Correct Response: D. One challenge facing freshwater ecosystems is the advent of harmful algal blooms, which can disrupt ecosystems. Algae require phosphorus and nitrogen to grow, and excess phosphorus in runoff is associated with more frequent blooms. For this reason, using phosphorus-free products, such as phosphate-free detergents, helps clean up freshwater ecosystems. Zooplankton (A) are a vital part of an aquatic ecosystem and can help keep algae populations in check, so disrupting their ability to osmoregulate would likely harm the ecosystem, rather than help it. Phosphorus increases the growth of algae and cyanobacteria (blue-green algae) in freshwater ecosystems. This will decrease, rather than increase, carbon dioxide levels because algae and cyanobacteria use carbon dioxide during photosynthesis. This tends to raise the pH of the water (B). Brown fatty tissues (C) are primarily found in mammals, not fish.
