National Environmental Policy Act of 1969 (NEPA)Requires federal agencies to prepare a detailed statement on the environmental impacts of their proposed major actions that are significantly affecting…
National Historic Preservation Act (NHPA)A federal law providing that property resources with significant national historic value be placed on the National Register of Historic Places.
National Historic TrailsThese trails are designated by Congress under the National Trails System Act of 1968 and follow, as closely as possible, on federal land, the original…
National Landscape Conservation System (NLCS)Created by the BLM in June 2000 to increase public awareness of BLM lands with scientific, cultural, educational, ecological, and other values.
National Recreation AreaAn area designated by Congress to assure the conservation and protection of natural, scenic, historic, pastoral, fish, and wildlife values, and to provide…
National Register of Historic Places (NRHP)A comprehensive list of districts, sites, buildings, structures, and objects that are significant in American history, architecture, archaeology…
Native AmericanOf, or relating to, a tribe, people, or culture that is indigenous to the United States. (See Native American Graves Protection and Repatriation Act)
Natural drainagesNatural systems that convey water (such as a stream channel) that may be perennial, intermittent, or ephemeral.
NatureServeA nonprofit organization that provides the scientific information and tools needed to guide effective conservation action.
NatureServe ExplorerA Web site from NatureServe that provides authoritative conservation information in a searchable database for more than 70,000 plants, animals, and…
Neotropical migrantsBirds (especially songbirds) that summer in North America but migrate to the tropics for the winter.
Net emissionsApplied to greenhouse gas emissions inventory in this report. "Net emissions" means gross emissions (including all industrial activities, mostly fossil…
Night-sky impactAn interference with enjoyment of dark night skies resulting from light pollution.
Nighttime mean rural background levelNighttime (10 p.m. to 7 a.m.) average sound level in the rural environment, from all sources, rather than a particular noise that is of interest.
Nitrogen dioxide (NO<sub>2</sub>)A toxic, reddish-brown gas that is a strong oxidizing agent, produced by combustion (as of fossil fuels).
Nitrogen Oxides (NOx)The products of all combustion processes formed by the combination of nitrogen and oxygen.
NoiseAny unwanted sound that interferes with speech and hearing, causes damage to hearing, or annoys a person.
Noise criteriaQuantitative noise limits, below which it is acceptable for people to hear. Typically, noise criteria are specified in ordinances, regulations, or…
Non-point source pollutionPollution whose source is not specific in location; the sources of the pollutant discharge are dispersed, not well defined or constant.
Nonattainment AreaThe EPA's designation for an air quality control region (or portion thereof) in which ambient air concentrations of one or more criteria pollutants exceed…
Nongame speciesThose species not commonly harvested either for sport or profit.
Nonmarket valueMost environmental goods and services, such as clean air and water, and healthy fish and wildlife populations, are not traded in markets, meaning that…
Nonpoint light sourceA light source that is sufficiently large in size and close enough to the viewer to appear as an illuminated surface rather than a star-like point of…
Nonpoint sourcesDiffuse pollution sources (i.e., without a single point of origin or not introduced into a receiving stream from a specific outlet).
Nonroad mobile sources (emissions)Sources such as farm and construction equipment, gasoline-powered lawn and garden equipment, and power boats and outdoor motors that emit pollutants.
Noxious weedsThose plants regulated by law or those that are so difficult to control that early detection is important.
Nurse plantsMature plants that create favorable conditions for seeds to germinate and for seedlings to survive and grow.