bluuebunny/crossref_metadata_2025 huggingface dataset:
Phytoremediation of Lead‐Contaminated Soils
Authors: Ioannidis Th. A. , Zouboulis A. I.
Published: April 2005

Several treatment technologies have been investigated for treating heavymetal‐contaminated soils, such as lead. Recently, among the most promising methods is “phytoremediation,” the use of certain plants to remove/accumulate or neutralize/degrade pollutants, of inorganic or organic nature. The systematic examination of plants, especially for removing lead from polluted soils has drawn serious attention, especially during the last decade. The overview of the specific technology and a brief description of the results obtained so far is briefly presented. Specific aspects that are of critical importance, such as the chemistry of soil and the interaction with the toxic metals, are also outlined.
Recharge in Arid Regions
Authors: Leonhart Leo S.
Published: April 2005

Groundwater recharge in arid regions or deserts is a process that requires a favorable combination of hydrologic factors. Accordingly, recharge, in arid regions occurs more rarely and supplies annual quantities of water to the groundwater table lower than typical of more humid regions. Many of the processes by which recharge occurs, such as surface infiltration, stream channel loss, and seepage from impounded water bodies, however, are common to both regions.

By definition, the aridity of a region is determined by the ratio of mean annual precipitation to mean annual potential evapotranspiration (PET). As shown in Fig. 1, arid regions in both the Northern and Southern Hemispheres are situated mostly between 10° and 35° latitude worldwide. Regions that have average annual precipitation (P) totaling less than 250 mm (10 in) make up an estimated 25% of the worldwide land areas outside of the polar regions. Arid regions are sometimes further classified as hyperarid, arid, or semiarid, according to the ranges in theP/PET ratio.

For several reasons, estimates of mean annual precipitation are difficult to relate directly to recharge in arid regions. Largely, this difficulty arises from characteristically high temporal and spatial variability in both the distribution of precipitation and recharge in arid regions. Longer term recharge to precipitation ratios (R/P) for various arid regions in the United States generally are typically less than 5%.
Remediation of Contaminated Soils
Authors: Sarkar Dibyendu , Datta Rupali , Davani Ali H.
Published: April 2005

Soil contamination is caused by a variety of industrial, agricultural, and domestic activities, and poses a major threat to the environment. Although soil contamination can result from a variety of organic and inorganic chemicals, this article focuses on remediation of metal‐contaminated soils. Heavy metals such as Pb, Cr, Cd, Zn, Cu, and Hg can cause significant damage to environmental and human health, particularly because of their indefinite persistence in the environment. In the United States alone, 1200 sites are on the National Priority List (NPL) for remediation of contaminated soils, of which 63% are contaminated with toxic heavy metals. A plethora of remediation techniques are now available for the cleanup of such contaminated sites. The selection of the most appropriate site remediation technique depends on various factors such as site characteristics, concentration, types of pollutants to be removed, and end use of the contaminated medium. The major technologies available to date can be grouped under the following categories: isolation, immobilization, toxicity reduction, physical separation, and extraction. This article provides an overview of the various sources of heavy metal pollution in soils, the common remediation technologies available for soil cleanup, and the various factors that influence the type of remediation method that would be most appropriate for effectively remediating metal‐contaminated soils.
Use of Anaerobic‐Aerobic Treatment Systems for Maize Processing Plants
Authors: Durán‐de‐bazúa María‐del‐carmen
Published: April 2005

After the discovery of the American continent by the Spaniards in the fifteenth century, corn (
Zea mays
), an indigenous plant from Mexico, spread all over the world and became a staple food for many human groups. Due to globalization, one of these maize products, “tortillas,” is now an extremely popular food that can be found in most countries of the world. The traditional production of “tortillas” involves a Precolumbian technique, known as “
nixtamalization
,” derived from the Aztec words
nextli
 = lime ashes and
tamalli
 = cooked corn dough. This ancient process, almost as old as corn domestication and cultivation, is a time‐ water‐ and energy‐consuming technique. Modernization of the traditional process to produce cornmeal instead of dough to lengthen its shelf life as well as some other changes for mass production have been introduced in the last 50 years. Some innovative processes that maintain these desirable nutritional and sensory characteristics, and at the same time, reduce energy and water consumption, and most importantly, processing time, have also been developed and started to be used. However, the traditional plants (more than 100,000 small‐scale and 25 large‐scale in Mexico) are still in operation, so methods to treat and stabilize the wastewater generated in the traditional process (so‐called “nixtamal” mills that process around 0.5 to 4 metric tons maize per day) or in its industrial modifications (so‐called precooked cornmeal or masa‐harina factories that process from 100–1,000 metric tons maize per day) and contain appreciable amounts of soluble and insoluble organic matter. These methods are based on anaerobic and aerobic systems, and the interesting issue is that by‐products from the treatment can be further used, giving added value to these treatment processes. For cornmeal industries, the anaerobic and the aerobic ones are compact and easy to operate. The saving in water and energy consumption, wastewater disposal costs, and the sale of biomass for fish protein‐rich feedlots make the treatment and recovery process economically feasible. The turnover rate is 1.5 years, that is, the money invested in the wastewater treatment plant together with the accessories to recover biogas and biomass and to reuse them is recovered in 18 months. Due to the size of nixtamal mills, it is not so economical to install an anaerobic‐aerobic process for treating their wastewaters (between 2.5 to 20 m
3
). An aerobic system is then used for these small establishments. The solid material collected from the filter press can be fed directly to small farm animals and, although the protein cannot be directly assimilated by the animals, it does not damage them. In this case, partially treated wastewater is sent to the municipal sewer system.
Hydrocarbon Treatment Techniques
Authors: Ashworth Samuel C.
Published: April 2005

