Answer:
The correct answer to the question "What does eutrophication cause?" is D. Toxic algae blooms.
Step-by-step explanation:
Eutrophication is the process by which a body of water becomes enriched with nutrients, particularly nitrogen and phosphorus. This enrichment leads to excessive growth of algae and other aquatic plants.
As these plants grow, they form dense mats on the water surface, blocking sunlight from reaching deeper areas. Without sunlight, other plants and organisms that require sunlight for photosynthesis cannot survive.
Eventually, these excessive plant growths die and sink to the bottom of the water body. Bacteria decompose these dead plants, consuming oxygen in the process. This causes a decrease in oxygen levels in the water, leading to hypoxia (low oxygen) conditions.
Under these low-oxygen conditions, certain species of algae, known as harmful algal blooms (HABs), can thrive. These HABs produce toxins that are harmful to aquatic life and can have negative effects on human health if consumed or exposed to.
Therefore, eutrophication ultimately leads to the formation of toxic algae blooms (option D) due to the excess nutrients and subsequent changes in oxygen levels in the water.