EPA adjusts Chesapeake Bay pollution figures

The Environmental Protection Agency said in late summer that more pollution is going into the Chesapeake Bay than it previously estimated.

For example, the federal agency raised its estimate of the nitrogen that flowed to the bay in 2008 from 258 million pounds to 283 million pounds.

That indicated a tougher job ahead in restoring the Chesapeake, adding 25 million pounds to the amount that Virginia and other states in the bay region must reduce to reach the clean-bay target of 175 million pounds a year.

This month, however, the EPA made other adjustments. Among them, it eased the nitrogen target from 175 million pounds a year to 200 million pounds.

Gone was that extra 25 million pounds that posed the potential problem for states.

Critics say the shifting numbers are unreliable. But EPA officials say the shifts exemplify their openness in releasing findings that change as scientists home in on the nature of bay pollution.

"We're getting a better sense" of that pollution, said Rich Batiuk, associate director for science for the Chesapeake Bay Program, the EPA-led cleanup effort.

"Some of these numbers are going to continue to change as we get better information" about the causes of pollution.

The pollution numbers are important because they ultimately will determine how much local governments, businesses, farmers and others -- under the eyes of the EPA and the states -- must cut their pollution.

The numbers are estimates derived by computer models, or simulations. EPA experts plan to adjust the numbers even more in 2010 before settling on firm figures in an important bay cleanup plan late in the year.

In addition to changes in nitrogen pollution, the latest estimates revised the amount of phosphorus that must be cut from 4.9 million pounds to 1.3 million pounds. (Batiuk said that 1.3 million is almost surely too low and probably will be revised early next year.)

Nitrogen and phosphorus, from sources such as stormwater runoff from farms and subdivisions, aid the growth of algae that foul the bay.

Howard R. Ernst, a U.S. Naval Academy political scientist who has written widely about the Chesapeake, said the bay program's numbers have been unreliable for years and continue to be.

The numbers long have been based on "outrageous assumptions," including a belief that farmers who pledge to reduce pollution actually are doing so, Ernst said.

"Ultimately the bay program ends up with an inaccurate virtual-reality model that does not reflect the condition of the bay," Ernst said.

Beth McGee, a senior scientist with the Chesapeake Bay Foundation, an environmental group, said the EPA should be commended "for being upfront" with the evolving figures.

"They are improving [the numbers], basically," she said.

Scientific tests on bay waters show how the Chesapeake is doing in various measurable ways -- for example, if oxygen levels are high enough. But there is no test to show how much pollution flowed into the bay during a particular year, or how much needs to be reduced.

That's where the computer models come in. EPA scientists, assisted by academic experts, plug in various assumptions -- for instance, how much pollution would run off of urban land and farmland under certain amounts of rainfall, and how much work has been done to reduce pollution. The computer then spits out the pollution figures.

New information can change those assumptions, and affect the overall numbers. For example, the increased estimates of nitrogen flowing to the bay in 2008 were based, in part, on research showing some pollution-fighting measures on farms weren't as effective as previously believed.

This much is certain: For the bay to be saved, lots of people must reduce lots of pollution. Ultimately, said McGee of the bay foundation, it might not matter a whole lot if, say, the nitrogen target on paper is 175 million pounds or 200 million.

"The bay will tell us when it's restored. . . . At some point it will become fixed."

Contact Rex Springston at (804) 649-6453 or .