The way to clean up the Chesapeake Bay can best be described by three letters and three words. The letters are "BMPs." The words are, "lots of them."

BMPs are shorthand for best management practices, which include a range of actions that reduce the flow of nutrients and sediment off the land and into waterways. The term covers everything from planting streamside forest buffers to changing farm animal diets to building stormwater detention ponds.

They are also the cornerstone for Bay cleanup plans. Tributary strategies written by the states detail exactly how extensively various BMPs need to be implemented to meet nutrient reduction goals-how many acres must be planted in cover crops, how many manure storage structures must be built and so on.

Soon, the plans might need even more BMPs.

A recently completed review by a team of scientists has concluded that many of those actions are less effective than thought.

Conservation tillage, forest buffers, cover crops planted in certain parts of the watershed, and some types of stormwater control practices are among the widely implemented BMPs that underwent review and were found to be less effective at reducing nutrient runoff than previously assumed by the state-federal Bay Program, which requested the review.

"The new estimates are a whole lot closer to reality than they were a year ago," said Tom Simpson, a soil scientist with the University of Maryland and the Mid-Atlantic Regional Water Quality Program which conducted the review. "And maybe even more important than that, is we understand them so much better, and understand the science we have behind them."

It could have a price tag, too. The cost of implementing tributary strategies has been estimated at nearly $30 billion. If more BMPs are needed, the cost could go up. Also, estimates of BMPs are used in nutrient credit trading programs-if a given BMP is less effective than thought, it's also less valuable for trading purposes.

Historically, understanding the effectiveness of BMPs has been important for strategic planning.

Since the late 1980s and early 1990s, the Bay Program has assigned levels of effectiveness for roughly two dozen BMPs to help make cleanup plans. For example, if 40 pounds of nitrogen was the average nitrogen loss from a crop field, and a buffer with a 25 percent removal efficiency was installed, it would theoretically keep 10 pounds of nitrogen out of the stream.

Using those figures, officials were able to determine what mix of BMPs was needed to meet nutrient reduction goals.

But those efficiencies were based on limited research, and the basis for many was never written down. "There was no documentation," said Sarah Weammert, of the Mid-Atlantic Water Quality Program, an association of regional agricultural universities that led the review effort. "When I tried to find what they have now, there is nothing. It was pretty much best professional judgement."

Those judgments were often based on limited field studies which were often conducted in carefully controlled settings. Scientists would monitor and maintain a practice-in some cases even artificially controlling rainfall-and report their results.

Unfortunately, that research often produced better results than in the real world.

That resulted in overly optimistic estimates of BMP effectiveness. In some cases, that contributed to computer models predicting greater nutrient reductions in watersheds than were observed in water quality monitoring-something for which the Bay Program has been sharply criticized.

In 2003, the Bay Program adjusted downward its effectiveness estimates for several widely used BMPs, such as nutrient management plans. But a white paper from the Bay Program's Scientific and Technical Advisory Committee in 2004 warned progress toward meeting nutrient reduction goals was still overstated and called for a more comprehensive review of other BMPs.

Other factors have added to the urgency.

Among those are the increasing use of the Bay Program's estimates of BMP effectiveness to determine the value of credits in nutrient trading programs being established in the watershed. And, in 2011, the Bay region will likely have to establish a Total Maximum Daily Load for the Bay watershed, which will bring a whole slate of additional regulatory actions.

"When you enter into the world of nutrient credit trading where you are giving them a market value, where you are using them to estimate whether or not you are going to achieve a TMDL, then you need to be able to say that you have done a pretty exhaustive look at the science, and that you had people with expertise on the topic look at them," Simpson said.

Instead of relying on an ad-hoc process to determine BMP effectiveness as in the past, the Bay Program contracted with the Mid-Atlantic Regional Water Quality Program to conduct an exhaustive review of BMP efficiencies.

A formal process was developed that reviewed all available literature for a given practice, with peer-reviewed studies getting greater weight than other literature. A team of experts then convened to evaluate each BMP.

But their recommendations had to go beyond looking at results from carefully controlled studies. They looked for real-world information about how various BMPs were maintained and performed-and even how they sometimes failed altogether-in making recommendations. "We wanted to be able to defend the numbers," Weammert said. "We also needed to come up with something that represented the operational condition -not a research plot that is managed in a highly controlled situation, where an 'expert' is installing and maintaining a BMP."

Many BMPs fail if not carefully maintained, or lose much of their effectiveness in heavy rains. The phosphorus control effectiveness of streamside buffers was reduced in part because small ruts and channels can form in the buffers and-unless carefully maintained-allow surface to flow directly into the stream, reducing the buffer's effectiveness.

The nitrogen effectiveness of the conservation tillage BMP was reduced downward as well. Reducing field plowing reduces surface runoff into streams. But some of the nitrogen that would have run off the surface simply sinks into the groundwater, and takes another route to the stream.

