bluuebunny/crossref_metadata_2025 huggingface dataset:
Rock Fracture
Authors: Priyadarshi Nitish
Published: April 2005

From their origin, rocks are more or less disturbed by forces acting within the lithosphere. When a mass of rock is not strong enough to resist forces that are tending either to compress it or to stretch it, the rock is deformed. The change of form is brought about by flow in the deeper parts of the lithosphere and fractures in the upper parts. Fractures in rocks are either joints or faults.

The term joint is most commonly used in reference to relatively continuous and through‐going fractures that are reasonably planar and along which there has been imperceptible movement. Joints may form as a result of either diastrophism or contraction.

A fault may be defined as a fracture along which there has been slipping of contiguous masses against one another. Points formerly in contact have been dislocated or displaced along the fracture. Solid rocks or unconsolidated sands, gravel, etc. may be dislocated in this way. Faulting may result from compression, tension, or torsion. Some faults in loose or weakly consolidated clays, sands, and gravels are produced by the removal of a support.
Safe Yield of an Aquifer
Authors: Wilson Eric S.
Published: April 2005

Safe yield is a controversial term and concept that may be defined for common usage as the amount of water an aquifer system can yield over a long period without producing unacceptable effects. Unacceptable effects may include an excessive decline in groundwater level, sometimes described as groundwater mining; reduction or elimination of riparian vegetation; reduction or elimination of water in streams, lakes, springs, and wetlands; aquifer compaction and land subsidence; reduction in groundwater underflow to downgradient aquifer systems; a change in groundwater temperature; an undesirable change in the chemical quality of groundwater; and salt water intrusion into aquifer systems adjacent to oceans or saline lakes.

The definition of safe yield has evolved for nearly a century; initially, it was defined by Lee (1) as “… the limit and quantity of water which can be withdrawn regularly and permanently without dangerous depletion of the storage reserve.” The definition was modified and expanded by Meinzer (2), Conkling (3), and Todd (4). Due to ambiguity and lack of agreement on the definition, many authors have suggested abandoning the term (5–7) for an alternate term such as “sustainable yield.”
Saline Seep
Authors: Moore John E.
Published: April 2005

Jackson defines saline seep as an intermittent or continuous saline water discharge at or near the soil surface under dryland conditions that reduces or eliminates crop growth. Human induced salinization of land and water resources due to water table rise is as old as the history of human settlement and irrigation. Early settlements in the valleys of the Tigris and Euphrates flourished about 4000
B.C.
: however, the irrigated farming of wheat resulted in salt accumulation, and in time the area was abandoned. Historic evidence from Russia, China, India, Pakistan, South American, United States, Canada, and Australia show that saline seeps are a worldwide problem. The number of saline seeps will probably increase in the future because an increase in world population will be accompanied by increases in irrigation.
Sensitivity of Groundwater to Contamination
Authors: Trojan Michael D.
Published: April 2005

For this discussion, groundwater sensitivity is defined asthe likelihood for contaminants to reach a specified position in the groundwater system after introduction at some location above the specified position. Sensitivity is a widely applied concept that has several uses. Sensitivity analyses often lead to the development of maps showing the relative sensitivity of groundwater across a geographic area. These maps are used as a screening tool for land‐use decisions and have increasingly been used in source water protection. Sensitivity analyses are also used in program development, such as identifying areas where groundwater monitoring will occur. The concept of groundwater sensitivity also has educational value because hydrogeologic concepts are easily expressed and the audience can visualize relationships between land use and aquifer protection.
Soil and Water Contamination by Heavy Metals
Authors: Brye Kristofor R. , Steele Kenneth F.
Published: April 2005

Soil and water contamination by heavy metals has a major adverse environmental impact. Concern has long existed over the threat of contamination of soil and water resources by heavy metals but has heightened in recent years as more knowledge has been gained about the negative and potentially serious affects that chronic exposure to heavy metals may have on the health of humans and other living organisms. Long‐term exposure to lead affects human cognition; cadmium affects kidney, liver, and gastrointestinal tract functioning; and arsenic affects the skin, kidneys, and central nervous system. This article will address terminology, sources, mobility, risk assessment, and management and remediation alternatives for heavy metals in the environment that may contaminate soil and water resources.
Water Level Drawdown
Authors: Steele Mark D.
Published: April 2005

Contrary to the popular image of caverns and underground rivers, ground water is the water that fills or saturates the soil in a specific location.
Water level drawdown
describes the effect on the actual or potential water surface of removing water from a well, trench, or sump. The water table is the interface between this saturated water/soil zone (or aquifer) and an unsaturated water/soil zone. The concept of an aquifer can be easily seen by filling a jar with rocks. Water can then be poured into the jar to fill up the empty spaces between the rocks. The level of the water in the jar is analogous to the subsurface water table, and the volume saturated with water is the aquifer. If one then placed a straw in the middle of the jar and began to pull out water, the water table would become depressed in a cone shape around the straw similar to the depression in the water level of a sink as the water goes down the drain. This depression in the water table is known as the cone of depression. The vertical difference, at any given point, between the original (or static) water level and the water surface formed by the cone of depression is called the
drawdown
.
Well Hydraulics and Aquifer Tests
Authors: Moore John E.
Published: April 2005

