April 8 - New sediment samples from the Gulf of Mexico show that the area's seasonal dead zone has increased in area and duration in the past 50 years.

The phenomenon, known as hypoxia, occurs naturally every year as nutrients wash into the Gulf from the Mississippi River, and phytoplankton populations increase with the excess nutrients. When the phytoplankton die, the decomposition process depletes the oxygen from the water, suffocating or forcing many animals to abandon the zone.

This seasonal dead zone has occurred annually since the 1800s, but recent work from the U.S. Geological Survey shows that the levels of phytoplankton have vastly increased since 1960, when commercial fertilizer use became common on farmlands along the Mississippi River.

A 2000 National Research Council report examines the problems of nutrient over-enrichment in coastal waters, including a look at the Gulf of Mexico's problems with hypoxia. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution proposes both immediate local action by coastal managers and a longer-term national strategy.

• Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution (2000)

• U.S. Geological Survey's The Gulf of Mexico Hypoxic Zone
• EPA's Site on Hypoxia in the Gulf of Mexico