NOAA Coastal Storms Program
Ecological Impacts
Introduction to Stormwater
Nonpoint Source Pollution and Stormwater
Oil sheen seen on the surface of Longfellow Creek, Washington
Stormwater runoff is emerging as one of the most significant threats to ecosystems along the coastal margins of the U.S. Stormwater runoff is a form of nonpoint source pollution, occurring when water runs over the land and picks up contaminants, transporting them to aquatic habitats. A wide array of potentially toxic chemicals is commonly found in stormwater runoff, including pesticides, petroleum hydrocarbons from cars, heavy metals, and other contaminants originating from agricultural, residential, commercial, and industrial land use activities.
Contaminants, Stormwater, and Land use
Human activities within a watershed have an important influence on stormwater quality. In agricultural areas, runoff from crops and livestock holding areas can contain a variety of insecticides, herbicides, fungicides, nutrients, pharmaceuticals, and pathogenic organisms. Residential development converts forests and fields to roads, parking lots, driveways, parks, and lawns. Runoff from these areas typically contains petroleum hydrocarbons and heavy metals (from motor vehicles) as well as detergents, pesticides, and various other chemicals used by homeowners and local governments. Stormwater in heavily urbanized areas may contain all of the above contaminants as well as toxics from industrial sites and combined sewer overflows. For more information on the relationship between land use and surface water quality throughout the United States, visit the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program.
Factors Impacting Stormwater
Various factors affect pollutant load and transport in stormwater. These factors can have complex interactions, influencing toxicity levels during and after a runoff event. Factors include
- Duration of the dry period prior to a storm (contaminants build up on roads, lawns, and other surfaces during dry periods);
- Storm intensity (affects how quickly the contaminants are transported);
- Pervious surfaces (water can soak through) versus impervious surfaces (water cannot soak through);
- Atmospheric deposition (particles suspended in the air are deposited by precipitation or wind into the ocean or rivers, or onto land).
To learn about how stormwater affects ecosystem health, see Ecological Impacts of Stormwater.
To learn about restoration and the impacts of stormwater, visit Restoration Considerations.