Names and abbreviations in biology

Names and abbreviations in biology

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After one year in college, I am quite surprised with the number of different abbreviations used in biology for the same thing.

I wonder if there are any rules for naming something new in biology, for example new genes, or if it is just up to the researchers without restriction? If there are rules, how did the confusion arise?

Elsewhere on SE Biology I have answered a related question regarding enzyme names. Here I will restrict myself to genes, as it seems that this is the main concern of the poster. (In talking about 'abbreviations' I think he is referring to what are generally termed gene 'symbols'.) The answer from @KarlKjer addressed current recommendations regarding gene nomenclature; mine addresses the causes of the current confusion.


  • Rules (actually recommendations) did not appear until a late stage in the development of the field of genetics, when the problem was already there and there was a need to do something about it.
  • Historically in animal systems the naming of new genes tended to relate to mutant phenotypes as this was how they were discovered. The function of the gene that had been mutated was generally unknown.
  • Sometimes different mutants of the same gene caused different phenotypes, either because of severity of damage to the protein, use of animals from a different development stage, or different growth conditions for bacteria. These mutants appeared to be of different genes, which were given different names.
  • Sometimes the same gene was discovered at about the same time by different workers and given different names in the laboratory while work was in progress and, hence, on publication.
  • Later it became possible in some cases to identify the products of genes for which there was no clear mutant phenotype - perhaps just lethality - and one method of naming was on the basis of the size of the protein, preceded by the letter 'p' (e.g. p63)
  • The current trend is to try to rename genes according to the function of their products, where these are known, i.e. to replace the name of a mutant phenotype by the name of an enzyme or structural protein.
  • The implementation of such rules or recommendations is imperfect, depending on the cooperation of authors and editors.

Illustration using some Drosophila genes

I shall use Drosophila melanogaster (the fruit fly) to provide some illustratations of the history of genetic nomenclature, because this was the organism used by Thomas Hunt Morgan (he of the centimorgan) to perform genetic studies after the rediscovery of Mendel's work in 1900. His laboratory was responsible for the discovery in 1910 of the first Drosophila mutant, a spontaneous sex-linked mutant that resulted in males having eyes that were white, rather than the normal red. The gene responsible for this mutant was named white, initiating the custom of naming genes after their mutant phenotype. (Drosophila gene names became italicized by convention.) What else could they have done? Not only was the protein product of this gene unknown, the whole idea of genes encoding proteins did not yet exist. The abbreviation (symbol) for this gene was merely w. Clearly, nobody anticipated that another 17,000 genes would follow, or suggested that a committee on gene nomenclature should be set up.

It is interesting to note that the product of the white gene was not identified until almost 90 years later. In 1999 it was established that this was a member of the ABC transporter family, responsible for bringing into cells the guanine and tryptophan needed to make the red pigment so characteristic of the eye of the wild-type Drosophila. The human version of white was identified roughly contemporaneously by sequence homology, and although it was initially referred to as hW (human homologue of white) is now named according to its gene product: ATP-binding cassette sub-family G member 1 (ABCG1). Its function in humans - who only have red eyes in flash photographs - is in lipid transport.

The era of of molecular genetics in the late twentieth century brought an avalanche of new genes, many not associated with a particular phenotype. The culture - accepted by scientific journals - was that if you discovered a new gene you had the right to name it as you pleased. A generation of young scientists were pleased to chose names that reflected twentieth century, rather than classical, culture. Flip through the names of Drosophila genes (try the autocomplete here) and you will find alien, bazooka, cactus, Dorothy, ether a go-go all the way to zucchini. Nor was it only the Drosophila geneticists that were responsible for this. The hedgehog segmentation gene, discovered in Drosophila, has three human homologues. One of these was named 'sonic hedgehog', which I am informed is the protagonist of a children's video game. O tempora, o mores!

A couple of final points will be made to illustrate the problems of nomenclatue of Drosophila genes. Several other mutations of the white gene have been observed which have different phenotypes (e.g. result in different eye colour). This is because they involve insertions into the gene rather than its complete deletion. This also illustrates one historic difficulty that could result in several names for the same gene. The other point is that many of the genes identified by genome sequencing, at least initially, were associated with no mutant phenotype and had no known function, and were so named simply be an accession number (CG1234 etc.). As functions emerged they would be renamed. And an example of the nomenclature situation can be seen in the NCBI entry for Drosophila gene TfIIS (RNA polymerase II elongation factor):

Also known as: BG:DS00929.12; br52; CG3710; DmelCG3710; DmS-II; DmSII; l(2)35cF; l(2)35Cf; l(2)br52; l35Cf; RnpSII; TFIIS; TFIISA; TFS-II

There are rules. Both genes and proteins are regulated in their formats, and standardized in terms of capitalization and italics. Different species have different rules. So for example SHH is a human gene, and Shh is the homologue in mouse. You can find these rules here: and read about them here: Also, amino acid abbreviations are standardized in both one and three letter forms. Also, things like restriction enzymes are given as the first letter of the genus, and then the first two letters of the species epithet, such as EcoR1 from E. coli. Note that since it comes from a Linnaean species (in Latin) it is italicized. Other enzymes like Taq polymerase, come from species names, and follow similar guidelines.

One reason why some genes have several different names is because they have been discovered several times by different teams in different species.

For instance mice Int1 being Wg of the fruit fly. Each team name their discovered genes independently and they eventually realise they're the same (homologous).

This was quite common before biologists understood/accepted the universality of homeobox genes.

GenealogyInTime Magazine

In many historic documents, first names were abbreviated. For example, old street directories and city directories always abbreviated common first names. Parish records often abbreviated familiar Christian names. This was done to save space and paper. In some jurisdictions, census enumerators would also abbreviate common first names when going door to door to save time.

Knowledge of first name abbreviations can be very helpful in tracking down ancestors. For example, knowing that Chas is a short form for Charles, Geo represents George, My means Mary and Hy means Henry opens up many more possibilities when looking through historic ancestral records.

It took us several years to collect and compile a list of common abbreviations for first names. To our knowledge, this is the most exhaustive list available on an important but often overlooked aspect of genealogy.

We recommend going the list below to familiarize yourself with common first name abbreviations and then reference the list as required when searching for specific ancestors.

Please note that when looking at old handwritten letters and records, the best indication of an abbreviation is that the author would usually superscript (raise the lettering of) the last one or two characters of the word. For example, a typed record might show an abbreviation for Joseph as Jos, whereas the handwritten record would usually show it as Jo s . Similarly for Elizabeth, it would appear Elizth in typed form and Eliz th in handwritten form.

Some authors also showed abbreviations by handwriting a horizontal line above or through the text, as in Dy for Dorothy.


The exact definition of taxonomy varies from source to source, but the core of the discipline remains: the conception, naming, and classification of groups of organisms. [1] As points of reference, recent definitions of taxonomy are presented below:

  1. Theory and practice of grouping individuals into species, arranging species into larger groups, and giving those groups names, thus producing a classification. [2]
  2. A field of science (and major component of systematics) that encompasses description, identification, nomenclature, and classification [3]
  3. The science of classification, in biology the arrangement of organisms into a classification [4]
  4. "The science of classification as applied to living organisms, including study of means of formation of species, etc." [5]
  5. "The analysis of an organism's characteristics for the purpose of classification" [6]
  6. "Systematics studies phylogeny to provide a pattern that can be translated into the classification and names of the more inclusive field of taxonomy" (listed as a desirable but unusual definition) [7]

The varied definitions either place taxonomy as a sub-area of systematics (definition 2), invert that relationship (definition 6), or appear to consider the two terms synonymous. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy (definitions 1 and 2), or a part of systematics outside taxonomy. [8] For example, definition 6 is paired with the following definition of systematics that places nomenclature outside taxonomy: [6]

  • Systematics: "The study of the identification, taxonomy, and nomenclature of organisms, including the classification of living things with regard to their natural relationships and the study of variation and the evolution of taxa".

