What agricultural practice can lead to water supply contamination?

Fertilization can lead to water supply contamination primarily due to the runoff of excess nutrients, particularly nitrogen and phosphorus, from agricultural fields into nearby water bodies. When fertilizers are applied to crops, especially in large quantities or during rainfall, they can leach into the soil and eventually reach surface or groundwater. This process can result in nutrient pollution, promoting harmful algal blooms that deplete oxygen levels in water and harm aquatic ecosystems.

In contrast, practices like crop rotation, irrigation, and pest control, while they can also impact water quality, do not have the same direct and immediate effects on water contamination as improper or excessive fertilization does. Crop rotation helps to maintain soil health and reduce nutrient depletion, irrigation can be managed to prevent runoff, and pest control, when done organically, can minimize chemical introduction into water supplies. Therefore, understanding the specific risks associated with fertilization highlights the need for careful management of this agricultural practice to protect water quality.