‘Dead zones’ won’t stay rare, study finds
Three years ago, the Chesapeake Bay was hit by an unusually large “dead zone,” a stretch of oxygen-depleted water that killed fish from the Baltimore Harbor to the mid-channel of the Potomac River and beyond, about a third of the bay.
Another giant dead zone returned last summer, smaller than the first but big enough to rank as the estuary’s eighth largest since state natural resources officials in Virginia and Maryland started recording them in the 1990s.
In a future with climate change, those behemoths might not seem so unusual, according to a new report by the Smithsonian. As the global temperatures warm, they will cause conditions such as rain, wind and sea-level rise that will cause dead zones throughout the world to intensify and grow, the report says.
Ninety-four percent of places where dead zones have been recorded are areas where average temperatures are expected to rise by about 4 degrees by the turn of the century. In addition to the Chesapeake Bay region, that includes the Black and Baltic seas, and the Gulf of Mexico, where a dead zone equal to the size of Connecticut took shape in August.
“Over 40 percent of the world’s population lives in coastal areas,” said Keryn Gedan, co-director of a conservation program at the University of Maryland and a researcher at the Smithsonian Environmental Research Center in Cambridge, Md. “We depend on these resources. No one wants to see a fish kill or harmful algal bloom at their local beach.”
Gedan was a co-author of the study with Andrew Altieri of the Smithsonian Tropical Research Institute in Panama. They found that the number of dead zone events have doubled each decade since the 1950s and that humans have likely contributed to their growth in intensity and size.
Dead zones are summer plagues that happen when waters warm. As the water temperatures increase, three key events pave the way for a catastrophe that kills any fish, crab, oyster and shrimp that relies on oxygen.
The metabolism of animals in the water revs up, turning them into hungry eaters that use more oxygen as they search and feed on algae that feeds on nutrient pollution that runs off farms in rains and pours out of overflowing sewers bloom and perish in a rapid and enormous death spiral. Microbes feed on the dead algae in a frenzy that sucks out oxygen to a point where it can no longer sustain life.
In a warming world, this process, which starts around May, will likely start sooner unless steps are taken to reduce the overabundance of nitrogen, phosphorous and other pollutants that flow into water.