What is one impact of using chemical fertilizers excessively?

Using chemical fertilizers excessively can lead to water pollution, which has significant impacts on the environment and human health. When fertilizers are applied in large amounts, particularly nitrogen and phosphorus, they can leach into groundwater or be washed into nearby bodies of water through runoff during rainfall. This process can lead to eutrophication, where an excess of nutrients in the water promotes algal blooms. These blooms can deplete oxygen levels in the water, harming aquatic life and creating dead zones where fish and other organisms cannot survive.

In contrast, the other options do not accurately reflect the consequences of excessive fertilizer use. For instance, while improvement in soil structure, conservation of moisture, and enhanced microbial activity are generally positive outcomes associated with healthy soil management practices, they are not typically results of using chemical fertilizers in high quantities. In many cases, excessive reliance on chemical fertilizers can degrade soil health rather than improve its structure or microbial activity, leading to long-term negative effects on agricultural productivity and sustainability.