Question

3. What happens to anoxic dead zone in coastal waters? Oxygen-rich water is mixed down in the fall when the stratification breaks down cyanobacteria begin to photosynthesis and the historic process of developing an oxygen-rich atmosphere on earth is replaced

Answer 1

Dead zone:

Dead zone are the areas of water bodies typically in ocean also in river and lakes which do not have enough oxygen to support life. This condition is known as hypoxic – lacking oxygen.

Dead zone is caused due to eutrophication – increase in chemical nutrients in water, which cause excessive bloom of algae that destroys the underwater oxygen level.

Nitrogen and phosphorous from agriculture run off is the major cause, sewage, industrial waste are also the cause of dead zones.

This occurs mostly near the coastal areas where the aquatic life is highly concentrated.

Cyanobacteria, green algae, coccolithophores, dinoflagellates and diatom algae are the commonly found algal groups.

The biomass degradation by bacteria of dead fish and dead algal blooms consumes more oxygen in the water, which creates hypoxic condition.

Natural cause of dead zone is due to coastal upwelling and change in water and wind circulation patterns.

Dead zone is seen in Gulf of mexico, along the East coast region.

Effects of Dead zone:

Low levels of oxygen has effect on the organisms

Fish has reduced size of the reproductive organs, low egg count in ovaries and lack of spawning.