Potential Environmental Impacts of Animal Feeding Operations
(Adapted in part from Livestock and Poultry Environmental Stewardship Curriculum, MidWest Plan Service; and Proposed US EPA Confined Feeding Rule.)
USEPA's 1998 National Water Quality Inventory indicates that agricultural operations, including animal feeding operations (AFOs), are a significant source of water pollution in the U.S. States estimate that agriculture contributes in part to the impairment of at least 170,750 river miles, 2,417,801 lake acres, and 1,827 estuary square miles (Table 1). Agriculture was reported to be the most common pollutant of rivers and streams.
However, one should not overlook the many positive environmental benefits of agriculture. For example, agricultural practices that conserve soil and increase productivity while improving soil quality also increase the amount of carbon-rich organic matter in soils, thereby providing a global depository for carbon dioxide drawn from the atmosphere by growing plants. The same farming practices that promote soil conservation also decrease the amount of carbon dioxide accumulating in the atmosphere and threatening global warming.
Other benefits compared to urban or industrial land use include greatly reduced storm runoff, groundwater recharge and water purification as infiltrating surface water filters through plant residue, roots and several feet of soil to reach groundwater.
In many watersheds, animal manures represent a significant portion of the total fertilizer nutrients added. In a few counties, with heavy concentrations of livestock and poultry, nutrients from confined animals exceed the uptake potential of non-legume harvested cropland and hayland. USDA estimates that recoverable manure nitrogen exceeds crop system needs in 266 of 3,141 counties in the U.S. (8%) and that recoverable manure phosphorus exceeds crop system needs in 485 counties (15%). It should be pointed out that while legumes are able to produce their own nitrogen, they will use applied nitrogen instead if it is available. The USDA analysis does not consider actual manure management practices used or transport of applied nutrients outside the county; however, it is a useful indicator of excess nutrients on a broad scale. Whole-farm nutrient balance is a very useful tool to identify potential areas of excess.
Air emissions from Animal Feeding Operations (AFO) can be odorous. Furthermore, volatilized ammonia can be redeposited on the earth and contribute to eutrophication of surface waters.
Animal manures are a valuable fertilizer and soil conditioner, if applied under proper conditions at crop nutrient requirements. Potential sources of manure pollution include open feedlots, pastures, treatment lagoons, manure stockpiles or storage, and land application fields. Oxygen-demanding substances, ammonia, nutrients (particularly nitrogen and phosphorus), solids, pathogens, and odorous compounds are the pollutants most commonly associated with manure. Manure is also a potential source of salts and trace metals, and to a lesser extent, antibiotics, pesticides and hormones. This problem has been magnified as poultry and livestock production has become more concentrated. AFO pollutants can impact surface water, groundwater, air, and soil. In surface water, manure's oxygen demand and ammonia content can result in fish kills and reduced biodiversity. Solids can increase turbidity and smother benthic organisms. Nitrogen and phosphorus can contribute to eutrophication and associated algae blooms which can produce negative aesthetic impacts and increase drinking water treatment costs. Turbidity from the blooms can reduce penetration of sunlight in the water column and thereby limit growth of seagrass beds and other submerged aquatic vegetation, which serve as critical habitat for fish, crabs, and other aquatic organisms. Decay of the algae (as well as night-time algal respiration) can lead to depressed oxygen levels, which can result in fish kills and reduced biodiversity. Eutrophication is also a factor in blooms of toxic algae and other toxic estuarine microorganisms, such as Pfiesteria piscicida. These organisms can impact human health as well as animal health. Human and animal health can also be impacted by pathogens and nitrogen in animal manure. Nitrogen is easily transformed into the nitrate form and if transported to drinking water sources can result in potentially fatal health risks to infants. Trace elements in manure may also present human and ecological risks. Salts can contribute to salinization and disruption of the ecosystem. Antibiotics, pesticides, and hormones may have low-level, long-term ecosystem effects.
In ground water, pathogens and nitrates from manure can impact human health via drinking water. Nitrate contamination is more prevalent in ground waters than surface waters. According to the U.S. EPA, nitrate is the most widespread agricultural contaminant in drinking water wells, and nearly 2% of our population (1.5 million people) is exposed to elevated nitrate levels from drinking water wells.
|Total Quantity in US||Amount of Waters Surveyed||Quantity Impaired by All Sources||Quantity Impaired by Agriculture|
|23% of total
|36% of surveyed
|59% of impaired
|Lakes, Ponds, and Reservoirs
|42% of total
|39% of surveyed
|31% of impaired
90,500 square miles
|32% of total
28,889 square miles
|38% of surveyed
11,025 square miles
|15% of impaired
1,827 square miles
Table 2 lists the leading pollutants impairing surface water quality in the U.S. Agricultural production is a potential source of most of these.
Table 2. Five Leading Pollutants Causing Water Quality Impairment in the U.S.
(Percent of incidence of each pollutant is shown in parentheses. For example, siltation is listed as a cause of impairment in 38% of impaired river miles.)
|1||Siltation (38%)||Nutrients (44%)||Pathogens (47%)|
|2||Pathogens (36%)||Metals (27%)||Oxygen-Depleting Substances (42%)|
|3||Nutrients (29%)||Siltation (15%)||Metals (23%)|
|4||Oxygen-Depleting Substances (23%)||Oxygen-Depleting Substances (14%)||Nutrients (23%)|
|5||Metals (21%)||Suspended Solids (10%)||Thermal Modifications (18%)|
List of Contaminants in Animal Manure:
- Oxygen-Demanding Substances
- Antibiotics, Pesticides, and Hormones
- Airborne Emissions from Animal Production Systems
- Comprehensive Nutrient Management Planning
- Study Questions