Aquatic ecosystem can be degraded by runoff and experience eutrophication: explosive algal growth that leads to depleted oxygen levels.

  1. Terrestrial runoff adds excess nutrients (nitrogen and phosphorous) and cause exponential growth of algae (bloom).

  2. Algal blooms block sunlight.

  3. Decreased underwater photosynthesis leads to decrease in dissolved oxygen.

  4. Algae eventually die and are decomposed by bacteria through respiration, further depleting oxygen levels.

The decrease in dissolved oxygen levels is called hypoxia and leads to decline of aquatic organisms.

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