How can the agricultural runoff of fertilizers lead to the destruction of marine habitats?

Answer:

Rain can wash excess nitrogen and phosphorus from fertilized fields into streams and rivers, which carry the nutrients to the ocean. The extra nutrients can cause algal blooms that block sunlight from reaching seagrasses and other underwater plants. When the algae die, bacteria decompose them and use up dissolved oxygen, creating hypoxic areas or “dead zones” where many fish and other organisms cannot survive. Some blooms also release toxins, further harming marine life and disrupting food webs and habitats.