Removal of nitrogen and phosphorus by harvesting oysters is trivial. As I pointed out in the scientific journal "Aquatic Geochemistry," even if we could return to the maximum harvest of oysters in the Potomac River at the turn of the last century of 1,600,000 bushels (about 480 million oysters; today's harvest is 0.3 percent of that), only 72,000 kilograms of nitrogen would be removed annually. Today's Potomac River pollution load is about 30,000,000 kilograms of nitrogen from all sources. About one-eighth of that is from disposal of poultry litter by land application in the guise of "free fertilizer."
The land application of animal waste, including poultry litter, causes about a quarter of Chesapeake Bay nutrient pollution, about the same as does the use of conventional chemical fertilizers. Dry chicken broiler litter contains about 29 kilograms of nitrogen per ton, only about 60 percent of which is crop-available. 12 kilograms of nitrogen (40 percent of 29 kilograms) is disposed by land application for every ton of litter, to no benefit of the crop, and constitutes potential pollution.
How many oysters would need to be harvested annually to balance the pollution from the land application of 550,000 tons of poultry litter in Maryland? About 6,400,000 kilograms of nitrogen would need to be consumed by oysters. One million market-sized (3-inch) oysters (3,300 bushels) contain 150 kilograms of nitrogen, so about 42 billion oysters, or 142 million bushels, are required. That is 20 times the maximum annual harvest ever recorded for the bay at the turn of the last century. And that is just from the cheap disposal of poultry litter in Maryland! Mr. Perdue is just being a "merchant of doubt," and his self-serving assertion is nonsense.
Pollution must be addressed quantitatively. There is absolutely no doubt that poultry litter (also sludge and manure) are massive sources of both nitrogen and phosphorous pollution of Chesapeake Bay, and the easiest source of pollution to eliminate. Harvest of oysters (the harvest of fish and crabs is larger) cannot even make a tiny dent in removing those pollutants. The only way to improve water quality is to stop polluting. Banning the practice of land application, or at least ensuring that it is phosphorous-based and provides only the amount of phosphorous the crop needs, based on a soil test, is very long overdue. A ban on the land application of animal waste would reduce bay nutrient pollution more than has been accomplished by expensive upgrades of wastewater treatment facilities.
Lynton S. Land, Ophelia Va.
The writer is professor emeritus of Geological Sciences at the University of Texas-Austin.