WASHINGTON — The number of oxygen-starved ‘dead zones” in the world’s seas and oceans has risen more than a third in the past two years because of fertilizer, sewage, animal waste and fossil-fuel burning, United Nations experts said Thursday. Their number has jumped to about 200, according to new estimates released by U.N. marine experts meeting in Beijing. In 2004, U.N. experts put the estimate at 149 globally. The damage is caused by explosive blooms of tiny plants known as phytoplankton, which die and sink to the bottom, and then are eaten by bacteria which use up the oxygen in the water. Those blooms are triggered by too many nutrients ─ particularly phosphorous and nitrogen. The U.N. report estimates there will be a 14 percent rise in the amount of nitrogen that rivers are pumping into seas and oceans globally over a period from when the levels were measured in the mid-1990s to 2030. Oxygen starvation robs the seas and oceans of many fish, oysters, sea grass beds and other marine life ─ and the number of such dead zones has grown every decade since the 1970s. Not all of them persist year-round, as they […]