Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning.
Dead zones are areas of water bodies where aquatic life cannot survive because of low oxygen levels. Dead zones are generally caused by significant nutrient pollution, and are primarily a problem for bays, lakes and coastal waters since they receive excess nutrients from upstream sources.
Types of Dead Zones
Permanent dead zones occur in very deep water. Oxygen concentrations rarely exceed 2 milligrams per liter. Temporary dead zones are hypoxic regions that last for hours or days. Seasonal dead zones occur every year during the warm months.
Hot temperatures can make dead zones worse by warming a layer of surface water that locks colder, denser water below where oxygen from the surface can't mix in. Heavy rainfall increases the amount of pollution washed into waterways.
Nutrient run-off triggers dead zones
(Read about a large dead zone in the Baltic Sea.) The largest dead zone in the world lies in the Arabian Sea, covering almost the entire 63,700-square mile Gulf of Oman. The second largest sits in the Gulf of Mexico in the United States, averaging almost 6,000 square miles in size.
Excess nutrients that run off land or are piped as wastewater into rivers and coasts can stimulate an overgrowth of algae, which then sinks and decomposes in the water. The decomposition process consumes oxygen and depletes the supply available to healthy marine life.
A new study in the March 23 issue of Science now estimates that even if the nitrogen runoff was completely eliminated, it would still take at least 30 years for the dead zone to recover. Nitrogen runoff from agriculture around the Mississippi Basin has been steadily draining into the Gulf of Mexico for decades.
Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. That is why these areas are called dead zones. Dead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen.
Fortunately, dead zones are reversible if their causes are reduced or eliminated.
Warmer waters will increase metabolism of marine creatures, thereby increasing their need for oxygen. Warmer temperatures and increased runoff of freshwater will increase stratification of the water column, thus further promoting the formation of dead zones.
The key to reducing the size and number of low-oxygen dead zones in coastal waters is to reduce the input of nutrients into estuaries and the coastal ocean. Nutrient-reduction strategies are a key part of efforts to restore the health of Chesapeake Bay.
What types of dead zones (hypoxia) exist? Different water bodies can experience hypoxia for long or short periods. Scientists classify water bodies in four broad categories: Permanent, temporary, seasonal, and diel cycling.
There are at least 700 known dead zones, and even if all of them were the size of the one in the Arabian Sea—over 60,000 square miles—that would account for about one percent of the world's total ocean area.
Use of chemical fertilizers is considered the major human-related cause of dead zones around the world. However, runoff from sewage, urban land use, and fertilizers can also contribute to eutrophication.
The occurrence of dead zones has doubled in frequency every decade since the mid-1900s. Rising temperature is likely to make the situation more severe. Not only does warmer water hold less dissolved oxygen, but it sits at the top of the water column like a balloon that is hard to submerge.
Dead zones most often occur during the warm summer months. This is due to the amount of rainfall that occurs during the spring, which washes excess nutrients off the land and into the water, as well as hot temperatures and weak winds in the summer which cause the dead zone to grow larger and last longer.
In terms of obstructions, a few common culprits include thick walls or bulky metal furniture like filing cabinets or refrigerators. Other devices that rely on radio waves, like baby monitors or connected security systems, can cause interference—and it's the same case with signal-producing appliances like microwaves.
How does the dead zone affect my health and those afternoon summer swims I love to partake in? The dead zone doesn't directly affect humans perse, since we don't rely on getting oxygen from the water. BUT, high levels of polluted runoff are a concern.
The majority of the world's dead zones are along the eastern coast of the US, and the coastlines of the Baltic States, Japan and the Korean Peninsula. Notable examples include the Gulf of Mexico and the Baltic Sea. The Gulf of Mexico has a seasonal hypoxic zone that forms every year in late summer.
Lou Codispoti explains that the increased amount of nitrous oxide (N2O) produced in low-oxygen (hypoxic) waters can elevate concentrations in the atmosphere, further exacerbating the impacts of global warming and contributing to ozone "holes" that cause an increase in our exposure to harmful UV radiation.
If you are continuing to experience “drift”, “slowturn” or unintended thumbstick movement, it is possibly because the game you are playing has tight “deadzone” settings or you may have modified those settings. Resolving the problem is as easy as adjusting the “deadzone”.
Deadzone is a setting that is primarily used for combating your controller's stick drift; controlling how much you have to move your analog stick for the game to register movement. Most of the top players use the default Deadzone (0.05), but Biffle and Booya use 0.03, while SuperEvan and Zlaner use 0.2.
The deadzone is super helpful when your sticks start to drift, you can increase your deadzone, you lose a little responsiveness but your controller is still going to work.
Diaz first found scientific reports of dead zones in the 1910s, when there were 4. Globally, the number of dead zones has approximately doubled each decade since the 1960s. The first dead zone in Chesapeake Bay was reported in the 1930s.
Dead zones can be categorized based on their duration. They can be Permanent, which are limited to very deep water. If they last for only hours or days, they are considered Temporary dead zones. Seasonal dead zones occur yearly during warmer months.