The objectives of an aquifer test are to identify the performance of a well (to estimate the yield capability) and to estimate aquifer properties. Accurate estimates of the hydraulic characteristics of aquifers depend on reliable aquifer test data. The tests are done on existing wells or a well drilled specifically for that purpose. An aquifer test is a controlled, field site experiment to determine hydraulic conductivity and aquifer storage. The test consists of measuring groundwater discharge and observing water level changes in the pumped well.
Groundwater Remediation Project Life Cycle
Authors: Jacobs James A.
Published: April 2005

During the past decade, the groundwater remediation project life cycle has been used to characterize the status of an environmental project. If groundwater or soil contamination is suspected, a general process from assessment to closure occurs. In some cases, the project may involve many stakeholders, including landowners, responsible parties, bankers, operators/tenants, consultants, and regulators. In addition, others in the process might include environmental attorneys, realtors, developers, and interested parties such as neighbors and the community. Although the timing and specific activities may vary from site to site, a general phased process occurs. Environmental evaluations of potential leakage or spillage of hazardous substances into the subsurface generally consist of four phases (Phase I through Phase IV). The generalized four‐phase approach reflects the realistic process required to take a potentially impacted property from assessment phase (Phase I) through to the final monitoring and site closure phase (Phase IV). The phases generally proceed in order starting with Phase I. Some sites where soil or groundwater contamination is already suspected or documented might start with Phase II when a site has an underground tank or even Phase III, in the case of visually stained surface soils.
Groundwater Contamination from Municipal Landfills in the
USA
Authors: Tonjes David J.
Published: April 2005

Groundwater contamination has been a significant environmental impact associated with landfills. Landfilling can affect groundwater quality through leachate releases, landfill gas migration, and runoff. Leachate releases are the most common and serious cause of impacts. Plume chemistry often limits extensive contamination to salts, ammonia, and redox‐sensitive metals. Liners and gas control systems are effective in preventing pollution at modern facilities.
Groundwater Dating with Radiocarbon
Authors: Priyadarshi Nitish
Published: April 2005

Groundwater age, based on measurement of the concentrations of chemical and isotopic substances in water, refers to the time elapsed since the introduction of the chemical or isotopic substance into the water, or to be more precise, the time elapsed since the chemical or isotopic substance was recharged and isolated from the modern reservoir. Although we often refer to dating of groundwater, we are actually dating a chemical substance that is dissolved in the groundwater, not the water itself.

Various environmental isotopes and tracers are used to determine the age of groundwater. Carbon‐14 is used to date ground waters older than 1000 years.

The
14
C generated in the atmosphere is carried down to the earth's surface by precipitation and becomes incorporated into the biomass or transported into waterbodies such as lakes, oceans, and groundwater.
14
C undergoes radioactive decay (to
14
N), so that once isolated from the atmosphere, the amount of
14
C decreases with time.
Infiltrometers
Authors: Holden Joseph
Published: April 2005

Infiltrometers allow measuring of the rate of infiltration of water into a given medium. Rain simulators, a particular type of infiltrometer, are discussed elsewhere (see entry R
AIN
S
IMULATORS
). Unlike rain simulators, other infiltrometers do not simulate raindrop activity but measure the rate of infiltration from a reservoir of water at the ground surface. Their main advantage is their simplicity and ease of use. There are two main types of infiltrometer, a ponded ring infiltrometer and a disk infiltrometer.
Irrigation Water Quality in District
H
ardwar,
U
ttaranchal,
I
ndia
Authors: Jain Chakresh K.
Published: April 2005

The groundwater quality of District Hardwar in the state of Uttaranchal (India) was assessed to determine the suitability of groundwater for irrigation. Two sets of 48 groundwater samples from shallow and deep aquifers were collected during pre‐ and postmonsoon seasons in the year 2002, and the suitability of the groundwater for irrigation was evaluated based on salinity, sodium adsorption ration (SAR), residual sodium carbonate (RSC), and boron content. The values of SAR ranged from 0.24–1.75 during the premonsoon season and from 0.22–1.92 during the postmonsoon season, respectively. Values of the SAR indicate that the majority of samples of the study area falls under the category of low sodium hazard, indicating no risk of sodification. In general, the groundwater of District Hardwar is safe for irrigation. According to the U.S. Salinity Laboratory classification of irrigation water, the majority of the samples (70%) falls under water type C2‐S1 followed by the C3‐S1 type.
Mt
BE
Authors: Jacobs James A.
Published: April 2005

Methyl tertiary‐butyl ether (MtBE) is a synthetic compound that was developed as a solution to the problem of air pollution from vehicle emissions. MtBE was originally added to gasoline as a fuel oxygenate in approximately 1979 to reduce air emissions and make the fuel burn cleaner, allowing more complete combustion in internal combustion engines. The concept was to improve air quality by producing fuels that were more readily oxidized and decrease the resulting tropospheric ozone production. In the late 1980s, the U.S. EPA supported the use of fuel oxygenates in reformulated gasoline to achieve air quality goals.

