Surface water quality Soil conservation practices adopted over the past 15 to 20 years have reduced soil erosion by wind and water and thus the amount of soil moving into waterways. As sedimentation is reduced, so too is the movement into water of substances attached to soil particles, such as phosphorus, pesticides, and bacteria. The amount of sediment entering surface water from farmland is lowest in the Prairies and highest in the potato-growing areas of the Atlantic provinces. Nitrogen seldom reaches toxic levels in surface waters but, together with phosphorus, may cause eutrophication. Concentrations of nutrients in surface water exceed water quality guidelines in some intensively farmed areas where large quantities of manure and fertilizer are used.
Pesticides enter surface water in runoff and by atmospheric deposition.
Pesticide concentrations are rarely measured at levels that exceed guidelines for drinking water. Guidelines for irrigation and for the protection of aquatic life are sometimes exceeded. Contamination by agriculturally derived bacteria is common. Bacteria numbers are generally elevated in runoff from manure-treated fields, although their abundance in surface waters has not been directly related to livestock density. Heavy metal contamination of surface waters derives mainly from natural sources and has not been reliably linked to agricultural practices, including land application of sewage sludge.