Absorb, absorption A process that incorporates liquid molecules into the molecular structure of a solid or incorporates gas molecules into liquid.
Acid deposition Acids in the air falling onto the Earth’s surface, including into surface waters and onto exposed soils, plant leaves, and all human structures. The acids come primarily from particulates emitted at sulfide ore smelters, coal-burning particulates at industrial sites and power plants, and sulfur, nitrogen, and carbon dioxide (CO2) in smog. Sulfur and the other pollutants interact with both water in rain clouds and water particles in drier air, creating sulfuric acid, nitric acid, and carbonic acid. The gases can travel thousands of miles before converting to acids and falling to the ground out of dry air as dry acid deposition, or in rain as acid rain. Acids accumulated on fallen snow can acidify snowmelt waters.
Acid mine drainage Acid waters commonly arising from metal and coal mining. Many common copper, lead, iron, and zinc ores and related ore minerals are sulfide minerals, which break down to hydrogen sulfide, sulfuric acid (when sulfur reacts with water in an oxygen-rich environment), and other acid products. Waste rock from coal mining also contains sulfide minerals. Mine entrances and waste rock heaps promote and concentrate this process, feeding toxic acidified waters into neighboring streams and water bodies. Acidic water can leach, or dissolve, metal compounds from rocks and wastes and carry them elsewhere.
Acid rain Acid deposition in rainfall. Acid-forming pollutants accumulate in the atmosphere between storms and acids form when storm episodes add moisture to the air. Rainfall removes the acids from the air and deposits them at ground level. Each acid rain event suddenly raises surface water acidity, administering an “acid shock” to aquatic plants and animals. Both acid rain and acid snowmelt leach nutrients out of soils, often poisoning vegetation and soil microorganisms. See acid deposition.
Acre-foot A liquid measure, normally for water: the amount that can cover an acre to a depth of one foot (a football field is about 1.1 acre)—about 325,900 gallons. In the United States, an acre-foot