Bay Pollution Progress Overstated
"It is the Cadillac of watershed models across the world," said Christopher S. Conner, director of communications for the Chesapeake Bay Program.
The model is useful, bay officials said, because it can take variations of rainfall and other factors into account. Even scientists who question its use for measuring progress credit the model with being well-constructed and useful for prediction.
But some scientists and other experts on the bay said the model is the wrong tool for reporting bay pollution because it relies on so many assumptions and because it continues to suggest more progress than water monitoring reports.
The Chesapeake Bay Program's revised computer model currently reports that phosphorus pollution has dropped about 28 percent since 1985 and that nitrogen pollution has dropped about 18 percent.
But according to the U.S. Geological Survey data, the observed concentrations of those chemicals flowing into the bay from the major rivers has changed little.
Eight of the nine major rivers entering the bay have shown no trend or have increased concentrations of phosphorus since the late '80s. Only one of the smaller rivers has shown a small decrease in phosphorus pollution.
Seven of the nine major rivers have shown no trend or increased concentrations of nitrogen, the other key bay pollutant. Two have shown slightly decreased concentrations.
"There's clearly mixed messages," said Mike Burke, the program's acting associate director. "The modeled data show a declining line [for pollution]. The other shows you a flat line."
Even aside from the varying numbers, however, several scientists said they were uneasy using a model to measure progress.
"Think of the weather," said Donald F. Boesch, president of the University of Maryland's Center for Environmental Science and one of several scientists who have advised the program. "You can use computer models to forecast the weather. But if we want to know what the weather is, we go out and see if it is raining and snowing.
"In other words, monitoring -- not modeling -- should be used to assess present conditions."
Scott Phillips, the Chesapeake Bay coordinator of the U.S. Geological Survey, agreed. "From our perspective, the first indicator [of the pollution reductions] should be the trends in observed concentration -- because that's what we actually measure in a river and what actually enters the bay," he said. "The model provides a prediction of what water quality will be, without the effects of annual changes in rainfall."
A critical weakness in the pollution estimates was revealed this spring when, at the urging of scientists, the Bay Program revised the assumptions in its computer model. Assumptions about the amount of pollution coming from certain agricultural lands were off, program leaders conceded, overestimating the overall pollution progress by about 10 to 15 percent, officials said.
"Scientists have to change what they're saying all the time. It's the nature of science," said Tom Simpson, a University of Maryland professor who led the group of scientists advocating a revision to the model. But "in the public arena, it's difficult to say, 'What we have actually achieved is less than we had previously reported.' "
It was not the first time a revision to the model assumptions significantly changed the results.
According to an October 1999 "State of the Chesapeake Bay" report, the model showed that the states were on course to achieve the phosphorus goal by 2000 and would come very close to the required reduction for nitrogen.
"To many, the steady restoration of the Chesapeake system is a budding success story," the report said.
Months later, however, the model assumptions changed, and the goals were further away than the program had reported. The earlier results, critics said, were used because the Bay Program felt pressure to show progress.
"The Chesapeake Bay Program's 'State of the Bay' reports have been inexcusable," Ernst said. "It's one thing to make a mistake once, but to consistently make mistakes in your own favor is suspicious."
© 2004 The Washington Post Company