A whole set of terms including taxonomy, systematic biology, systematics, biosystematics, scientific classification, biological classification, and phylogenetics have at times had overlapping meanings – sometimes the same, sometimes slightly different, but always related and intersecting. [1] [9] The broadest meaning of "taxonomy" is used here. The term itself was introduced in 1813 by de Candolle, in his Théorie élémentaire de la botanique. [10]

Monograph and taxonomic revision Edit

A taxonomic revision or taxonomic review is a novel analysis of the variation patterns in a particular taxon. This analysis may be executed on the basis of any combination of the various available kinds of characters, such as morphological, anatomical, palynological, biochemical and genetic. A monograph or complete revision is a revision that is comprehensive for a taxon for the information given at a particular time, and for the entire world. Other (partial) revisions may be restricted in the sense that they may only use some of the available character sets or have a limited spatial scope. A revision results in a conformation of or new insights in the relationships between the subtaxa within the taxon under study, which may result in a change in the classification of these subtaxa, the identification of new subtaxa, or the merger of previous subtaxa. [11]

Alpha and beta taxonomy Edit

The term "alpha taxonomy" is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. [12] In earlier literature, the term had a different meaning, referring to morphological taxonomy, and the products of research through the end of the 19th century. [13]

William Bertram Turrill introduced the term "alpha taxonomy" in a series of papers published in 1935 and 1937 in which he discussed the philosophy and possible future directions of the discipline of taxonomy. [14]

. there is an increasing desire amongst taxonomists to consider their problems from wider viewpoints, to investigate the possibilities of closer co-operation with their cytological, ecological and genetics colleagues and to acknowledge that some revision or expansion, perhaps of a drastic nature, of their aims and methods, may be desirable . Turrill (1935) has suggested that while accepting the older invaluable taxonomy, based on structure, and conveniently designated "alpha", it is possible to glimpse a far-distant taxonomy built upon as wide a basis of morphological and physiological facts as possible, and one in which "place is found for all observational and experimental data relating, even if indirectly, to the constitution, subdivision, origin, and behaviour of species and other taxonomic groups". Ideals can, it may be said, never be completely realized. They have, however, a great value of acting as permanent stimulants, and if we have some, even vague, ideal of an "omega" taxonomy we may progress a little way down the Greek alphabet. Some of us please ourselves by thinking we are now groping in a "beta" taxonomy. [14]

Turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy (pp. 365–366).

Later authors have used the term in a different sense, to mean the delimitation of species (not subspecies or taxa of other ranks), using whatever investigative techniques are available, and including sophisticated computational or laboratory techniques. [15] [12] Thus, Ernst Mayr in 1968 defined "beta taxonomy" as the classification of ranks higher than species. [16]

An understanding of the biological meaning of variation and of the evolutionary origin of groups of related species is even more important for the second stage of taxonomic activity, the sorting of species into groups of relatives ("taxa") and their arrangement in a hierarchy of higher categories. This activity is what the term classification denotes it is also referred to as "beta taxonomy".

Microtaxonomy and macrotaxonomy Edit

How species should be defined in a particular group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy. [17] [18] [12] By extension, macrotaxonomy is the study of groups at the higher taxonomic ranks subgenus and above. [12]

While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, a truly scientific attempt to classify organisms did not occur until the 18th century. Earlier works were primarily descriptive and focused on plants that were useful in agriculture or medicine. There are a number of stages in this scientific thinking. Early taxonomy was based on arbitrary criteria, the so-called "artificial systems", including Linnaeus's system of sexual classification for plants (Of course, Linnaeus's classification of animals was entitled "Systema Naturae" ("the System of Nature"), implying that he, at least, believed that it was more than an "artificial system"). Later came systems based on a more complete consideration of the characteristics of taxa, referred to as "natural systems", such as those of de Jussieu (1789), de Candolle (1813) and Bentham and Hooker (1862–1863). These classifications described empirical patterns and were pre-evolutionary in thinking. The publication of Charles Darwin's On the Origin of Species (1859) led to a new explanation for classifications, based on evolutionary relationships. This was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler (1883) and Engler (1886–1892). The advent of cladistic methodology in the 1970s led to classifications based on the sole criterion of monophyly, supported by the presence of synapomorphies. Since then, the evidentiary basis has been expanded with data from molecular genetics that for the most part complements traditional morphology. [19] [ page needed ] [20] [ page needed ] [21] [ page needed ]

Pre-Linnaean Edit

Early taxonomists Edit

Naming and classifying our surroundings has probably been taking place as long as mankind has been able to communicate. It would always have been important to know the names of poisonous and edible plants and animals in order to communicate this information to other members of the family or group. Medicinal plant illustrations show up in Egyptian wall paintings from c. 1500 BC, indicating that the uses of different species were understood and that a basic taxonomy was in place. [22]

Ancient times Edit

Organisms were first classified by Aristotle (Greece, 384–322 BC) during his stay on the Island of Lesbos. [23] [24] [25] He classified beings by their parts, or in modern terms attributes, such as having live birth, having four legs, laying eggs, having blood, or being warm-bodied. [26] He divided all living things into two groups: plants and animals. [24] Some of his groups of animals, such as Anhaima (animals without blood, translated as invertebrates) and Enhaima (animals with blood, roughly the vertebrates), as well as groups like the sharks and cetaceans, are still commonly used today. [27] His student Theophrastus (Greece, 370–285 BC) carried on this tradition, mentioning some 500 plants and their uses in his Historia Plantarum. Again, several plant groups currently still recognized can be traced back to Theophrastus, such as Cornus, Crocus, and Narcissus. [24]

Medieval Edit

Taxonomy in the Middle Ages was largely based on the Aristotelian system, [26] with additions concerning the philosophical and existential order of creatures. This included concepts such as the Great chain of being in the Western scholastic tradition, [26] again deriving ultimately from Aristotle. The aristotelian system did not classify plants or fungi, due to the lack of microscopes at the time, [25] as his ideas were based on arranging the complete world in a single continuum, as per the scala naturae (the Natural Ladder). [24] This, as well, was taken into consideration in the Great chain of being. [24] Advances were made by scholars such as Procopius, Timotheos of Gaza, Demetrios Pepagomenos, and Thomas Aquinas. Medieval thinkers used abstract philosophical and logical categorizations more suited to abstract philosophy than to pragmatic taxonomy. [24]

Renaissance and Early Modern Edit

During the Renaissance and the Age of Enlightenment, categorizing organisms became more prevalent, [24] and taxonomic works became ambitious enough to replace the ancient texts. This is sometimes credited to the development of sophisticated optical lenses, which allowed the morphology of organisms to be studied in much greater detail. One of the earliest authors to take advantage of this leap in technology was the Italian physician Andrea Cesalpino (1519–1603), who has been called "the first taxonomist". [28] His magnum opus De Plantis came out in 1583, and described more than 1500 plant species. [29] [30] Two large plant families that he first recognized are still in use today: the Asteraceae and Brassicaceae. [31] Then in the 17th century John Ray (England, 1627–1705) wrote many important taxonomic works. [25] Arguably his greatest accomplishment was Methodus Plantarum Nova (1682), [32] in which he published details of over 18,000 plant species. At the time, his classifications were perhaps the most complex yet produced by any taxonomist, as he based his taxa on many combined characters. The next major taxonomic works were produced by Joseph Pitton de Tournefort (France, 1656–1708). [33] His work from 1700, Institutiones Rei Herbariae, included more than 9000 species in 698 genera, which directly influenced Linnaeus, as it was the text he used as a young student. [22]

The Linnaean era Edit

The Swedish botanist Carl Linnaeus (1707–1778) [26] ushered in a new era of taxonomy. With his major works Systema Naturae 1st Edition in 1735, [34] Species Plantarum in 1753, [35] and Systema Naturae 10th Edition, [36] he revolutionized modern taxonomy. His works implemented a standardized binomial naming system for animal and plant species, [37] which proved to be an elegant solution to a chaotic and disorganized taxonomic literature. He not only introduced the standard of class, order, genus, and species, but also made it possible to identify plants and animals from his book, by using the smaller parts of the flower. [37] Thus the Linnaean system was born, and is still used in essentially the same way today as it was in the 18th century. [37] Currently, plant and animal taxonomists regard Linnaeus' work as the "starting point" for valid names (at 1753 and 1758 respectively). [38] Names published before these dates are referred to as "pre-Linnaean", and not considered valid (with the exception of spiders published in Svenska Spindlar [39] ). Even taxonomic names published by Linnaeus himself before these dates are considered pre-Linnaean. [22]