There are various criteria concerning hydrocarbons for water needs. Some water users have little concern for dissolved hydrocarbons (e.g., agriculture), and some have strict standards (e.g., drinking water). In general the presence of organic compounds, including hydrocarbons, in water can lead to a buildup of biofilms. Biofilms can be problematic in many situations including drinking water, cooling water, recirculating water, and water used for various other industrial processes. During biofilm formation, the first substances on the surface are not bacteria but trace organics. Almost immediately after the clean pipe surface comes into contact with water, an organic layer deposits on the water/solid interface. These organics form a conditioning layer that neutralizes excessive surface charge and surface free energy that may prevent a bacteria cell from approaching near enough to initiate attachment. In addition, the adsorbed organic molecules often serve as a nutrient source for bacteria.

Though there are many criteria, the thrust of this article is on the treatment, including the removal and destruction of hydrocarbons for whatever purpose. It is assumed in this article that the hydrocarbons are dissolved in water, so that technologies such as incineration or decantation will not apply. The focus will be on water‐phase separation and destruction. No economic evaluation is considered. In reality, the trade‐offs would need to be considered, for example, waste disposal costs, electrical cost, and materials.
Industrial Cooling Water—Corrosion
Authors: Bott T. R.
Published: April 2005

Corrosion is often a problem when metals are in contact with an aqueous environment. It may be defined as the deterioration and loss of metal due to some form of chemical attack. In general, it results from impurities in the water, which need only to be in trace quantities to initiate corrosion. Trace impurities can include gases dissolved from the atmosphere, particularly oxygen and carbon dioxide, that play important roles in the corrosion process. Small amounts of mineral salts in water can also become involved in corrosion reactions. Where the metal makes up an essential component of a structure, such as a bridge or equipment forming part of an industrial process, for example, a cooling water circuit, constant vigilance is required to maintain the integrity of the structure and the equipment involved. Corrosion is a complex phenomenon dependent on chemical and physical conditions within the particular system.
Industrial Cooling Water—Scale Formation
Authors: Bott T. R.
Published: April 2005

Any source of naturally occurring water used of industrial cooling has been in contact with the earth, soil, and rock formations. As a result, soluble inorganic salts have been taken into solution that can give rise to “scaling” in industrial equipment. The phenomenon is apparent in domestic kettles that have been used to boil so‐called “hard water.” A whitish‐brown deposit forms on the areas within the kettle that are subject to the highest temperatures, for example, the heating element in electric kettles. In cooling water circuits that usually employ water from natural sources such as rivers or lakes, deposition of inorganic salts, or “scaling” as it is often called, can represent a serious problem. The presence of these salts usually results in operating problems. The accumulation of deposits on heat transfer surfaces can lead to severe loss in cooling efficiency if not effectively controlled.
Evaporation
Authors: Endreny Theodore A.
Published: April 2005

Evaporation of water is a solar energy driven phase change from liquid to vapor that maintains the hydrologic cycle by transferring liquid water at the earth's surface to water vapor in the atmosphere, where it may lift, condense, and precipitate to earth as liquid water. In this discussion, evaporation is defined to include the closely associated transpiration process as a subcategory. The coupled processes are often called as evapotranspiration, or ET, where transpiration focuses on the transport of liquid water through the plant roots, stem, and leaf prior to evaporation through the leave's stomata. Further, when the discussion does not make a clear distinction between potential and actual evaporation, potential should be assumed. Potential evaporation refers to the amount of water that available energy and diffusion processes can transfer into atmospheric vapor, which is typically greater then the amount actually transferred due to limits on soil water volumes and resistances in the path.
Frost
Authors: Holst Arthur M.
Published: April 2005

Essentially, a type of dew, frost is ice formed by the condensation of atmospheric water vapor on a surface. It generally occurs at night, and when frost forms, it can sometimes be seen in patterns of ice crystals. Frost can be extremely damaging to outdoor crops and plants. Researchers and weather services throughout the world monitor the effects of damaging frosts. Frost forms on any surface, including cars, grass, and buildings. Frost forms through one of two processes: the formation of dew that subsequently freezes, or deposition, which is the process wherein a gas changes to a solid. In frost formation, this gas is water vapor, and the solid state is ice crystals. These two processes will occur when the air is saturated. Saturation occurs when the air holds as much water vapor as is possible at its temperature and pressure. The temperature at which frost is deposited is known as the frost point temperature.
Frost Damage
Authors: Holst Arthur M.
Published: April 2005

