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Agriculture and Water Quality in the Canadian Great Lakes Basin: IV. Nitrogen¹

ABSTRACT

Eleven agricultural watersheds in southern Ontario were sampled approximately 3,000 times during the years 1975–1977 for Total Kjeldahl N (TKN) and NO₃-N as part of the Canadian activities of the Pollution from Land Use Activities Reference Group (PLUARG).

Only 12% of runoff samples had NO₃-N concentrations below 0.3 mg L^–1, while 3% of the samples exceeded the 10-mg L^–1 Ontario drinking water standard. Two-year-average total N stream loadings ranged from 3.5 to 29.2 kg N watershed-ha^–1. The NO₃-N loads averaged 75% of total N loads over all 11 watersheds. Both NO₃-N and total N unit-area loads were significantly correlated with total N addition to the watershed, and with percent of watershed under cultivation, in row-crops and corn (Zea mays L.), or tile-drained. The TKN loads were positively correlated with watershed surface-soil clay content and with extent of soils with high surface runoff potential.

Remedial measures to reduce stream N loading should only be considered for watersheds where stream N loading much exceeds inputs of N from precipitation. In these watersheds, improved fertilizer N efficiency in corn production may provide the greatest potential for reduced stream N loading. Proper location of manure storage sites is most important to minimize N pollution from livestock activities. About 70% of both stream NO₃-N and total N loading occurred from January to April during the spring runoff season. Agronomic practices that reduce either postharvest teachable soil N or erosion during spring runoff merit future research.

Key Words: watershed • stream loading • seasonal N runoff • nitrogen pollution reduction

¹ Contribution no. 528, Agriculture Canada Research Station, Summerland, British Columbia; and no. 96, Land Resource Research Institute, Ottawa, Ontario.

² Research Scientist, Agriculture Canada Res. Stn., Summerland; Physical Scientist, Land Resource Res. Inst.; Research Scientist. Agriculture Canada Res. Stn.; Swift Current, Saskatchewan; respectively.

Received for publication December 4, 1980.