A pattern of groups nested within groups was specified by Linnaeus' classifications of plants and animals, and these patterns began to be represented as dendrograms of the animal and plant kingdoms toward the end of the 18th century, well before On the Origin of Species was published. [25] The pattern of the "Natural System" did not entail a generating process, such as evolution, but may have implied it, inspiring early transmutationist thinkers . Among early works exploring the idea of a transmutation of species were Erasmus Darwin's 1796 Zoönomia and Jean-Baptiste Lamarck's Philosophie Zoologique of 1809. [12] The idea was popularized in the Anglophone world by the speculative but widely read Vestiges of the Natural History of Creation, published anonymously by Robert Chambers in 1844. [40]

With Darwin's theory, a general acceptance quickly appeared that a classification should reflect the Darwinian principle of common descent. [41] Tree of life representations became popular in scientific works, with known fossil groups incorporated. One of the first modern groups tied to fossil ancestors was birds. [42] Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842. [43] [44] The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th centuries, palaeontologists worked to understand the history of animals through the ages by linking together known groups. [45] With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of the evolution of the major groups was in place. As evolutionary taxonomy is based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use. [46]

The cladistic method has emerged since the 1960s. [41] In 1958, Julian Huxley used the term clade. [12] Later, in 1960, Cain and Harrison introduced the term cladistic. [12] The salient feature is arranging taxa in a hierarchical evolutionary tree, with the desideratum that all named taxa are monophyletic. [41] A taxon is called monophyletic if it includes all the descendants of an ancestral form. [47] [48] Groups that have descendant groups removed from them are termed paraphyletic, [47] while groups representing more than one branch from the tree of life are called polyphyletic. [47] [48] Monophyletic groups are recognized and diagnosed on the basis of synapomorphies, shared derived character states. [49]

Cladistic classifications are compatible with traditional Linnean taxonomy and the Codes of Zoological and Botanical Nomenclature. [50] An alternative system of nomenclature, the International Code of Phylogenetic Nomenclature or PhyloCode has been proposed, whose intent is to regulate the formal naming of clades. [51] [52] Linnaean ranks will be optional under the PhyloCode, which is intended to coexist with the current, rank-based codes. [52] It remains to be seen whether the systematic community will adopt the PhyloCode or reject it in favor of the current systems of nomenclature that have been employed (and modified as needed) for over 250 years.

Kingdoms and domains Edit

Well before Linnaeus, plants and animals were considered separate Kingdoms. [53] Linnaeus used this as the top rank, dividing the physical world into the vegetable, animal and mineral kingdoms. As advances in microscopy made classification of microorganisms possible, the number of kingdoms increased, five- and six-kingdom systems being the most common.

Domains are a relatively new grouping. First proposed in 1977, Carl Woese's three-domain system was not generally accepted until later. [54] One main characteristic of the three-domain method is the separation of Archaea and Bacteria, previously grouped into the single kingdom Bacteria (a kingdom also sometimes called Monera), [53] with the Eukaryota for all organisms whose cells contain a nucleus. [55] A small number of scientists include a sixth kingdom, Archaea, but do not accept the domain method. [53]

Thomas Cavalier-Smith, who published extensively on the classification of protists, recently [ when? ] proposed that the Neomura, the clade that groups together the Archaea and Eucarya, would have evolved from Bacteria, more precisely from Actinobacteria. His 2004 classification treated the archaeobacteria as part of a subkingdom of the kingdom Bacteria, i.e., he rejected the three-domain system entirely. [56] Stefan Luketa in 2012 proposed a five "dominion" system, adding Prionobiota (acellular and without nucleic acid) and Virusobiota (acellular but with nucleic acid) to the traditional three domains. [57]

1735 [58]
1866 [59]
1925 [60]
1938 [61]
1969 [62]
Woese et al.
1990 [63]
1998 [56]
2015 [64]
2 kingdoms 3 kingdoms 2 empires 4 kingdoms 5 kingdoms 3 domains 2 empires, 6 kingdoms 2 empires, 7 kingdoms
(not treated) Protista Prokaryota Monera Monera Bacteria Bacteria Bacteria
Archaea Archaea
Eukaryota Protoctista Protista Eucarya Protozoa Protozoa
Chromista Chromista
Vegetabilia Plantae Plantae Plantae Plantae Plantae
Fungi Fungi Fungi
Animalia Animalia Animalia Animalia Animalia Animalia

Recent comprehensive classifications Edit

Partial classifications exist for many individual groups of organisms and are revised and replaced as new information becomes available however, comprehensive, published treatments of most or all life are rarer recent examples are that of Adl et al., 2012 and 2019, [65] [66] which covers eukaryotes only with an emphasis on protists, and Ruggiero et al., 2015, [67] covering both eukaryotes and prokaryotes to the rank of Order, although both exclude fossil representatives. [67] A separate compilation (Ruggiero, 2014) [68] covers extant taxa to the rank of family. Other, database-driven treatments include the Encyclopedia of Life, the Global Biodiversity Information Facility, the NCBI taxonomy database, the Interim Register of Marine and Nonmarine Genera, the Open Tree of Life, and the Catalogue of Life. The Paleobiology Database is a resource for fossils.

Biological taxonomy is a sub-discipline of biology, and is generally practiced by biologists known as "taxonomists", though enthusiastic naturalists are also frequently involved in the publication of new taxa. [69] Because taxonomy aims to describe and organize life, the work conducted by taxonomists is essential for the study of biodiversity and the resulting field of conservation biology. [70] [71]

Classifying organisms Edit

Biological classification is a critical component of the taxonomic process. As a result, it informs the user as to what the relatives of the taxon are hypothesized to be. Biological classification uses taxonomic ranks, including among others (in order from most inclusive to least inclusive): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species, and Strain. [72] [note 1]

Taxonomic descriptions Edit

The "definition" of a taxon is encapsulated by its description or its diagnosis or by both combined. There are no set rules governing the definition of taxa, but the naming and publication of new taxa is governed by sets of rules. [8] In zoology, the nomenclature for the more commonly used ranks (superfamily to subspecies), is regulated by the International Code of Zoological Nomenclature (ICZN Code). [73] In the fields of phycology, mycology, and botany, the naming of taxa is governed by the International Code of Nomenclature for algae, fungi, and plants (ICN). [74]

The initial description of a taxon involves five main requirements: [75]

  1. The taxon must be given a name based on the 26 letters of the Latin alphabet (a binomial for new species, or uninomial for other ranks).
  2. The name must be unique (i.e. not a homonym).
  3. The description must be based on at least one name-bearing type specimen.
  4. It should include statements about appropriate attributes either to describe (define) the taxon or to differentiate it from other taxa (the diagnosis, ICZN Code, Article 13.1.1, ICN, Article 38). Both codes deliberately separate defining the content of a taxon (its circumscription) from defining its name.
  5. These first four requirements must be published in a work that is obtainable in numerous identical copies, as a permanent scientific record.

However, often much more information is included, like the geographic range of the taxon, ecological notes, chemistry, behavior, etc. How researchers arrive at their taxa varies: depending on the available data, and resources, methods vary from simple quantitative or qualitative comparisons of striking features, to elaborate computer analyses of large amounts of DNA sequence data. [76]

Author citation Edit

An "authority" may be placed after a scientific name. [77] The authority is the name of the scientist or scientists who first validly published the name. [77] For example, in 1758 Linnaeus gave the Asian elephant the scientific name Elephas maximus, so the name is sometimes written as "Elephas maximus Linnaeus, 1758". [78] The names of authors are frequently abbreviated: the abbreviation L., for Linnaeus, is commonly used. In botany, there is, in fact, a regulated list of standard abbreviations (see list of botanists by author abbreviation). [79] The system for assigning authorities differs slightly between botany and zoology. [8] However, it is standard that if the genus of a species has been changed since the original description, the original authority's name is placed in parentheses. [80]

In phenetics, also known as taximetrics, or numerical taxonomy, organisms are classified based on overall similarity, regardless of their phylogeny or evolutionary relationships. [12] It results in a measure of evolutionary "distance" between taxa. Phenetic methods have become relatively rare in modern times, largely superseded by cladistic analyses, as phenetic methods do not distinguish common ancestral (or plesiomorphic) traits from new common (or apomorphic) traits. [81] However, certain phenetic methods, such as neighbor joining, have found their way into cladistics, as a reasonable approximation of phylogeny when more advanced methods (such as Bayesian inference) are too computationally expensive. [82]

Modern taxonomy uses database technologies to search and catalogue classifications and their documentation. [83] While there is no commonly used database, there are comprehensive databases such as the Catalogue of Life, which attempts to list every documented species. [84] The catalogue listed 1.64 million species for all kingdoms as of April 2016, claiming coverage of more than three quarters of the estimated species known to modern science. [85]


Projects in the Energy and Wildlife program use many abbreviations to describe partners, equipment, and places. The list below gives the abbreviation and full name of the abbreviations used throughout the Energy and Wildlife program website.


