Trace element patterns in uncontaminated soils: The imprint of trees.

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The research proposal is a central component of our long-term program on the biogeochemistry of TE in terrestrial ecosystems. The proposal focuses on the development of trace element (TE) patterns in soils of uncontaminated forest areas. Indeed, TE not only accumulate in soils of polluted areas but they also form patterns, with localized hot spots, in soils of uncontaminated areas. Processes responsible for pattern development have yet to be established but the uplift of TE by trees is among the main mechanisms invoked. The TE arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) are analyzed because they are common contaminants in soils of Canada and because they are potentially toxic to the biota and to humans. The trees investigated grow in deciduous forest stands and include Sugar maple, Yellow birch, American beech, and Trembling aspens. This program is the very first to attempt at bridging this significant knowledge gap in the field of terrestrial biogeochemistry.The working hypothesis driving the proposal is: The spatial distribution of individual trees from distinct species within a given forest stand has a direct impact on the development of spatial TE patterns in the surface horizons of the underlying soils. The four interconnected questions asked to test the hypothesis are: 1) What are the characteristics of soil TE patterns forming in the surface horizons of uncontaminated forest soils? 2) What are the biogeochemical processes involved in the development of soil TE patterns? 3) What is the timescale required for the establishment of the properties and metrics characterizing soil TE patterns? and 4) What is the potential for generalization of the scientific knowledge generated by the proposal?Our scientific approach combines original field experiments in forested ecosystems, state-of-the-art analytical techniques and innovative multivariate statistical analyses to gather high-quality data on the TE chemistry of soil patterns in uncontaminated forested ecosystems. The field work will be conducted in range of watersheds and forest stands that are representative of the terrestrial environments found in southeastern Canada and northeastern USA. The broad range of environmental conditions studied will allow to evaluate the impact of a series of soil properties and of tree species on TE pattern development and will insure the assessment of the generality of findings generate by the proposal.Advances in knowledge in the area of TE research are needed by our society to anticipate the response of terrestrial ecosystems to environmental changes, such as shifts in climatic conditions, in atmospheric TE deposition or in dominant tree species, to further the development of efficient green technologies for the remediation of TE-contaminated soils and to manage the flow of TE along the food-chain in a context of sustainable food production.