The virtual Chesapeake Bay used to evaluate cleanup progress may soon look more like its cousin, the real Chesapeake—it’s going to get dirtier.

The state-federal Bay Program has long measured nutrient reduction progress primarily through the use of a sophisticated computer model that estimates nitrogen, phosphorus and sediment runoff from the Chesapeake’s 64,000-square-mile watershed.

The result, though, was a modeled “virtual Bay” that was getting cleaner, while the real Chesapeake was showing far less improvement. In some cases, the model showed sharp nutrient reductions in rivers where water quality monitoring showed nutrient increases.

A major reason, officials acknowledge, is that they have long overestimated the effectiveness of nutrient reduction efforts being used in the watershed: Bad assumptions going into the model resulted in misleading numbers coming out.

Now, the Bay Program is taking a new look at the effectiveness of the wide array of agricultural “best management practices”—known as BMPs—used to control nutrient runoff, and how fully those practices are being implemented.

“We want to believe the numbers that we are working with, and that there is some accountability in them,” said Russ Perkinson, of the Virginia Department of Conservation and Recreation, who headed a group that worked on the changes. “For some of the BMPs, there is evidence they were a little optimistic in the initial projections.”

He and others said it was critical to make the adjustment now. Earlier this year, the EPA and all of the states within the Bay watershed agreed to new water quality goals for the Chesapeake.

Attaining those goals means that the amount of nutrients in the Bay would have to be cut nearly in half from the mid-1980s levels. The amount of nitrogen entering the Bay is to be slashed to 175 million pounds a year, and the amount of phosphorus cut to 12.8 million pounds.

Based on that, each major river feeding the Bay has been assigned a maximum allowable nutrient “load” and states are in the process of writing tributary-specific plans to meet those goals.

The new changes almost certainly mean that tributary strategies will have to achieve greater nutrient reductions than previously thought to make up for previous overestimates.

Further, because assumptions about BMP effectiveness are used in writing tributary strategies, the plans will likely have to call for even more nutrient control practices than previously thought—something that could increase implementation costs.

“It takes what was already challenging and makes it quite a bit more challenging,” said Tom Simpson, a soil scientist at the University of Maryland’s College of Agriculture and Natural Resources, and chair of the Bay Program’s Nutrient Subcommittee. “I think it is essential for us to be as technically honest and accurate as we can be, but it is going to be really difficult.”

No one knows for sure, but some officials say the changes could reduce by a quarter the amount of nutrient reductions previously awarded to agricultural sources.

From 1985 through 2000, the watershed model had estimated that the amount of nitrogen running off the watershed and into the Bay in an average year decreased from 334 million pounds to 285 million pounds.

Of that, the model estimated that agricultural efforts reduced nitrogen runoff by more than 25 million pounds—accounting for about half of the reductions achieved. The corrected figures will likely reduce that to less than 20 million pounds, and perhaps less than 15 million.

In recent years, the Bay Program has refined its estimates of other nutrient sources, such as wastewater treatment plant discharges and urban runoff, but revisions to agricultural estimates will have a greater impact because agriculture is the largest single source of nutrients in the Chesapeake.
Officials in recent years have become increasingly concerned that their assumptions about the effectiveness of many common agricultural nutrient reduction practices were overly optimistic.

One recent study showed that the aggressive implementation of two major nutrient reduction practices—nutrient management plans and cover crops—produced only a 25 percent reduction in nitrogen runoff when used everywhere in a test watershed [See “Farm Study yields benefits in water quality,” Bay Journal, July-August 2003].

Yet in some river systems, the Bay Program’s model has shown reductions that exceed that level of nutrient reduction, even though the areas had lower levels of implementation.

Those concerns were heightened after scientists at a May workshop agreed that many reductions counted by the Bay Program existed only on paper [See “Scientists examine past–and future–of farm runoff,” Bay Journal, June 2003].

After that, many officials agreed that correcting those estimates needed to be fast-tracked. Otherwise, the tributary strategies would be working with the wrong numbers and need to be rewritten within the next few years—giving little time to achieve the goals before the Bay Program’s 2010 deadline.

“To me, it’s sort of a pay me now, or pay me later issue,” said Russ Mader, of the U.S. Department of Agriculture’s Natural Resource Conservation Service, who has been working on the revisions. “The impact is fairly substantial. But the long-term ramifications of not doing it are pretty high. No one wants to have to go out and do new strategies.” He and others hope the changes will be finalized this fall—possibly by the end of October.

Simpson said the changes reflect new research, and better implementation information than what existed when the Bay Program launched its efforts to track nutrient reduction progress a decade ago. “We were the first and remain the first to attempt to quantify our progress using BMP efficiencies,” he said. “I remain unapologetic about the need to change it. This is advancing knowledge.”

Originally, nutrient reduction values assigned for various runoff control practices were drawn from research. In reality, though, practices in the field are not implemented with the rigor of a research project.

Further, those calculations did not take into account the fact that the effectiveness of some practices diminish over time, or that they may not be effective during severe storms.

In other cases, overestimates are made by using unrealistic assumptions about common farm plans that guide nutrient use and runoff control efforts. The Bay Program assumes Soil and Water Conservation Plans and Nutrient Management Plans are fully implemented, although surveys show that is often not the case. Changes being considered would reflect more realistic implementation levels.

Not all of the changes would reduce the effectiveness of practices. Research shows that fall cover crops, if applied quickly after harvest, are more effective at absorbing nutrients left on the field. Proposed changes would give more nutrient reduction credit for cover crops implemented early, and less credit for those planted later in the fall.

In addition, nutrient reduction credits will be counted for some practices previously overlooked, such as the use of food additives that reduce phosphorus in chicken waste.

The changes are part of an overall effort in the Bay Program to improve accountability and ensure that what happens on the land is resulting in improvements in water quality.

Whereas the watershed model was the primary tool used to monitor progress in the past, officials plan a more broader suite of information to evaluate progress in the future. For instance, they plan to monitor fertilizer sales in the watershed—if nutrient reduction programs are being fully implemented, it should be reflected in reduced fertilizer sales.

Stepped-up water quality monitoring in the watershed, including shallow water areas of the Bay, should provide an earlier indicator of whether on-the-land actions are resulting in water quality improvements, or whether more needs to be done.

Ultimately, the goal is for the actions on the land to be reflected in improved habitat for fish, expanded underwater grass beds and less algae in the water.

“The accountability is no longer just in counting the number of BMPs,” said Rich Batiuk, associate director for science with the EPA’s Bay Program Office. “It’s accountability in water quality, and accountability in source reductions. We’re talking about accounting for all the variables that connect the source to the resource.”