AEA — Alaska Energy Authority

AWEA — American Wind Energy Association

BCI — Bat Conservation International

BLM — Bureau of Land Management

BOEM — Bureau of Ocean Energy Management

BOR — Bureau of Reclamation

BSEE — Bureau of Safety and Environmental Enforcement

DEEP SEARCH — Deep-Sea Exploration to Advance Research on Coral/Canyon/Cold Seep Habitats

DISCOVRE — Diversity, Systematics and Connectivity of Vulnerable Reef Ecosystems

DNA — deoxyribonucleic acid

DOE — U.S. Department of Energy

DOI — U.S. Department of the Interior

DRECP — Desert Renewable Energy Conservation Plan

EIA — U.S. Energy Information Administration

EPA — U.S. Environmental Protection Agency

FSC — floating surface collector

GIS — geographic information system

GoMMAPPS — Gulf of Mexico Marine Assessment Program for Protected Species

GPS-GSM — Global Positioning System-Global System for Mobile Communications


Projects in the Energy and Wildlife program use many abbreviations to describe partners, equipment, and places. The list below gives the abbreviation and full name of the abbreviations used throughout the Energy and Wildlife program website.


AEA — Alaska Energy Authority

AWEA — American Wind Energy Association

BCI — Bat Conservation International

BLM — Bureau of Land Management

BOEM — Bureau of Ocean Energy Management

BOR — Bureau of Reclamation

BSEE — Bureau of Safety and Environmental Enforcement

DEEP SEARCH — Deep-Sea Exploration to Advance Research on Coral/Canyon/Cold Seep Habitats

DISCOVRE — Diversity, Systematics and Connectivity of Vulnerable Reef Ecosystems

DNA — deoxyribonucleic acid

DOE — U.S. Department of Energy

DOI — U.S. Department of the Interior

DRECP — Desert Renewable Energy Conservation Plan

EIA — U.S. Energy Information Administration

EPA — U.S. Environmental Protection Agency

FSC — floating surface collector

GIS — geographic information system

GoMMAPPS — Gulf of Mexico Marine Assessment Program for Protected Species

GPS-GSM — Global Positioning System-Global System for Mobile Communications

In fact, there are eleven of the abbreviations for the elements which don't seem to match the modern name. Those are subtle reminders of the history of the Periodic Table and the process of the discovery of elements over the millennia. Eight of these oddities are Au (gold), Ag (silver), Cu (copper), FE (iron), SN (tin), Pb (lead), Sb (antimony), and Hg (mercury): All were among the elements recognized by the ancient Greeks and Romans, and the abbreviations for those are based on a Latin or Greek term for the element.

Potassium was identified during the Middle Ages, and it's "K" is for kalium, a medieval Latin term for potash. W stands for tungsten because it was first identified in 1780 within the mineral known as wolframite, by French scientist Antoine Lavoisier (1743–1794). And finally, sodium gets an Na because it was first isolated by the English chemist Humphry Davy (1778–1829) in 1807 and he was referring to natron, an Arabic word for the salt used by the Egyptians to mummify people.

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Click a column header, such as Name, to sort the table by that item.
SEE Notes at the bottom of the Table.

