bluuebunny/crossref_metadata_2025 huggingface dataset:
Acid–Base Chemistry of Water
Authors: Kreller David , LoBue James , Rojanathanes Rojrit
Published: December 2019

A broad range of qualitative and quantitative concepts relating to aqueous acid–base chemistry are discussed. We first discuss the fact that much aquatic acid–base chemistry arises based on the properties of the H
2
O molecule, which has the key features of being bent, polar, and amphoteric. We present a sequence of sections that discuss Brönsted–Lowry hydrogen ion transfer reactions, water autoionization, the pH scale, the behavior of strong and weak acids and bases, the behaviors of acidic and basic salts, the behavior of diprotic acids and bases, and buffered solutions. Furthermore, we discuss neutralization reactions and illustrate how they are the basis of volumetric analyses, i.e. acid–base titrations. In the discussion of titrations, some detail is given to the roles of (primary and secondary) standards and standardization and the properties and behavior of pH indicators. Most topics are first discussed qualitatively (with a review of key concepts, reactions, and equilibria) and then treated quantitatively with sample calculations. A special discussion is devoted to the indicator phenolphthalein, focusing on the way that the photophysical (light absorbance) properties of its various ionization structures depend on π‐bonding conjugation in those structures.
Effective Models for Transport in Complex Heterogeneous Hydrologic Systems
Authors: Sund Nicole , Aquino Tomás , Bolster Diogo
Published: December 2019

Time and time again, transport behaviors that cannot be described by traditional simple advection dispersion equations (ADE) are observed in hydrologic systems, both in surface and subsurface environments. Such departures from classical predictions have been termed anomalous. In all cases, the presence of processes and heterogeneities spanning a broad range of temporal and spatial scales leads to a breakdown in assumptions inherent to classical ADEs and complicates modeling efforts. Developing approaches that account for these complexities naturally leads to the use of upscaling and stochastic modeling frameworks. We briefly introduce these ideas from both Lagrangian and Eulerian perspectives. We start with classical ADE models, highlighting many of the assumptions they are built on. By relaxing these assumptions, models capable of reproducing observed anomalous behaviors have been developed. Here, we briefly review three of the most popular models: continuous time random walks (CTRW), fractional advection dispersion equations (fADE), and multirate mass transfer (MRMT). While all three have enjoyed success, they too have their limitations. We conclude this article with a discussion of these shortcomings and present three very recent models that aim to address them as well as a brief discussion on future challenges.
Carbon Dioxide and Carbonate Chemistry of the Oceans
Authors: Cai Wei‐Jun
Published: December 2019

This article describes the acid–base properties of dissolved inorganic carbon (DIC) and the features of its distribution and cycling in the ocean. The DIC pool increases and becomes more enriched in molecular carbon dioxide (CO
2
) and lower in pH from surface to subsurface and from younger to older waters. Waters “age” and accumulate CO
2
as the deep ocean current moves around the global ocean, as organic matter settling from the productive sea surface is decomposed into CO
2
by microbes, and as calcium carbonate minerals are dissolved in the deep sea. In at least the past 500 000 years, CO
2
in the atmosphere regularly varied tightly between an upper bound of 280 and a lower bound of 180 ppm over several glacial cycles, indicating that the Earth's climate system and ocean carbon cycle were stable. Such stability has been disturbed at an unprecedented rate since the Industrial Revolution as human use of fossil fuel, and deforestation have released large amounts of CO
2
into the atmosphere and have pushed the atmospheric CO
2
level to over 400 ppm today. Part of the released anthropogenic CO
2
is taken up by the ocean, which has slowed down the greenhouse gas increase in the atmosphere but has acidified the seawater and altered ocean chemistry. This process, called ocean acidification, will continue and likely endanger marine organisms and ocean biological systems.
Ice Jams: Causes and Effects
Authors: Pawłowski Bogusław
Published: December 2019

In winter, in the temperate and cold climate zone, ice phenomena occur in rivers and lakes. Where the whole surface of water freezes up, an ice cover develops, and affecting the flow of water in rivers. An ice jam is a situation where a local accumulation of ice restricts the water flow. Ice jams can develop both in the initial phase of ice cover formation period and at the time of its breakup. Ice jams usually occur due to hydro‐meteorological conditions and local morphological properties of the river channel. They are formed by ice floes and frazil ice. The most important effect of an ice jam is the swelling of the river section upstream of the jam. The swelling may progress quickly and lead to flooding. The development of ice jams also results in changes of the river channel morphology and – in extreme cases – outside the channel, causing damage to engineering infrastructure. Despite the application of a number of measures to reduce the threat and consequences of ice jams, the phenomena are very difficult to predict. In the last decades, in some regions, their intensity has been curbed by global warming.
Removal of Contaminants of Emerging Concern from Wastewater
Authors: Dosoretz Carlos G.
Published: December 2019