MtBE, a byproduct of gasoline refining, was inexpensive, and readily available nationwide. Ironically, the use of this air‐saving gasoline additive has taken its toll on groundwater and surface water resources throughout the nation.
Phytoextraction of Zinc and Cadmium from Soils Using Hyperaccumulator Plants
Authors: Datta Rupali , Sarkar Dibyendu
Published: April 2005

Zinc (Zn) and cadmium (Cd) are ubiquitous pollutants that tend to occur together at many contaminated sites. The cost of using conventional soil remediation technologies is generally very high, so the use of plants to clean up soils contaminated by pollutants, a technique known as phytoremediation, is emerging as a new tool forin situremediation. Among the various ways in which plants can help in remediating contaminated soils, the technique of phytoextraction depends on the ability of plants to take up metals from soils and concentrate them in aboveground tissues. Those few plants that can accumulate metals to exceptionally high concentrations in their shoots are called hyperaccumulators. The main drawback of using hyperaccumulators for phytoextraction of Zn and Cd is their typically slow growth rate and low biomass. This has prompted researchers to investigate the possibility of developing genetically engineered plants with high biomass and better phytoextractive capacity. In recent years, major scientific strides have been made in understanding the soil chemical and plant molecular–genetic mechanisms that drive metal hyperaccumulation in plants. However, extensive field deployment of this technique on a large scale is still being hampered by a lack of specific understanding of the complex interactions between metal, soil, and plant systems that are instrumental in Zn/Cd uptake, translocation, and storage in plants. A multidisciplinary research effort that integrates the work of plant biologists, soil chemists, microbiologists, and environmental engineers is essential for the success of phytoextraction as a viable soil cleanup technique in Zn‐ and Cd‐contaminated sites.
Qanats: An Ingenious Sustainable Groundwater Resource System
Authors: Saghafian Bahram
Published: April 2005

A qanat system consists of an underground tunnel that conveys water by gravity from highland aquifers to the ground surface at lower elevations. Blended with ingenuity, its purpose is simply to collect and bring underground water to the surface for use. Qanat, invented and originated in Iran more than 2700 years ago, is considered a hydraulic engineering system of an Old World era providing water to settlements since its invention. The overwhelming climate of Iran is arid and semiarid; two thirds of the country area in central, southern, and eastern parts receive an average of about 150 mm of rainfall annually. Yet, Iran is considered a farming country where diverse crops are grown. This remarkable achievement in agricultural development of arid lands has materialized partly by building qanats to tap underground water in regions where surface water is lacking or unreliable during seasons of high water demand. Numerous urban and rural qanat‐watered settlements are vivid examples that not all civilizations were rooted by the sides of rivers. Qanats have helped to transform barren lands into productive assets. Thanks to its simple and efficient technique, the idea behind this sustainable water resource system was passed from one generation to the next and traversed geographic boundaries. Qanat's use is not confined to Iran and has been adopted in many regions across the world.
Risk Analysis of Buried Wastes from Electricity Generation
Authors: Cohen Bernard L.
Published: April 2005

An important aspect of generating electricity from nuclear power is the disposal of the high level radioactive waste. The most widely anticipated plan is to convert it into a rock‐like material and bury it deep underground, typically 600 meters below the surface. In evaluating the safety of this procedure, a key element is to estimate the probability per year,P, for an atom of this buried waste to be dissolved by groundwater and eventually enter a human stomach. Obviously, this probability is site dependent and depends on present underground characteristics and future events in the region, many of them unpredictable, including climate changes, geological land uplifting causing rivers to change their courses, volcanoes, earthquakes, and human intrusion.
Fog
Authors: Holst Arthur M.
Published: April 2005

Fog is a cloud that materializes near the ground or over water. It is a reaction that occurs when the temperature near the ground cools to the temperature required to produce dew and causes the water vapor in the air to become visible in the form of a cloud of precipitation. There are different types of fog, which occur when different variables are involved. The two conditions necessary for fog formation are mild or no winds and air temperatures that are equivalent to the temperature at the dew point. Mild or no winds are important because obstructions in the way of a strong wind can cause it to blow in an up and down motion, which brings warmer air down and pushes the colder air up. Cool air is a requirement for fog formation so wind prevents it from happening.
Hydrologic Cycle
Authors: Jain Sharad K. , Singh Vijay P.
Published: April 2005

The hydrologic cycle, the endless circulation of water between the earth, the oceans, and the atmosphere, is fundamental to the study of the waters of the earth. The cycle entails a huge turnover of water driven by the energy of the Sun and gravity. It has a profound influence on the landscape and the earth's climate. The major components of the hydrologic cycle are precipitation, evapotranspiration, interception, infiltration, overland and channel flow, and groundwater flow. Quantitatively, the hydrologic cycle is represented by a mass balance or continuity equation. The relative significance of the terms of this equation depends on the space and timescale. Human activities and the hydrologic cycle are interactive and influence the earth's climate.
Hydrologic Cycle, Water Resources, and Society
Authors: Hubbart Jason A.
Published: April 2005

