In the regions of the dead zone in the Gulf of Mexico just west of the Mississippi River delta, oxygen levels are
A) highest at the bottom of the ocean, where the algae do not get enough sunlight to survive.
B) highest at middle ocean depths, where plants produce the most oxygen.
C) highest at the ocean surface, away from oxygen depleting bacteria.
D) lowest at the ocean surface, where fertilizers bind to and remove the oxygen.
Question 2
Noticing large amounts of algal growth in her small farm pond, a farmer adds about 20 grass carp to feed on the abundant algae and plants. After several years, the carp grow large, exceeding 20 pounds each in size.
Late one summer, the farmer notices that the carp and most of the other fish are dead. The water also smells very bad. Which one of the following is the most likely explanation for the death of these fish? A) The algae overgrew the pond and produced toxic levels of ozone.
B) The large carp grew so large that they could not get enough oxygen.
C) Bacteria feeding on the large volume of carp feces depleted the oxygen.
D) Carbon dioxide released by the carp and algae eventually suffocated the fish in the pond.
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