Second of five articles

St. James Parish, La. -- The breeze blowing from the Mississippi River across sugar cane fields to Emelda West's house carries the sting of ammonia. Since West's girlhood, the nation's densest concentration of fertilizer factories has risen along the river upstream from New Orleans. The two closest to her home are among America's top 25 sources of toxic pollution.

Folks in West's neighborhood hardly ever swim in the river anymore. Even in stifling heat, they close their windows to shut out the breeze. "You can be blindfolded," the 74-year-old woman says. "When that wind is blowing across the river, oh, it's awful."

St. James Parish is the first link in a chemical connection that binds Gulf Coast fishermen to heartland farmers far up the Mississippi.

On its journey from the river's mouth to the fields of the Midwest, man-made nitrogen is a life-giver. The fertilizer manufactured here makes the Midwest the world's most bountiful granary.

But returning downstream, fertilizer becomes a destroyer. Runoff transforms the river into a nutrient pipeline loaded with almost three times as much nitrogen as 50 years ago.

And where the Mississippi meets the Gulf of Mexico, the excess nitrogen threatens to destroy an age-old chemical balance that supports a rich gumbo of sea life.

The imbalance starves the water of oxygen, creating a dead zone in the middle of the most important commercial and recreational fishing zone in the United States, according to a federal scientific task force.

The cycle of upriver abundance and downstream devastation raises fundamental questions that could affect every American: how much we pay for grains and meat, how much tax money is spent on environmental restoration, and how well some of the world's finest farmland will sustain future generations.

Farmers are taking a lot of heat for the riverborne pollution. But scientists say they are not ultimately to blame. The real driving force, they say, is a booming population that expects America's breadbasket to produce wave upon wave of cheap grain and meat, regardless of environmental costs.

For more than 25 million years, the Mississippi has been the Gulf of Mexico's life-giver, nourishing bayous and sea creatures. But because of the man-made changes, the downstream basin that some call "America's sea" is being force-fed a crippling overdose of nitrogen.

Barged and piped upstream to the farms of the Midwest, the nitrogen fertilizer washes into countless creeks and sloughs in the great river's drainage, which stretches from Glacier National Park in northwestern Montana to the Youghiogheny River in Western Maryland, embracing two-fifths of the land in the lower 48 states.

It takes about a week for a nitrogen molecule to flow downriver from Iowa to Louisiana, where nutrients pouring from the mouth of the Mississippi River create the Western Hemisphere's biggest "dead zone" -- a summertime swath of oxygen-starved water up to 2ยจ times the size of the Chesapeake Bay, where virtually nothing can live.

Worldwide, there are at least 50 of these oxygen-starved zones in oceans and bays, including parts of the Chesapeake. The Gulf of Mexico's zone is the world's third-largest, after Europe's Baltic and Black seas.

In a typical dead zone, an overdose of nitrogen fuels runaway algae blooms. The blooms consume bacteria in a process that sucks oxygen from the water. As oxygen levels drop, shrimp and fish swim away. Crabs, clams, snails, worms and other captive bottom-dwellers are killed. Sometimes there is no oxygen in the water at all.

The Gulf dead zone threatens the source of two-thirds of the nation's shrimp catch and more than half of its oysters. The Gulf region's annual catch is bigger than the combined seafood harvest of the Great Lakes and the southern Atlantic Coast, from the Chesapeake Bay to the Florida Keys.

Smokestack pollution, parking lot runoff and cities' sewage contribute to the problem. But farming and livestock manure are by far the largest sources, responsible for about three-fourths of the nitrogen, according to the federal task force.

Now government officials and environmentalists -- along with scientists, some farmers and even a few fertilizer salesmen -- are trying to reduce fertilizer pollution by prodding the Midwest's $98 billion agricultural industry for sweeping changes in the way it grows crops. But the nitrogen connection won't be broken easily.

"The agricultural community is in denial that they're a part of the problem," says L. D. McMullen, director of the Des Moines Waterworks, which draws its supply from the Mississippi Basin's most fertilizer-polluted river, the Raccoon. "It's like a tug of war going back and forth now. But there appears to be a glimmer of light. Things may be changing."