Water is more or less constantly moving and changing from one state to another (solid, liquid, or vapor) while interacting with the physical processes in the atmosphere, lithosphere, and biosphere. These changes and movements of water are linked together into a grand scheme called the hydrologic cycle. Components of the hydrologic cycle include the water vapor and clouds in the atmosphere, and also liquid surface waters (oceans, lakes, and streams) on continents as well as groundwater. Other important components of the hydrologic cycle include glacial ice held on continents and water in biomass. Plants and animals are about 70% water by volume. Water evaporates in enormous quantities from the oceans and then falls as precipitation either on land or ocean. That portion which falls on land evaporates, evapotranspires, runs off, or infiltrates by some measure. Eventually, all water ends up back in the ocean. Between the various stages of the hydrologic cycle, water moves between temporary storage areas often called reservoirs. These movements are controlled by climatic conditions, which include rain, snow, wind, and other meteorologic processes.
Hydrologic History, Problems, and Perspectives
Authors: Hubbart Jason A.
Published: April 2005

Since humans first settled along the banks of lakes and rivers, there has been a keen interest in the proper management of fresh water resources both as a necessity for life as well as to avoid potential health hazards. Along the Indus in Pakistan, the Tigris and Euphrates in Mesopotamia, the Hwang Ho in China, and the Nile in Egypt, the first “hydraulic engineers” created canals, levees, dams, subsurface water conduits, and wells as early as 5000–6000 years ago. Hydrologic information became vital to these early civilizations. The flow rates and yields of rivers were monitored by the Egyptians as early as 3800 years ago, and rainfall measuring instruments were first used approximately 2400 years ago by Kautilya of India.

The idea that a global hydrologic cycle actually exists dates back at least 3000 years when early Greek philosophers such as Thales, Anaxagoras, Herodotus, Hippocrates, Plato, and Aristotle conceptualized the basic ideas governing the process. Many initial ideas established by the Greeks about the hydrologic cycle were quite reasonable. However, many of the initial mechanisms concerning the routes by which water returned from the sea and entered rivers were devoid of as much logic. Despite apparent gaps in hydrologic mechanisms, the Romans developed aqueduct systems reflecting an extensive practical understanding of hydrology and hydraulics and did so using the basic hydrologic ideas established and passed along by the Greeks.
Snow Surveys
Authors: Singh Pratap
Published: April 2005

The basic objective of conducting snow surveys is assessing the spatial distribution of the snow water equivalent accumulated in the basin at a specific time. The distribution of snow is affected by several factors, including topography, orientation, vegetation, and wind speed. During strong winds, the drifting and blowing of snow create a highly uneven spatial distribution of snow depth. Therefore, to account for uneven distribution of snow in a basin, snow surveys are needed. Snow surveys are primarily a field activity that include determining the depth and vertically integrated density. An estimate of the snow water equivalent at a site is computed by multiplying the snow depth by the density of the accumulated snow. Snow surveys are made at regular intervals during both accumulation and ablation periods. Snow surveys conducted just after winter are considered especially important because they provide information about the total snow water equivalent accumulated during the winter. Such information helps in assessing the water resource potential of the deposited snow and is used for forecasting the volume of water expected from snowmelt.
Unit Hydrograph Theory
Authors: Singh Vijay P.
Published: April 2005

The fundamental premise of unit hydrograph theory is that the hydrologic system is linear and time invariant. Although the assumptions implied or made in the theory are, strictly speaking, seldom true, the theory, nevertheless, does yield reasonable results in practice. The theory is applicable to a wide range of problems in hydrology and water resources.

The unit hydrograph is based on these postulates: (1) For a given drainage basin, the duration of surface runoff is constant for all uniform‐intensity storms of the same duration, regardless of differences in the total volume of surface runoff. (2) For a given drainage basin, if two uniform‐intensity storms of the same length produce different total volumes of surface runoff, then the rates of surface runoff at corresponding times, after the beginning of the two storms, are in the same proportion to each other as their total volumes of surface runoff. (3) The time distribution of surface runoff from a given storm period is independent of concurrent runoff from antecedent storm periods.
Water Cycle
Authors: Holst Arthur M.
Published: April 2005

The water cycle—a series of steps through which virtually all water on earth is constantly cycling. The names of these steps vary, but they generally follow this order: storage, evaporation, transpiration, condensation, precipitation, infiltration, and runoff.

