While evaluating tree rings in birch from New Brunswick, a fire-scarred tree was found. The fire event was recorded as a 1.5‰ decrease in delta 15N values adjacent to the scar with elevated Ba, Ca, Mg, Sr, and Mn concentrations relative to non-scarred trees. The results suggest that variations in tree-ring chemistry may be useful in mapping the extent and assessing the magnitude of historic fire events.;The effect of physiological stress can effect on the elemental concentrations in tree-rings from red and white oaks, which might obscure the use of tree rings in developing pollution chronologies, was assessed. Nutrient (Ca, Mg, Mn) concentrations were erratic during historic periods of stress while chemically similar non-nutrients (Ba, Sr) and the anthropogenic pollutant Pb were not. This behavior during historic periods of stress suggest that nutrient concentrations arenot passively recorded by tree rings, but non-nutrient availability can be.