The Addition of Excess Phosphorus Causes Lakes to Become Eutrophic

question 29

Multiple Choice

The addition of excess phosphorus causes lakes to become eutrophic because the nutrients trigger blooms of photosynthetic cyanobacteria. Why do these blooms cause low oxygen levels in lakes?

• A) Cyanobacteria use up more oxygen than they produce.
• B) Excess phosphorus binds to dissolved oxygen in the water.
• C) Cyanobacteria are net producers of oxygen while alive, but when they die aerobic bacteria use oxygen while decomposing them.
• D) Cyanobacterial blooms only occur in waters naturally low in oxygen.
• E) Cyanobacteria are aerobic heterotrophs, consuming oxygen and producing carbon dioxide.

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