Concentrations of nutrients in surface water often exceed one or more water quality guidelines in intensively farmed areas such as southern Quebec, where large quantities of manure and fertilizer are used. Improvements in tillage practices, manure storage, and fertilizer use are reducing the problem. Pesticides enter surface water in surface runoff from agricultural land and by atmospheric deposition. They are detected in surface waters, but rarely at levels that exceed guidelines for drinking water. Guidelines for irrigation and for the protection of aquatic life are sometimes exceeded.
Bacteria are common in surface waters.
Elevated numbers are found in runoff from manured fields, though abundance in surface waters has not been linked to livestock density. Heavy metal contamination of surface waters derives mainly from natural sources and has not been reliably linked to agricultural practice, including land application of sewage sludge. Introduction Surface water quality refers to the physical, chemical, and biological characteristics of lakes, rivers, and estuarine waters. Water quality changes with the seasons and between geographic areas, even when no pollution is present. The background chemistry of river and lake water is determined by the soil, geologic formations, terrain, and vegetation in the drainage basin.