Abiotic: Without life; pertains to nonliving factors of the environment.
Acid rain: Rain or other precipitation containing nitric and sulfuric acids derived from air pollutants, such as industrial or automobile emissions.
Acute effect: An effect that appears shortly after exposure to a pollutant.
Adaptation: Structural, physiological, or behavioral characteristics that enhance the ability of the organism to survive and reproduce in a particular environment.
Administrative agency: A governmental unit, like the Environmental Protection Agency or Nuclear Regulatory Commission, established by the legislative or the executive branch to execute certain functions of the government; it allows governmental business to be transacted under the authority of the legislative or executive branch by units that specialize in certain tasks.
Age structure: The division of a population according to age groupings. The different age levels of a population are expressed in percentages; it is often depicted graphically as an age pyramid.
Albedo: The fraction or incident of light or electromagnetic radiation that is reflected by a body as compared to the reflectivity of a perfect reflector of the same size, shape, orientation, and distance; it is usually given as a percentage.
Algal bloom: A population explosion of photosynthetic organisms (particularly algae and blue-green algae) typically caused by nutrient enrichment in aquatic ecosystems.