Table 1. Auxiliary variables.

List of geological, climatic, environmental and topographic variables used for the regression.

	Variables	Initial resolution	Source
Variable	Elevation	90 m	[61]
Clay	Surficial Soil Clay (Weight%)	250 m	[62]
Ph	Soil pH in H2O solution	250 m	[62]
MAT	Mean Annual Temperature (WorldClim)	30-arc sec	[63]
MAP	Mean Annual Precipitation (WorldClim)	30-arc sec	[63]
PET	Global potential evapotranspiration	30-arc sec	[64]
Elevation	Global elevation dataset	30-arc sec	[65]
SUL	Sulphur Deposition (CMIP3 NINT simulation)	2.5-degrees	[66]
BCB	Biomass Black Carbon (CMIP3 NINT simulation)	2.5-degrees	[66]
BCA	Industrial Black Carbon (CMIP3 NINTsimulation)	2.5-degrees	[66]
AOD	Aerosol Optical Depth (Particles < 2.5microns)	0.1-degrees	[67]
Salt	Sea Salt Deposition (CCSM.3 Simulation)	1.4-degrees	[68]
Dust	Dust deposition (Multi-model average)	1.0-degrees	[68]
Nfert	Global Fertilizer, Version 1	0.5 degrees	[69]
Nman	Global Manure, Version 1	0.5 degrees	[69]
Corn	Distance to major corn producing center in Canada*	1 km	This study
sugar	Distance and type of sugar refineries**	1 km	This study

** Calculated using the distance tool in ArcGIS and centroids from the two major corn producing centers in Canada: Southern Ontario and Saint Lawrence River valley

** Calculated using the Inverse Distance Weighing tool in ArcGIS and locations of the 5 Canadian sugar refineries with 0 = beat sugar refinery and 1 = sugarcane refiner