Unusually large numbers of dying sea lions and manatees. Shellfish poisoning. Widespread fish kills. Loss of sea grass beds. “Killer” algae. Coal reef destruction. “Dead zones” in coastal waters.

They are different problems plaguing different areas, but a new scientific report cites a common source of blame: too many nutrients pouring off the land — and dropping from the sky — into coastal waters.

The report from the National Academy of Sciences concludes that nutrient-related problems are “the greatest pollution threat faced by the coastal marine environment,” and it calls for a nationwide strategy to combat excess nitrogen and phosphorus.

“Conditions in many coastal areas are expected to worsen unless action is taken now to reduce nutrient pollution,” warned Robert Howarth, professor of ecology and environmental biology at Cornell University, who chaired the committee that wrote the report.

It’s not news that nutrients are a problem for coastal areas — the Bay Program has worked to control nutrients for more than a decade. But the report, coming from one of the nation’s leading scientific organizations, adds new urgency to the issue, and provides a scientific consensus that excess nutrients are degrading coastal water quality — something that has been disputed in some areas of the country.

“Estuaries and coastal zones are among the most productive ecosystems on Earth,” the report said. “There is strong concern that the natural resources they represent are in danger from eutrophication and other problems caused by excess input of nutrients.”

The report acknowledges that nutrient issues are often complex and their effects vary from place to place. But it warns that “decision-makers should not be tempted to defer action while waiting for ‘perfect’ knowledge.” The problems are clear enough to warrant action now, the report said, noting that 44 of 139 coastal areas recently assessed by the National Oceanic and Atmospheric Administration were “severely” affected by nutrients — including the Chesapeake Bay — and another 40 were suffering moderate impacts.

In response, the report called for a national goal of reducing the number of coastal waterbodies with severe nutrient problems 10 percent by 2010 and 25 percent by 2020. In addition, the report called for ensuring that no coastal area now considered healthy develops symptoms related to nutrient over- enrichment over the next 20 years.

While scientists have long recognized that eutrophication is a problem for freshwater lakes — where pollution is readily trapped — scientists have learned only in recent decades that eutrophication also affects coastal waters, especially in estuaries and other semi-confined areas near the mouths of rivers, which accumulate nutrients washed in from their watersheds.

Eutrophication is the overenrichment of a system by nutrients. Large amounts of nutrients result in algae blooms; the loss of important habitats such as underwater grass beds and coral reefs; changes in the makeup of fish populations; and the depletion of oxygen in the water which can result in fish kills.

In addition, the report said, nutrient overenrichment has been linked to harmful — sometimes toxic — algae blooms. Those, in turn, have caused alterations in the aquatic food web in some areas, and have been linked to the deaths of sea lions in California and manatees in Florida.

Eutrophication can affect local economies as well as sea life, the report said. “A single harmful algal bloom, taking place in a sensitive area during the right season, might cost millions of dollars in lost tourism or lost seafood revenues,” the report said.

While some of the worst problems are in the Bay and other Mid-Atlantic estuaries, the report said eutrophication is a problem along all U.S. coasts, including Massachusetts, New York, Louisiana, Florida, California, Texas and Washington.

Many of those coastal areas are under stress. Coastal counties account for only 17 percent of the U.S. landmass, but they hold 141 million people, nearly half of the nation’s population. Further, 17 of the nation’s 20 fastest-growing counties are on the coast, the report notes, and nearly 14,000 new housing units are built in coastal counties every week. Air pollution, runoff from lawns and streets, and wastewater from expanding populations all contribute to nutrient problems.

But controlling nutrients, the report warns, is an issue that often begins far from the shorelines where the problems are most evident.

On a global scale, the nitrogen cycle has been increasingly out-of-whack since World War I, when Germany discovered how to “fix” otherwise inert nitrogen gas from the atmosphere to meet the nitrate needs of its munitions industry. Since then, humans have increasingly tapped the atmosphere — where nitrogen is the most abundant element — to make fertilizer for use on the land. About half of all the inorganic nitrogen fertilizer ever used on the planet was used in the past 15 years, according to the report.

