parts per million (ppm)
Number of parts of a chemical found in 1 million parts of a particular gas, liquid, or solid.
Subject:
Chapter 19 - Water Pollution
parts per billion (ppb)
Number of parts of a chemical found in 1 billion parts of a particular gas, liquid, or solid.
Subject:
Oxygen demanding wastes
Organic materials that are usually biodegraded by aerobic (oxygen-consuming) bacteria if there is enough dissolved oxygen in the water. See also biological oxygen demand.
Subject:
nonpoint source
Large or dispersed land areas such as cropfields, streets, and lawns that discharge pollutants into the environment over a large area. Compare point source.
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neutral solution
Water solution containing an equal number of hydrogen ions (H+) and hydroxide ions (OH-); water solution with a pH of 7. Compare acid solution, basic solution.
Subject:
indicator species
Species that serve as early warnings that a community or ecosystem is being degraded. Compare keystone species, native species, nonnative species.
Subject:
eutrophication
Physical, chemical, and biological changes that take place after a lake, estuary, or slow-flowing stream receives inputs of plant nutrients--mostly nitrates and phosphates--from natural erosion and runoff from the surrounding land basin. See cultural eutrophication.
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dredge spoils
Materials scraped from the bottoms of harbors and streams to maintain shipping channels. High levels of toxic substances that have settled out of the water often contaminate these materials. See dredging.
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Cultural eutrophication
Overnourishment of aquatic ecosystems with plant nutrients (mostly nitrates and phosphates) because of human activities such as agriculture, urbanization, and discharges from industrial plants and sewage treatment plants. See eutrophication.
Subject:
coastal zone
Warm, nutrient-rich, shallow part of the ocean that extends from the high-tide mark on land to the edge of a shelflike extension of continental land masses known as the continental shelf. Compare open sea.
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