An independent review of the EPA's computer models of the Chesapeake Bay found that they overstated the impact of various improvements on the bay's health.
Simpson and other researchers were asked by the bay program to review some of the calculations plugged into its computer model. These equations described the impact of certain save-the-bay tactics: plant X amount of cover crops to hold fertilizer on farm fields, thus achieving a decline of Y in fertilizer-polluted runoff.Similar problems have been noted by previous reviews, as in a report from the GAO in 2005. It is hard to be optimistic about the bay's health under the best of circumstances. (See Jeremy's explanation of the ecology of the blue crab for a few of the reasons why.) Today's report suggests that even the good news needs to be tempered.
But Simpson said his review found that many of the equations were based on small-scale experiments that might not predict what would happen on a large farm. Others were based on the educated guesses of experts.
"A lot of them, there was very little data" when the calculations were devised about 10 years ago, Simpson said. "So a lot of it was just professional opinion."
And, as it turned out, a lot of the assumptions were off target, Simpson said. He and a team of university researchers with the Mid-Atlantic Regional Water Program reviewed new research that documented how much good each of these practices did in the real world.
According to the bay program, they found that 18 of the 36 measures actually had less of an effect than they had been credited for.
For instance, a practice called conservation tillage, in which farmers try to plant crops with minimal disturbance of the soil, was supposed to deliver an 18 percent reduction in nitrogen pollution. But the real number was more like 8 percent, Simpson's team found.
Another tactic was using fencing and water troughs to keep livestock from drinking and standing in streams. This keeps cows from polluting bay tributaries with their waste, and it was believed to deliver a 60 percent drop in nitrogen. But Simpson's team found the number was more like 25 percent.