Frost is ice formed by the condensation of atmospheric water vapor on a surface. When low temperatures are present in a certain region, the potential for frost damage to plant life exists in that region. Frost damage can injure plants permanently or slow plant development. Several factors dictate the extent and severity of frost damage to plants in any given region.
Isohyetal Method
Authors: Jain Sharad K. , Singh Vijay P.
Published: April 2005

The isohyetal method is used to estimate the mean precipitation across an area by drawing lines of equal precipitation. The method uses topographic and other data to yield reliable estimates. Isohyets are contours of equal precipitation analogous to contour lines on a topographic map. In the isohyetal method, precipitation values are plotted at their respective stations on a suitable base map, and isohyets are drawn to create an isohyetal map. Isohyetal lines are based on interpolation between rain gauge stations. While constructing isohyets, it is assumed that rainfall between two stations varies linearly, unless abrupt changes in topography indicate otherwise.
Permanent Frost
Authors: Holst Arthur M.
Published: April 2005

Frozen soil or rock that remains at a temperature of 0°C (32°F) or below for 2 or more years is permafrost. Permafrost is defined solely by temperature and is not determined by the amount of snow cover, soil moisture content, or its location. Permafrost may contain more than 30% ice or no ice at all, and may be topped by meters of snow cover or no snow at all. The defining characteristic of permafrost is its temperature.
Remote Sensing of Applications in Hydrology
Authors: Black Jessica , Endreny Theodore
Published: April 2005

Remote sensing is the science of observing and analyzing an area, object, or phenomenon based on data collected by sensors physically separated from the target. The sensors are mounted on platforms such as ground‐based, airplane, or satellite platforms. Physical radiation transfer is the foundation for remote sensing. Typically, the observation is of radiation reflected or emitted from the object of interest. There are two types of remote sensing: active and passive. In active remote sensing, the object is illuminated by radiation of a known wavelength (or frequency); the backscatter from the object is recorded by the sensor. In passive remote sensing, the sensor records radiation generated from natural sources, such as the sun, or radiation emitted from the earth or atmosphere. Radiation that the sensor receives has a spectral response that reveals properties of the atmosphere and object of interest. By extending remote sensing applications to improve the spatial and temporal resolution of certain key water resource variables, scientists can better understand and quantify water resource processes.
Snow and Snowmelt
Authors: Singh Pratap
Published: April 2005

Snow is a solid form of precipitation. The formation of snow crystals inside a cloud depends on the presence of ice nuclei, water vapor, motion of the cloud, and the temperature of the cloud. Snow crystals are formed when the cloud temperature is below freezing. These crystals experience diffusional, accretional, and aggregational growth inside the cloud. At temperatures greater than about −5°C, crystals usually stick together, and aggregation of ice crystals forms snowflakes. Snowflakes obtain their maximum size when the temperature of a cloud is near 0°C. Aggregation of ice crystals ceases at temperatures below −20°C. Due to changes in the ambient condition of the cloud, the size and form of the crystals change when they descend through a cloud. In a typical cloud, a snowflake of 1 mm diameter can grow to 10 mm in about 20 minutes. Because of the irregular shapes of snowflakes, measurement of their linear dimensions is difficult. The maximum diameter of snowflakes may range from 0.1 mm to several centimeters.
Cloud Seeding
Authors: Holst Arthur M.
Published: April 2005

Cloud seeding is the deliberate treatment of certain clouds or cloud systems to affect the precipitation process within those clouds. The treating of clouds can alter weather conditions, thus cloud seeding is also called weather modification. The technology that led to cloud seeding has been developed only during the past 60 years. Yet as this technology becomes more efficient, increased worldwide application of cloud seeding for practical use is likely to continue into the future.
Waterspout
Authors: Holst Arthur M.
Published: April 2005

Tornadic waterspouts are tornadoes over water. These are stronger, larger, and faster than fair weather waterspouts. However, they do tend to form over land as true tornadoes before moving over water. Fair weather waterspouts form differently from tornadoes. Rather than developing downward, they begin at the surface, building up toward the sky.

For waterspouts to form, a series of things must occur. First, a small portion of air over the surface of water must become heated. As this warm air begins to rise, the cool air around it starts to form a small vortex of rotating air. This vortex of swirling air is carried upward by rising water vapor; waterspouts usually form over warm water because there is more water vapor present. Upon rising to an overhead cloud mass, the vortex forms a funnel cloud. At this point, a fair weather waterspout begins its five‐stage life cycle.
Cyclones
Authors: Holst Arthur M.
Published: April 2005

Cyclones are hazardous weather conditions characterized by extreme gusts of wind moving in a circular pattern, low pressure, and intense rain. They form over tropical or subtropical waters; however, some can reach land, where they have in the past inflicted great amounts of damage on buildings and communities.