Increased awareness regarding water pollution and resources conservation due to water scarcity and climate change, combined with intensive urbanization and agricultural production, have raised the need for removal of contaminants of emerging concern (CEC) from treated effluents. CEC include, among others, pharmaceuticals, cleaning and sanitation products, endocrine disrupting compounds, suspected carcinogens, and nanomaterials at trace concentration. Added to this are antibiotic‐resistant bacteria (ARB) and antibiotic‐resistant genes (ARG). Conventional wastewater treatment removes bulk organic contaminants leaving CEC in the effluents. This article discusses the incorporation of advanced treatments such as oxidation processes, adsorption, and tight membrane separation, i.e. reverse osmosis (RO), aimed at removing CEC from effluents. Owing to its generic capability to remove dissolved organic and inorganic contaminants at once, RO appears as the core technology for effluents purification. Besides improvements of existing municipal effluents, changes in conception, management and planning of the urban water systems, e.g. reduction at source and decentralization approaches, are required. Removal of dissolved organic pollutants and mineral contaminants at trace levels cannot be done without consuming energy. The water–energy nexus and related life cycle analyses need to be rethought in terms of environmental and health risks and deterioration of water resources and soils.
Advanced Oxidation Processes
Authors: Kovacic Marin , Kusic Hrvoje , Loncaric Bozic Ana , Dionysiou Dionysios D.
Published: December 2019

The efficient water purification is of high priority because water quality faces ever‐increasing challenges due to the pollution by a vast array of various organic pollutants, causing negative impact due to documented and suspected toxicity toward aquatic organisms and humans as well. In current focus are contaminants of emerging concern (CECs), including cyanotoxins, flame retardants, organohalogens and perfluorinated compounds, personal care products, pesticides, plasticizers, and pharmaceuticals, which are largely unaffected by current (waste)water treatment technologies, thus needing upgrade with a tertiary treatment. A potential solution for such water quality issues is advanced oxidation processes (AOPs), technologies exploiting the high reactivity, and nonselectivity of the hydroxyl radical (HO●) that can be generated by either chemical, radiation, electrical, or mechanical energy. Accordingly, AOPs can be classified into chemical, photo‐assisted, electrical, and mechanical (latter two can be gathered under the term “high energy”) processes that are described from the mechanistic point of view in this article.
Management of the Marine Environment: Transdisciplinary and Systemic Approach
Authors: Prouzet Patrick , Monaco André , Sébastien Léa
Published: December 2019

Since the beginning of the twentieth century, observations have shown a significant degradation of aquatic environments. This degradation has got worse in the past century in all regions of the Globe. This is observed in many estuarine areas vital for the growth of high‐value species. Given the state of degradation of these coastal environments, their vulnerability to the anthropic effects and the natural hazards has become stronger whereas their resilience capacities have become significantly lower. The same goes for the many human communities living from the exploitation of living resources that can no longer ensure the sustainability of their fishing or farming activities. In addition to all these modifications the impacts, now proven, of climate change alter the temperature of water masses and biogeochemical characteristics of marine ecosystems. This integrated vision of the marine environment and of the aims of research makes it possible to address the issue of environmental governance and the problems involved in coordinating the knowledge and functions of scientific, social, economic and political actors. The three authors who are specialized in different fields of research exchange their points of view, redefine the terms, notions, concepts, and the questions related to the exercise of transdisciplinarity.
Applications of SPM to Studies of Mineral–Water Interface Chemistry
Authors: Higgins Steven R. , Bertagni Angela L.
Published: December 2019

