Geochemical landscapes

A geochemical landscape is the geochemical characterization of a given part of the earth based on the joint influence of climate, relief, geology and vegetation on the chemical processes over a region. The primary purposes for assessing geochemical landscapes are for: agriculture, mineral exploration, environmental and human health studies and are carried out through geochemical surveys. The scale of a geochemical survey determines the sampling density and is generally focused on the scale of the geochemical process that is being measured. A rule of thumb is that the sample density should be 1/2 the size of the geochemical target being sought. Sample density and the spatial extent of a geochemical survey dictate the overall number of sites for the survey, Influences on the geochemistry of soils in Canada are characterized by the ecozone classification, regional bedrock geology and soils. The North American Soil Geochemical Landscapes Project (NASGLP) was designed to capture the geochemical variability of the continent at the Ecoprovince level at a spacing of one sample site per 40 km2. Sample design is an essential element of a geochemical survey. There are at least two ways to design a geochemical survey that is statistically defensible. The Generalized Random Tesselation Stratified Design (GRTS) is based on a spatially balanced selection of points over an area. Alternatively, an unbalanced, nested random sample design based on a designated sample resolution permits the use of statistical techniques such as analysis of variance to test the representivity of the data. Ecoregion designation is well established across Canada at the zone, region and district levels. Soil and bedrock geology maps have been compiled by various provincial territorial agencies but are not continuous across the country. The vertical profile of soils varies widely across the country. Northern soils are dominantly cyrosols and brunosols. Both the west coast and eastern part of Canada are dominated by podzolic soils and the western interior plains are dominated by chernozemic and luvisolic soils. The nature of the soil profile plays a role in the geochemical response that is observed from the base of the C horizon to the upper most layers.