What happens after algae bloom in eutrophication?

• A. Water becomes oxygen-rich
• B. Algae continue to flourish unimpeded
• C. Algae die and decomposers break them down
• D. Sediment resuspension occurs

Answer: (C)

When a eutrophication-driven algal bloom ends, the algae die and decomposers break them down. This decomposition consumes a lot of dissolved oxygen in the water, often driving oxygen levels down and creating cloudy, low-oxygen conditions that stress or kill aquatic life. That drop in oxygen is the key consequence of the bloom’s aftermath.

Oxygen-rich water isn’t the outcome because the breakdown of dead algae uses up oxygen rather than adding it. The idea that algae would keep thriving unimpeded doesn’t fit the pattern, since the bloom is followed by a die-off and decay rather than continued unchecked growth. Sediment resuspension isn’t the defining result of the post-bloom phase, though it can occur as a secondary effect; the critical issue after decay is the consumption of oxygen by decomposers.