The scanning probe microscope (SPM) has been utilized in studies of solid surfaces for nearly four decades. With resolution as high as the single atom level, valuable information on the structure and other properties of solid surfaces can be obtained. One of the most exciting areas of application for the SPM is in the study of mineral–water interfaces where the chemical reactions taking place are both of fundamental interest as well as important from an environmental/geochemical perspective. In this article, the basic design of one type of SPM, the atomic force microscope (AFM), is introduced followed by an examination of the different levels of resolution that may be exploited to obtain fundamental information on kink, step, and surface microtopography from mineral surfaces immersed in reactive solutions. The examples of these particular applications highlight the influence of solution chemistry on the rates and mechanisms of mineral growth and dissolution reactions that are readily followed with
in‐situ
AFM instrumentation.
Quantification of Anoxia and Hypoxia in Water Bodies
Authors: Nürnberg Gertrud K.
Published: December 2019

Anoxia and hypoxia are wide‐spread in freshwater systems and have been increasing in response to anthropogenic disturbances and climate change with biological and chemical implications. The concept of the
anoxic factor
to quantify anoxia and of the
hypoxic factor
for higher levels of dissolved oxygen concentration (DO) in lakes, reservoirs, and river sections has facilitated the exploration of hypoxia in a number of applications. This method condenses information from numerous individual DO profiles into annual values or
factors
that are comparable between and within lakes and hence invites the formulation and testing of hypotheses related to the DO status in water bodies. Besides the definition of the factors, proven and potential applications are described. They include the description of annual and spatial trend in anoxia or hypoxia, the evaluation of restoration techniques with respect to hypolimnetic oxygen depletion, the determination of internal phosphorus loading in stratified and polymictic lakes, the exploration of habitat constraints of fish due to hypoxia, and the examination of potential effects of climatic change on DO content and internal phosphorus loading.
Biofuels, Water Footprints, and Green Perspectives
Authors: Reijnders Lucas
Published: December 2019

Biofuels that are applied using advanced conversion technologies are promoted as green alternative to fossil fuels. The water footprint, the freshwater consumption, linked to current life cycles of such biofuels is much larger than the corresponding consumption associated with fossil fuels. Wind‐ and photovoltaic energy are also characterized by water footprints that are much lower than the corresponding consumption linked to biofuels. Food production and biofuel production increasingly compete for scarce freshwater resources and freshwater stress may increase when biofuel production expands. Availability of freshwater may be a limiting factor in biofuel production. Biofuel life cycles can also be associated with substantial water pollution burdens of nitrate, phosphate, pesticides, and organic substances. On the other hand, it has been proposed to use wastewater for the production of microalgal biofuels. So far, however, no full‐scale production based on this proposal that meets standards achieved by state‐of‐the‐art wastewater treatment facilities has been reported. In many respects relevant to green perspectives, except the consumption of geochemically scarce mineral resources, solar and wind‐based technologies tend to outperform biofuel‐based energy supply technologies. There would seem to be a case for modest expectations as to the share of biofuels that are applied using advanced conversion technologies in future energy supply.
Barometric Efficiency
Authors: Rasmussen Todd C.
Published: December 2019

The barometric efficiency is used to describe how water levels in wells fluctuate in response to atmospheric pressure. Normally, water levels rise whenever the barometric pressure falls, and vice versa. This phenomenon is observed in both confined and in deep, unconfined aquifers. In confined aquifers, the change in water level is caused by a change in the load (or force) applied to the Earth's surface by the atmospheric pressure. Higher atmospheric pressures increase the load, which is transferred to water in deeper aquifers, causing an increase in fluid pressures within the aquifer. In unconfined aquifers, the water level response is caused by a difference between air movement through the borehole and the existing pressure in the unsaturated zone. This deficit results in rapid water level change in the borehole region followed by a delayed change to the original level once the air pressure change reaches the water table. The slower change is a factor of the thickness and air permeability of the unsaturated zone.
Earth's Surface Energy Balance
Authors: Ohmura Atsumu
Published: December 2019

The Earth's surface energy balance is presented with the up‐to‐date information. The flow of energy is traced from the Sun through the atmosphere till it reaches the Earth's surface. The attenuation of solar radiation in the atmosphere is presented with respect to scattering and absorption, using satellite measurements, model simulations, and the radiation measurements at the surface. The transformation of solar radiation at the surface into various forms of energy is quantitatively illustrated with information obtained by direct flux observations and simulations by GCM. The atmosphere/surface‐combined system absorbs 70% of radiation coming from the Sun, of which 27% and 43% are absorbed by the atmosphere and the Earth's surface, respectively. On the surface, the largest amount of energy, 25% of the primary solar radiation, is expended for evaporation, 13% for net longwave cooling, and 5% for direct heating of the atmosphere. Therefore, the radiative energy at the surface is mainly converted into water vapor and participates for heating the system only by forming clouds. While evaporation takes place slowly from the entire Earth's surface, the formation of clouds happens in restricted space and time. This mechanism contributes to the enhancement of extreme precipitation and temperature in warming climate.
Evapotranspiration Monitoring
Authors: Fuster Rodrigo , Moletto‐Lobos Italo , Vargas Catherine , Mattar Cristian
Published: December 2019