More nitrogen has meant increased crop yields in the past half-century, but it has also led to water quality problems. More fertilizer than what is needed by the crops is often applied, leaving more to run off the land. While the report said improvements in fertilizer use efficiency may have been made in the past decade, more progress can be made.

Besides fertilizer production, humans have altered the global nitrogen budget by burning fossil fuels, which release nitrogen oxides into the air (unlike nitrogen gas, nitrogen oxides can readily be converted to usable nitrate) and by planting nitrogen-fixing crops, such as soybeans and other legumes, which draw nitrogen directly from the atmosphere and put it into the ground.

Worldwide, human activities are now releasing as much nitrogen as is produced naturally. That is not evenly spread around the globe, though. In some areas, such as the Chesapeake Bay, scientists have estimated the amount of nitrogen could be six to eight times what naturally occurs.

And the rate is speeding up. Human fixation of nitrogen — including fertilizers, the combustion of fossil fuels and the production of nitrogen-fixing crops — more than doubled between 1960 to 1990, and continues to accelerate.

Likewise, with phosphorus, humans are generating huge additional amounts by mining underground deposits and releasing them as fertilizers, detergents and products. Globally, humans are releasing about 1.5 times more phosphorus than would occur naturally. Still, the primary culprit in coastal eutrophication is nitrogen, although phosphorus is a concern, the report said.

Despite the scope of the problem, the report said the nation lacks any comprehensive strategy for dealing with nutrient pollution. Several state, federal and regional programs exist — such as the Bay Program — but they often operate independently.

To clean up the coasts, the report said that maximum loads should be set for estuaries based on the needs of their resources. That is the approach endorsed in the Bay Program’s Chesapeake 2010 Agreement, which seeks to set new nutrient reduction goals based on the water quality needs of underwater grasses, fish and other resources.

Meeting nutrient reduction goals will require actions from all levels of government, and in most areas will require a mix of voluntary and mandatory programs, the report said. Some of the most effective nutrient control actions can be addressed at the state and local level, through programs that deal with urban stormwater runoff, farm runoff and wastewater treatment plant discharges.

But the report said federal leadership and resources are critical to success. Federal resources are needed to help identify the most critical nutrient sources, especially in large watersheds and those that span multiple states. In particular, the report said, the federal government must make sure that one region’s problem is not solved simply by shifting it to another region. To deal with the issue, the report called for the development of a national nutrient management strategy that can coordinate state, regional and national efforts.

Examples of problems the federal government needs to deal with are air pollution, which causes nitrogen oxides to be transported hundreds of miles from where they are released, and the transport of animal feed from one region to areas with large populations of hogs, chickens or cows that turn the feed into nutrient-rich waste.

Before World War II, farming communities tended to be self-sufficient; enough feed was grown locally to feed animals, and the manure was recycled onto crop lands. Today, the grain fed to animals is often grown hundreds of miles away with cheap nitrogen fixed from the atmosphere.

As a result, the nutrient-laden animal wastes accumulate far away, where there are not enough crop lands to absorb the nitrogen and phosphorus. An example of the problem cited in the report is the Bay watershed where, in 1939, animal waste could not have provided enough nutrients for all the watershed’s corn production. Today, the situation is reversed. Wastes from the growing animal population far exceed what is needed by the corn crop for most of the watershed, creating a problem of excess manure — and nutrients.

Citing studies that indicate up to 40 percent of the nitrogen in some coastal waters comes from atmospheric deposition, the report said air pollution is a “substantial” part of the nutrient problem that the federal government needs to address. The overall amount of nitrogen released through fossil fuel burning is dwarfed by the amount used as fertilizer, but the report pointed to several studies indicating that nitrogen from fossil fuel combustion seems to move through the landscape more readily than fertilizer placed on cropland.