In addition, the team set different levels of effectiveness for variables such as soil types. For example, nitrogen-absorbing cover crops are more effective in some soils than others. And in the case of cover crops, effectiveness was further fine-tuned to reflect when the crops are planted-the more quickly they are planted after harvest, the greater their nutrient reduction value. Further cover crop revisions are in the works to reflect crop type-rye is generally more effective than other plants in nitrogen removal.

The Bay Program adopted the recommendations this fall, but assessing their exact impact is difficult. The changes are being incorporated into an all new computer model that will go into use next year. The model includes a huge number of other changes-sorting out those stemming from the BMP changes alone would be impossible.

"We are improving a whole host of things," said Rich Batiuk, associate director for science with the EPA's Bay Program office. "We're not anticipating the overall nutrient loads to dramatically change, but those efficiencies will contribute to a more accurate model and a higher level of confidence in the resulting management scenarios."

Batiuk said the review process set an important precedent that will be followed for all future BMP reviews, ensuring all get equal levels of scrutiny and have certain levels of data available to support conclusions.

"We now have a level of evidence needed to establish an efficiency that will be is consistent with the way others were derived," he said.

That will be put to work next year. Most of the changes this year focused on re-evaluating existing BMPs, but the team in 2008 will review a slate of new BMPs that do not have efficiencies.

Among those on tap is quantifying the effectiveness of "precision feeding" of dairy animals to reduce nutrients in their manure; horse pasture management techniques; stream restoration; and programs that promote infiltration rather than runoff of stormwater.

That, in effect, will add more tools in the nutrient reduction toolbox-many people are reluctant to spend money installing practices if they won't be counted toward nutrient reduction goals.

Still, Simpson cautioned against concluding that any specific figure for BMP effectiveness is "right"-the impact of any practice will vary in a given place based on a host of factors.

The ultimate test, he said, is whether the figures are close enough to reality so-when implemented-they achieve the anticipated improvements in Bay water quality.

"The changes in BMP efficiencies themselves will have no effect on progress," he said. "Progress is what we really achieve. This only becomes important to the Bay's living resources when we are good enough to be able to match computer predictions up with the monitoring data."

Once Just A Planning Tool, Getting Right BMP Now Has Big Consequences

Changes in best management practices effectiveness not only represent a better understanding of how they work on the landscape-they also reflect changes in the policy landscape.

When first created, estimates of BMP effectiveness were used primarily as strategic planning tools. By placing various mixes of BMPs in computer models, they produced general ideas of the level of actions needed to meet early, voluntary cleanup goals that sought general improvements in Bay water quality.

Today's cleanup plans are driven by the need to meet specific water quality standards-a job that could have a $30 billion price tag. Instead of a voluntary cleanup, the Bay cleanup has a growing number of regulatory elements, and those are expected to increase further. In 2011 the region will be required to adopt a cleanup plan known as a Total Maximum Daily Load which would form the basis of further regulatory actions.

A TMDL would be similar to a tributary strategy in assigning nutrient reduction goals for various nutrient sources in each river.

But the EPA's rules for TMDLs have added safeguards. For instance, it requires that pollution control plans incorporate a "margin of safety" to account for uncertainty. Typically, the margin of safety requires an additional 10 percent pollution reduction.

This means each of the states would need plans that go significantly further than today's tributary strategies.

Rich Batiuk, associate director for science with the EPA's Bay Program Office, said that by incorporating conservative assumptions about BMP effectiveness and other factors that affect nutrient delivery to the Chesapeake within the model, the Bay region will be in a position to argue that a margin of safety already exists.

"We should get closer to what is the actual maximum daily load for the system," he said.

Highlights of Changes in BMP Effectiveness

Conservation Tillage

  • Nitrogen: Decreased from 18 percent removal to 8 percent
  • Phosphorus: Decreased from 30 percent removal to 22 percent
  • Sediment: Unchanged

Off-stream Watering with Fencing in Pastures

  • Nitrogen: Decreased from 60 percent removal to 25 percent
  • Phosphorus: Deceased from 60 percent removal to 40 percent
  • Sediment: Decreased from 75 percent removal to 40 percent

Off-stream Watering without Fencing in Pastures

  • Nitrogen: Decreased from 30 percent removal to 15 percent
  • Phosphorus: Decreased from 30 percent removal to 22 percent
  • Sediment: Decreased from 38 percent removal to 30 percent

Riparian Forest Buffers

  • Nitrogen: Different levels of effectiveness exist for different regions and geologic conditions. In the review, most were decreased 10-20 percent from previous levels.
  • Phosphorus: Phosphorus decreased for all areas. Generally, the decreases were of a larger magnitude than those for nitrogen.

Urban Wetlands & Wet Ponds

  • Nitrogen: Decreased from 30 percent removal to 20 percent
  • Phosphorus: Decreased from 50 percent removal to 45 percent
  • Sediment: Decreased from 80 percent removal to 60 percent

Urban Dry Extended Detention Basins

  • Nitrogen: Decreased from 30 percent removal to 20 percent
  • Phosphorus: 20 percent removal; no change
  • Sediment: 60 percent removal; no change