Millennium Ecosystem Assessment released by the United Nations in 2005 reported that the supply of nitrogen-containing compounds input to the world's oceans grew by 80 percent from 1860 to 1990. For individual coastal water bodies, the increase has been as high as 100 fold or more.
The Baltic Sea has one of the largest coastal water hypoxic zones in the world. In 2011 the area of water with dissolved oxygen concentration <2 mg/L was nearly 80,000 km2.
The use of synthetic fertilizers for the cultivation of nitrogen‐fixing crops and increased emissions of NOX have all contributed to soaring levels of reactive nitrogen in the environment.
Upwelling of low oxygen water can cause massive fish kills but also brings nutrient-rich waters to the surface to fuel fisheries production.
Over 500 coastal water bodies now report dissolved oxygen concentrations below 2mg/L