Habitat

That space that is or can be successfully occupied (inhabited) by a species or biotic community or some broader (taxonomic or phylogenetic) entity. Habitat is simply the place where an organism or group of closely related organisms live naturally.

Hacking

Practice of raising animals in captivity, acclimating them to natural conditions and then releasing them into the wild (referred to in regard to bald eagles).

Half-life

The period of time necessary for one half of a substance introduced to a living system or ecosystem to be eliminated or disintegrated by natural processes.

Hazardous Air Pollutants (HAPs)

Any air pollutant listed as such in Title III of the 1990 Clean Air Act Amendments. These are chemicals that have the potential to cause serious health effects. HAPs are released by mobile sources and industrial sources. Also referred to as air toxics. Also see "Clean Air Act."

Hazardous Waste

A waste which, because of its quantity, concentration, or characteristics, may be hazardous to human health or the environment when improperly treated, stored, transported, or disposed. Specific definitions of hazardous waste vary by statute or regulation.

Heavy metals

A group of metals that might be present in municipal and industrial wastes that pose long-term environmental hazards if not disposed of properly. Heavy metals can contaminate ground and surface waters, fish, and food. The metals of greatest concern are arsenic, cadmium, chromium, copper, lead, mercury, selenium, and zinc.

Hexachlorobenzene (HCB)

A pollutant of concern once used as a pesticide for grain protection until banned by the U.S. in 1976. It is still produced as a byproduct during the manufacture of other chlorinated hydrocarbons. It is a persistent toxic substance and is found in the tissues of fish, animals, and humans from the Great Lakes basin. Limited uses of HCB are still permitted.

Hexagenia

See "Burrowing mayfly."

House Great Lakes Task Force

A bipartisan coalition of U.S. Representatives from Great Lakes states that works to advance the economic and environmental health of the Great Lakes region.

Human Health

"A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity." [World Health Organization (WHO), 1984]

Human Health Criteria

These are descriptive or numeric expressions that specify how much of a pollutant can be allowed in a water body and still allow for the protection of human health. See also water quality criteria. Also see "Great Lakes Initiative."

Hydric Soils

Soils that are saturated, flooded, or ponded long enough during the growing season to develop anoxic conditions in the upper part of the soil profile.

Hydrocarbons

A class of compounds that contain hydrogen and carbon. This group of compounds includes the naturally occurring hydrocarbons produced by plankton, as well as many petroleum-based products like gasoline and motor oil. Chlorinated hydrocarbons, a subclass of hydrocarbons, are human derived and generally toxic.

Hydrophytic Vegetation

Plant life capable of growing in wet conditions, such as in water or in soil or other substrate that is periodically saturated with water. The presence of hydrophytic plants is one of the indicators used in wetland identification and delineation.

Hypolimnion

The cooler, lower most layer of water in a thermally stratified lake.