‘Dead zones’ – coming to a coast near you


The ‘dead zone’ that’s making life difficult in Chesapeake Bay for blue crabs, fish and shellfish has plenty of company, it seems. A new study led by a Virginia marine scientist reports a one-third increase worldwide over the last 12 years in the number of such dead spots on the sea bottom – where there’s too little oxygen in the water for most fish and shellfish.
The study published in the Aug. 15 issue of Science found 405 dead zones in coastal waters globally.  The total sea bottom deprived of life-sustaining oxygen is about 95,000 square miles – roughly the size of New Zealand. 
The authors, Robert Diaz of the Virginia Institute of Marine Science and Swedish researcher Rutger Rosenberg, say dead zones are the "key stressor" in coastal waters, on a par with overfishing, habitat loss and toxic algae blooms.
The biggest dead zone in this country is in the Gulf of Mexico at the mouth of the Missisisippi River, the report notes.  The one in the Chesapeake forms every summer and spreads over up to 40 percent of the main bay’s bottom.
Dead zones form when too many nutrients – nitrogen and phosphorus – get into the water and feed algae blooms.  The massive growths of tiny water-borne plants suck the oxygen out of the water after they die and sink to the bottom, where they decompose.  The nutrients come from fertilizer and human and animal wastes getting into the water, along with fallout from burning coal, oil and gasoline.
Dead zones were once rare, the researchers say. The first one in the Chesapeake, for instance, was reported in the 1930s.  Go here to see a Google map showing the zones around the world.