Based on wind strength, cyclones are given various names. Tropical depressions have maximum surface winds of less than 39 mph. Those cyclones whose maximum winds are between 39 and 74 mph are known as tropical storms. Upon attaining 74‐mph surface winds, a cyclone is known as one of a number of names that are all regional equivalents of the same type of storm.
Droughts
Authors: Holst Arthur M.
Published: April 2005

A drought is a period of time during which weather is in one way or another excessively dry. A drought's severity is determined by the degree of moisture deficiency in the affected area, as measured by various methods. Droughts are a standard, recurring, and normal feature of long‐term climate. There are four generally accepted categories of drought: meteorological, socioeconomic, hydrologic, and agricultural.
Guide to Selection of Water Treatment Processes
Authors: Muntisov Michael
Published: April 2005

Selecting the appropriate treatment process is a critical step in providing safe, reliable, good quality drinking water at a cost‐effective price.

This article provides guidance in selecting appropriate treatment processes taking into account raw water quality and costs.

There is a need for raw water quality data covering an extended period sufficient to show seasonal and extreme events to make a sound decision on appropriate treatment processes.

Before any process is finally selected, it is important to carry out treatability testing on the actual source water. All waters have subtle differences, and these can have a significant effect on process selection and performance. As a minimum, coagulation jar tests should be performed.

To allow comparison between process options, particularly on a cost basis, it is appropriate to define a “benchmark” process.

The benchmark process is based on the most commonly used treatment configuration in the world, coagulation/clarification/granular media filtration.
Multistage Filtration: An Innovative Water Treatment Technology
Authors: de Jong Dick , Smet Jo
Published: April 2005

The technology of multiple stage filtration (MSF) presented here is a combination of coarse gravel prefiltration and slow sand filtration (SSF). This combination allows treating of surface water that has considerable levels of contamination, well above the levels that can be treated by SSF alone. To improve the performance of MSF, other treatment processes such as simple sedimentation, sand traps, and screens can precede MSF technology. Wherever possible, terminal disinfection needs to be included as a safety barrier after MSF.

MSF retains the advantages of SSF in that it is a robust and reliable treatment method that can be maintained by operators who have low levels of formal education. It is much better suited than conventional chemical water treatment to conditions in rural communities and small and medium size municipalities in the South as well as in more remote areas in the North. The article provides a summary description of the components of MSF systems and the findings of recent research. It gives an overview of cost implications and ends with a selection guide.
Municipal Watersheds
Authors: Downs Timothy J.
Published: April 2005

In a humid environment, as a society moves from a preindustrial economy to an industrial economy, its watersheds experience three main stages of development: (1) few encroachments on water resources; more than enough water for everyone; water is free; (2) transitional infrastructure, including dams for energy and irrigation and interbasin transfers between water‐rich and water‐scarce watersheds; and (3) maximum streamflow regulation achieved, and aquifers are at maximum sustainable yield, so further development is both expensive and threatens to be unsustainable. Unfortunately, in the case of several megacity watersheds, a fourth stage of overexploitation by intensifying exploitive infrastructure and interbasin transfers is testing the functional viability of municipal watersheds.
Reverse Osmosis, Membrane Foulants
Authors: Ning Robert Y.
Published: April 2005

Periodic cleaning of reverse osmosis (RO) membranes is generally accepted as a necessary routine maintenance operation in running water purification plants. Common foulants found in RO membrane elements include calcium carbonate, calcium sulfate, strontium sulfate, barium sulfate, calcium fluoride, calcium phosphate, ferric hydroxide, aluminum hydroxide, silica, silt, polymers from natural sources, and synthetic polymers used in pretreatment. These foulants may occur singly or in most cases, in complex combinations. Single foulants are simpler to address in prevention and dissolving (except for barium sulfate) during cleaning. Complex foulants usually resulting from coagulation of colloidal particles, offer the greatest challenge in prevention and removal during cleaning.
Reverse Osmosis, Process Chemistry
Authors: Ning Robert Y.
Published: April 2005

The RO process is sensitive to upstream treatments and itself impacts downstream operations. The almost infinite variety of contaminants that enter the membrane systems with the feedwater and the economic necessity to expend minimal resources on raw water pretreatment pose a major challenge to RO process chemistry design and control. RO process chemistry itself is important in understanding and controlling the quality of the product permeate water which may be further polished to remove trace contaminants to meet the ultrapure specifications needed in industries such as pharmaceuticals, microelectronics, and power generation. Presented here are the chemistry of feedwater membrane fouling mechanisms, composition of foulants, and chemicals used to prevent fouling.
Ten Key Trends That will Shape the Future of the World Water Industry
Authors: Maxwell Steve
Published: April 2005

Scholarly studies estimating future water demand and prerequisite capital expenditures are being released in rapid‐fire fashion—and each proclaims a more serious future water crisis than the last. The Water Environment Federation has estimated that wastewater capital requirements during the next 20 years in this country will total hundreds of billions of dollars. The AWWA itself published a report in 1999, which estimated that capital expenditures for upgrading the drinking water infrastructure could total more than $300 billion during the next 20 years. Finally, a report done for the House Water Resources Subcommittee leapfrogged all recent studies and estimated that the cost of building, operating, and maintaining the water and wastewater infrastructure in this country during the next two decades will exceed $2
trillion
!

