Chesapeake Bay: Numbers behind EPA’s nutrient diet could be a recipe for disaster


WASHINGTON — A new report questions the data used by the Environmental Protection Agency (EPA) to set pollution limits for the Chesapeake Bay.

Commissioned by a coalition of agricultural groups, the report contrasts EPA’s estimate of the bay’s “nutrient diet” with those of the USDA, which are much more favorable to farmers.

It asks EPA to not issue a rule setting the bay’s “pollution loads” until the inconsistencies can be reconciled. The report was prepared by LimnoTech, one of the nation’s leading water sciences and environmental engineering consulting firms. It compared EPA’s Total Maximum Daily Loads with those in the draft USDA report, Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region.


Inconsistencies in data and modeling were found for:

• Land use and total acreage of the Chesapeake Bay watershed;

• Hydrology;

• Assumptions about conservation practices;

• Model frameworks; and

• Model results

The report calls for a “timeout” on the bay TMDL to make sure that EPA does not push the use of its pollutant estimation model beyond its original design.

“USDA estimates that seven percent of cropped acres are under conventional tillage, five percent of cropped acres have a level of tillage between conservation tillage and conventional tillage, and 88 percent of cropped acres are under conservation tillage (mulch till or no-till) practices…EPA estimates that 50 percent of cropped acres are under conventional tillage and 50 percent are under conservation practices.

In general, the cultivated cropland conservation practices incorporated in USDA’s model framework are documented and statistically valid in sufficient detail to allow a general understanding of practices accounted for in the modeling, the assumptions made regarding specific conservation practices, and the level of implementation. A similar level of detail and documentation is not, however, available for the EPA model framework.”

“If USDA’s numbers are correct, agriculture has already significantly surpassed EPA targets for reductions in sediment and phosphorus,” said National Association of Corn Growers Director of Public Policy Rod Snyder.

“It is crucial that farmers in the Bay watershed receive appropriate credit for their efforts to be good stewards of our land and water resources.”

Report findings

The LimnoTech report also found that USDA and EPA make different assumptions about animal feeding operations (AFOs) and concentrated animal feeding operations (CAFOs).

EPA attempts to model loads from the CAFO production areas, where animals are housed and manure stored, while USDA does not.

Both EPA and USDA appear to model manure application on cropland on a nitrogen basis. USDA estimates that 38 percent of cropped acres have manure applied. According to the study, it is not possible to determine from the available EPA documentation how much of the cropland in the EPA model receives manure.

“The ANPC wanted to know if the differences in EPA and USDA estimates were significant enough to call the draft TMDL into question,” said Lisa Kelley of the National Council of Farmer Cooperatives.

“The LimnoTech study provides a resounding ‘yes’ to that question and we are urging EPA to step back and re-examine the precision and accuracy of its data.”

Representing real world

According to the LimnoTech study, the USDA model framework seems to more accurately represent real world, Chesapeake Bay watershed agricultural operations and management practices including consideration of crop rotations, varying levels of tillage (no-till, mulch till, conventional till) and actual nutrient management practices.

“Through the Bay TMDL, EPA is implementing a rule that will have significant impact on economic growth and development, including food production, in the watershed,” said American Farm Bureau Federation Senior Director of Regulatory Relations Don Parrish.

“It is critical for EPA to get the facts right including providing an accurate accounting for existing management and conservation practices before it imposes potential economic disaster on agricultural producers in the Bay watershed.”

The LimnoTech report is available at


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