Due to the nature of the water cycle, there is really no “beginning” or “end”, but for simplicity, the cycle can be said to begin at the storage stage. Storage is the storing of water on, in, and above the earth. There are about 340 million cubic miles of water on the earth. This water is stored in many places: glaciers, seas, rivers, lakes, polar ice caps, and all living things on the planet. The largest percentage of water, approximately 97.25%, exists as salt water in the ocean. Water is also stored in the earth's atmosphere and as groundwater. Groundwater in the top few miles of the earth's crust is easily obtainable, whereas groundwater further down is chemically attached to rocks and usually cannot be accessed.
Entropy Theory for Hydrologic Modeling
Authors: Singh Vijay P.
Published: April 2005

Hydrologic systems are inherently spatial and complex, and our understanding of these systems is less than complete. Many of the systems are either fully stochastic or part stochastic and part deterministic. Their stochastic nature can be attributed to randomness in one or more of the following components that constitute them: (1) system structure (geometry), (2) system dynamics, (3) forcing functions (sources and sinks), and (4) initial and boundary conditions. As a result, a stochastic description of these systems is needed, and entropy theory enables the development of such a description.
Arsenic in Natural Waters
Authors: Ning Robert Y.
Published: April 2005

Average concentrations of arsenic in the earth's crust reportedly range from 1.5 to 5 mg/kg. Higher concentrations are found in some igneous and sedimentary rocks, particularly in iron and manganese ores. Common minerals containing arsenic are shown in Table. Arsenopyrite, realgar, and orpiment are the most important of these minerals, and they are commonly present in the sulfide ores of other metals, including copper, lead, silver, and gold. Arsenic may be released from these ores to the soil, surface water, groundwater, and the atmosphere.

Natural concentrations of arsenic in soil typically range from 0.1 to 40 mg/kg; an average concentration is 5 to 6 mg/kg. Arsenic can be released to ground or surface water by erosion, dissolution, and weathering. Geothermal waters can be sources of arsenic in groundwater.
Consumer Confidence Reports
Authors: Franklin Susan L.
Published: April 2005

On August 19, 1998, the U.S. Environmental Protection Agency (USEPA) promulgated a final rule (40 CFR Parts 141 and 142) requiring community water systems to prepare and provide annual water quality reports to their customers. Mandated by the 1996 amendments to the Safe Drinking Water Act, these “Consumer Confidence Reports” (CCRs) provide the missing link for consumers to have easy access to valuable water quality information. Just as food products have labeling requirements, CCRs are the public's “right‐to‐know” resource.
Cryptosporidium
Authors: Brabants Jacqueline
Published: April 2005

Cryptosporidiaare small, spherical, obligate, intracellular sporozoan parasites that infect the intestinal tract of a wide range of mammals, including humans.Cryptosporidiumoocysts range in size from 2 to 8 µm, depending on the species and the stage of the life cycle. Oocysts are commonly found in many of the lakes and rivers that supply public drinking water as a result of runoff from sewage and animal wastes applied to nearby fields and pastures or from areas of wildlife or livestock activity. Infection, resulting from ingesting oocysts, manifests as cryptosporidiosis. AlthoughCryptosporidiumwas first described in 1907, human infection was not reported until 1976. Today,Cryptosporidium parvumis well recognized as the cause of the disease cryptosporidiosis in humans and cattle and is one of the more opportunistic agents seen in patients with AIDS that occurs primarily in individuals with compromised immune systems. Currently, there is no totally effective therapy for cryptosporidiosis.
Private Sector Participation, Marketing and Corporate Strategies in Municipal Water Supply and Sewerage
Authors: Owen David Lloyd
Published: April 2005

The entry will describe how financial, commercial, and technical services are being mobilized to enable economic and social services to be provided and improved by water sector organizations in the North (the developed economies) and the South (developing economies). These needs are different because the policy contexts (politics and governance), standards, and risks experienced by entities installing and improving water services in the North and the South are different. It will be shown that the international water sector companies have evolved a diverse suite of financial and contractual arrangements often in association with international financial institutions (e.g., the World Bank). It will also be shown that the water sector is evolving as new companies shape their financial and technical competence to operate and compete internationally.

Private sector participation (PSP) refers to the formal provision of municipal water and sewerage services by the private sector. This involves providing these services commercially, where infrastructure work is funded by private capital or through a combination of finance from private investors and multilateral agencies.
Emerging Waterborne Infectious Diseases
Authors: Nel Louis H.
Published: April 2005

Humanity is plagued at present by at least 1709 different infectious diseases. These diseases are caused by pathogens, which are microscopic and parasitic organisms of diverse natures, including infectious proteins (prions), viruses, bacteria, fungi, and protozoa. Compared to diseases like cancer and metabolic diseases that have genotypic roots, including heart disease, diabetes, and the like, progress in the fight against infectious diseases has been rapid during the last half century. Whereas infectious diseases such as smallpox, measles, polio, rabies, plague and numerous other bacterial diseases have once been a global scourge, many of these diseases have now become controllable due to spectacular advances in public health practices, including improvements in the quality of water and sanitation and by immunization, education, early diagnosis, and the use of antibiotics/antimicrobials and other drug therapies. However, globally, 45% of all deaths and 63% of early childhood deaths are still caused by infectious diseases.
Estuarian Waters
Authors: Dissanayake Priyanka K.
Published: April 2005

Estuaries are in many ways the most complicated and variable of aquatic ecosystems. An estuary is a place where salt water from an ocean mixes with freshwater from the land and creates a unique and special environment in which marine species live, feed, and reproduce. Estuaries and intertidal regions are naturally exposed to stressful conditions.

