The report is intended to improve the understanding of the causes and consequences of water pollution in agriculture, as well as means of preventing it. The fourth section reviews the policy responses in the various OECD countries regarding the status of water pollution, which, in turn, acts as an impetus for farm systems, practices, and inputs used in agriculture.
Farms contribute to water pollution in the form of pesticides, improper waste management, and soil runoff. Pesticides can seep into the ground and kill certain plants and animals. Animal waste can enter the watershed and nourish harmful algal blooms. And soil can enter nearby bodies of water to render them cloudy.
The rest of the section explores farm pollution from the perspective of major farm drivers that influence water pollution, particularly nutrient use and pesticides (Figure 1). A global review on agricultural water pollution, explains that agriculture, rather than human settlements or industries, is the largest contributor to water pollution.
Farms Threaten Clean Water Supplies
One of the nation’s gravest, persistent threats to clean drinking water is contamination caused by runoff from factory farms. There are myriad major environmental problems in the modern world, and factory farms are among the leading causes of pollution. Runoff from both synthetic fertilizers and animal wastes has the potential to poison drinking water and aquatic ecosystems, harming both human health and wildlife.
Nitrogen-based fertilizers generate powerful greenhouse gases and can overwhelm waterways with hazardous contaminants; chemical pesticides, with different toxicological effects, can pollute our air and water, or be found directly in our food.
Excess nutrients from fertilizers leech into surface and groundwater, creating algae blooms and nitrate pollution, impacting drinking water, recreation activities (such as swimming and boating), fish/shellfish harvesting, and marine and aquatic ecology. Excessive runoff of nutrients into streams impacts drinking water supplies, and can in some cases lead to serious health problems.
Dissolved contaminants from agricultural land may travel through the soil to reach groundwater, where they may pose a health threat to humans should this water be used for drinking. The risk to human health of groundwater. Contaminated water can contain disease-causing organisms, which may rapidly spread if animals are drinking from the same water well.
Animal Sicknesses Contribute to the Problem
Ill animals may then discharge millions of infectious germs into the ground, further polluting other water sources. Farming soils may become contaminated, for instance, from excessive or improper use of fertilizers and pesticides. Pesticides and fertilizers used in agriculture may contaminate both groundwater and surface water, as may organic wastes from livestock, antibiotics, slurry effluents, and processed wastes from crop plants.
There can be surface runoff from pesticides, fertilizers, and animal manure, or leaching nitrogen into groundwater, whose fate is to discharge into surface water bodies.
Pathogens can persist from being sprayed on agricultural fields, leaching into groundwater, or being transported into surface waters from runoff. When the nutrients in plants–from synthetic fertilizer or organic fertilizer, decomposing crop residues, and farm waste products–such as milk sewage–runoff into freshwater, it accelerates the eutrophication of water bodies. The migration of plant nutrients from agriculture to freshwater has the potential to drastically disrupt a water body’s biological balance.
Pesticides and Excrement Are the Main Problems
Livestock and crop-growing practices may introduce pollutants, such as sediment, nutrients from fertilizers and animal manure, pesticides, herbicides, and bacteria from livestock manure, into the local waterways.
Antibiotic-resistant bacteria may then travel from the CAFOs through the air and water, including the water used for irrigation of crops, and may find their way into the animal waste used for crop fertilization. Farm water can be contaminated through various means, and potentially transmits bacteria, viruses, and parasites to crops and animals.
When farming activities are not monitored and managed properly, some practices may adversely impact water quality. Impacts of agricultural activities on surface and groundwater may be minimized through the use of conservation practices tailored for the particular location.
Farmers can conserve water resources by using water more efficiently, improving water storage on the farm, reducing water use, and increasing soil cover and soil moisture. Farmers must adopt practices that will hold stormwater and irrigation water within their properties, preventing contaminated runoff into neighboring streams and rivers. Farmers can greatly reduce nutrient runoff by improving soil health practices such as planting cover crops, water quality practices such as planting streamside buffer crops, and following best practices with fertilizer.
Certain Farming Practices Are Better than Others
In turn, depending on-farm practices and systems, the use of agricultural inputs will impact environmental conditions in terms of rates of soil erosion (which impacts pollutant leaching), water quality, and impacts on aquatic ecosystems (in either freshwater or marine waters). In addition to contributing sediment, nutrients, and pesticides, farm runoff can contribute salt, increased water temperatures, disease-causing microorganisms (pathogens), and naturally occurring metals to water in California. Surface and groundwater pollution (a major threat to aquatic ecosystems) and excess nitrates in drinking water (a major threat to public health) are caused by CAFO contamination.
The proportion of monitored sites with rivers, lakes, and ocean waters exceeding recommended national limits or guidelines for environmental protection and recreational use is far higher, and agriculture is a primary source of these pollutions in many cases. Washington has over 2000 listed polluted glasses of water in areas where agriculture is a major land-use activity.
Current Initiatives to Stop the Pollution
EPI found half the miles of rivers and streams, 55% of the acres of lakes, and 25% of the bays and estuaries it evaluated were impaired, meaning that they could not be used safely for swimming, fishing, and drinking water, or other public uses. Pollution from runoff, known as nonpoint source agricultural pollution, was the largest cause of water quality damage in the rivers and streams surveyed, third-largest in lakes, and second largest in wetlands.
The 2002 National Water Quality Inventory Report noted that agricultural runoff is the leading cause of harm in rivers and streams, and the second-leading cause of harm in lakes, ponds, and reservoirs, which includes fertilizer runoff, which usually occurs as rainfall transports fertilizer to the waterways.
The Environmental Protection Agency’s Agriculture Strategic Plan for the Pacific Southwest Region notes agriculture is the leading national source of ground, surface, and coastal water contamination. Water contamination caused by improperly managed storage and waste management controls resulting from the meat industry poses substantial risks to local communities and their right to clean water.
Unsafely using unconventional sources of water–particularly wastewater–in agricultural operations may lead to the accumulation of microbiological and chemical contaminants in crops, livestock products, and soils and water resources, and eventually lead to serious health impacts for exposed food consumers and agricultural workers; it also can increase antimicrobial resistance. Contaminated water used in the growing, harvesting, and processing of crops may cause health problems.