Choose your number, but it is clear that the costs of providing clean water to an expanding population and growing economy will continue to mount. This has led to a gradual reawakening of a rather sleepy water business, and a period of substantial consolidation and realignment has transformed the industry. Ten overarching trends and developments characterize the U.S. drinking water industry and will combine to shape the business in the future.
Water Distribution System Operation
Authors: Buenfil‐Rodriguez Mario O.
Published: April 2005

The operational tasks for distributing clean water in a city involve monitoring flows, pressures, storage levels, and water quality at different network locations; controlling and moving valves; attending to reports and enquiries from the public; billing and charging for consumption; keeping updated infrastructure maps and consumer records and census; repairing leaks; and replacing or improving pipes, hydrants, pumps, and other water distribution networks components.

There is no clear or definite boundary between operational and maintenance tasks, and their distinction is merely the intensity or frequency of a given job. Sometimes, the same employee team performs operational, preventive, or corrective maintenance tasks. In contrast, other rather specialized tasks can require a contract with a private service provider (
as analyzing water samples to detect a specific and difficult pollutant or controlling and supervising a sophisticated automated pump
).
Seasonal Coupling Between Intertidal Macrofauna and Sediment Column Porewater Nutrient Concentrations
Authors: Magni Paolo , Montani Shigeru
Published: April 2005

It is well established that dense bivalve assemblages play a major role in the processes of benthic nutrient regeneration in coastal marine ecosystems. In recent years, there is increasing evidence of the close relationship between nutrient concentrations in sediments and macrofauna‐influenced upward flux of nutrients that enhances benthic primary productivity. This coupling has been shown, to varying degree, for a variety of benthic communities dominated by both suspension and deposit feeders. The former, including semi‐infaunal mussel species, such as
Musculista senhousia
and
Modiolus americanus
, filter particulate matter from the water column; the latter, such as holothurians, consume high amounts of sediment bacteria, microalgae, and dead organic matter. Due to the complexity and multiplicity of mechanisms that govern nutrient cycling in coastal ecosystems, these studies highlight the need for integrated investigations on the variability of porewater nutrient concentrations and the composition, biology, and behavior of
in situ
macrofaunal species.
Chlorine‐36 and Very Old Groundwaters
Authors: Kazemi Gholam A.
Published: April 2005

Chlorine has nine isotopes whose mass numbers range from 32 to 40, but only three of these occur naturally. The remaining six have half‐lives shorter than 1 hour, and this is why they do not occur in nature. The three abundant isotopes of chlorine include two stable isotopes, chlorine‐35 and chlorine‐37, with 75.53% and 24.47% abundances, respectively, and one radioactive isotope, chlorine‐36, with a half‐life of 301,000 ± 2000 years (some references ± 4000 years). The natural mixture of these three isotopes makes up environmental chlorine.

Weapon testing of fusion devices starting in late 1952 and extending through mid‐1958 has led to the production of up to 70,000 atoms m
−2
s
−1
. Chlorine‐36 produced by this phenomenon is used as a marker to age‐date young groundwaters that are less than 50 years old.
Conductivity‐Electric
Authors: Gray David M.
Published: April 2005

Electrical conductivity is the ability of a material to carry electrical current. In water, it is generally used as a measure of mineral or other ionic concentration. Conductivity is a measure of the purity of water or the concentration of ionized chemicals in water. However, conductivity is only a quantitative measurement: it responds to all ionic content and cannot distinguish particular conductive materials in the presence of others. Only ionizable materials will contribute to conductivity; materials such as sugars or oils are not conductive.

In a metal conductor, electrical current is the flow of electrons and is called
electronic
conductance. In water, electrical current is carried by ions because electrons do not pass through water by themselves. This is
electrolytic
conductance.

When a voltage is applied between two inert electrodes immersed in a solution, any ions between them will be attracted by the electrode that has an opposite charge. Ions will move between electrodes and produce a current depending on the electrical resistance of the solution. This is the basis of conductivity measurement—an application of Ohm's law. For high purity waters, it is common to express conductivity as its reciprocal, resistivity.
Dissolved Organic Carbon
Authors: Lead Jamie R.
Published: April 2005

The importance of dissolved organic carbon (DOC) lies in its role in the biogeochemical carbon cycle, as a necessary basis for aquatic microbial processes and in aquatic chemistry. Although the global burden of carbon is dominated by sediments, dissolved organic carbon is of obvious importance as carbon is the basis of life, an energy and nutrient source for microorganisms. DOC is also of significance in trace pollutant binding (and consequently in pollutant transport and bioavailability), in the charge and aggregation behavior of colloids, in weathering, in pH buffering, and in acid–base and redox chemistry of natural waters. It thus has a large and essential role in determining the chemical composition of natural waters. Although microbiological and chemical aspects are frequently taught and researched in isolation, it may be impossible to understand the composition and regulation of natural waters without simultaneously considering the microbiological and chemical processes because they are so closely interlinked. Any distinction between the two processes is therefore likely to be arbitrary and misleading.
Freshwater
Authors: Kazemi Gholam A.
Published: April 2005

