Click on the picture to see the whole thing, it's helpful to understanding dead zones!
Eutrophication means "nutrient pollution", and a dead zone is an area where there is no to low oxygen in water.
Dead zones are caused by excess nitrates and phosphates from fertilizers, industrial runoff, and runoff from homes entering water sources. (Freshwater areas are affected more by the phosphates, while salt water areas are affected more by the nitrates). These excess nutrients cause an algal bloom. When all these algae die, they sink to the bottom. Decomposing bacteria consume the phytoplankton, and with all this excess food creates a growth in the population of the bacteria. They consume all the oxygen dissolved in the area, while the algae reduce the amount of light that reaches the depths of the ocean, and aquatic life begins to die. Anaerobic bacteria soon take over, and release hydrogen and sulfuric gas, making the water even more acidic and unsuitable for life.
More Related Terms:
Hypoxia- Waters that have dissolved oxygen (DO) concentrations less than 2mg/L
Anoxia- No DO present in the water.
Oxygen depletion is further caused by stratification preventing oxygen refreshment.
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