The main sources of pollution are excess nutrients (nitrogen and phosphorus) and sediment. Nutrients cause algae blooms which—along with sediment—reduce water clarity. This prevents sunlight from reaching—and therefore kills—underwater plants that provide important food and habitat for crabs, fish and waterfowl.

When the algae die, they sink to the bottom and decompose in a process that removes oxygen from the water, contributing to low-oxygen conditions and “dead zones” with no oxygen at all.

Excess nutrients and sediment can also affect the types of algae that grow in the Bay, creating conditions favorable to some nuisance species that are not the desired food for fish and small predators near the base of the food web.

What’s the goal of the cleanup effort?

The ultimate goal of the Chesapeake restoration effort is a clean Bay—one that meets its water quality standards. For years, the Bay had water quality standards that differed between the states and were neither attainable, nor protective of the creatures living in it.

In recent years, scientists and state and federal officials have worked to develop new water quality criteria for the Chesapeake designed to ensure that different types of fish, shellfish, underwater grasses and other organisms have the water conditions they need in the right places, and at the right time of the year.

The new approach divides the Bay into five different habitat zones (called designated uses) and establishes measurable water quality criteria (for dissolved oxygen, water clarity and chlorophyll a) needed by the species that live in each zone.

The designated uses and criteria were adopted in the past year as enforceable state water quality standards by all jurisdictions with tidal waters—Maryland, Virginia, Delaware and the District of Columbia.

What has to be done to meet the goal?

In 2003, the Bay Program, using computer models, established nutrient and sediment reduction goals needed to meet the water quality standards. Overall, those goals required a 48 percent reduction in nitrogen, and a 53 percent reduction in phosphorus, measured from a 1985 baseline.

How will those reductions be made?

The road maps used by states to get to cleaner rivers, and a cleaner Bay, are called tributary strategies. They are river-specific plans that spell out in detail exactly what mix of actions is required to meet the nutrient and sediment goals for each basin: the miles of riparian forest buffers that must be restored, the number of acres of cover crops that must be planted, the number of wastewater treatment plants upgraded and so on.

The six states in the watershed and the District of Columbia worked to write a total of 36 tributary strategies. The area covered by an individual strategy generally is a state’s portion of a particular river basin. (The Potomac, for instance, has separate strategies for Virginia, Maryland, West Virginia, Pennsylvania and the District of Columbia.) Also, some large rivers, such as the Susquehanna, are divided into subbasins within states in order to write more localized strategies—there were 13 in Pennsylvania alone.

Strategies were drafted independently by each state, typically using the input of stakeholder groups, with the aim of building support among those who will have to implement large portions of the plans, such as farmers, local government officials and watershed groups.

Isn’t air pollution a problem?

Absolutely. Huge amounts of nitrogen are deposited on the watershed as the result of air pollution. Much of it is taken up by plants, but a sizable amount still runs off the land and enters the Bay. Estimates vary, but somewhere between a quarter and a third of all the nitrogen entering the Bay stems from air pollution.

It arrives in two main forms. About two-thirds is the result of nitrogen oxide emissions from fossil fuel combustion, including such sources as cars, power plants, industries, trucks, boats, tractors, lawn mowers and almost anything that burns oil or coal.

The remaining third results from ammonia emissions. These overwhelmingly come from agriculture, primarily animal farm operations. But significant amounts also originate from car exhaust, refrigerants and some industries.

Where’s the air in this report?

Air pollution contributed at least a quarter of the nitrogen entering the Bay, but it doesn’t look that way in this supplement. Atmospheric nitrogen is distributed among the land uses it falls upon. Most regulatory programs that are under way are not expected to significantly change nitrogen deposition rates by 2010. So efforts to deal with air pollution mainly hinge upon land-based nutrient control efforts that deal with pollution after it is deposited on the ground.

A recent regulation from the EPA that would cap nitrogen oxide emissions from power plants could reduce the amount of nitrogen from air pollution reaching the Bay by 8 million to 10 million pounds a year.

Won’t oysters help?

Oysters, as well as other filter feeders such as menhaden—and even more acres of underwater grasses—would help to clear the water. Right now, those efforts are not included among nutrient reduction strategies because it is difficult to quantify their exact benefit. In addition, efforts to restore an oyster population large enough to make a difference in water quality—either with native, or a nonnative species—would likely take decades. Further, scientists generally caution that the Bay is so overwhelmed with nutrients—inputs have roughly doubled since 1950—that actions such as oyster restoration should only be thought of as a supplement to nutrient reduction efforts—not a substitute.

How much will it cost?

According to Bay Program figures, fully implementing tributary strategies written by the states could cost about $28 billion in upfront capital costs, plus another $2.7 billion in costs that would recur each year, such as the operation and maintenance of wastewater treatment plants and stormwater controls, as well as annual payments to farmers for conservation efforts.

Those estimates have drawn skepticism because states included many high-cost practices, such as retrofitting stormwater controls on old development sites and replacing existing septic systems, which produce relatively small nutrient reductions. Some strategies included actions covered by regulations and—in some cases—included court-ordered water quality actions that had minimal benefits to the Bay.

As a result, a Bay Program analysis of the tributary strategies showed that about 80 percent of the nutrient reductions—those from agriculture and wastewater discharges—could be achieved for about 20 percent of the total cost.

A report by the Chesapeake Bay Commission, an independent panel representing state legislatures, reached similar conclusions.

By widely using the most economical nutrient control techniques, 78 percent of the region’s nitrogen reduction goal, 75 percent of its phosphorus goal and all of its sediment goal could be accomplished for $623 million a year, according to the commission’s report.

Will these reductions achieve the goals?

Computer models indicate that the nutrient reductions should achieve all or most of the dissolved oxygen and chlorophyll a goals. It’s likely that the water clarity goals would not be fully met, though. That’s because slightly more than half of the water-clouding sediment entering the Bay comes from erosion along the Chesapeake shoreline—not down the rivers. Right now, there are no goals to control that shoreline erosion, although they are expected in the future.