Higher amounts of nitrogenous compounds will increase algal blooms, leading to less available oxygen in the water, and decrease biodiversity. -------- Let's take a look at each option and consider them in light of our knowledge. 1. These compounds will combine into larger molecules as they interact in the nitrogen cycle and become food for fish and other animals, increasing biodiversity. * This has some problems. Yes, the fertilizers will cause an increase in the food supply, but that doesn't spontaneously cause an increase in biodiversity. The only way to increase the biodiversity is to introduce new organisms. And this isn't such a mechanism. I won't pick this choice. 2. The water cycle will remove excess fertilizer naturally through evaporation, with no impact on biodiversity. * There's some issues here as well. Think about how much fertilizer runoff is considered a pollution issue. If this option were true, then we wouldn't be seeing so many news articles complaining about fertilizer running causing pollution problems. So this answer isn't any good either. 3. Nitrogenous compounds will be recycled into carbon compounds to create new organisms and increase biodiversity. * Still running into the "spontaneous increase in biodiversity" issue here. How would more carbon compounds suddenly increase the biodiversity? This answer isn't any good either. 4. Higher amounts of nitrogenous compounds will increase algal blooms, leading to less available oxygen in the water, and decrease biodiversity. * This is a real problem. Some might think that "Algae is a plant. Plants produce oxygen. Why would more algae cause the oxygen supply to decrease?" Well, the answer is pretty simple. Individual algae cells don't live very long. So you have a log of algae being produced. Releasing oxygen to the air, and then dying. And the dead algae then proceeds to decay, which does consume dissolved oxygen in the water. Which does cause the death of fish and other animals that are dependent upon that dissolved oxygen. And that does reduce the biodiversity in the area. So this is a reasonable and correct answer.
