Explain why allowing nitrogen or phosphorus fertilizers to run into a body of water can negatively affect life in it?

Answer 1

Strangely enough, Fertilizers do not DIRECTLY affect waterways negatively. let me explain a little more.

natural bodies of water have dissolved chemicals and minerals in the water that microorganisms and plants absorb to live

All natural bodies of water have a trace amount of Nitrogen and Phosphorous already in them.

the reason why it is ill advised to get Nitrogen or Phosphorous into natural waterways is that Microorganisms, such as algae, which are naturally balanced in the ecosystem by the natural amount of the chemicals, thrive and explode in population because of the sudden increase in those chamicals. you may have heard the term "Algal Bloom", that's what it is, a spike in amount of a normally restricted nutrient has caused the Algae to grow into a cloud-like colony.

these algal colonies are what harm the other organisms in the water. the algae drains up all the dissolved Oxygen in the water and suffocates other oganisms such as fish, insect larvae in the water, and amphibians. then this creates a ripple effect because ther's less food for predator species that would normally eat the fish, insects, and amphibians.

your local Department of Agriculture and Game and Wildlife bureau may have more information on how much Nitrogen and Phosphorous you should have in your fertilizer if you are planning on putting it on your lawn.