Explained: What are dead zones and how are they created?
Water bodies across the world are turning into dead zones, but do you know what these dead zones are and how are they created? Are these zones natural or man-made?
What are dead zones?
These are low-oxygen areas in the oceans and lakes across the world where aquatic life cannot survive. Only a few organisms can survive in hypoxic conditions, and other needs oxygen to survive, hence, these areas are called dead zones.
How are dead zones created?
When a water body receives too many nutrients such as phosphorus and nitrogen, it causes a change in the productivity of the ecosystem and is called eutrophication, a process due to which dead zones occur.
When the level of these nutrients is normal, it helps in the growth of cyanobacteria or blue-green algae, but when the levels of these nutrients are more than the required amount, cyanobacteria grow out of control, which can be dangerous. They deplete the water of oxygen before decomposing, thereby suffocating the species living in that area.
World's first dead zone
In the 1970s, the first-ever dead zone was identified on the East Coast of the United States-- The Chesapeake Bay. The high levels of nitrogen in the region were caused by two factors, urbanization and agriculture. Atmospheric nitrogen accounts for one-third of the nitrogen entering the bay.
The western part of the bay houses factories and urban centres that emit nitrogen into the atmosphere while the eastern part of the bay is a centre of poultry farming that produces a huge amount of manure.
Since then, the Chesapeake Bay Foundation has initiated a number of programs that aims to improve the bay's water quality and curb pollution runoff. The bay still has a dead zone and its size varies with the season and weather.
Let's dig deep into the process of Eutrophication to get a clear picture of how and why dead zones develop.
What is eutrophication?
Eutrophication is mainly due to the rapid increase in intensive agricultural practices, industrial activities, and population growth. The aforementioned processes emit a large amount of nitrogen and phosphorous which enter air, soil and water.
In developed nations such as the US, hefty use of animal manure and commercial fertilizers in agriculture have contributed much to eutrophication. Runoff from large agricultural fields enters creeks and bays because of rain or irrigation practices.
In developing countries such as India, untreated water from sewage and industry are the main causes of eutrophication. This is because in developing countries wastewater is often dumped into creeks, rivers, lakes, or the ocean.
The burning of fossil fuels and fertilizers release nitrogen in the atmosphere, which is redeposited on land and water through rain and snow, thereby contributing to eutrophication.
According to the estimates, around 10% or more oceans around the world are now dead zones. This year's Gulf of Mexico dead zone was the largest ever recorded. The dead zone is spread over 16,400 square kilometres.