Water is an important solvent and is sometimes called the universal solvent (1). It dissolves, to the extent possible, the material with which it comes in contact. Salinity is a measure of various constituents dissolved in water, including solids, liquids, and gases. Total dissolved solids (TDS), another form of expressing the amount of dissolved ingredients in water, is the sum of total solids that have been dissolved in water [note that TDS at 180°C = Sum of ions + SiO
2
 − 0.5082 × mg/l HCO
3
; (2)]. However, many references do not differentiate between TDS and salinity because the absolute majority of the dissolved constituents of water are usually the solids. Both parameters have units of mg/l or ppm. These two units, ppm and mg/l, are almost the same except for high salinity waters for which 1 mg/l = 1 ppm × density of water. The salinity of groundwater ranges from 25 mg/l in quartzite springs to more than 300,000 mg/l in brine (3), and the salinities of distilled water, River Murray in South Australia, seawater, and the Dead Sea are 0, 553, 35,000, and 385,000 mg/l, respectively (4).
Iron
Authors: Roy William R.
Published: April 2005

The average concentration of iron in the earth's crust is about 5%, and it occurs in a wide variety of oxide, carbonate, silicate, and sulfide compounds either as metallic ores or in rock‐forming minerals. Iron also occurs naturally in water from the dissolution of iron‐containing minerals. Iron in water can occur in a dissolved form, a colloidal form that is combined with organic matter, and as suspended, iron‐containing particles. Dissolved iron occurs in water in two oxidation states: ferrous iron, Fe (II), and ferric iron, Fe (III). In solution, iron can occur as a cation (Fe
2+
) and in combination with other ions to form complexes and neutral ion pairs. Iron does not generally occur as the trivalent cation (Fe
3+
) in significant concentrations in water. Trivalent iron generally exists in combination with other constituents. Depending on the occurrence of anions, such as sulfate, carbonate, and phosphate, and the pH and reduction‐oxidation potential (
E
h
), the major iron species found in natural waters include a sulfate complex (FeSO
4
0
), a carbonate form [Fe(HCO
3
)
2
], phosphate complexes (FeHPO
4
0
, FeH
2
PO
4
+
), and various hydroxide species such as FeOH
+
, Fe(OH)
2
+
, Fe(OH)
3
0
, Fe(OH)
4
−
, and FeOH
2+
. The relative proportion of ferrous iron and ferric iron depends on the
E
h
of the water; ferrous iron is the dominant form in oxygen‐poor water (reducing conditions). In oxygen‐rich water (oxidizing conditions), ferric forms of iron dominate.
Isotope Fractionation
Authors: Kazemi Gholam A.
Published: April 2005

In general chemistry, fractionation is the separation of a mixture, usually of chemically related components, into fractions that possess different properties. A mixture of liquids having different boiling points, may be separated by collecting fractions that boil at different temperatures in a fractionating column. This is a long, vertical column containing plates or bubble caps attached to a still. As a consequence of internal reflux, a gradual separation occurs between high and low boiling point fractions of the liquid mixture.

In hydrochemistry, the fractionation factor is a ratio which shows the depletion or addition of ions in rainwater compared to seawater (2). In other words, the fractionation factor is the ratio of two ions in rainwater to the ratio of the same ions in seawater. For example, for Cl
−
relative to Na
+
, the fractionation factor
F
Na
is:(2)

urn:x-wiley:9780471478447:media:pc336:xm1

In this equation, the units of concentration can be mg/l, mmol/l, meq/l, etc.
Silica in Natural Waters
Authors: Ning Robert Y.
Published: April 2005

Silica and silicates are generic names given to the family of silicon dioxide compounds derived from the dehydration–polymerization of silicic acid [Si(OH)4]. Silicic acid, variously called orthosilicic acid, monosilicic acid, or silicic acid monomer, is a weak tetravalent acid that has pKavalues of 9.9, 11.8, and 12. Although silicic acid is prevalent in natural waters and is readily available from acidification of commercial crystalline sodium silicate or metasilicate, it has a great propensity to polymerize by dehydration to form Si–O–Si anhydride bonds:urn:x-wiley:9780471478447:media:pc478:xm1

Thus silicon dioxide (SiO2, silica) is the final and most stable product in normal conditions of silico‐oxygen acid polymerization. The molecule of silica represented by the formula SiO2is polymeric and is more accurately represented by the formula (SiO2)n, where n is a large number.
Soft Water
Authors: Kazemi Gholam A.
Published: April 2005

The author, here, wishes to draw the reader's attention to one other point and pose a question as well. He believes that “softness” would have had an identical application and a similar meaning to hardness if it would have been there. Therefore, it is interesting to speculate as to what was the rationale for use of the term “hardness”, not softness. One reason might be that hard water is generally easier to notice because of its unwanted and disappointing characteristics and our predecessors looked for something to describe it. In other words, the term hardness was created to explain easily noticeable hard water, not to describe soft water. This is why there is no such practice as water hardening, changing soft water to hard water, in contrast to the well‐established exercise of water softening which changes hard waters to soft waters.

