Tuesday, November 14, 2006

Preferential flow: A Component of National Risk Indicators of Water Contamination.

Suzanne E. Allaire1, Eric Van Bochove2, Georges Thériault2, Farida Dechmi2, Ed Topp2, and David Lapen2. (1) Université Laval, Hochelaga, Québec, QC G1K 7P4, Canada, (2) Agriculture and Agri-Food Canada, Hochelaga, Québec, QC G1V 2J3, Canada

Risk indicators of water contamination by agricultural activities are important tools for land management, contamination assessment, legislation on agriculture, and politics. Such risk indicators developed for different contaminants (e.g. pesticides, pathogens, nitrogen and phosphorus) at the Canadian national level are required to be science-based. The risk indicators are meant to classify different area entities such as soil polygons and watersheds within five risk classes (very low, low, medium, high and very high). The risk indicators must respond to land and climate characteristics but also to changes in agricultural management practices. Major input parameters for the preferential flow (PF) component determination of the risk indicators are soil texture and layering, tile drainage characteristics, climate data, crop type and area, water infiltration and surface runoff data, and contaminant sorption coefficients. Most of these input parameters are available through Census of Agriculture data, climate data, pedological reports, and pesticide registration data. The PF component will be presented using the indicator of risk of water contamination by phosphorus as an example. Different subdivisions of the PF component, such as finger flow, burrow flow, crack flow and pipe flow will be considered. Advantages and limits of the PF component will also be discussed.