IAS Gyan

Daily News Analysis


20th June, 2024 Geography


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Picture Courtesy: https://www.indiatimes.com/technology/science-and-future/there-s-a-dead-zone-in-the-arabian-sea-bigger-than-tamil-nadu-and-it-s-still-growing-344701.html

Context: The National Oceanic and Atmospheric Administration (NOAA) recently forecasted an above-average summer "dead zone" in the Gulf of Mexico.


  • NOAA predicts the dead zone to be around 5,827 square miles, which is larger than the long-term average of 5,205 square miles over the past 37 years.
  • The dead zone is primarily caused by excess nutrient pollution entering the Gulf of Mexico from the Mississippi-Atchafalaya River Basin. These nutrients, primarily nitrogen and phosphorus, originate from various human activities such as agricultural runoff and urban discharges.

The National Oceanic and Atmospheric Administration (NOAA) is a US scientific and regulatory agency responsible for forecasting weather, monitoring oceanic and atmospheric conditions, managing fishing and protection of marine mammals and endangered species in the US exclusive economic zone. 

About Dead Zone

  • Dead zones are areas in oceans or large lakes where the oxygen levels are so low (hypoxia) that they cannot support most marine life. These zones can cause significant disruptions to marine ecosystems, leading to declines in fish and other marine species.

Causes of Dead Zones

Nutrient Pollution

  • Nutrient pollution is a primary cause of dead zones, largely resulting from human activities. This includes the introduction of excess nutrients like nitrogen and phosphorus into water bodies, which promote the overgrowth of algae. When these algae die and decompose, the process consumes oxygen, leading to hypoxic conditions.
  • Agricultural Runoff:
    • Fertilizers: The use of nitrogen and phosphorus-rich fertilizers in agriculture is a major contributor to nutrient pollution. Rainwater can wash these nutrients from fields into nearby water bodies.
    • Animal Manure: Livestock operations generate large amounts of manure, which can also be a significant source of nitrogen and phosphorus if not managed properly.
  • Urban Runoff:
    • Sewage: Untreated or inadequately treated sewage contains high levels of nutrients that can enter waterways.
    • Detergents: Phosphates in detergents can contribute to nutrient loads in water bodies.
  • Industrial Discharges: Industrial processes can release nutrient-rich effluents into rivers and lakes, exacerbating the problem of nutrient pollution.

Physical Factors

  • Physical conditions in the water can also influence the development and persistence of dead zones.
  • Stratification:
    • Temperature Differences: Warmer surface waters and cooler bottom waters can create layers that do not mix, preventing oxygen from reaching deeper layers.
    • Salinity Differences: Variations in salinity can similarly lead to stratification, contributing to hypoxia in bottom waters.
  • Climate Change:
    • Rising Temperatures: Increasing global temperatures can exacerbate stratification and reduce the solubility of oxygen in water.
    • Altered Weather Patterns: Changes in precipitation and storm patterns can affect nutrient runoff and the physical mixing of water layers.

Process Leading to Dead Zones

  • Eutrophication: It is the process by which water bodies become enriched with nutrients, particularly nitrogen and phosphorus. This enrichment leads to excessive growth of algae and other aquatic plants.
  • Nutrient Enrichment: The primary sources of nutrient enrichment are agricultural runoff, urban runoff, and industrial discharges. These nutrients are typically derived from fertilizers, sewage, detergents, and animal manure.
  • Increased Algae Growth (Algal Blooms): The influx of nutrients into a water body promotes the rapid growth of algae, leading to what is known as algal blooms. These blooms can cover large areas and severely affect water quality.
  • Algae Die and Decompose: When the algal blooms die, they sink to the bottom of the water body. The decomposition of these algae is carried out by bacteria, which consume large amounts of oxygen during the process.
  • Bacterial Decomposition Consumes Oxygen: The decomposition process by bacteria significantly reduces the oxygen levels in the water. This consumption of oxygen leads to a decrease in available dissolved oxygen, creating hypoxic (low oxygen) or anoxic (no oxygen) conditions.
  • Oxygen Depletion: The depletion of oxygen in the water column results in the formation of hypoxic or anoxic zones, commonly referred to as dead zones. These areas are unable to support most marine life due to the lack of oxygen.

