A  |   B  |   C  |   D  |   E  |   F  |   G  |   H  |   I  |   J  |   K  |   L  |   M  | N  |   O  |   P  |   Q  |   R  |   S  |   T  |   U  |   V  |   W  |   X  |   Y  |   Z

M

M&I (MUNICIPAL AND INDUSTRIAL) WATER USE—Water supplied for municipal and industrial uses provided through a municipal distribution system.

MAAR—A flat-bottomed, roughly circular volcanic crater of explosive origin that is often filled with water.

MACROCLIMATE—The general large-scale climate of a large area or country, as distinguished from Mesoclimate and Microclimate.

MACRONUTRIENT—A chemical element necessary in relatively large amounts (usually more than one part per million [ppm] in the plant) for the growth of plants.

MACROPHYTE—A member of the macroscopic plant life, especially of a body of water.

MACROPHYTIC ALGAE—Algal plants large enough either as individuals or communities to be readily visible without the aid of optical magnification.

MAELSTROM—A whirlpool of extraordinary size or violence.

MAGMA—(Geology) Molten rock found in the mantle, beneath the cruse of the earth. When forced toward the surface, magma cools and solidifies to become Igneous rock.

MAGMATIC WATER—Water driven out of Magma during crystallization.

MAGNETIC SEPARATION—The use of magnets to separate ferrous materials from mixed municipal waste stream.

MAIN—A relatively large pipe in a distribution system for drinking water or in a collection system for municipal wastewater. Of or relating to utility distribution mains for transferring water. Often used in the plural, as in water mains.

MAIN CANAL SYSTEM—A canal that delivers water from a primary source of supply to several points of diversion or canal-side turnouts to smaller distribution systems.

MAIN CHANNEL POOL [California]—A pool formed by mid-channel scour that encompasses greater than sixty percent of the wetted channel.

MAINSTEM—The major reach of a river or stream formed by the smaller tributaries which flow into it.

MAJOR FLOODING—Flood conditions resulting in extensive inundation and property damage. Typically characterized by the evacuation of people and livestock and the closure of both primary and secondary roads. Also see Minor Flooding and Moderate Flooding.

MAJORS—Larger Publicly-Owned Treatment Works (POTWs) with flows equal to at least one million gallons per day (mgd) or servicing a population equivalent to 10,000 person, certain other POTWs having significant water quality impacts. Contrast with Minors.

MAKEUP WATER—Water added to the flow of water used to cool condensers in electric power plants. This new water replaces condenser water lost during passage of the cooling water through cooling towers or discharged in blowdowns.

MANAGEMENT INDICATOR SPECIES (MIS)—(Environmental) A species selected because its welfare is presumed to be an indicator of the welfare of other species in the habitat. A species whose condition can be used to assess the impacts of management actions on a particular area. Managing for these species usually requires significant allocations of land or resources. Also see Indicator Species.

MANAGERIAL CONTROLS—(Irrigation) Methods of nonpoint source pollution control based on decisions about managing agricultural wastes or application times or rates for agrochemicals.

MANGROVE—Tropical evergreen trees and shrubs that have stilt like roots and stems, and often form dense thickets along tidal shores. Also see Mangrove Swamp.

MANGROVE SWAMP—A tidal swamp forest populated by plant species capable of growth and reproduction in areas that experience periodic tidal submergence in seawater with a resulting increase in saline conditions. These forests develop along coastal regions in tropical climates. Mangrove swamps are dominated by trees referred to as red mangrove, Rizophora mangle, black mangrove, Avicennia germinans, and white mangrove, Laguncularia racemosa. Typically, these trees have large, exposed root systems.

MANMADE LAKE—Any manmade body of water, including lakes, ponds, lagoons, and reservoirs (excluding tank-type reservoirs which are fully enclosed and contained), that are filled or refilled with water or reclaimed wastewater from any source and used for recreational, scenic, or landscape purposes, except swimming pools.

MANOMETER—An instrument for measuring pressure which usually consists of a U-shaped tube containing a liquid, the surface of which in one end of the tube moves proportionally with changes in pressure on the liquid in the other end. The term is also applied to a tube-type differential pressure gage.

MANTLE—(Geology) The division of the earth's interior between the core and the crust. It is composed mainly of silicate rock and is around 2,900 kilometers (1,800 miles) thick.

MARE CLAUSUM—A navigable body of water, such as a sea, that is under the jurisdiction of one national and closed to all others.

MARE LIBERUM—A navigable body of water, such as a sea, that is open to navigation by vessels of all nations.

MARE NOSTRUM—A navigable body of water, such as a sea, that is under the jurisdiction of one nation or that is shared by two or more nations.

MARICULTURE—The cultivation of marine organisms for use as a food resource. Compare to Aquiculture.

MARINA—A water-based facility used for storage, service, launching, operation, or maintenance of watercraft.

MARINE—(1) Of or pertaining to the sea; having to do with the ocean or the things peculiar to the ocean. (2) A system within the Wetlands and Deepwater Habitat Classification System. Also see Deepwater Habitats and Wetlands. [See Appendix W-3 for an explanation of the Wetland and Deepwater Habitat Classification System according to USFWS criteria.]

MARINE LIFE—Plants and animals of the sea, from the high-tide mark along the shore (also see Shore Life) to the depths of the ocean. These organisms fall into three major groups: (1) Benthos—plants such as kelp and animals such as brittle stars that live on or depend on the bottom; (2) Nekton—swimming animals such as fishes and whales that move independently of water currents; and (3) Plankton—various small to microscopic organisms that are carried along by the currents.

MARINE PROTECTION, RESEARCH, AND SANCTUARIES ACT (MPRSA)—A 1972 federal law that includes provisions requiring citizens of the United States to obtain a permit from the U.S. Environmental Protection Agency (EPA) before disposing of materials in the oceans. Subsequent amendments to the act have limited the types of waste that may be permitted for ocean disposal.

MARINE SANITATION DEVICE—Any equipment or process installed on board a vessel to receive, retain, treat, or discharge sewage.

MARINE (NAUTICAL) SURVEYING—The branch of surveying that comprises a topographic survey of the coast and a hydrographic survey of adjacent waters. Also see National Oceanic and Atmospheric Administration (NOAA).

MARITIME LAW—Branch of law relating to commerce and navigation on the high seas and on other navigable waters. Specifically, the term refers to the body of customs, legislation, international treaties, and court decisions pertaining to ownership and operation of vessels, transportation of passengers and cargo on them, and rights and obligations of their crews while in transit.

MARK—(Nautical) A knot