Name Sym. M.P.
(g/cm 3 )
crust (%)*
Group* Electron configuration Ionization
energy (eV)
1 1.008HydrogenH-259-2530.090.14177611s 1 13.60
2 4.003HeliumHe-272-2690.18 1895181s 2 24.59
3 6.941LithiumLi1801,3470.53 18171[He] 2s 1 5.39
4 9.012BerylliumBe1,2782,9701.85 17972[He] 2s 2 9.32
5 10.811BoronB2,3002,5502.34 180813[He] 2s 2 2p 1 8.30
6 12.011CarbonC3,5004,8272.260.09ancient14[He] 2s 2 2p 2 11.26
7 14.007NitrogenN-210-1961.25 177215[He] 2s 2 2p 3 14.53
8 15.999OxygenO-218-1831.4346.71177416[He] 2s 2 2p 4 13.62
9 18.998FluorineF-220-1881.700.03188617[He] 2s 2 2p 5 17.42
10 20.180NeonNe-249-2460.90 189818[He] 2s 2 2p 6 21.56
11 22.990SodiumNa988830.972.7518071[Ne] 3s 1 5.14
12 24.305MagnesiumMg6391,0901.742.0817552[Ne] 3s 2 7.65
13 26.982AluminumAl6602,4672.708.07182513[Ne] 3s 2 3p 1 5.99
14 28.086SiliconSi1,4102,3552.3327.69182414[Ne] 3s 2 3p 2 8.15
15 30.974PhosphorusP442801.820.13166915[Ne] 3s 2 3p 3 10.49
16 32.065SulfurS1134452.070.05ancient16[Ne] 3s 2 3p 4 10.36
17 35.453ChlorineCl-101-353.210.05177417[Ne] 3s 2 3p 5 12.97
18 39.948ArgonAr-189-1861.78 189418[Ne] 3s 2 3p 6 15.76
19 39.098PotassiumK647740.862.5818071[Ar] 4s 1 4.34
20 40.078CalciumCa8391,4841.553.6518082[Ar] 4s 2 6.11
21 44.956ScandiumSc1,5392,8322.99 18793[Ar] 3d 1 4s 2 6.56
22 47.867TitaniumTi1,6603,2874.540.6217914[Ar] 3d 2 4s 2 6.83
23 50.942VanadiumV1,8903,3806.11 18305[Ar] 3d 3 4s 2 6.75
24 51.996ChromiumCr1,8572,6727.190.0417976[Ar] 3d 5 4s 1 6.77
25 54.938ManganeseMn1,2451,9627.430.0917747[Ar] 3d 5 4s 2 7.43
26 55.845IronFe1,5352,7507.875.05ancient8[Ar] 3d 6 4s 2 7.90
27 58.933CobaltCo1,4952,8708.90 17359[Ar] 3d 7 4s 2 7.88
28 58.693NickelNi1,4532,7328.900.02175110[Ar] 3d 8 4s 2 7.64
29 63.546CopperCu1,0832,5678.96 ancient11[Ar] 3d 10 4s 1 7.73
30 65.390ZincZn4209077.13 ancient12[Ar] 3d 10 4s 2 9.39
31 69.723GalliumGa302,4035.91 187513[Ar] 3d 10 4s 2 4p 1 6.00
32 72.640GermaniumGe9372,8305.32 188614[Ar] 3d 10 4s 2 4p 2 7.90
33 74.922ArsenicAs816135.72 ancient15[Ar] 3d 10 4s 2 4p 3 9.79
34 78.960SeleniumSe2176854.79 181716[Ar] 3d 10 4s 2 4p 4 9.75
35 79.904BromineBr-7593.12 182617[Ar] 3d 10 4s 2 4p 5 11.81
36 83.800KryptonKr-157-1533.75 189818[Ar] 3d 10 4s 2 4p 6 14.00
37 85.468RubidiumRb396881.63 18611[Kr] 5s 1 4.18
38 87.620StrontiumSr7691,3842.54 17902[Kr] 5s 2 5.69
39 88.906YttriumY1,5233,3374.47 17943[Kr] 4d 1 5s 2 6.22
40 91.224ZirconiumZr1,8524,3776.510.0317894[Kr] 4d 2 5s 2 6.63
41 92.906NiobiumNb2,4684,9278.57 18015[Kr] 4d 4 5s 1 6.76
42 95.940MolybdenumMo2,6174,61210.22 17816[Kr] 4d 5 5s 1 7.09
43*98.000TechnetiumTc2,2004,87711.50 19377[Kr] 4d 5 5s 2 7.28
44 101.070RutheniumRu2,2503,90012.37 18448[Kr] 4d 7 5s 1 7.36
45 102.906RhodiumRh1,9663,72712.41 18039[Kr] 4d 8 5s 1 7.46
46 106.420PalladiumPd1,5522,92712.02 180310[Kr] 4d 10 8.34
47 107.868SilverAg9622,21210.50 ancient11[Kr] 4d 10 5s 1 7.58
48 112.411CadmiumCd3217658.65 181712[Kr] 4d 10 5s 2 8.99
49 114.818IndiumIn1572,0007.31 186313[Kr] 4d 10 5s 2 5p 1 5.79
50 118.710TinSn2322,2707.31 ancient14[Kr] 4d 10 5s 2 5p 2 7.34
51 121.760AntimonySb6301,7506.68 ancient15[Kr] 4d 10 5s 2 5p 3 8.61
52 127.600TelluriumTe4499906.24 178316[Kr] 4d 10 5s 2 5p 4 9.01
53 126.905IodineI1141844.93 181117[Kr] 4d 10 5s 2 5p 5 10.45
54 131.293XenonXe-112-1085.90 189818[Kr] 4d 10 5s 2 5p 6 12.13
55 132.906CesiumCs296781.87 18601[Xe] 6s 1 3.89
56 137.327BariumBa7251,1403.590.0518082[Xe] 6s 2 5.21
57 138.906LanthanumLa9203,4696.15 18393[Xe] 5d 1 6s 2 5.58
58 140.116CeriumCe7953,2576.77 1803101[Xe] 4f 1 5d 1 6s 2 5.54
59 140.908PraseodymiumPr9353,1276.77 1885101[Xe] 4f 3 6s 2 5.47
60 144.240NeodymiumNd1,0103,1277.01 1885101[Xe] 4f 4 6s 2 5.53
61*145.000PromethiumPm1,1003,0007.30 1945101[Xe] 4f 5 6s 2 5.58
62 150.360SamariumSm1,0721,9007.52 1879101[Xe] 4f 6 6s 2 5.64
63 151.964EuropiumEu8221,5975.24 1901101[Xe] 4f 7 6s 2 5.67
64 157.250GadoliniumGd1,3113,2337.90 1880101[Xe] 4f 7 5d 1 6s 2 6.15
65 158.925TerbiumTb1,3603,0418.23 1843101[Xe] 4f 9 6s 2 5.86
66 162.500DysprosiumDy1,4122,5628.55 1886101[Xe] 4f 10 6s 2 5.94
67 164.930HolmiumHo1,4702,7208.80 1867101[Xe] 4f 11 6s 2 6.02
68 167.259ErbiumEr1,5222,5109.07 1842101[Xe] 4f 12 6s 2 6.11
69 168.934ThuliumTm1,5451,7279.32 1879101[Xe] 4f 13 6s 2 6.18
70 173.040YtterbiumYb8241,4666.90 1878101[Xe] 4f 14 6s 2 6.25
71 174.967LutetiumLu1,6563,3159.84 1907101[Xe] 4f 14 5d 1 6s 2 5.43
72 178.490HafniumHf2,1505,40013.31 19234[Xe] 4f 14 5d 2 6s 2 6.83
73 180.948TantalumTa2,9965,42516.65 18025[Xe] 4f 14 5d 3 6s 2 7.55
74 183.840TungstenW3,4105,66019.35 17836[Xe] 4f 14 5d 4 6s 2 7.86
75 186.207RheniumRe3,1805,62721.04 19257[Xe] 4f 14 5d 5 6s 2 7.83
76 190.230OsmiumOs3,0455,02722.60 18038[Xe] 4f 14 5d 6 6s 2 8.44
77 192.217IridiumIr2,4104,52722.40 18039[Xe] 4f 14 5d 7 6s 2 8.97
78 195.078PlatinumPt1,7723,82721.45 173510[Xe] 4f 14 5d 9 6s 1 8.96
79 196.967GoldAu1,0642,80719.32 ancient11[Xe] 4f 14 5d 10 6s 1 9.23
80 200.590MercuryHg-3935713.55 ancient12[Xe] 4f 14 5d 10 6s 2 10.44
81 204.383ThalliumTl3031,45711.85 186113[Xe] 4f 14 5d 10 6s 2 6p 1 6.11
82 207.200LeadPb3271,74011.35 ancient14[Xe] 4f 14 5d 10 6s 2 6p 2 7.42
83 208.980BismuthBi2711,5609.75 ancient15[Xe] 4f 14 5d 10 6s 2 6p 3 7.29
84*209.000PoloniumPo2549629.30 189816[Xe] 4f 14 5d 10 6s 2 6p 4 8.42
85*210.000AstatineAt3023370.00 194017[Xe] 4f 14 5d 10 6s 2 6p 5 9.30
86*222.000RadonRn-71-629.73 190018[Xe] 4f 14 5d 10 6s 2 6p 6 10.75
87*223.000FranciumFr276770.00 19391[Rn] 7s 1 4.07
88*226.000RadiumRa7001,7375.50 18982[Rn] 7s 2 5.28
89*227.000ActiniumAc1,0503,20010.07 18993[Rn] 6d 1 7s 2 5.17
90 232.038ThoriumTh1,7504,79011.72 1829102[Rn] 6d 2 7s 2 6.31
91 231.036ProtactiniumPa1,568015.40 1913102[Rn] 5f 2 6d 1 7s 2 5.89
92 238.029UraniumU1,1323,81818.95 1789102[Rn] 5f 3 6d 1 7s 2 6.19
93*237.000NeptuniumNp6403,90220.20 1940102[Rn] 5f 4 6d 1 7s 2 6.27
94*244.000PlutoniumPu6403,23519.84 1940102[Rn] 5f 6 7s 2 6.03
95*243.000AmericiumAm9942,60713.67 1944102[Rn] 5f 7 7s 2 5.97
96*247.000CuriumCm1,340013.50 1944102 5.99
97*247.000BerkeliumBk986014.78 1949102 6.20
98*251.000CaliforniumCf900015.10 1950102 6.28
99*252.000EinsteiniumEs86000.00 1952102 6.42
100*257.000FermiumFm1,52700.00 1952102 6.50
101*258.000MendeleviumMd000.00 1955102 6.58
102*259.000NobeliumNo82700.00 1958102 6.65
103*262.000LawrenciumLr1,62700.00 1961102 4.90
104*261.000RutherfordiumRf000.00 19644 0.00
105*262.000DubniumDb000.00 19675 0.00
106*266.000SeaborgiumSg000.00 19746 0.00
107*264.000BohriumBh000.00 19817 0.00
108*277.000HassiumHs000.00 19848 0.00
109*268.000MeitneriumMt000.00 19829 0.00
Name Sym. M.P.
(g/cm 3 )
Earth crust
Group* Electron configuration Ionization
energy (eV)

&bull Density of elements with boiling points below 0°C is given in g/l. In a sorted list, these elements are shown before other elements that have boiling points >0°C.
&bull Earth crust composition average values are from a report by F. W. Clarke and H. S. Washington, 1924. Elemental composition of crustal rocks differ between different localities (see article).
&bull Group: There are only 18 groups in the periodic table that constitute the columns of the table. Lanthanoids and Actinoids are numbered as 101 and 102 to separate them in sorting by group.
&bull The elements marked with an asterisk (in the 2nd column) have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Abbreviations and Definitions:

No. - Atomic Number M.P. - melting point B.P. - boiling point

Atomic number: The number of protons in an atom. Each element is uniquely defined by its atomic number.

Atomic mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. Atomic mass is measured in Atomic Mass Units (amu) which are scaled relative to carbon, 12 C, that is taken as a standard element with an atomic mass of 12. This isotope of carbon has 6 protons and 6 neutrons. Thus, each proton and neutron has a mass of about 1 amu.

Isotope: Atoms of the same element with the same atomic number, but different number of neutrons. Isotope of an element is defined by the sum of the number of protons and neutrons in its nucleus. Elements have more than one isotope with varying numbers of neutrons. For example, there are two common isotopes of carbon, 12 C and 13 C which have 6 and 7 neutrons respectively. The abundances of different isotopes of elements vary in nature depending on the source of materials. For relative abundances of isotopes in nature see reference on Atomic Weights and Isotopic Compositions.

Atomic weight: Atomic weight values represent weighted average of the masses of all naturally occurring isotopes of an element. The values shown here are based on the IUPAC Commission determinations (Pure Appl. Chem. 73:667-683, 2001). The elements marked with an asterisk have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Electron configuration: See next page for explanation of electron configuration of atoms.

Ionization energy (IE): The energy required to remove the outermost electron from an atom or a positive ion in its ground level. The table lists only the first IE in eV units. To convert to kJ/mol multiply by 96.4869. Reference: NIST Reference Table on Ground states and ionization energies for the neutral atoms. IE decreases going down a column of the periodic table, and increases from left to right in a row. Thus, alkali metals have the lowest IE in a period and Rare gases have the highest.

