Which type of pollution is characterized by rainfall or snowmelt moving overland and collecting contaminants?

Non-point source pollution is characterized by the phenomenon where rainfall or snowmelt moves overland, picking up and transporting contaminants as it flows. This type of pollution does not originate from a single, identifiable source but rather results from broader land usage patterns. For example, when precipitation runs over agricultural fields, urban areas, or erodible landscapes, it can carry fertilizers, pesticides, sediments, oils, and other pollutants into waterways.

This process complicates management and remediation efforts, as these pollutants may come from many diffuse sources rather than a specific discharge point. Understanding and addressing non-point source pollution is crucial for water quality management and protecting aquatic ecosystems, as it often contributes significantly to waterway degradation.

In contrast, point-source pollution comes from a single identifiable source, such as a discharge pipe from a factory. Thermal pollution refers to changes in temperature of water bodies primarily due to industrial discharges, while groundwater contamination typically refers to pollutants that seep through the soil into underground water supplies. Each of these options provides a different perspective on pollution sources and types, but the phenomenon of overland flow collecting contaminants specifically fits the definition of non-point source pollution.