How do dead zones occur

Once a dead zone forms, other factors can influence its size and duration. For example, wind can mix oxygen from the surface into deeper water and help break up dead zones. But while weather can play a role, the best way to reduce algal blooms and dead zones is to stop pollution at its source by implementing the Chesapeake Clean Water Blueprint.

The location, extent, and severity of the dead zones can change throughout the year, usually peaking during the summer months. On average , the Chesapeake Bay dead zone covers between 0. Dead zones are not a direct threat to humans, but they are extremely harmful to fish, crabs, oysters, and other aquatic animals that humans rely on for seafood and livelihoods.

In addition, the algal blooms that fuel dead zones can be detrimental to tourism and recreation because they can make water unsafe for swimming, release unpleasant odors, and cause fish kills that can wash hundreds of dead fish onto beaches. Shrinking the dead zone is one of the primary goals of the Chesapeake Clean Water Blueprint, the science-based plan to reduce pollution and restore the Bay to health.

On October 28, , the Chesapeake Bay Program announced that the Maryland Department of Natural Resources reported that the dead zone was the second smallest observed in the Maryland portion of the Chesapeake Bay since monitoring began in The Bay Program also announced that researchers from the Virginia Institute of Marine Science reported the dead zone there was smaller than 80 percent of dead zones reported in the 35 previous years.

The best way we can reduce algal blooms and dead zones is to implement the Blueprint by putting in place best management practices that control pollution from urban and agricultural lands, as well as wastewater treatment plants and septic systems. This includes things like planting trees as buffers along rivers and streams, improving soil health on farms, reducing the amount of hard surfaces in cities, and upgrading wastewater treatment plant technology.

Together, and only together, can we prevent dead zones and ensure vibrant habitats for aquatic life in the Chesapeake Bay. Restoring the Bay and preventing future dead zones go hand in hand. Here are actions you can take to fix the dead zones in the Chesapeake Bay:. Stay up to date about the Bay! Sign Up. Cod eat sprat s, a small, herring-like species that eat microscopic zooplankton , which in turn eat algae.

Fewer cod and more sprats mean more algae and less oxygen. Categorizing Eutrophic Systems Scientists have identified dead zones worldwide.

Hypoxic areas have increased dramatically during the past 50 years, from about 10 documented cases in to at least in As a result of the dramatic increase in dead zones, scientists have categorized coastal systems experiencing any symptoms of eutrophication. An area of concern is a coastal system that exhibits effects of eutrophication, such as elevated nutrient levels, harmful algal blooms, and negative changes in the benthic community.

Areas of concern are at the most risk of developing hypoxia. Major concentrations of areas of concern are located along the western coast of Central and South America, and the coastlines of Great Britain and Australia.

There are areas of concern around the world. A system in recovery is one that once exhibited low oxygen levels and hypoxia, but is now improving. For example, the Black Sea once experienced annual hypoxic events, but is now in a state of recovery.

These are the results of better industrial and wastewater controls. There are only 13 coastal systems in recovery around the world. Natural Dead Zones Not all dead zones are caused by pollution. The largest dead zone in the world, the lower portion of the Black Sea, occurs naturally.

Oxygenated water is only found in the upper portion of the sea, where the Black Sea's waters mix with the Mediterranean Sea that flows through the shallow Bosporus strait. Also called cyanobacteria and in freshwater habitats pond scum. Carbon dioxide is also the byproduct of burning fossil fuels.

Also called blue-green algae even though it is not algae and in freshwater habitats pond scum. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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An element is a substance that cannot be broken down into a simpler format. They are distinguished by a unique atomic number. The elements are organized by their atomic number in the periodic table, which highlights elements with similar properties. Water is an example of a compound, a mixture of two or more elements, and is created when two hydrogen atoms bond to an oxygen atom. Use these resources to examine the properties and uses of elements and compounds. Dead zones are areas of the oceans that lack enough dissolved oxygen to support life.

The water cycle is part of our everyday lives, but climate change may have dire consequences for everyday water access. Hypoxic conditions continue to plague the Gulf of Mexico, however, with matters made worse by pollution unleashed by Hurricane Katrina and the BP oil spill, as well as by a federal push to increase Midwest corn production, which effectively loads even more algae-inducing nutrients into the already overloaded system.

But with industrial and agricultural activity throughout Gulf and Midwestern states only increasing—and Mother Nature not making the job any easier—the task force has an uphill battle on its hands to say the least. Send questions to: earthtalk emagazine. Subscribe : www. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options.