When the oxygen level of an area of the water body becomes low, that area is called Dead Zone. This area is also known as Hypoxic Area. Normally the concentration of dissolved oxygen in oceanic water is 9 ml of oxygen/L in the polar region and 4 ml of oxygen/ L in the equatorial region. It helps to make a balance of Marine eutrophication. The most serious threat from eutrophication is seen when the dissolved oxygen (DO) levels in bottom waters are started decreasing. Due to this incident, planktonic algae die. The hypoxic condition occurs when dissolved oxygen falls less than 2 ml of O2/liter. So in the Dead Zone, marine life cannot outlive it. Dead Zones are not a permanent situation in an area, if their causes are eliminated or reduced, Marine life will increase gradually.
Recently scientists identified a new dead zone in the Bay of Bengal in the Indian Ocean, this is typically a large area of water from 50 to 100 meters below the sea surface, to depths of many hundreds of meters, currently, the largest dead Zone was found under the Gulf of Mexico which is measured around 6,334 square miles.
Causes of Dead Zone
1. Raise of Temperature
There has much evidence which suggests that due to global climate change the average temperature of the oceanic region is also increasing. As a result, the average low-oxygen level of the ocean is decreasing. It influences the creation of dead zones.
- Cold water contains a high concentration of dissolved oxygen while hot water contains a low concentration of dissolved oxygen. Due to global warming, the contamination of dissolved oxygen in ocean water is decreased. As a result, part of that region of the ocean becomes a Dead Zone.
- When temperature increase by 1°C the dissolved oxygen of ocean water decrease by 2%.
- When the ocean water becomes warm, marine creatures increase their metabolism rate. In such a situation, marine creatures need more dissolved oxygen, hence, the level of dissolved oxygen in the oceanic body decrease.
- Normally, due to the water column, warm water moves toward the cold water region and cold water moves toward the hot water region, which indirectly creates suitable environments for the formation of the Dead Zone.
2. Oxygen Depletion
- Oxygen Depletion increases the causes of mortality of Marine creatures in the coastal water region. As a result, the larger part of the oceanic region turned into a Dead Zone. In marine life, Microorganisms get their food from biodegradable substances. When biodegradable substances are increased, the number of microorganisms also increases.
- In aquatic environments, as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system, such phenomenon is known as Oxygen depletion.
- When oxygen depletion occurs in a particular area of an ocean, environments for aquatic creatures are becomes challenging to survive, such as low-concentration oxygen areas also known as Hypoxic regions.
3. Nutrient Pollution:
- The maximum concentration of phosphorus and nitrogen in the water body may cause the excessive growth of algae in a very narrow time period. These excessive numbers of algae consume dissolved oxygen from the oceanic body and work as a shade. This shade block the sunlight. Due to the lack of oxygen, aquatic life cannot survive and they shift from that place.
- Increased numbers of algae produce toxins that are also harmful to aquatic life as well as to human beings. It mainly happens in the coastal region, excess toxic become the major cause of illness and contaminate drinking water for both human and aquatic life.
- In every summer season, nutrient Pollution is seen in the basin of the Mississippi River.
Impact of Dead Zone:
1. Impact on Global Warming
When oxygen Depletion occurs, it increases the formation of nitrous oxide. N²O is one of the important components of greenhouse gas and among the greenhouse gases, it is 300 times more powerful than carbon dioxide. So, due to the increase of nitrous oxide in the environment, global warming also increases as well as the average temperature of the ocean water also increases.
2. Impact on Coral
Corals play an important role in the Marine ecosystem. It works as a shelter for many oceanic creatures. Corals cannot survive in the ocean where the average dissolved oxygen is less than 2 ml/lit.
3. Impact on Human
The human also suffers at the economic level due to the Dead Zone. In the year 2016, when a toxic tide hit the coastal region of Chile. It smashed 20% of salmon fish. For this incident, Chile faced a loss of 1 billion dollars. This incident happened due to the Dead Zone situated nearby Chile. The toxic water came from this region which polluted the coastal water of the country Chile.
4. Impact on Fish
Dead Zone is working as an invisible Dead trap. There is no way to escape the Marine creature. Even fish cannot detect the Dead Zone before entering the region. Due to lack of oxygen, when fishes enter the Dead Zone, at first they lost consciousness. Soon after they died.
Number of Dead Zones
- There are many Dead Zones around the world. In the year 1970, the first Dead Zone was identified in the Chesapeake Bay of the USA.
- Around 416 Dead Zones have been identified by scientists around the world. After 1970 this number has increased day by day. The maximum Dead Zones are found on the coastline of the Baltic state, the East Coast of the USA, the Korean peninsular, Japan peninsular, etc. Almost 232 areas around the world are concerned with the risk of the Dead Zone.
Prevention or Reduce of Dead Zones
Dead Zone is a reversible process. Once the causes are removed, the zone becomes habitable for Marine species. For example, many regions of the Black Sea becomes Dead Zone. But after the 1990s, the Dead Zones of this area disappeared. The Rhine river became the Dead Zone during the time of the industrial revolution. But, when sewage and industrial emissions are reduced, the Dead Zones of the Rhine river disappeared. Now, in the world, there is 14 Hypoxic region which is recovered.
- People should keep away animal waste or manage livestock waste from the water body. Too much phosphorus and nitrogen may damage the water ecosystem.
- Some kinds of plants such as cloves Grass or grains minimize soil erosion and recycle excess soil nutrients. They absorb excess nutritional waste before they meet at a water body. It is helpful to balance the water ecosystem and reduce the probability of spreading dead zone.
- Planting plants around the border water bodies can help by absorbing or filtering out nutrients before they reach a water body.
- Managing soil erosion, soil compaction, and soil runoff, can reduce nutrient drain from agricultural fields and help to prevent the degradation of the water in the local water bodies.