DEAD ZONES AND EUTROPHICATION

DEAD ZONES AND EUTROPHICATION

Dead zones are low-oxygen, or hypoxic, areas in the world’s oceans and lakes caused due to eutrophication. Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. That is why these areas are called dead zones.

EUTROPHICATION

Causes:

• Point Sources: Pollution from contaminants that enter a waterway from a single identifiable source like stationary locations or fixed facilities.
  • Examples: Discharges from a sewage treatment plant or industrial plants and fish farms.
• Agriculture: Surface runoff from fertilized farms carry with them nutrients like nitrogen and phosphorus causing dense algal and plant growth in the water bodies.
• Natural Causes: Eutrophication can also take place naturally over thousands of years as the lakes grow old and get filled with sediments.
• Reduction of self-purification capacity: Over the years, lakes accumulate large quantities of solid material transported by the water.
• Invasive Species: It has been observed how invasive species altered a lake food web, amplifying the harmful effects of cultural eutrophication and impairing water clarity.
• Aquaculture: Aquaculture is a technique of growing shellfish, fish, and even aquatic plants (without soil) in water containing dissolved nutrients.

Reasons for Dead Zones:

• Eutrophication: Surface runoff of nutrients, especially from farms using inorganic fertilizers, can cause eutrophication and thus destroy the native marine ecosystem.
  • Example: The dead zone in the Gulf of Mexico, fueled by the nutrient-laden water spilling from the mouth of the Mississippi River, is the second-largest in the world.
• Algal Bloom: The overgrowth of algae consumes oxygen and blocks sunlight from underwater plants. When the algae eventually die, the oxygen in the water is consumed. The lack of oxygen makes it impossible for aquatic life to survive.
• Hypoxia: Hypoxia occurs when algae and other organisms die from a lack of oxygen and available nutrients. Hypoxia events often follow algal blooms. The cyanobacteria, algae, and phytoplankton sink to the seafloor and are decomposed by bacteria.
• Natural Reasons: The largest dead zone in the world, the lower portion of the Black Sea, occurs naturally. Oxygenated water is only found in the upper portion of the sea, where the Black Sea’s waters mix with the Mediterranean Sea that flows through the shallow Bosporus strait.

Ecological

• Algal Toxins: Harmful algal blooms sometimes create toxins that are detrimental to fish and other animals which are often bioaccumulating.
• Air Pollution: Airborne nitrogen compounds like nitrogen oxides contribute to the formation of other air pollutants such as ground-level ozone, a component of smog that can restrict visibility.
• Kelp and Underwater Forests: These ecosystems are vital for overall marine well-being, eutrophication can lead to its destruction and also the native species.
• Migration Routes: Large seas and lakes like the Aral Sea had been on migratory routes of birds, with eutrophication, the routes had been affected resulting in changes in population and migration.
• Water Suitability: Lakes and water bodies are sources of freshwater for animals and local human populations, thus eutrophication results in the deterioration of water quality.

Commerce

• Fishing Stocks: Hypoxia and anoxia as a result of eutrophication continue to threaten lucrative commercial and recreational fisheries worldwide.
• Tourism: It can reduce the tourism potential of the area, resulting in the loss of revenue for the region.
• Aesthetic Quality: Dead zones within water bodies ruin the aesthetic look and environment of the region.
• Impact on Agriculture: Water bodies which are sources of irrigation for farmlands, if eutrophied can impact agriculture.

Preventive Measures

• Composting: Eutrophication mainly arises from the use of nitrate and phosphate fertilizers. In a bid to address the phenomenon, composting can be used as a solution. Composting is the practice of converting organic matter such as food residues and decaying vegetation into compost manure.
• Reducing Pollution: Just like composting, limiting pollution is an easy and effective method of cutting back on the amount of nitrogen and phosphates discharged into water systems.
• Strengthening Laws: Strengthening laws and regulations against nonpoint water source pollution can substantially control eutrophication.
• Ultrasonic Irradiation: The world is constantly seeking advanced methods for resolving some of the environmental problems. When it comes to eutrophication, the use of ultrasonic irradiation is one such mechanism that has been exploited as an alternative solution to control and manage algal blooming.

Others

• Removal and treatment of hypolimnetic water: Deep water in contact with the sediments and rich in nutrients as it is in direct contact with the release source.
• Drainage of the first 10-20 cm of sediment: That is subject to biological reactions and with high phosphorus concentrations.
• Oxygenation of water: For reducing the negative effects of the eutrophic process and restoring the ecological condition like the absence of oxygen and toxic compounds’ formation deriving from anaerobic metabolism.
• Chemical precipitation of phosphorus: By adding iron or aluminum salts or calcium carbonate to the water, which gives rise to the precipitation of the iron, aluminum, or calcium orthophosphates, thereby reducing the negative effects arising from the excessive presence of phosphorus in the sediments.