Nitrate Distribution in the Ground Water of the Alliston Region of Ontario, Canada

Nitrate‐N concentrations during the Summers of 1980 and 1981 exceeded 10 mg/1 in 68 of the 164 ground‐water samples collected from a shallow water‐table aquifer underlying a sand plain near Alliston, Ontario. Three extensive zones of nitrate contamination were associated with major potato‐growing areas on the sand plain. Nitrate concentrations were positively correlated with both the percentage area of heavily fertilized crops (potatoes, corn, sod and asparagus) and nitrogen fertilizer application rates in the vicinity of ground‐water sampling sites. Chloride levels in ground water exhibited a positive association with KCl fertilizer application rates. Ground water under potato fields had relatively consistent C1/NO 3 ‐N ratios despite considerable variations in nitrate‐N and chloride concentrations. Ground water with a low nitrate content was found beneath forest and permanent pasture. These data suggest that the use of commercial nitrogen fertilizer is a major source of nitrate in the aquifer.