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That's a Lot of Chickens - The Impact of AFOs on the Delmarva Peninsula

Date Posted: February 8, 2001

The Delmarva Peninsula is an area of land encompassing Delaware, Maryland and Virginia. One hundred and eighty miles long and up to seventy-one miles wide, it includes the eastern shore areas of Maryland and Virginia and the southern half of Delaware. The Delmarva Peninsula is one of the largest poultry areas in the United States, producing some 600 million chickens and 1.6 billion pounds of manure annually. Most of these animals are kept and raised in confined situations, known as animal feeding operations (AFOs). AFOs congregate animals, feed, manure and urine, dead animals, and production operations on a small land area. Feed is brought to the animals rather than the animals grazing or otherwise seeking feed in pastures, fields, or on rangeland. Manure and wastewater from AFOs have the potential to contribute pollutants such as nitrogen and phosphorus, organic matter, sediments, pathogens, heavy metals, hormones, antibiotics, and ammonia to the environment. Excess nutrients in water (i.e., nitrogen and phosphorus) can result in or contribute to low levels of dissolved oxygen, an overabundance of plant life, and toxic algal blooms. Decomposing organic matter (i.e., animal waste) can reduce oxygen levels and cause fish kills. In addition, these conditions may be harmful to wildlife and human health and, in combination with other circumstances, have been associated with outbreaks of microbes such as Pfiesteria piscicida. In mid-April, the Service’s Chesapeake Bay Field Office (CBFO) began a study to evaluate potential water quality impacts of upstream animal feeding operations (AFOs) on National Wildlife Refuges (NWR) on the Delmarva Peninsula. The study is a collaborative effort between the CBFO, the Service’s Delaware Bay Estuary Project, the University of Maryland, and the U.S. Geological Survey’s Columbia Environmental Research Center. The objectives of the study are to: 1) map locations of AFOs in the vicinity of refuge lands and identify watersheds at high and low risk for AFO-related impact; and 2) conduct studies to evaluate chemical and biological impacts to these watersheds. In addition to nutrients, chemical analysis will include measurement of “nontraditional” contaminants associated with AFOs, including arsenic, selenium, and zinc which are found in animal feed additives, and â-estradiol, a naturally produced hormone found in poultry manure that is also a potent endocrine (hormone) disruptor. Biological evaluations will include an assessment of benthic macroinvertebrate (small aquatic "bottom-living" invertebrate) health and measurement of the egg yolk protein vitellogenin in resident male fish as an indicator of potential endocrine disruption. This protein, normally completely absent in males, is now viewed as a sensitive and specific biomarker for the exposure of male fish to feminizing environmental chemicals. Studies are currently underway at Primehook NWR in Delaware and Blackwater NWR in Maryland.


Beth McGee, (410) 573-4524.


CAFOs Feed a Growing Problem (Endangered Species Bulletin article January/February 1999)

U.S. Environmental Protection Agency, Office of Water. Animal Feeding Operations (AFOs).

Last updated: June 12, 2015