One of the most important components of the earth's surface water balance is evapotranspiration, which regulates the exchange of energy between ground and atmosphere. The effects of global warming intensify the water demand and therefore, the potential scarcity of water could affect several landscapes and agricultural systems. Therefore, it is essential to monitor evapotranspiration in order to assess water use efficiency and drought risks. There are a several methods to estimate and monitor evapotranspiration (ET), which differ in accuracy, cost and complexity. In this article, we present a general background of ET concepts, then, direct, empirical and remote sensing‐based methods to estimate it and finally we conclude with some recent ET applications in Chile.
Ghijben–Herzberg Equilibrium
Authors: Holzbecher Ekkehard
Published: December 2019

The Ghijben–Herzberg equilibrium concerning the relation between the elevation of the freshwater table and the depth of the fresh–salt–water interface in coastal aquifers was formulated at the turn between the nineteenth and twentieth century. It was independently stated by Ghijben in the Netherlands and Herzberg in Germany and provides a simple formula based on the densities of the two water bodies. In the time past since its origin, there have been lots of different studies in research and applications. Limitations have been formulated and discovered. Extensions have been proposed to overcome the limitations and improve the applicability. Analytical and numerical methods have been developed and can be used nowadays for more detailed computations. However, the Ghijben–Herzberg formula has proved to be an easy rule of a thumb and a valid approximation in laboratory experiments and in the field.
Stable Isotopes of Water in Hydrogeology
Authors: Tweed S. , Leblanc Marc , Cartwright I. , Bass A. , Travi Y. , Marc V. , Bach T. Nguyen , Duc N. Dang , Massuel S. , Kumar U. Saravana
Published: December 2019

Groundwater is a pivotal resource for many human populations and ecosystems. However, in groundwater sciences (hydrogeology), there remain many challenges in understanding key processes; including groundwater origins, water fluxes, and controls on water quality. The stable isotopes of water are naturally occurring, form part of the water molecule, can be measured at high spatial and temporal resolutions and have predictable fractionations that may be used to understand key water cycle processes. Such qualities mean that stable isotopes are a key tracer in defining the spatial and temporal heterogeneity of groundwater systems. This article provides an overview of the use of stable isotopes to analyze (i) groundwater recharge from both rainfall and irrigation water, and presents case studies that highlight the use of stable isotopes to determine the frequency, rapidity, and origins of recharge; (ii) groundwater flow pathways including paleo‐groundwater and mixing processes, and case studies of deeply circulating mineral waters, groundwater mixing, and origins of paleo‐groundwater; (iii) groundwater discharge via evaporation, surface waters, and case studies that highlight the modeling of dynamic tropical river inflows and submarine groundwater discharge; and (iv) groundwater salinity, including a comparison of processes driving salinization in two regional groundwater basins.
Drinking Water and Human Health Challenges in the Twenty‐First Century
Authors: Makris Konstantinos C.
Published: December 2019

Water and human health issues are intertwined within a changing urban setting. There is a momentum of societal demand to act on the aging drinking water pipe infrastructure to protect human health and at the same time to devise control options that will promote further the well‐being and quality of urban life in the developed world. The main objective of this work was to critically review the main challenges, opportunities, and risks associated with drinking water's current and emerging pressures as exerted on human health in urban centers of middle‐ and high‐income countries. Discussion about drinking‐water distribution systems did not focus on their portion extending from the water meter to the home tap, i.e. the premise plumbing system characteristics. One city does not hold a single water quality metric that remains constant because it changes in the urban space and time. Bigger urban centers will be differentially more complex to address water and health risks because of their numerous neighborhoods (district‐metered areas, DMA) being spread apart geographically in large distances. The water and health issues are multidisciplinary in nature and demand the close cooperation among health scientists, engineers, environmental scientists, social scientists, economists, and policymakers to address each city's unique risks.
Optimization for Booster Chlorination
Authors: Islam Nilufar , Rodriguez Manuel J.
Published: December 2019

