Agricultural Effects on Ground and Surface Waters: Research at the Edge of Science and Society (Proceedings of a symposium held at Wageningen. October 2000). IAHS Publ. no. 273. 2002. 379 Nutrient losses from agriculture: effects on Canadian surface and ground waters PATRICIA A. CHAMBERS, MARTHA GUY, GARY GROVE Environment Canada, National Water Research Institute, II Innovation Blvd, Saskatoon, Saskatchewan S7N 3H5, Canada e-mail: patricia.chambers(S>,ec.gc.ca ROBERT KENT, ELIZABETH ROBERTS & CHRISTIAN GAGNON Environment Canada, Environmental Quality Branch, 351 St Joseph Blvd, Hull, Québec K1A 0H3, Canada Abstract In 1996, Canada had a nutrient surplus of 4.3 kg ha" 1 nitrogen (N) and 0.8 kg ha" 1 phosphorus (P) for all agricultural land. Although this N surplus is low compared to many European countries, nutrient losses from agricultural land have contributed to environmental problems in Canada: accelerated eutrophication of certain aquatic ecosystems; fish kills; a decline in amphibian numbers; toxic algal blooms; and an increase in the extent to which the drinking water guideline for nitrate has been exceeded in ground- waters. To minimize nutrient release from agricultural activities in Canada, most provinces have adopted or are revising nutrient management strategies for managing the production, storage and utilization of agricultural nutrients. Key words agriculture; budgets; Canada; impacts; lakes; nitrogen; nutrients; phosphorus; rivers INTRODUCTION During the past three decades, concerns have been raised worldwide about the effects of increased agricultural production on environmental quality. Only 7%, or approx- imately 68 xlO 6 ha of Canada's total land area is agricultural land. However, increases in cattle and hog density from 39 to 64 animal units per farm between 1976 and 1996 have raised questions about the long-term environmental effects of Canadian agriculture. This paper presents information on N and P losses as a result of crop and livestock production, the impacts of these losses on surface and ground water quality, and agricultural nutrient management practices in Canada. METHODS N and P budgets for agricultural land were calculated by quantifying inputs (fertilizer, manure, biosolids, N fixed by legumes, and atmospheric N deposition) and outputs (harvested crop). Fertilizer usage (quantity and the fertilized land base) was obtained from Agriculture and Agri-Food Canada (1998) and Statistics Canada (1997a). Manure N and P production was estimated by multiplying livestock numbers by manure N and P production for each animal type (Statistics Canada, 1997b). We assumed that N in