alleryStart learning →Fertilizer runoff triggers a heavy algal bloom in a lake. Why do fish then die?
AGrowing algae strip the oxygen out
BDecaying algae raise the water pH
CGrowing algae block the fish gills
DDecaying algae strip the oxygen out
Answer & Solution
Correct answer: D. Decaying algae strip the oxygen out
1. Nitrogen and phosphorus are the limiting nutrients for algae in lakes.
2. A large input of both lets algal growth run away into a bloom.
3. The bloom shades the water so that photosynthesis below it stops.
4. When the algae die, decomposers consume oxygen as they break the material down.
5. Severe oxygen depletion follows and the fish, which need oxygen, die.
_Source: OpenStax Biology 1e (CC BY 4.0), Chs 44 and 46, section 44.4 Aquatic Biomes_
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