The definition of soft water varies slightly among researchers. Based on Table 1, soft water is defined as water whose hardness is less than 60 or 75 mg CaCO3/L. This means that waters with less than 15 mg Ca2+/L and 10 mg Mg2+/L are soft; higher concentrations in waters belong to the other categories such as hard water or very hard water. However, some researchers argue that there is no exact definition for determining soft or hard water because it depends, at least partially, on what one is accustomed to. What is soft water for one person, may be moderately hard for another and vice versa.
Strontium Isotopes in Water and Rock
Authors: Kazemi Gholam A.
Published: April 2005

The Sr isotopic ratio in natural water reflects the contribution made by various minerals as they dissolve in water. Rivers are the major provider of strontium to the oceans and define, to a great extent, the marine
87
Sr/
86
Sr ratio. Strontium in rivers is mainly derived from two end members: limestone and evaporites as one end member (high Sr and low
87
Sr/
86
Sr ratio of 0.706–0.709) and silicate rocks as the other end member that are low in Sr and have a higher
87
Sr/
86
Sr ratio. Processes such as atmospheric deposition, cation exchange, and biological cycling, too, influence the Sr isotope ratio in water. However, unless there have been recent anthropogenic or natural disturbances, annual gains or losses of Sr from cation exchange and biological pool should be minimal.
Carbonate in Natural Waters
Authors: Ning Robert Y.
Published: April 2005

Carbonate is the divalent anion resulting from complete neutralization of carbonic acid. In natural waters, it is in dynamic equilibrium with carbon dioxide gas, carbonic acid, bicarbonate anion, and solid forms of insoluble carbonate minerals—mainly calcium carbonate:urn:x-wiley:9780471478447:media:pc81:xm1Various aspects of the CO2–carbonate systems in natural waters have been extensively reviewed. Practical interests lie in the areas of geochemistry, biochemistry, water treatment and usage, and environment.
Submerged Aquatic Plants Affect Water Quality in Lakes
Authors: Havens Karl E.
Published: April 2005

This chapter addresses four questions:

What types of submerged plants occur in lakes, and how does type of plant relate to water quality benefits?

What factors control the biomass and spatial extent of submerged plants?

What are the processes whereby plants affect lake water quality, in particular, the concentrations of nutrients, turbidity, and the occurrence of noxious algae?

How can lakes be managed to promote the development of submerged plants that will help to improve water quality?
Surface Runoff and Subsurface Drainage
Authors: Holden Joseph
Published: April 2005

Runoff is the movement of water across or through the land surface. Sometimes, the word runoff is used simply to refer to river discharge. However, there are many different types of runoff, including overland flow (surface runoff) or throughflow (subsurface runoff, sometimes also called interflow). Precipitation can either hit the surface of the hillslope directly or be intercepted by vegetation. This intercepted water can be stored on leaves and tree trunks which shelter the ground beneath, or it can trickle down to reach the surface via stem flow. There are then two possibilities for direct precipitation or stem flow, once it reaches the hillslope, either to infiltrate into the soil or to pond up and flow over the surface as overland flow. Water that enters the soil may percolate down or move laterally through the soil as throughflow, or it may return to the surface where the soil becomes saturated. The following sections provide details on each of the main interlinked overland flow and subsurface drainage mechanisms.
Trace Elements in Water, Sediment, and Aquatic Biota—Effects of Biology and Human Activity
Authors: Priyadarshi Nitish
Published: April 2005

Trace elements are defined here as those elements that generally occur in water at concentrations of less than 1 mg/L.

Trace elements enter the aquatic environment in small soil particles that are redistributed during runoff as suspended particles in streams, lakes, and coastal marine locations. Trace elements in water are important; they are toxic to humans and aquatic life in excess, and they accumulate in food chains. Trace element activity in aquatic systems depends on the element species formed by natural hydrodynamic, chemical, and biological forces.

