Final answer:
Nitrates and phosphates from human activities like fertilizer use lead to eutrophication in the Mississippi watershed, creating dead zones by depleting oxygen and harming aquatic life.
Step-by-step explanation:
Nitrates and phosphates have a substantial impact on the Mississippi watershed by contributing to the process of eutrophication, which is a form of water pollution. When these nutrients, often originating from fertilizer runoff and sewage, enter waterways, they promote the excessive growth of algae and other microorganisms. This bloom of algae eventually dies off and decomposes, which depletes the dissolved oxygen in the water, making it difficult for other aquatic life, such as shellfish and finfish, to survive.
This depletion of oxygen leads to the creation of dead zones, where the aquatic environment becomes inhospitable to most marine life. These dead zones are prevalent at the mouths of major rivers, including the Mississippi, where the nutrient load from upstream has the greatest impact. Human activities such as agriculture amplify this process by increasing the amount of nitrogen and phosphorus that wash into water systems, with erosion also contributing to this problem.