An estuary and its immediate catchments form a complex system of ecological, physical, chemical, and social processes that interact in a highly involved and, at times, unexpected fashion. Estuaries are the end point for the detrimental effects of many upstream catchment activities. Materials carried from the land by rivers vary in quality and quantity, sometimes with strong seasonal patterns of high biological significance. Tidal oscillations cause vigorous reversals of flow. Inherent hydrographic patterns can lead to accumulation of materials and to upstream transport from the point of addition. The estuaries as recipients of wastes from rivers entering them and cities and industries along their shores are obviously more immediately susceptible to pollution damage than any other part of the marine system. Increased loads of nutrients and sediments from activities in the surrounding catchments are the two key threats to marine and estuarine water quality.
Chloroflurocarbons (CFCs)
Authors: Kazemi Gholam A.
Published: April 2005

The use of CFCs in hydrology began when Thompson et al. (1) the usefulness of a special type of fluorocarbon known as Freon 11, as a tracer in both groundwater and surface water hydrology. They found good agreement between CCl3F data and hydrologic and tritium age data. Brown (2) also examined the use of fluorocarbons as groundwater tracers through soil column studies. There was no significant use of or development in CFC dating techniques during the 1980s, possibly due to the availability of other methods such as the tritium method and the low resolution of the available CFC analytical techniques. From 1992, the application of CFCs in groundwater studies, especially for age dating and determination of rainfall recharge became important (3).
Heavy Water
Authors: Kazemi Gholam A.
Published: April 2005

Each of the atoms of hydrogen and oxygen, which form the water molecule, has three isotopes;
1
H,
2
H (D),
3
H (T) for hydrogen and
16
O,
17
O, and
18
O for oxygen.

The abundances of these isotopes in the hydrosphere, biosphere, and lithosphere and in different stages of the water cycle vary slightly from these figures.

Considering the six isotopes of hydrogen and oxygen, 18 combinations of HOH or “18 varieties of water” are possible (2, 3).

Of the above eighteen varieties of waters,
1
H
2
16
O has a mass of 18 and is the most common; it is generally known as “water” or sometime called ordinary or light water. Deuterium oxide (D
2
16
O) has a mass of 20 and is known as “heavy water.” Some references use the term “semiheavy water” for HD
16
O. Washburn and Urey (4) were the first to enrich deuterium oxide in water in 1932. Some of the 18 varieties of water are extremely rare. An interesting, though trivial, point is that the molecular weight of the most common form of water
1
H
2
16
O (18), equals the number of different varieties of water, 18.
H
enry's Law
Authors: Viadero Roger C.
Published: April 2005

William Henry (1774–1836) established the fundamental relationship to define the partitioning of a soluble (or partially soluble) chemical species between gas and liquid phases, at equilibrium, in a dilute aqueous solution.

Three main limitations must be considered when applying Henry's law: (1) the state of equilibrium, (2) the solute concentration, and (3) the veracity of using standard data for calculations in contaminated water systems. The application of Henry's law is limited to cases where chemical equilibrium has been reached in a dilute solution (< 1% solute concentration). However, the concentrations of most water constituents are normally less than 1%, so the application of Henry's law is typically valid.
Mariotte Bottle—Use in Hydrology
Authors: Holden Joseph
Published: April 2005

A Mariotte bottle is a device that allows constant flow of a fluid from a container, even when the fluid level in the container changes. It is named after Edme Mariotte (1620–1684), a French physicist, who, independently from Boyle, discovered the law that states that the volume of a gas varies inversely with its pressure. Mariotte bottles have a wide range of applications in engineering and science (such as fuel supply) and are used in a variety of hydrologic applications ranging from river discharge gauging to infiltration measurement.
Sodium in Natural Waters
Authors: Priyadarshi Nitish
Published: April 2005

Sodium is a light alkali metal which floats on water in its pure state. However, it is very chemically active and is rarely found in its pure state. All natural waters contain sodium; nearly all sodium compounds readily dissolve in water, and it naturally leaches from rocks and soils.