Contamination in water distribution network (DN) can be catastrophic if free residual disinfection is not present. To ensure drinking water quality in a DN, ensuring detectable levels of free residual chlorine is a common practice in most municipalities. Higher chlorine doses can be applied in this respect, but this can produce detrimental disinfection by‐products (DBPs) such as trihalomethane and Haloacetic acids, and chlorine‐related taste and odor complaints. Booster chlorination can be a possible solution in this regard where additional chlorine dosages are applied where free residual chlorine concentration is less or zero. However, that requires optimization studies to balance various issues related to over chlorination including higher cost related to installation and operation, higher DBPs, and taste and odor complaints. These optimization studies can not only help us in selecting dosages but also can help us in various other aspects including locating booster stations, deciding number of stations, and pumping scheduling. Unlike other optimization studies, booster chlorination‐related optimization studies also require appropriate variables, kinetics, objective functions, constraints, mathematical formulation, algorithm selection, and proper optimization operation. This article will highlight details of all these steps specific to booster chlorination.
Microbial Biofilms
Authors: Maurice Patricia A.
Published: December 2019

A biofilm is a microbial community held together by extracellular attachment features known as extracellular polymeric substances (EPS) in a distinct 3‐dimensional structure or “architecture.” In addition to the organic microbial and EPS components, biofilms generally also include abiotic components such as mineral particles or tooth or bone structures that serve as support and sometimes as sources of nutrients. Biofilms can occur in many environmental settings, from soils to streambeds to suspended particulates in estuaries. Biofilms are important not just in the environment but also in biomedicine; they can occur, for example, on the surfaces of hip and other joint replacements and in the lungs of cystic fibrosis patients. This article serves as an introduction to biofilms, which are covered in greater depth in a variety of other articles in the
Encyclopedia
, particularly within the realm of microbiology and water and wastewater technology.
Deep‐Sea Hydrothermal Vents
Authors: Luke Tara H.
Published: December 2019

Hydrothermal vents were first discovered on the Galapagos Rift in 1977, and in the intervening 4 decades we have learned a great deal about these unique oases of life in the cold, dark, high pressure environments of the deep seafloor. Found on mid‐ocean ridges, back‐arc basins, and seamounts around the world, they result from the interaction of cold seawater with oceanic crust that has been superheated by underlying volcanic activity. Hydrothermal fluids leave the seafloor and form sulfide chimneys. These fluids are highly reducing, and contain toxic materials such as hydrogen sulfide, which provides the necessary components of life for the chemoautotrophic organisms forming the base of the food web in these ecosystems. Animals living at these vents have adapted to the harsh conditions by relying on chemoautotrophic microorganisms, either directly as a source of food, or in symbiotic association. They use varied strategies to maintain their symbiotic associations and to thrive at hydrothermal vents. While many animals characterize vent communities, some specific examples including tubeworms, Pompeii worms, mollusks, and crustaceans are described in more detail here. As we learn more about these widely spaced communities biogeographical patterns emerge, increasing our understanding of the evolution of vent communities.
Environmental and Public Health Issues: Community Engagement in Environmental Justice Populations
Authors: Neet Matthew J. , Ellis Jamelle H. , Hart Zachary H. , Scott Geoffrey I. , Friedman Daniela B. , Kelsey Rense Heath , Porter Dwayne E.
Published: December 2019

Environmental factors, ranging from the air we breathe to the food and water we consume to the places where we live and work, serve as major determinants of human health. A particularly relevant source of environmental risk is fish consumption, which provides an important source of protein and other nutrients for communities worldwide. The health risks associated with consuming contaminated fish are pronounced among environmental justice communities – communities that experience a disproportionate exposure to environmental contamination such as water pollution or air pollution. In these communities, which are typically situated in low‐income areas, the fish caught from local waters for sustenance are more likely to contain unsafe levels of contaminants or pathogens. Community engagement is now recognized as an essential strategy for designing and delivering messages that reduce exposure to a range of environmental risks to public health, especially among environmental justice communities. This article reviews a method for identifying environmental justice communities and then discusses a case study in which community engagement was employed successfully to better understand exposure to environmental health risks and examine state‐issued fish consumption advisories within an environmental justice community.
Glaciers and Land‐to‐Ocean Flux of Carbon
Authors: Paulsen Maria L. , Robson Benjamin A.
Published: December 2019

