Final answer:
The minnow population increases by 5% annually but faces a declining algae food source, decreasing by 750 each year. Nitrogen and phosphorus cause algal blooms, affecting oxygen levels in the pond, potentially impacting minnow survival.
Step-by-step explanation:
The minnow population in the pond is initially 20,000 and is increasing at a rate of 5% per year. However, the minnow's food source, algae, is decreasing because it supports 750 fewer minnows each year.
Nitrogen and phosphorus are important nutrients that limit phytoplankton growth. A large input of these nutrients can cause algal blooms, which can lead to severe reductions in water oxygen levels when they decompose. This can be detrimental to organisms like minnows that require oxygen to survive.
The minnows' population will, therefore, be affected by both the increase due to reproduction and the decline in food resources. Over time, this could lead to a decrease in minnow population if the loss of algae becomes too severe and the pond's ecosystem becomes imbalanced.