Hypoxia and Medicine

hypoxic or "dead zone"?

I am writing a paper on the Gulf of Mexico's hypoxic or "dead zone". I am confused about what causes the oxygen to be depleted. Some people say it is caused by the overwhelming nutrients like nitrogen running into the gulf. others say its from algea blooms dying off and sinking to the bottom where bacteria consume them and use up all the oxygen. and finally some say that its from the fresh water floating on top the salt water and not alowing oxygen to enter through to the salt water.

Public Comments

1. Nitrogen and phosphorous in the runoff water that gets into the Mississippi leads to runaway growth of algae. Once these algae die, they sink to the bottom, and along the way the microorganisms (mostly bacteria) that digest the dead algae use up a lot of the dissolved oxygen in metabolizing the dead algae food they are consuming (just as we consume atmospheric air as we metabolize our food). This is what causes the hypoxia of the water. The other thing is that during the summer months, the turbidity of the water increases due to higher flow and increased erosion on land from rainfall (this rain actually fell in the late spring and is just now flowing out to sea). This turbidity also makes it hard for a lot of fish to breathe, and it cuts down on the amount of photosynthetic photo-plankton that can effectively "do their thing", as only photo-plankton on the very top can effectively get any sunlight.