Dead zones don’t talk
Marine and coastal dead zones are the result of a phenomenon called hypoxia—a state of low dissolved oxygen that occurs when excess pollutants, such as nitrogen and phosphorus, accumulate in bodies of water. These nutrients feed blooms of algae that, when they die and decompose, deplete the oxygen in the surrounding water. Hypoxia is a silent killer, suffocating organisms that can’t escape the low-oxygen zone quickly enough, and causing others to flee.
As we wrote a year ago when the National Oceanographic and Atmospheric Administration (NOAA) predicted an “average” (roughly Connecticut-sized) Gulf dead zone, even average is not the same as normal. Nitrogen and phosphorus can come from many sources, but the largest are due to human activity, including sewage discharges and fertilizers from farm fields running off into rivers and streams.
In 2010, researchers at the University of Illinois showed that the problem of runoff from industrialized, corn-and-soybean intensive agriculture, with its system of underground drainage channels, dwarfs the impact of cities and other nutrient sources in the Midwest. Essentially, each year the Mississippi River and its many tributaries meandering through the Corn Belt quietly funnel a vast amount of agricultural pollution into the Gulf.