Final answer:
An excess of nitrogen and phosphorus would trigger an algal bloom, which results in ecosystem damage by reducing light penetration and creating oxygen-depleted dead zones, affecting aquatic life and potentially human health through toxic byproducts.
Step-by-step explanation:
The excess of nutrients, particularly nitrogen and phosphorus, would create an algal bloom. These nutrients are usually introduced into bodies of water through fertilizer runoff from farms and lawns, as well as sewage. An algal bloom is characterized by the excessive growth of algae in water, leading to various negative ecosystem impacts.
When an algal bloom occurs, the algae can become so plentiful that they reduce light penetration, creating aphotic zones where photosynthetic plants cannot survive. Following the death of the algae, decomposition by bacteria leads to severe oxygen depletion, resulting in dead zones. Such areas can no longer support aquatic life that requires oxygen. Furthermore, some algal blooms, such as red tides caused by dinoflagellates, produce toxins that are harmful to wildlife and can contaminate seafood, posing a risk to human health.