In yet another indictment of industrial farming methods and another threat to fish, researchers are reporting vast growth of ocean “dead zones.” Once rare, dead zones are multiplying and now total more than 400 around the world’s coastal waters, putting stresses on marine life by upsetting the underwater food chain, according to an August article in the journal Science.
Worse, these dead areas, created mainly by the dumping of agricultural fertilizers, have grown faster than ever in the last 12 years, increasing by one-third since 1995, according to the study by Professor Robert Diaz of the Virginia Institute of Marine Science.
“Dead zones were once rare. Now they’re commonplace,” Diaz says.
The dead zones form when excess nutrients, mainly fertilizers, cause the overgrowth of algae, which then dies and sinks to the bottom. Bacteria feed on the algae and the decomposition depletes the dissolved oxygen in the waters, leaving them unfit for fish and other marine life.
The largest dead zone in the United States has grown to an enormous 8,500 square miles at the mouth of the Mississippi River. Another dead zone is at the bottom of the main channel of Chesapeake Bay, each summer occupying about 40 percent of its area and up to five percent of its volume, according to researchers.
The situation is causing a decline in fishery production around the world, and can only be improved if farmers can avoid inadvertently adding so much nitrogen-rich fertilizers into runoff waters, say Diaz and collaborating researcher Rutger Rosenberg of the University of Gothenburg in Sweden (who is based near another huge dead zone in the Baltic Sea).
“Scientists and farmers need to continue working together to develop farming methods that minimize the transfer of nutrients from land to sea,” Diaz said, noting that many farmers would be amenable to helping because they could lower their costs for nitrogen fertilizers.
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