The concentrations of trace elements in water are often much lower than would be expected from either equilibrium solubility calculations or supply to water from various sources. The most common reason for the low concentrations is adsorption of elements onto a solid phase.
Cultural Eutrophication
Authors: Priyadarshi Nitish
Published: April 2005

The phrase “cultural eutrophication” (=cultural enrichment) is becoming widely used to denote organic pollution resulting from human activities. Humans, through their various cultural activities, have greatly accelerated this process in thousands of lakes around the globe. Cultural or anthropogenic “eutrophication” is water pollution caused by excessive plant nutrients. Increased productivity in an aquatic system sometimes can be beneficial. Fish and other desirable species may grow faster, providing a welcome food source (1). Eutrophication produces “blooms” of algae or thick growths of aquatic plants stimulated by elevated phosphorus or nitrogen levels. There has been some uncertainty as to whether algal blooms result from increased concentrations of nitrate or phosphate or from some other cause. It is now commonly accepted that algal growth in fresh waters is generally restricted by phosphate concentrations, whereas in marine waters, it is restricted by nitrate concentration (2). In freshwaters, the nitrate concentration might, however, influence the kinds of algae that grow, some of which taint in drinking water or are toxic to animals.
Urban Flooding
Authors: Mark Ole
Published: April 2005

Flooding in urban areas is an inevitable problem in many cities, and it causes huge costs to the society in structural and nonstructural damage. The problems that arize from urban flooding range from minor ones such as water getting into the basement of a few houses, to major incidents, where large parts of cities are inundated for several days. Most modern cities in the industrialized part of the world usually experience smaller scale local problems due mainly to insufficient capacity in their sewer systems during heavy rainstorms. Cities in other regions, including those in South/Southeast Asia, often have more severe problems because of much heavier local rainfall and lower drainage standards. This situation is continuously getting worse because many cities in the developing countries are growing rapidly these days but do not have the necessary funds to extend and rehabilitate their existing drainage systems.
Urban Water Studies
Authors: Brettschneider Karen D.
Published: April 2005

The urban landscape contains many elements that can alter the water quality of a waterbody. Before development occurs, grass and other natural vegetation hold sediment in place. Streams flowing through undeveloped terrain have no major sources of contaminants, such as bacteria (except for wildlife), that affect contact recreation. There are also no major sources of toxins that could negatively impact humans and wildlife. Development (residential, commercial, industrial, and agricultural, for example) brings issues that have the potential to compromise the character of streams through point source pollution or nonpoint source pollution. The best way to prevent or deal with these issues is to have cooperation among a broad group of stakeholders in each watershed, the area of land (and tributaries) that drains to a particular waterbody. These individuals must work together to develop sound watershed management to protect or to restore the health of the ecosystem of that watershed.
Water Quality in Surburban Watersheds
Authors: Kirby Charles W.
Published: April 2005

The story of water quality in suburban watersheds is primarily that of nonpoint source pollution (NPS). There may be instances where point sources contribute significantly to degraded water quality in suburban areas, such as privately owned or municipal sewage treatment plants, but the most salient characteristic of suburban basins is the conversion of land from a previous forested or agricultural land cover to highly impervious surfaces such as rooftops, roads, and sidewalks.

Alteration of the land surface within a watershed reduces infiltration and increases the proportion of precipitation running directly into the waterways as runoff. The increase in the percentage of impervious surface from urbanization in a stream basin is the primary threat to water quality in suburban areas.
Dilution‐Mixing Zones and Design Flows
Authors: Jha Ramakar , Bhatia K. K. S. , Ojha C. S. P.
Published: April 2005

The possibility that a pollutant will be discharged accidentally or intentionally into a stream/river is a matter of constant concern to those diverting and using water from streams and rivers. It is essential for water resources planners and managers to understand the physical processes involved in a stream/river prior to the implementation of any water resources projects. When a pollutant is discharged into a stream/river, it is subjected to initial dilution immediately due to the density difference between the receiving water and the pollutant.

The longitudinal, vertical and two‐dimensional profiles of pollutant concentration indicate the density gradient between the pollutant and the receiving water. After initial dilution, the processes are governed by advection, reaction, and dispersion phenomena that tend to modify the initial pollutant concentration.

Advection phenomena represent the downstream transport of a discrete element of the waste load by the stream flow.

The reaction phenomena represent the decay of biodegradable materials in the waste under the action of naturally occurring bacteria in the stream. The dispersion phenomena represent that under the influence of turbulence, eddy currents, and similar mixing forces, a discrete element of the waste load tends not to remain intact, but mixes with adjacent upstream and downstream elements. In rivers and streams, the influence of dispersion phenomena is usually relatively small compared with advection and reaction phenomena; however, it can be important in some circumstances.
Fisheries: History, Science, and Management
Authors: Lackey Robert T.
Published: April 2005

The overall goal of fisheries management is to produce sustainable biological, social, and economic benefits from renewable aquatic resources. Fisheries are classified asrenewablebecause the organisms of interest (fish, shellfish, reptiles, amphibians, and marine mammals) usually produce an annual biological surplus that, with judicious management, can be harvested without reducing future productivity. In contrast,nonrenewableresources (oil, coal, iron, and copper) are available in fixed quantities and are not replaced except over geologic time.

The benefits that humans gain from a fishery are diverse and may be enumerated in several ways. Most commonly, benefits are computed ascommodityoutput—the weight or number of fish produced. Commodity output may be further split between the animals harvested by capture (fishing for wild animals) or culture (produced as captive animals)—commonly called thecapturefisheries and theculturefisheries, respectively.