Where does acronym come from?

The first records of the word acronym come from the 1940s. It comes from a combination of acr- (a variant of acro–, meaning “tip end” and referring to using the first letters of each word in a phrase) and –onym, meaning “name” (as seen in words like synonym, antonym, and pseudonym).

Some common words started as acronyms: radar comes from an acronym for radio detection and ranging laser comes from an acronym for lightwave amplification by stimulated emission of radiation. As you can see in these two terms, acronyms are not always formed from just the first initial of each word, and not every word in the phrase always contributes a letter. There aren’t any strict rules—acronyms are typically formed in whatever way results in a word that’s easy to say.

This is the most technical sense of acronym—an abbreviation pronounced as a word. But it’s often used in a more general way to refer to any abbreviation, such as common text and chat abbreviations like brb and ttyl. These are more technically called initialisms.

Some abbreviations can be pronounced both as single words and letter-by-letter. For example, ASAP (for as soon as possible) is commonly pronounced A-S-A-P, but it can also be pronounced AY-sap. Still, terms like brb, ttyl, and ASAP are commonly thought of as acronyms.

Acronyms are commonly used to abbreviate organization names, but they’re used in all different contexts, including science, the military, government, slang, and pop culture.

Sometimes, people try to claim that a word actually came from an acronym when it really didn’t. This is called a backronym. Popular examples include the word posh, which is said to come from the phrase port out, starboard home, and tag, which is said to be an acronym for touch and go. Neither of these are true.

Dictionary of Water Terms

Here's a list of water-related terms that might help you understand our site better. It is compiled from a number of sources and should not be considered an "official" U.S. Geological Survey water glossary.

acequia--acequias are gravity-driven waterways, similar in concept to a flume. Most are simple ditches with dirt banks, but they can be lined with concrete. They were important forms of irrigation in the development of agriculture in the American Southwest. The proliferation of cotton, pecans and green chile as major agricultural staples owe their progress to the acequia system.

acid--a substance that has a pH of less than 7, which is neutral. Specifically, an acid has more free hydrogen ions (H + ) than hydroxyl ions (OH - ).

acre-foot (acre-ft)--the volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters.

adhesion--the process of water being attracted or adhering to other substances

alkaline--sometimes water or soils contain an amount of alkali (strongly basic) substances sufficient to raise the pH value above 7.0 and be harmful to the growth of crops.

alkalinity--the capacity of water for neutralizing an acid solution.

alluvium--deposits of clay, silt, sand, gravel, or other particulate material that has been deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain.

appropriation doctrine--the system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid west as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to Beneficial Use has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through nonuse they can also be sold or transferred apart from the land. Contrasts with Riparian Water Rights.

aquaculture--farming of plants and animals that live in water, such as fish, shellfish, and algae.

aqueduct--a pipe, conduit, or channel designed to transport water from a remote source, usually by gravity.

aquifer--a geologic formation(s) that is water bearing. A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people's uses.

aquifer (confined)--soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.

aquifer (unconfined)--an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.

artesian water--groundwater that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. See flowing well

artificial recharge--an process where water is put back into groundwater storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells.

atmosphere--layers of gases which surround the Earth. Although the atmosphere may not be a great storehouse of water, it is the superhighway used to move water around the globe.

base flow--sustained flow of a stream in the absence of direct runoff. It includes natural and human-induced streamflows. Natural base flow is sustained largely by groundwater discharges.

base--a substance that has a pH of more than 7, which is neutral. A base has less free hydrogen ions (H + ) than hydroxyl ions (OH - ).

basin--an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel.

bay--a body of water that is partly surrounded by land and partly surrounded by another body of water.

bedrock--the solid rock beneath the soil and superficial rock. A general term for solid rock that lies beneath soil, loose sediments, or other unconsolidated material.

brook--a small stream

capillary action--the means by which liquid moves through the porous spaces in a solid, such as soil, plant roots, and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in plants and animals.

commercial water use--water used for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.

condensation--the process of water vapor in the air turning into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation.

consumptive use--that part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumed.

conveyance loss--water that is lost in transit from a pipe, canal, or ditch by leakage or evaporation. Generally, the water is not available for further use however, leakage from an irrigation ditch, for example, may percolate to a groundwater source and be available for further use.

creek--a natural stream of water normally smaller than and often tributary to a river.

cubic feet per second (cfs)--a rate of the flow, in streams and rivers, for example. It is equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One "cfs" is equal to 7.48 gallons of water flowing each second. As an example, if your car's gas tank is 2 feet by 1 foot by 1 foot (2 cubic feet), then gas flowing at a rate of 1 cubic foot/second would fill the tank in two seconds.

desalination--the removal of salts from saline water to provide freshwater. This method is becoming a more popular way of providing freshwater to populations.

dew--liquid water droplets that form by means of condensation on grass, spider webs, and other cool surfaces in the early morning or late evening.

discharge--the volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second.

domestic water use--water used for household purposes, such as drinking, food preparation, bathing, washing clothes, dishes, and dogs, flushing toilets, and watering lawns and gardens. About 85% of domestic water is delivered to homes by a public-supply facility, such as a county water department. About 15% of the Nation's population supply their own water, mainly from wells.

drainage basin--land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. Also called a "watershed."

drawdown--a lowering of the groundwater surface caused by pumping.

drought--a period of drier-than-normal conditions that results in water-related problems.

drip irrigation--a common irrigation method where pipes or tubes filled with water slowly drip onto crops. Drip irrigation is a low-pressure method of irrigation and less water is lost to evaporation than high-pressure spray irrigation.

effluent--water that flows from a sewage treatment plant after it has been treated.

erosion--the process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream.

estuary--a place where fresh and salt water mix, such as a bay, salt marsh, or where a river enters an ocean.

evaporation--the process of liquid water becoming water vapor, including vaporization from water surfaces, land surfaces, and snow fields, but not from leaf surfaces. See transpiration

evapotranspiration--the sum of evaporation and transpiration.

flood--An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean.

flood, 100-year--A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent chance of being equaled or exceeded in any given year.

flood plain--a strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.

flood stage--The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.

floodway--The channel of a river or stream and the parts of the floodplain adjoining the channel that are reasonably required to efficiently carry and discharge the flood water or flood flow of a river or stream.

flowing well/spring--a well or spring that taps groundwater under pressure so that water rises without pumping. If the water rises above the surface, it is known as a flowing well.

freshwater, fresh water--water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids generally, more than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses.

gage height--the height of the water surface above the gage datum (zero point). Gage height is often used interchangeably with the more general term, stage, although gage height is more appropriate when used with a gage reading.

gaging station--a site on a stream, lake, reservoir or other body of water where observations and hydrologic data are obtained. The U.S. Geological Survey measures stream discharge at gaging stations.

geyser--a geothermal feature of the Earth where there is an opening in the surface that contains superheated water that periodically erupts in a shower of water and steam.

giardiasis--a disease that results from an infection by the protozoan parasite Giardia Intestinalis, caused by drinking water that is either not filtered or not chlorinated. The disorder is more prevalent in children than in adults and is characterized by abdominal discomfort, nausea, and alternating constipation and diarrhea.

glacier--a huge mass of ice, formed on land by the compaction and recrystallization of snow, that moves very slowly downslope or outward due to its own weight.

greywater--wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks.

groundwater--(1) water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust.

groundwater, confined--groundwater under pressure significantly greater than atmospheric, with its upper limit the bottom of a bed with hydraulic conductivity distinctly lower than that of the material in which the confined water occurs.

groundwater recharge--inflow of water to a groundwater reservoir from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.

groundwater, unconfined--water in an aquifer that has a water table that is exposed to the atmosphere.

hardness--a water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium. If the water you use is "hard" then more soap, detergent or shampoo is necessary to raise a lather.

headwater(s)--(1) the source and upper reaches of a stream also the upper reaches of a reservoir. (2) the water upstream from a structure or point on a stream. (3) the small streams that come together to form a river. Also may be thought of as any and all parts of a river basin except the mainstream river and main tributaries.

hydroelectric power water use--the use of water in the generation of electricity at plants where the turbine generators are driven by falling water.

hydrologic cycle--the cyclic transfer of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans.