Effects of Dead Zones

  • Marine Life: Many fish and invertebrates cannot survive in low oxygen conditions, leading to mass die-offs. Mobile species like fish and shrimp may migrate out of the hypoxic zone in search of oxygen-rich waters, disrupting their natural habitats and behaviours.
  • Biodiversity Loss: Hypoxic conditions can lead to a significant reduction in species diversity, as only those species that can tolerate low oxygen levels survive. The loss of certain species can disrupt the entire food chain, affecting predator-prey relationships and overall ecosystem stability.
  • Fishing Industry: The decrease in fish populations due to hypoxia affects commercial and recreational fisheries, leading to reduced catches. The decline in fish populations can result in significant economic losses for communities that rely on fishing as a primary source of income.
  • Tourism: Coastal areas affected by dead zones may see a decline in tourism revenue as water quality deteriorates, making these areas less attractive to tourists. Recreational activities such as boating, swimming, and fishing can be adversely affected by the poor water quality and reduced marine life in dead zones.

Preventative Measures

Sustainable Farming

  • Crop Rotation and Diversification: Planting different crops in succession on the same land to improve soil health and reduce dependency on chemical fertilisers. This can help lower the runoff of nutrients like nitrogen and phosphorus.
  • Cover Cropping: Growing cover crops, such as clover or rye, during off-seasons to prevent soil erosion, improve soil fertility, and reduce nutrient runoff.
  • Precision Agriculture: Utilizing technology such as GPS and soil sensors to apply fertilisers more efficiently, reducing excess application and runoff.
  • Buffer Strips: Planting strips of grass, shrubs, or trees along the edges of agricultural fields and waterways to intercept pollutants before they enter water bodies. These buffers trap sediments and absorb nutrients from runoff.

Urban Planning

  • Rain Gardens and Bioswales: Landscaped areas designed to absorb and filter stormwater, reducing the volume and velocity of runoff entering storm drains and water bodies.
  • Green Roofs: Roofs covered with vegetation that absorb rainwater, provide insulation and reduce the urban heat island effect.
  • Permeable Pavements: Pavement materials that allow water to infiltrate through the surface, reducing runoff and promoting groundwater recharge.
  • Advanced Treatment Technologies: Upgrading wastewater treatment plants to include processes such as biological nutrient removal (BNR) and advanced oxidation, which can significantly reduce the concentrations of nitrogen and phosphorus in effluent.

Habitat Restoration and Creation of Marine Protected Areas (MPAs)

  • Re-establishing wetlands that have been drained or degraded. Wetlands act as natural filters, trapping sediments and absorbing excess nutrients before they reach larger water bodies.
  • Establishing protected areas in marine environments where human activities are restricted or managed to preserve ecosystems and biodiversity.
  • According to the International Union for Conservation of Nature (IUCN), MPAs contribute to the recovery of marine habitats and can enhance resilience against nutrient pollution and hypoxia.

International Agreements

●The International Convention for the Prevention of Pollution from Ships (MARPOL) is an international agreement aimed at minimising pollution from ships. Annex IV of MARPOL addresses the discharge of sewage and mandates the use of sewage treatment plants on ships.

●Various regional agreements, such as the Helsinki Convention for the Baltic Sea and the OSPAR Convention for the North-East Atlantic, aim to protect marine environments from pollution, including nutrient pollution.


  • Dead zones in aquatic environments require a multifaceted strategy involving strict regulations, public awareness, and scientific innovation. Sustainable agricultural practices, urban wastewater treatment, and habitat restoration can reduce nutrient pollution. International cooperation and research investment are crucial for developing effective solutions and ensuring marine ecosystem health in the long term.




Ocean service


Q. What are the primary factors that lead to the formation of dead zones, areas in aquatic ecosystems where oxygen levels are severely depleted, thereby threatening marine life?

A) Elevated levels of oxygen

B) Insufficient levels of carbon dioxide

C) Excessive quantities of nutrients like nitrogen and phosphorus

D) The presence of natural minerals

Answer: C