Final answer:
Excess fertilizer from US farms often leads to water pollution through leaching into groundwater or running off into waterways, which contributes to eutrophication of lakes and rivers. This surplus of nutrients, like nitrogen and phosphorus, results in algal blooms and can create dead zones that endanger aquatic life.
Step-by-step explanation:
The excess fertilizer that is applied to US farms often has negative environmental impacts. When more fertilizer is used than plants can absorb, the surplus can leach into groundwater or run off into nearby waterways. This process contributes to both groundwater and surface water pollution, primarily through the eutrophication of aquatic systems. Eutrophication is caused by high levels of nutrients, such as nitrogen and phosphorus, which lead to excessive growth of algae (algal blooms). These blooms consume large amounts of oxygen when the algae die and decompose, which can create dead zones incapable of supporting most aquatic life.
Fertilizer runoffs are a major environmental concern because they can cause severe ecological damage. For example, in the United States, about half of all lakes are eutrophic due to nutrient pollution primarily from phosphates. Furthermore, nitrogen-rich fertilizer runoffs contribute to both freshwater and saltwater eutrophication, causing overgrowth and death of algae which result in anaerobic conditions that harm aquatic organisms. Overuse of fertilizers in residential areas can also add to the nutrient load in water bodies, exacerbating eutrophication and related problems.