Nitous Oxide

Nitrogen makes up almost 80 percent of the air in Earth’s atmosphere. But, since the 1960s, it has had a growing — and increasingly unsustainable — presence in the planet’s waterways, as well.

The 1960s was when the use of chemical fertilizers began to take off. Over the years, those fertilizers washed into rivers, bays and, eventually, oceans, becoming a major contributor to coastal pollution and “dead zones.”

One of the world’s largest dead zones today stretches from the mouth of the Mississippi River west along Louisiana's Gulf Coast. In the Chesapeake Bay, an annual summer dead zone results in multiple fish kills a year. Meanwhile, airborne nitrogen pollution from vehicles and power plants is affecting inland, high-altitude lakes, according to a study in last week's issue of the journal Science.

The runoff from farms and from urban and suburban communities carries excess nutrients that eventually settle into coastal ecosystems. These nutrients provide food for huge algae blooms that both form a layer preventing the oxygen in the atmosphere from reaching deeper water and, when the algae die, use up the water’s oxygen as they decompose, thus creating the numerous dead zones that now dot the world’s seas.

In the Chesapeake Bay, the federal government is starting to take action.