ice--water in it's solid state. Water turns to ice at 32 degrees Fahrenheit.

impermeable layer--a layer of solid material, such as rock or clay, which does not allow water to pass through.

industrial water use--water used for industrial purposes in such industries as steel, chemical, paper, and petroleum refining. Nationally, water for industrial uses comes mainly (80%) from self-supplied sources, such as a local wells or withdrawal points in a river, but some water comes from public-supplied sources, such as the county/city water department.

infiltration--flow of water from the land surface into the subsurface.

injection well--refers to a well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don't deliver drinking water, unused aquifers, or below freshwater levels.

irrigation--the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall. Here's a quick look at some types of irrigation systems.

irrigation water use--water application on lands to assist in the growing of crops and pastures or to maintain vegetative growth in recreational lands, such as parks and golf courses.

kilogram--one thousand grams.

kilowatthour (KWH)--a power demand of 1,000 watts for one hour. Power company utility rates are typically expressed in cents per kilowatt-hour.

lake--where surface-water runoff (and maybe some groundwater seepage) have accumulated in a low spot, relative to the surrounding countryside.

leaching--the process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water.

lentic waters--ponds or lakes (standing water).

levee--a natural or manmade earthen barrier along the edge of a stream, lake, or river. Land alongside rivers can be protected from flooding by levees.

livestock water use--water used for livestock watering, feed lots, dairy operations, fish farming, and other on-farm needs.

lotic waters--flowing waters, as in streams and rivers.

marsh--a primarily grassy area where water covers the ground most of the time. A marsh may be prone to flooding during wet seasons.

maximum contaminant level (MCL)--the designation given by the U.S. Environmental Protection Agency (EPA) to water-quality standards promulgated under the Safe Drinking Water Act. The MCL is the greatest amount of a contaminant that can be present in drinking water without causing a risk to human health.

milligram (mg)--One-thousandth of a gram.

milligrams per liter (mg/l)--a unit of the concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1 liter of water. It is approximately equal to one part per million (PPM).

million gallons per day (Mgal/d)--a rate of flow of water equal to 133,680.56 cubic feet per day, or 1.5472 cubic feet per second, or 3.0689 acre-feet per day. A flow of one million gallons per day for one year equals 1,120 acre-feet (365 million gallons).

mining water use--water use during quarrying rocks and extracting minerals from the land.

municipal water system--a water system that has at least five service connections or which regularly serves 25 individuals for 60 days also called a public water system

nephelometric turbidity unit (NTU)--unit of measure for the turbidity of water. Essentially, a measure of the cloudiness of water as measured by a nephelometer. Turbidity is based on the amount of light that is reflected off particles in the water.

NAVD--The North American Vertical Datum of 1988 (NAVD 88) is the vertical control datum established in 1991 by the minimum-constraint adjustment of the Canadian-Mexican-United States leveling observations. It held fixed the height of the primary tidal bench mark, referenced to the new International Great Lakes Datum of 1985 local mean sea level height value, at Father Point/Rimouski, Quebec, Canada.

NGVD--National Geodetic Vertical Datum. (1) As corrected in 1929, a vertical control measure used as a reference for establishing varying elevations. (2) Elevation datum plane previously used by the Federal Emergency Management Agency (FEMA) for the determination of flood elevations. FEMA current uses the North American Vertical Datum Plane.

NGVD of 1929--National Geodetic Vertical Datum of 1929. A geodetic datum derived from a general adjustment of the first order level nets of the United States and Canada. It was formerly called "Sea Level Datum of 1929" or "mean sea level" in the USGS series of reports. Although the datum was derived from the average sea level over a period of many years at 26 tide stations along the Atlantic, Gulf of Mexico, and Pacific Coasts, it does not necessarily represent local mean sea level at any particular place.

non-point source (NPS) pollution--pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides.

ocean--Earth's largest bodies of water are called oceans. They divide Earth's continents and contain saline water.

organic matter--plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.

osmosis--the movement of water molecules through a thin membrane. The osmosis process occurs in our bodies and is also one method of desalinating saline water.

outfall--the place where a sewer, drain, or stream discharges the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body.

oxygen demand--the need for molecular oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen will dissolve in water, it is extremely important in biological and chemical processes.

pH--a measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions.
View a diagram about pH.

particle size--the diameter, in millimeters, of suspended sediment or bed material.
Particle-size classifications are:
[1] Clay—0.00024-0.004 millimeters (mm)
[2] Silt—0.004-0.062 mm
[3] Sand—0.062-2.0 mm and
[4] Gravel—2.0-64.0 mm.

parts per billion--the number of "parts" by weight of a substance per billion parts of water. Used to measure extremely small concentrations.

parts per million--the number of "parts" by weight of a substance per million parts of water. This unit is commonly used to represent pollutant concentrations.

pathogen--a disease-producing agent usually applied to a living organism. Generally, any viruses, bacteria, or fungi that cause disease.

peak flow--the maximum instantaneous discharge of a stream or river at a given location. It usually occurs at or near the time of maximum stage.

per capita use--the average amount of water used per person during a standard time period, generally per day.

percentile --The value below which a given percentage of observations in a group of observations fall. For example, the 20th percentile is the value below which 20 percent of the observations may be found.

percolation--(1) The movement of water through the openings in rock or soil. (2) the entrance of a portion of the streamflow into the channel materials to contribute to groundwater replenishment.

permeability--the ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas impermeable material, such as clay, don't allow water to flow freely.

point-source pollution--water pollution coming from a single point, such as a sewage-outflow pipe.

polychlorinated biphenyls (PCBs)--a group of synthetic, toxic industrial chemical compounds once used in making paint and electrical transformers, which are chemically inert and not biodegradable. PCBs were frequently found in industrial wastes, and subsequently found their way into surface and groundwaters. As a result of their persistence, they tend to accumulate in the environment. In terms of streams and rivers, PCBs are drawn to sediment, to which they attach and can remain virtually indefinitely. Although virtually banned in 1979 with the passage of the Toxic Substances Control Act, they continue to appear in the flesh of fish and other animals.

porosity--a measure of the water-bearing capacity of subsurface rock. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer because the pores are usually so small.

potable water--water of a quality suitable for drinking.

potentiometric surface/piezometric surface--the imaginary line where a given reservoir of fluid will "equalize out to" if allowed to flow a potentiometric surface is based on hydraulic principles.

precipitation--rain, snow, hail, sleet, dew, and frost.

primary wastewater treatment--the first stage of the wastewater-treatment process where mechanical methods, such as filters and scrapers, are used to remove pollutants. Solid material in sewage also settles out in this process.

prior appropriation doctrine--the system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid West as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to beneficial use has a higher priority of right than a subsequent user. The rights can be lost through nonuse they can also be sold or transferred apart from the land. Contrasts with riparian water rights.

public supply--water withdrawn by public governments and agencies, such as a county water department, and by private companies that is then delivered to users. Public suppliers provide water for domestic, commercial, thermoelectric power, industrial, and public water users. Most people's household water is delivered by a public water supplier. The systems have at least 15 service connections (such as households, businesses, or schools) or regularly serve at least 25 individuals daily for at least 60 days out of the year.

public water use--water supplied from a public-water supply and used for such purposes as firefighting, street washing, and municipal parks and swimming pools.

rating curve--A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station.

reach--any length of a stream or river. The term is often used by hydrologists when they’re referring to a small section of a stream or river rather than its entire length.

recharge--water added to an aquifer. For instance, rainfall that seeps into the ground.

reclaimed wastewater--wastewater-treatment plant effluent that has been diverted for beneficial uses such as irrigation, industry, or thermoelectric cooling instead of being released to a natural waterway or aquifer.

recycled water--water that is used more than one time before it passes back into the natural hydrologic system.

reservoir--a pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.

return flow--(1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.

return flow (irrigation)--irrigation water that is applied to an area and which is not consumed in evaporation or transpiration and returns to a surface stream or aquifer.

reverse osmosis--(1) (Desalination) The process of removing salts from water using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through, while the salt waste (brine) is removed and disposed. This process differs from electrodialysis, where the salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. (2) (Water Quality) An advanced method of water or wastewater treatment that relies on a semi-permeable membrane to separate waters from pollutants. An external force is used to reverse the normal osmotic process resulting in the solvent moving from a solution of higher concentration to one of lower concentration.

riparian water rights--the rights of an owner whose land abuts water. They differ from state to state and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the streamflow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on nonriparian land.

river--A natural stream of water of considerable volume, larger than a brook or creek.

runoff--(1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it.

saline water--water that contains significant amounts of dissolved solids.