The sodium ion, the sixth most abundant metallic ion in the earth's crust, is a natural constituent of both food and water from several sources. Most water supplies contain less than 20 mg of sodium per liter, but in some countries, levels can exceed 250 mg/liter. Saline intrusion, mineral deposits, seawater spray, sewage effluents, industrial brines, chemicals used in paper processing, soap, glass, and glass‐wool industries, food processing, slaughtering and meat packing industries and salt used in road deicing all contribute significant quantities of sodium to water. In addition, water treatment chemicals, such as sodium fluoride, sodium bicarbonate, and sodium hypochlorite can together result in sodium levels as high as 30 mg/liter. Domestic water softeners can give levels of over 300 mg/liter. A much more important source of sodium in fluvial waters is the input from leaching of halite from sedimentary or evaporite deposits. More than 40% of the sodium in fluvial waters comes from this source. Sodium is also derived from the weathering of silicate minerals, principally sodic plagioclase feldspar. This source accounts for more than 20% of the sodium in river water. It is also an important element in mica, amphibole, and pyroxene.
Technetium in Water
Authors: Clausen Jay
Published: April 2005

Technetium, element 43, was predicted on the basis of its location in the periodic table. Twenty‐two isotopes of technetium whose masses range from 90 to 111 are known, and all are radioactive. Technetium has three long‐lived radioactive isotopes: technetium‐97 [97Tc] (half‐life {T1/2} = 2.6 × 106years),98Tc (T1/2 = 4.2 × 106years), and99Tc (T1/2 = 2.13 × 105years). An important isotope is95mTc (“m” stands for metastable state) [T1/2 = 61 days], which is used in tracer work. However, the most useful isotope of technetium is99mTc (T1/2 = 6.01 hours), which is used in many medical radioisotope tests because of its short half‐life, easy detection of the gamma ray it emits, and the ability of technetium to bind chemically to many biologically active molecules

Technetium‐99 is a surface water and groundwater contaminant at a number of DOE sites such as the Paducah Gaseous Diffusion Plant (PGDP) in Paducah, Kentucky; the Portsmouth Gaseous Diffusion Plant in Piketon, Ohio; Currently, the largest annual release of99Tc to the environment occurs at the two nuclear fuel‐reprocessing facilities in Sellafield, United Kingdom.

The most extensive groundwater distribution of99Tc is at the PGDP where amile long plume of99Tc contaminated groundwater is commingled with the solvent trichloroethene. The99Tc was introduced to the site during the 1970s when fissioned uranium was reprocessed.

The technologies explored for remediating99Tc in water include ion exchange, liquid–liquid extraction, precipitation with various forms of iron, redox manipulation, the FORAGER sponge, granular activated carbon (GAC), and natural attenuation.
Unit Hydrograph
Authors: Cudennec Christophe
Published: April 2005

On the scale of a hydrologic event, a river basin schematically has two influences. The first is the yield of rainfall transformed into effective rainfall (in terms of runoff production), and the second is the transfer of runoff flows generated all over the basin territory to the unique outlet. The concept assumes that all transfer processes of the whole basin can be synthesized in a single linear function, called the unit hydrograph of the basin considered. It is at the root of the idea of the transfer function and is a kind of functional signature of the basin. This means that a characteristic function can be identified for a given basin. It is assumed that this function underlies any rainfall–runoff event and synthesizes all relevant hydrologic processes and geographic influences on the temporal scale of the event and the spatial scale fixed by the basin territory. Furthermore this means that the unit hydrograph should really be the hydrograph at the outlet, following an average impulse unit effective rainfall input, and that the response of the basin to any actual effective rainfall chronicle can be simulated through the sum of successive elementary affinities of the unit hydrograph. Such a holistic purpose necessarily faces problems of simplifying the natural complexity and of identifying the unit hydrograph itself.
Wetlands: Uses, Functions, and Values
Authors: McCartney Matthew P.
Published: April 2005

Throughout history, wetlands have played an important role in human development. They have brought benefits, but also caused difficulties for people. Their perceived value to society has varied from place to place and has changed over time.

In many arid and semiarid regions of the world, societies have flourished because of the water and other resources provided by wetlands.

In recent years, it has been realized that wetlands are valuable ecosystems. It is now understood that they maintain environmental quality, sustain livelihoods, support immense biodiversity, and have important recreational and aesthetic qualities.
Episodic Acidification
Authors: Mitchell Myron J.
Published: April 2005

Episodic acidification is the short‐term decrease (≤0 µmol
c
L
−1
) in acid neutralizing capacity (ANC) of surface waters due to both natural and anthropogenic factors. ANC is a measure of the ability of water or soil to neutralize added acids and is defined by the reaction of hydrogen ions with inorganic (e.g., HCO
3
−
) or organic ions. Decreases in ANC generally result in a decline in pH, sometimes dropping to levels below 4.5. Episodic acidification most commonly occurs during snowmelt or precipitation that results in rapid increases in the discharge rates of surface waters. Typically the decrease in ANC and pH of streams and lakes is accompanied by increases in Al

n
+

concentrations. These decreases in ANC and pH and increases in Al

n
+

concentrations have marked effects on water chemistry and freshwater biota.
Adsorption of Metal Ions on Bed Sediments
Authors: Jain Chakresh K.
Published: April 2005

