Which of the following is a common source of nitrogen pollution in waterways?

Runoff from agricultural fields or livestock waste is a significant source of nitrogen pollution in waterways. In agricultural practices, fertilizers that are high in nitrogen are often applied to crops to enhance growth and yield. When it rains, excess nitrogen from fertilizers can leach into nearby water bodies through surface runoff. Similarly, livestock waste contains substantial amounts of nitrogen; when not managed properly, it can wash into streams, rivers, and lakes. This influx of nitrogen can lead to eutrophication, resulting in harmful algal blooms that deplete oxygen levels in water and adversely affect aquatic life.

The other options may contribute to water pollution in different ways, but they are not as direct or significant in the context of nitrogen specifically. Runoff from urban areas may introduce various pollutants, including nitrogen, but agriculture is more closely associated with high nitrogen loads. Industrial waste can also be problematic but often consists of different contaminants. Natural occurrences like wildfires produce various emissions but typically don’t directly cause nitrogen pollution in waterways in a concentrated manner.