Corn Field, Quebec. Source: Coreyu, http://www.flickr.com/photos/coreyu/If not properly managed, agricultural activities can contaminate both surface water and groundwater sources. Grazing animals trample shoreline vegetation which increases runoff and decreases soil absorption, animals also can also excrete directly into the water source. Field ploughing can increase soil erosion and runoff, and fertilizer application, pesticide spraying, irrigation and animal faecal matter are all potential direct sources of agricultural pollution.

Wastewater from agricultural activities may contain a number of polluting ingredients:

• Animal wastes in liquid and solid form. Animal waste is not only a strong source of nutrients; it can contain parasites, bacteria, antibiotics and synthetic hormones.
• Silage (grass semi-fermented to be used as winter feed for cattle and sheep) liquor is the liquid produced during the fermentation process in the production of silage. Silage liquid is a pollutant due to its high organic content and acidic pH.
• Pesticides, insecticides and chemical fertilisers may runoff land into receiving waters, especially if they have been applied excessively.
• Milking parlour wastes include milk, animal wash water, animal wastes and cleaning products. The organic waste increases the nutrient content of a water body, which can result in eutrophication. Cleaning products may contain toxic chemicals that can be fatal to aquatic wildlife if they are not removed during treatment.
• Slaughtering waste is animal blood, waste, and cleaning products. Slaughtering waste can have the same effect as milk parlour wastes if not properly treated.
• Vegetable washing water contains small amounts of pesticides, vegetable pieces and soil.

Next: Fertiliser

Adapted from Pollution Probe's Source Water Protection Primer and Drinking Water Primer