Put another way, that means a pound of atmospherically deposited nitrogen is more likely to make it to coastal waters than a pound of nitrogen fertilizer. As a result, the report said, “nitrogen from from fossil-fuel sources may be disproportionately important to coastal eutrophication and other adverse impacts of nutrient overenrichment.”

The importance of air pollution to water quality — which is difficult to monitor — is likely to vary from watershed to watershed. In some areas, it may be unimportant, the report said, while in others it could be the most cost-effective way to reduce nitrogen runoff from the watershed. In any event, the report said that controlling air pollution to benefit coastal waters should be a “key consideration” in any reauthorization of the Clean Air Act.

Nutrient reductions alone should not be the focus of local and national strategies, the report added. It said that managers should emphasize the restoration of wetlands and other natural buffers that protect water quality and remove nutrients.

More emphasis should also be placed on water quality monitoring. Assessing whether conditions are getting better or worse means the nation needs a bigger monitoring commitment than the federal government has made, the report said.

That monitoring would also help rank coastal areas for their susceptibility to nutrient impacts — some estuaries get more nutrients than others, and some are more effective at trapping nitrogen and phosphorus, making them more vulnerable to nutrient pollution. Identifying those areas most at risk would help national targeting efforts, the report said.

The report, “Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution,” is available from the National Academy Press for $44.95, plus $4.50 shipping and handling. Call 1-800-624-6242.

100 Pounds of Nitrogen

The process used to extract nitrogen from the atmosphere was developed in Germany to meet its needs for nitrate in the production of munitions during World War I. It remains the most economical way to produce chemical nitrogen fertilizers, although in the past decade, ammonia (another form of nitrogen) derived from natural gas has become another source of nitrogen fertilizer. That has led to a dramatic increase in the amount of fertilizer used — and increased the potential for nitrogen to leak into the water.

On average in North America, this is what happens to every 100 pounds of nitrogen applied to cropland:

  • about 20 pounds leach into the surface or ground water.
  • about 2 pounds volatilize into the air as ammonia, possibly being redeposited somewhere else.
  • about 13 pounds are either denitrified (turned into inert nitrogen gas, effectively being removed from the system) or build up in the soil.
  • about 65 pounds are harvested in crops.

But that is not the end of the story.

Of the 65 pounds harvested in crops:

  • about 10 pounds are consumed directly by humans when they eat vegetables.
  • about 10 pounds are lost during food processing and end up in landfills or are discharged into surface waters from food-processing plants.
  • about 45 pounds are fed to animals as feed.

Still, that is not the end of the story.

Of the 45 pounds fed to animals:

  • about 15 pounds volatilize into the air from animal wastes, and may be redeposited somewhere else.
  • about 25 pounds remain in animals wastes which may be applied to farm land or accumulate somewhere in the watershed.
  • about 4 pounds are consumed by humans.

Of the nitrogen consumed by humans, either through vegetable crops or meat, some is released through wastewater treatment plants and septic systems.

Recommendations from Coastal Waters Report

  • Expand monitoring and assessment programs to provide better estimates of nutrients in waterways along the coast, identify their sources and evaluate the success of control efforts.
  • Exert federal leadership on issues that span multiple jurisdictions or threaten federally protected natural resources. In particular, the federal government should play a leading rule in setting limits on nutrients allowed in waterways and developing incentives and other programs to control nutrient releases.
  • Address overlaps and gaps in existing and proposed federal legislation. Some federal programs dealing with coastal issues overlap, while some important issues are not clearly addressed. Dealing with excess nutrients should get important consideration in reauthorizations of the Clean Water Act, the Clean Air Act and the Coastal Zone Management Act.
  • Provide data, information and technical assistance to state and local coastal authorities.
  • Develop a classification scheme to provide better information in the likelihood that excess nutrients will damage various coastal areas. That will help managers identify the most effective strategies for protecting different areas.