Despite growing concern over the last two decades about the low-oxygen “dead zone” that emerges each summer in the fisheries-rich Gulf of Mexico, the nitrate pollution at the root of the problem continues to rise.
That’s the upshot of a study just released by the U.S. Geological Survey (USGS), which monitored nitrate trends at eight key locations in the Mississippi River Basin over the 30-year period from 1980-2010.
At the outlet where the Mississippi empties into the Gulf of Mexico, nitrate levels rose 12 percent just between 2000 and 2010.
High levels of nitrate –sometimes referred to as a “nutrient,” because it encourages plant growth – can cause an abundance of algae in water bodies, which in turn robs water of oxygen as bacteria break down the excess organic matter.
Fish and other aquatic animals get increasingly stressed as the oxygen level declines. The point at which they begin to suffocate varies, but stress is usually evident when oxygen drops below 3 milligrams per liter of water. (For comparison, oxygen levels in air are about 280 milligrams per liter.)
Last summer, the Gulf of Mexico’s dead zone spanned 5,840 square miles, an area about the size of Connecticut