‘Dead zones,’ oxygen-depleted water, due to climate change
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 Harbour to the midchannel 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 of climate change, those behemoths might not seem so unusual, according to a new report by the Smithsonian. As the global temperatures warm, they will create 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 per cent of places where dead zones have been recorded are areas where average temperatures are expected to rise by about four degrees Fahrenheit 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 per cent of the world’s population lives in coastal areas,” said Keryn Gedan, codirector of a conservation programme at the University of Maryland and a researcher at the Smithsonian Environmental Research Centre in Cambridge, Maryland. “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.
“We just don’t know how much of this doubling is due to climate change or nutrient runoff,” Gedan said. More studies with more “sophisticated modelling” are needed to determine that, she said. 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. Algae that feeds on nutrient pollution that runs off farms in rains and pours out of over-flowing 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 currently starts around May, will likely start sooner unless steps are taken to reduce the over-abundance of nitrogen, phosphorous and other pollutants that flow into water. Gedan said the Chesapeake Bay cleanup plan is one example of how government can act to mitigate climate driven impacts that create dead zones. Previous research supports that assertion.
A study of the bay’s water quality by researchers for Johns Hopkins University and the University of Maryland Centre for Environmental Science found that dead zones have been reduced since pollution limits were first implemented in the 1980s. — WP-Bloomberg