The adsorption characteristics of cadmium on bed sediments of the River Ganga (India) have been studied to determine the tolerance of the river system for the heavy metal load. The effect of various controlling parameters, initial concentration, solution pH, sediment dose, contact time and particle size, have been evaluated. The optimum contact time needed to reach equilibrium was approximately 60 minutes and was independent of the initial concentration of cadmium ions. The adsorption curves are smooth and continuous leading to saturation, suggesting a possible monolayer coverage of cadmium ions on the surface of the adsorbent. The extent of adsorption increases with pH. Furthermore, the adsorption of cadmium increases as adsorbent doses increase and as adsorbent particle size decreases. The two geochemical phases, iron and manganese oxides, probably support the adsorption of cadmium ions. The adsorption data have been analyzed by using the Langmuir and Freundlich adsorption models to determine the mechanistic parameters of the adsorption process. Isotherms have been used to obtain thermodynamic parameters, free energy change (ΔGo), enthalpy change (ΔHo) and entropy change (ΔSo). The negative values of free energy change (ΔGo) indicate the spontaneous nature of the adsorption of cadmium on bed sediments, and the positive values of enthalpy change (ΔHo) suggest the endothermic nature of the adsorption process. The uptake of cadmium is controlled by bulk as well as intraparticle diffusion mechanisms.
Greenhouse Gas Emissions from Hydroelectric Reservoirs
Authors: Barrette Nathalie
Published: April 2005

The presence of certain trace gases (e.g., CO2and CH4) in the atmosphere is related to human activity (fossil fuel combustion, deforestation, and intensive agriculture), and to the biogeochemical processes that occur in natural environments (tropical and boreal forests and tundra). For many years now, scientists have been trying to determine the importance of natural environments as sinks for or sources of these trace gases (1, 2, 3). The terrestrial biosphere constitutes a major carbon sink (4); more than a third of the anthropic CO2emissions are fixed there (5). However, certain changes in land use (e.g., deforestation and the draining of marshes for agriculture) can lead to changes in the way greenhouse gases (GHGs) are produced or fixed by modifying the physicochemical characteristics of these soils. In the medium and long term, these changes are likely to invert the carbon sink capacity that has been attributed until now to certain natural environments (e.g., boreal regions). This article examines how one of these land‐use changes, the creation of hydroelectric reservoirs, significantly modifies the carbon cycle in natural environments.
Hydroelectric Power
Authors: Jain Sharad K.
Published: April 2005

Hydropower generation follows a simple concept: water falling from the force of gravity turns the blades of a turbine, which is connected to a generator. The rotating generator produces electricity. Prehistoric man was aware of the energy contained in falling water. One of the earliest devices to use this energy was the water wheel. The Romans used the energy of falling water to do many useful things. They constructed paddle wheels that turned with river flow and lifted water to troughs built higher than river level. The Egyptians and Greeks harnessed the power of river currents to turn wheels and grind grain before 2000
B.C.
In the Middle Ages, more efficient water wheels were built for milling grain.

In the nineteenth century, the water turbine gradually replaced the water wheel, and dams were built to control the flow of water. Since then, the hydroelectric potential of rivers continued to be developed. The first modern turbine design was developed in 1849 by James Francis. According to estimates, hydroelectric power production has now risen to 2,000 billion kilowatt hours worldwide.
Reservoirs‐Multipurpose
Authors: Jain Sharad K.
Published: April 2005

Reservoirs are developed for two main functions. The first is to store water to even out the fluctuations in river flow and match the availability to demand. Generally, the major part of annual stream flow is available during the few months of the rainy season, but the demand for water arises all year round. Therefore, it is necessary to store the excess water in the months of high flows and use it when the natural stream flow is inadequate to meet the demand. The water stored in a reservoir may also be diverted to faraway places where it is needed.

The second function is to raise the level of the water upstream of the dam to provide a hydraulic head. The creation of storage and head allows dams to generate electricity. The other important purpose of a reservoir is to control flooding in downstream areas.
River Basin Planning and Coordination
Authors: Hjorth Peder
Published: April 2005

A river basin is a functional entity where water is the integrating factor. What happens in one location will impact any downstream location. Sometimes there are upstream impacts as well, for instance, backwater effects upstream of a dam. Thus, water management must be coordinated and concerted to result in desired outcomes in different parts of a drainage basin. To this end, there is a need for effective communication across institutional and disciplinary boundaries.
Rivers and Streams: One‐Way Flow System
Authors: Cudennec Christophe
Published: April 2005

Broadly speaking, rivers and streams are inscribed in the structural relief lines of the lowest local altitudes, the thalwegs. But they do not necessarily strictly follow these lines when they are considered on a very precise scale, because their exact drawing is constrained by local particularities such as the substratum, the vegetation, and anthropic artifacts. Inversely, there is not necessarily a river or a stream in a thalweg because the permanent flow and the landscape marking depend on many hydrologic and geomorphological factors.

Because of this particular position of rivers and streams, they have a major role in hillslope drainage, whatever the kinds of waterways through the hillslopes are. Then, any river or stream receives water from the sides and from upward, and makes it flow downward through a slope‐oriented sense. Thus, a point of a stream or a river has a topological and functional relationship with all of its up and downward points. This relationship leads to defining the so‐called ‘one‐way flow system’ and makes structured objects emerge on a larger scale. Rivers and streams meet and are organized in a hierarchical branched network.