It has become apparent the last few years that everyday actions by humans can have profound effects that were not even thought possible a few decades ago.

A case in point, according to Donald Boesch, director of the the University of Maryland's Center for Estuarine and Environmental Studies, is nitrogen.

Though Boesch noted that "nitrogen is our friend" - it's the most common element in the air and a component of all living things - excess amounts of the wrong forms of nitrogen can cause problems.

Not only does it contribute to nutrient pollution in coastal waters where it causes algae blooms, but it can overfertilize the landscape causing some plant species to thrive at the expense of others. Meanwhile, nitrogen oxides in the atmosphere - a byproduct of fossil fuel combustion - is a major air pollutant.

"It's a triple threat," said Boesch, who moderated a panel discussion on air pollution and the Bay at the annual meeting of the Alliance for the Chesapeake Bay which took place in Alexandria, Va. on May 9.

Boesch, the former president of the Alliance, cited four major sources for excess nitrogen entering the region: increased use of "nitrogen fixing" plants such as soybeans, which "fix" nitrogen from the air into the soil; fertilizers; food imports from other parts of the country; and air pollution.

"If you want to deal with excess nitrogen entering the coastal waters and the Chesapeake Bay, you can't ignore any of these," he said. "They all have to be dealt with."

The realization that air must be dealt with has become evident in recent years as the Bay states struggle to achieve - and maintain - a 40 percent reduction in the amounts of two nutrients, nitrogen and phosphorus, that enter the Chesapeake.

About a quarter of all the nitrogen entering the Bay results from air pollution, most of which stems from the emissions of nitrogen oxides. About a third of NOx emissions comes from power plants, another third from motor vehicles and the rest from a variety of other sources.

Beyond the Bay, the issue of NOx control is taking center stage in Washington, where the EPA has proposed tougher air quality standards for ground level ozone - the key component of summertime smog - and fine particulates to protect human health. Because NOx contributes to both those problems, the standards would also benefit the Chesapeake.

The standards have drawn sharp criticism from affected industries - largely in Midwestern states - and many members of Congress.

A final proposal from the EPA was expected to be delivered to the White House for review in late May or early June, with a final decision expected by mid-July.

Controlling NOx has been a formidable task. In fact, while emissions of many air pollutants have declined in the past two decades, NOx emissions rose 14 percent nationwide from 1970 through 1995. Further complicating the problem is that NOx emissions can travel hundreds of miles.

Many power plants have escaped NOx controls aimed at reducing ozone pollution because they are located in areas that meet the EPA's air quality standards.

In fact, a recent report from the Natural Resources Defense Council found that 82 percent of all utility NOx emissions are in areas that attain the ozone standard. The same study found that 80 percent of all utility emissions are within 200 miles of a nonattainment area.

"They are close enough to be influencing the air quality in these nonattainment areas," said David Hawkins, NRDC senior attorney.

Because of that, the NRDC report found that many of the most polluting power plants were concentrated in the Midwest - just upwind of the Bay watershed.

"As a result of this Balkanized nonattainment system, it's not surprising that if you look at the emission rates by electric utility companies, you see some pretty dramatic differences," Hawkins said. "Tighter air quality standards [for ozone and particulates] will mean more nonattainment areas on the map, which means more areas that will need to focus on their homegrown sources and bring about reductions."

Elizabeth Bauereis, of the Baltimore Gas & Electric Co. and a longtime member of the Bay Program's Citizens Advisory Committee, acknowledged that utilities contribute to the problem but noted power plants have made major strides to reduce emissions.

Under acid rain rules contained in the 1990 Clean Air Act, many of the largest power plants have already installed "low NOx burners" which reduce NOx emissions by about 35 percent. EPA figures show a drop in NOx emissions from power plants - but not other sources - between 1994 and 1995, which Bauereis said could be an "early sign" that the acid rain rule is having an effect.

In addition, power plants within the Northeast Ozone Transport Region, which stretches from Northern Virginia through Maine, will be reducing NOx emissions by another 65 percent to help reduce the chronic ozone pollution problem that runs along the Interstate 95 corridor from Washington through Maine.

Ultimately, Bauereis said that addressing pollution from vehicles along that corridor will also be critical, noting that emissions from cars in major coastal metropolitan areas are more likely to be deposited directly on the Bay while emissions from power plants are more likely to land in the watershed, where much of the nitrogen is absorbed before reaching the Bay.

"I'm not saying we're not part of the problem," she said. "We are part of the problem. But we may be talking about a major source in the transportation sector - a third of the problem - that may be much tougher to get at than stationary sources."

Indeed, EPA data show that NOx emissions from motor vehicles has remained steady for more than two decades, despite tougher pollution control requirements. The chief reasons are that older, higher- polluting cars are slow to come off the highway and people are driving more than ever, largely offsetting the effectiveness of pollution controls on new cars. Also, the popularity of sport utility vehicles, classified as trucks and therefore subject to less stringent emissions controls, are helping to cause emissions levels to increase.

"It does not have an easy solution," said Bill Matuszeski, director of the EPA's Chesapeake Bay Program Office. "We have pushed the technology on automobiles and we can push it some more. But if you push beyond a certain point, you begin to run into two things: One is people's love of the internal combustion engine, and two is people's love of driving in general."

Trying to control the amount that people drive, he said, is "a major challenge, one that I'm not sure the Bay Program is capable and ready to take on."

Matuszeski said education about the issue is critical not only for the public, but also for bureaucrats working at state and federal levels to implement clean air policy.

For example, he said, cutting NOx emissions to reduce ozone pollution will have limited benefit to the Bay and other coastal water bodies if those reductions take place only during the summer, when ozone is a problem. Nitrogen enters water bodies from the sky all year, he said, so controls are needed during all seasons.

"We do have some issues that are our issues, and the air folks - if left to their own devices - will not deal with them," Matuszeski said.

Robert Perciasepe, the EPA assistant administrator for water, agreed that "there are significant institutional barriers" involved in merging air pollution control policies with water quality issues.

But, he added that, "I'm very optimistic that not only is the science growing, but the institutional barriers are weakening."

Perciasepe also said that it is unclear what legal means exist that allow air pollution to be regulated to benefit water quality. The Clean Air Act is written to protect human health, not water bodies.

The issue shows that pollution problems need to be dealt with more holistically, he said, rather than being viewed as air issues or water issues.

The issue is important not only for nitrogen deposition on coastal water, he said, but also for the air deposition of toxics in water bodies across the nation.

"We have many, many lakes in the United States that have fish advisories for mercury and there are no known sources of mercury discharges into those lakes," Perciasepe said. "The only real source is out of the air. And that is almost a global situation."