Mains Practice Questions

Introduction:

Dead zones—regions in oceans or large water bodies where dissolved oxygen levels fall below the threshold required to sustain most marine life—have expanded rapidly in recent decades.

• Over 415 dead zones have been identified globally, from the Gulf of Mexico to the Baltic Sea and the Bay of Bengal.
• Their growth reflects the dangerous interplay of anthropogenic pressures and climate-induced ocean changes, posing a major threat to marine ecology, coastal livelihoods, and global environmental stability.

Body :

Causes of Expanding Dead Zones

• Anthropogenic Causes:
  • Nutrient Runoff (Eutrophication): Excessive agricultural use of nitrogen and phosphorus fertilizers, combined with sewage discharge and livestock waste, causes algal blooms. When algae die and decompose, oxygen levels plunge.
    • Example: Mississippi River nutrient runoff drives the Gulf of Mexico’s seasonal dead zone.
  • Untreated Wastewater and Industrial Pollution: Inadequate sewage treatment in growing coastal cities and effluents from industries introduce organic waste, heavy metals, and toxic chemicals that accelerate oxygen depletion.
  • Coastal Urbanisation and Habitat Loss: Land reclamation, construction, and dredging increase sedimentation and disrupt tidal flushing, trapping pollutants.
  • Overfishing: Decline of predator species affects marine food webs and nutrient cycling, making ecosystems more vulnerable to hypoxia.
• Climate-Related Causes:
  • Ocean Warming: Warm water holds less dissolved oxygen. Rising global temperatures intensify ocean deoxygenation, especially in tropical regions.
  • Water Column Stratification:Warming at the surface reduces mixing between oxygen-rich upper layers and deeper waters, expanding hypoxic zones.
  • Changing Currents and Weather Extremes:Weakened ocean circulation and increased floods deliver more nutrients into coastal waters, accelerating eutrophication.

Impacts on Marine Ecology

• Loss of Marine Biodiversity: Fish, crustaceans, and benthic organisms suffocate in hypoxic waters.
  • Example: The Baltic Sea dead zone has caused major declines in cod populations.
• Collapse of Food Webs: Death of bottom-dwelling organisms disrupts trophic chains, enabling hypoxia-tolerant invasive species to dominate.
• Coral Reef and Coastal Ecosystem Decline: Combined stress from warming and hypoxia leads to coral bleaching and seagrass degradation, reducing essential nursery habitats.

Impacts on Coastal Economies

• Decline in Fish Catch and Livelihoods: Artisanal fishers suffer reduced income, while commercial fisheries face long-term unsustainability.
• Impact on Tourism : Coral death, foul-smelling waters, and fish kills harm tourism-dependent economies in Southeast Asia, the Caribbean, and parts of India.
• Economic Losses and Food Security Risks: Coastal nations dependent on marine protein face rising food insecurity. Governments bear higher costs for restoration and health interventions.

Policy-Level Solutions

• National Policies:
  • Nutrient Management: Precision agriculture, fertilizer caps, wetland buffers, and stricter control on sewage and industrial effluents.
  • Integrated Coastal Zone Management (ICZM): Mangrove restoration, coastal land-use planning, and pollution zoning.
  • Strengthened Wastewater Treatment: Mandatory tertiary treatment in coastal towns.
• International and Regional Policies:
  • Stronger Climate Commitments (NDCs) to limit warming.
  • Regional cooperation through initiatives like the Bay of Bengal Programme.
  • Marine Spatial Planning and Blue Economy frameworks under UNCLOS.
  • Global hypoxia monitoring through UNEP and IOC-UNESCO.
• Scientific and Technological Measures:
  • Satellite-based algal bloom detection.
  • Autonomous ocean oxygen sensors.
  • Bioremediation using wetlands and microbial consortia.

Conclusion:

Expanding dead zones reflect a deeper crisis of ocean health, climate instability, and unsustainable coastal development. Addressing this challenge requires a multi-level strategy that integrates pollution control, climate action, sustainable fisheries, and international collaboration. Protecting ocean oxygen levels is essential for safeguarding biodiversity and coastal economies, and for achieving SDG 14 (Life Below Water).