GLEAM

Great Lakes Environmental Assessment and Mapping Project

Nonpoint Pollution

NOAA)Runoff from land includes materials transported by surface and subsurface (including through infrastructure) runoff. We consider materials that originate from both point and diffuse sources, including watersheds and atmospheric sources.

Nutrient enrichment of aquatic ecosystems stimulates biological activity and has undesirable effects including algal blooms and oxygen depletion. Cultural eutrophication, or nutrient enrichment caused by human activities, is the most common water quality impairment of lakes, rivers, and coastal waters in the U.S.

The nonpoint pollution category includes four stressors.

Combined sewer overflows

Combined sewers collect sanitary sewage and stormwater run-off into a single pipe system. Combined sewers frequently overflow during heavy storms because they are not designed to handle the large volumes of stormwater runoff. These overflows result in the discharge of untreated sewage into surface waters.

Nitrogen loading

Various forms of nitrogen in fresh water may stimulate algal growth and contribute to eutrophic conditions. Nitrogen input to the Great Lakes is represented by nitrate (+nitrite), which typically comprises the majority of total inorganic nitrogen.

Phosphorus loading

Phosphorus runoff from watersheds is considered one of the most important drivers of eutrophication and the proliferation of nuisance algae because phosphorus often limits algal growth in freshwater ecosystems.

Sediment loading

Sediments exported from rivers cause turbidity, which can interfere with algal growth and prey location by visual predators, and alter benthic habitat conditions.

Lake Stressors

Aquatic Habitat
Climate Change
Coastal Development
Fisheries
Invasive Species
Nonpoint Pollution
Toxic Chemicals