Here are our parameters for saline water:
Fresh water - Less than 1,000 parts per million (ppm)
Slightly saline water - From 1,000 ppm to 3,000 ppm
Moderately saline water - From 3,000 ppm to 10,000 ppm
Highly saline water - From 10,000 ppm to 35,000 ppm

sea--a body of water that is smaller than an ocean and usually located where the land and ocean meet.

secondary wastewater treatment--treatment (following primary wastewater treatment) involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems and which generally removes 80 to 95 percent of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or chemical-physical methods. Activated sludge and trickling filters are two of the most common means of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.

sediment--usually applied to material in suspension in water or recently deposited from suspension. In the plural the word is applied to all kinds of deposits from the waters of streams, lakes, or seas.

sedimentary rock--rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water and (2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.

sedimentation tanks--wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.

self-supplied water--water withdrawn from a surface- or groundwater source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.

seepage--(1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.

septic tank--a tank used to detain domestic wastes to allow the settling of solids prior to distribution to a leach field for soil absorption. Septic tanks are used when a sewer line is not available to carry them to a treatment plant. A settling tank in which settled sludge is in immediate contact with sewage flowing through the tank, and wherein solids are decomposed by anaerobic bacterial action.

settling pond (water quality)--an open lagoon into which wastewater contaminated with solid pollutants is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the lagoon and the liquid is allowed to overflow out of the enclosure.

sewage treatment plant--a facility designed to receive the wastewater from domestic sources and to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water. The substances removed are classified into four basic areas:
[1] greases and fats
[2] solids from human waste and other sources
[3] dissolved pollutants from human waste and decomposition products and
[4] dangerous microorganisms.
Most facilities employ a combination of mechanical removal steps and bacterial decomposition to achieve the desired results. Chlorine is often added to discharges from the plants to reduce the danger of spreading disease by the release of pathogenic bacteria.

sewer--a system of underground pipes that collect and deliver wastewater to treatment facilities or streams.

sinkhole--a depression in the Earth's surface caused by dissolving of underlying limestone, salt, or gypsum. Drainage is provided through underground channels that may be enlarged by the collapse of a cavern roof.

snow--precipitation in the form of ice crystals. Snow forms when the air temperature is at or below 32 degrees Fahrenheit.

solute--a substance that is dissolved in another substance, thus forming a solution.

solution--a mixture of a solvent and a solute. In some solutions, such as sugar water, the substances mix so thoroughly that the solute cannot be seen. But in other solutions, such as water mixed with dye, the solution is visibly changed.

solvent--a substance that dissolves other substances, thus forming a solution. Water dissolves more substances than any other, and is known as the "universal solvent".

specific conductance--a measure of the ability of water to conduct an electrical current as measured using a 1-cm cell and expressed in units of electrical conductance, i.e., Siemens per centimeter at 25 degrees Celsius. Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality, specific conductance is used in groundwater monitoring as an indication of the presence of ions of chemical substances that may have been released by a leaking landfill or other waste storage or disposal facility. A higher specific conductance in water drawn from downgradient wells when compared to upgradient wells indicates possible contamination from the facility.

sprain--an archaic term (1600's) referring to a spring or branch of a river. Spelling was "sprayne".

spray irrigation--an common irrigation method where water is shot from high-pressure sprayers onto crops. Because water is shot high into the air onto crops, some water is lost to evaporation.

spring--a water body formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of groundwater at or below the local water table, below which the subsurface material is saturated with water.

stage--the water level above some arbitrary point in the river and is commonly measured in feet.

steam--water in a gas state. See vapor

storm sewer--a sewer that carries only surface runoff, street wash, and snow melt from the land. In a separate sewer system, storm sewers are completely separate from those that carry domestic and commercial wastewater (sanitary sewers).

stream--a general term for a body of flowing water natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal.

streamflow--the water discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation.

subsidence--a dropping of the land surface as a result of groundwater being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.

supernatum --the top level of a fluid at rest important in many applications of water and wastewater treatment. In particular, it is of concern and often measured in settling tanks and skimmers.

surface tension--the attraction of molecules to each other on a liquid's surface. Thus, a barrier is created between the air and the liquid.

surface water--water that is on the Earth's surface, such as in a stream, river, lake, or reservoir.

suspended sediment--very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.

suspended-sediment concentration--the ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.

suspended-sediment discharge--the quantity of suspended sediment passing a point in a stream over a specified period of time. When expressed in tons per day, it is computed by multiplying water discharge (in cubic feet per second) by the suspended-sediment concentration (in milligrams per liter) and by the factor 0.0027.

suspended solids--solids that are not in true solution and that can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods.

tertiary wastewater treatment--selected biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment practices the additional treatment of effluent beyond that of primary and secondary treatment methods to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process: (1) First, in the primary wastewater treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes (2) Second, in the secondary wastewater treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds and (3) Third, the tertiary wastewater treatment process consists of flocculation basins, clarifiers, filters, and chlorine basins or ozone or ultraviolet radiation processes.

thermal pollution--a reduction in water quality caused by increasing its temperature, often due to disposal of waste heat from industrial or power generation processes. Thermally polluted water can harm the environment because plants and animals can have a hard time adapting to it.

thermoelectric power water use--water used in the process of the generation of thermoelectric power. Power plants that burn coal and oil are examples of thermoelectric-power facilities.

transmissibility (groundwater)--the capacity of a rock to transmit water under pressure. The coefficient of transmissibility is the rate of flow of water, at the prevailing water temperature, in gallons per day, through a vertical strip of the aquifer one foot wide, extending the full saturated height of the aquifer under a hydraulic gradient of 100-percent. A hydraulic gradient of 100-percent means a one foot drop in head in one foot of flow distance.

transpiration--process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. See evapotranspiration.

tributary--a smaller river or stream that flows into a larger river or stream. Usually, a number of smaller tributaries merge to form a river.

turbidity--the amount of solid particles that are suspended in water and that cause light rays shining through the water to scatter. Thus, turbidity makes the water cloudy or even opaque in extreme cases. Turbidity is measured in nephelometric turbidity units (NTU).

unsaturated zone--the zone immediately below the land surface where the pores contain both water and air, but are not totally saturated with water. These zones differ from an aquifer, where the pores are saturated with water.

vapor--created when a substance (such as water) is in a gas state. Particles of the substance will be suspended or diffused in the air. See evaporation

volume--the amount of space that a substance (such as water) occupies.

wastewater--water that has been used in homes, industries, and businesses that is not for reuse unless it is treated.

wastewater-treatment return flow--water returned to the environment by wastewater-treatment facilities.

water cycle--the circuit of water movement from the oceans to the atmosphere and to the Earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transportation.

water year--a continuous 12-month period selected to present data relative to hydrologic or meteorological phenomena during which a complete annual hydrologic cycle normally occurs. The water year used by the U.S. Geological Survey runs from October 1 through September 30, and is designated by the year in which it ends.

water quality--a term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose.

water table--the top of the water surface in the saturated part of an aquifer.

water use--water that is used for a specific purpose, such as for domestic use, irrigation, or industrial processing. Water use pertains to human's interaction with and influence on the hydrologic cycle, and includes elements, such as water withdrawal from surface- and groundwater sources, water delivery to homes and businesses, consumptive use of water, water released from wastewater-treatment plants, water returned to the environment, and instream uses, such as using water to produce hydroelectric power.

watershed--the land area that drains water to a particular stream, river, or lake. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large watersheds, like the Mississippi River basin contain thousands of smaller watersheds.

watthour (Wh)--an electrical energy unit of measure equal to one watt of power supplied to, or taken from, an electrical circuit steadily for one hour.

well (water)--an artificial excavation put down by any method for the purposes of withdrawing water from the underground aquifers. A bored, drilled, or driven shaft, or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach undergroundwater supplies or oil, or to store or bury fluids below ground.

withdrawal--water removed from a ground- or surface-water source for use.

xeriscaping--a method of landscaping that uses plants that are well adapted to the local area and are drought-resistant. Xeriscaping is becoming more popular as a way of saving water at home.
More on xeriscaping: Colorado WaterWise Council

yield--mass per unit time per unit area

Some of this information is courtesy of the Nevada Division of Water Resources.

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