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- 1From:The Gale Encyclopedia of Science (Vol. 4. 6th ed.)Leaching usually refers to the movement of dissolved substances with water percolating through soil. Sometimes, leaching may also refer to the movement of soluble chemicals out of biological tissues, as when rainfall...
- 2From:Congressional Research Service (CRS) Reports and Issue BriefsLarge quantities of carbon are actively exchanged between the atmosphere and the other carbon storage pools, including the oceans, vegetation, and soils on the land surface. The exchange, or flux, of carbon among the...
- 3From:The Gale Encyclopedia of Science (Vol. 6. 6th ed.)Geologists define permafrost as soil or rock that remains frozen for a time period in excess of two years. The composition of permafrost can vary widely depending on the geology and geomorphology of the area in which the...
- 4From:The Gale Encyclopedia of Science (Vol. 4. 6th ed.)Indicator species are plants and animals that, by their presence, abundance, lack of abundance, or chemical composition, demonstrate some aspect of the character or quality of an environment. For example, in places...
- 5From:The Gale Encyclopedia of Science (Vol. 4. 6th ed.)Humus is an amorphous, dark brown, organic material that is formed by the incomplete decomposition of organic material. Humus is composed of organic residues that are sufficiently fragmented and decomposed by microbial...
- 6From:The Gale Encyclopedia of Science (Vol. 4. 6th ed.)The word horizon generally is defined as the line that separates two layers or divisions. It originated from the Greek word orizein, which means to limit. It is oftentimes used to mean the line that separates earth (its...
- 7From:The Gale Encyclopedia of Science (Vol. 2. 6th ed.)Centipedes (phylum Arthropoda, class Chilopoda) occur throughout the world in both temperate and tropical regions, living in soil and humus and beneath fallen logs, bark, and stones. Because they lack a hard outer...
- 8From:The Gale Encyclopedia of Science (Vol. 5. 6th ed.)Nitrification is an aerobic microbial process by which specialized bacteria oxidize ammonium to nitrite and then to nitrate. Nitrification is a very important part of the nitrogen cycle, because for most plants nitrate...
- 9From:The Gale Encyclopedia of Science (Vol. 3. 6th ed.)Germination is the process by which a seed begins its development into a mature plant. It begins with an increase of metabolic activity within the seed. The first visible sign of germination in angiosperms (flowering...
- 10From:The Gale Encyclopedia of Science (Vol. 3. 6th ed.)Flies belong to the order Diptera, a group that also includes mosquitoes, gnats, and midges. Flies make up the fourth largest order of insects, with about 100,000 species recognized. Dipterans are among the most advanced...
- 11From:The Gale Encyclopedia of Science (Vol. 3. 6th ed.)A fruit is an often-edible part of a plant that is derived from a fertilized, ripened ovary. As a dietary staple, fruits are appreciated for their sweetness and as a rich source of nutrients, especially vitamins....
- 12From:The Gale Encyclopedia of Science (Vol. 2. 6th ed.)Decomposition is the natural process in which large organic (carbon-containing) materials and molecules are broken down into simpler ones. The process is driven by microorganisms. The ultimate products of decomposition...
- 13From:The Gale Encyclopedia of Science (Vol. 5. 6th ed.)Nitrogen fixation refers to the chemical conversion of nitrogen gas (dinitrogen, N2) to an oxidized form (a form with fewer electrons), usually nitric oxide (NO) or ammonia (NH3). Nitrogen fixation can occur through...
- 14From:The Gale Encyclopedia of Science (Vol. 3. 6th ed.)Groundwater refers to water that occupies space between particles underground. Generally groundwater is free from many contaminants, as it has percolated down through the soil to reach its final location. However,...
- 15From:The Gale Encyclopedia of Science (Vol. 2. 6th ed.)Decontamination refers to efforts to safeguard property and people that have been exposed to chemical, nuclear, or biological agents. The intent of decontamination is twofold. The first objective is to make the...
- 16From:AEI Paper & StudiesFrom their earliest days of the 1930s New Deal, farm bills in the US have included conservation programs. Those programs have always had multiple goals, which have evolved as the US economy has changed. Initially, there...
- 17From:Geotechnical Engineering for Disaster Mitigation and Rehabilitation: Proceedings of the 1st International ConferenceStrength softening and liquefaction of soft clayey soils are a major source of damage to civil engineering works in earthquake-prone zones. Extensive liquefaction research over the past few decades has helped determine...
- 18From:The Gale Encyclopedia of Science (Vol. 6. 6th ed.)Pollution can be defined as unwanted or detrimental changes in a natural system. Usually, pollution is associated with the presence of toxic substances in some large quantity, but pollution can also be caused by the...
- 19From:The Gale Encyclopedia of Science (Vol. 4. 6th ed.)Lichens are an intimate symbiosis, in which two species live together as a type of composite organism. Lichens are an obligate mutualism between a fungus mycobiont and an alga or blue-green bacterium phycobiont. Each...
- 20From:The Gale Encyclopedia of Science (Vol. 5. 6th ed.)The nitrogen cycle refers to the movement of nitrogen through the air, water, and soil of Earth. Nitrogen is a critically important nutrient for organisms, being one of the most abundant elements in their tissues and...