The Manure Menace

LITTLE of the 2.7 trillion pounds of manure -- about five tons for each American -- generated by livestock in this country each year is treated, and a large amount of it is spread on nearby fields. The map above shows the counties where, it is estimated, more phosphorus and nitrogen from animal manure, two major contributors to water pollution, exist than can be removed from soil by crops. Many highlighted counties contain huge corporate meat- and milk-production operations that import tremendous amounts of phosphorous and nitrogen in the form of animal feed.

Last September, in North Carolina (where a fourfold increase in the number of hogs from 1986 to 1996 means that swine now outnumber people), an ocean of nitrogen-rich hog manure flowed into local estuaries after back-to-back hurricanes caused waste lagoons to flood. The ecological effects of the spill will not be fully known until this summer, when warmer temperatures could result in large-scale algae blooms that kill fish. It is more commonly smaller mistakes that cause contamination: whenever farmers apply more manure or chemical fertilizer to their fields than their crops need, the excess seeps into groundwater or is carried by rain into waterways. In Delaware and Maryland, where about 600 million chickens a year are raised on poultry farms, the runoff of excess nutrients into rivers feeding the Chesapeake Bay is believed to have triggered an outbreak of the microbe that killed tens of thousands of fish in 1997. Waste seepage from dairies in the Chino Basin of southern California has for years contributed to the contamination of groundwater under thousands of acres of land.

Efforts are under way at several levels to address these hazards. New federal regulations for large-animal farms were imposed last year, and a number of states have tightened their laws governing manure management. At the local level, some farms avoid excess runoff by selling manure. The Tyson Foods mill in Harrisonburg, Virginia, adds an enzyme to feed that reduces the phosphorus content of chicken droppings. Meanwhile, the scale of the problem grows. The ultimate effect of excess phosphorus and nitrogen is to reduce the amount of dissolved oxygen in water. Agricultural runoff may be a cause of marine "dead zones" like the one at the mouth of the Mississippi River, which is as big as New Jersey, and growing.

Brad Edmondson is the vice-president of, a provider of demographic information.

The Atlantic Monthly; May 2000; The Manure Menace - 00.05; Volume 285, No. 5; page 75.