Glaciers, ice caps, and ice sheets currently cover 12% of the Earth's land surface. The vast majority of glaciers worldwide are now in a state of retreat at unprecedented rates, with the most substantial mass loss originating from Greenland (37% of the global). The mass of ice‐locked organic matter is substantial and represents a hitherto poorly understood reservoir of organic carbon. In this article, we aim to summarize the current data on the concentrations of organic carbon across glacial systems and its origin and fate. Further, we aim to discuss the land‐to‐ocean flux of organic carbon and the effect on downstream environments. Several studies have suggested the glacial dissolved organic carbon (DOC) to have a pronounced impact on the coastal ecosystems because glacial DOC is highly bioavailable, i.e. has a high potential to feed downstream heterotrophic organisms. These studies, however, do not consider that the bioavailable carbon of coastal systems is in fact higher than in the glacial runoff. Contrary to previous studies, we, therefore, stress that glaciers are not a major source of neither DOC or bioavailable DOC and instead identify new focus areas in the field, such as the influence of the catchment area and the role of particulate organic carbon.
Microplastics: A Global Water Pollution Problem
Authors: Weinstein John E. , Viado Hildehardo F. , Leads Rachel R. , Deloughry Emma , Schandera Louisa , Liddy Karlee , Scott Geoffrey I.
Published: December 2019

Microscopic particles of plastic, known as microplastics, have become a ubiquitous contaminant in the environment. Their presence in the marine environment has been correlated to the exponential increase in global plastic production over the past 70 years and the subsequent increased abundance of plastic litter in the oceans. Other sources of microplastics include synthetic microfibers associated with the washing of textiles and tire particles associated with the abrasion and wear of the tread on automobile tires. Microplastics are recognized as contaminants of emerging concern because they occupy the same size fraction as plankton and sediment, making them bioavailable to a wide range of organisms, and they have the potential to adversely impact environmental health. Ingestion of microplastics by humans is likely, but confounding any assessment of health impacts is the lack of estimates on the total human exposure to these particles. This article will review the magnitude of plastic production and waste, provide an overview of the major sources of microplastics in the aquatic environment and the hazards they pose to both environmental and human health, and present a case study of ongoing efforts to characterize the sources and fate of microplastic contamination in Charleston Harbor, SC, USA.
Lead in Groundwater: Chemical Behavior and Treatment
Authors: Jacobs James A.
Published: December 2019

Lead (Pb) is the most abundant of the heavy metals on Earth, with the average Pb content of the crust ranging from 13 to 16 parts per million (ppm). Although Pb is widely used in many applications, it can pose substantial health risks, including Pb poisoning. This article discusses the occurrence and properties of Pb, along with controls on fate and transport and common methods of Pb remediation.
Mercury in Groundwater: Chemical Behavior and Treatment
Authors: Jacobs James A.
Published: December 2019

Mercury is highly toxic and is rarely found as a pure metal. It is the only metal element that is a liquid at room temperature. There are three forms of mercury in the environment: elemental, inorganic, and organic mercury. All forms of mercury are toxic. This article discusses the forms and occurrence of mercury, along with health risks, controls on fate and transport, and potential methods of remediation. Specific regulatory guidelines in the United States are also discussed.
Remediation and Case Closure Policy for Petroleum Hydrocarbons
Authors: Vance David B. , Jacobs James A.
Published: December 2019

This article discusses regulatory changes regarding more realistic enforcement and achievable cleanup standards for petroleum hydrocarbons. Advantages of a risk‐based and future‐use approach to managing subsurface contamination are described in detail. Regulatory environmental goul evolve over time related to improvements in assessments of ecosystem impacts, human health exposure and remedial experience.
In SituAeration and Volatilization of Petroleum Hydrocarbons in Groundwater
Authors: Vance David B. , Jacobs James A.
Published: December 2019

There are a variety of groundwater remediation processes for petroleum hydrocarbons that usein situaeration and volatilization as a part of their technology. Some of these technologies have a bioremediation component to them as well. This article discusses groundwater remediation technologies including soil venting, soil vapor extraction, air sparging, bioventing, and biosparging. A case study of biosparging is described in detail.
Soil Vapor Data: Groundwater Applications
Authors: Hartman Blayne , Jacobs James A.
Published: December 2019

Soil vapor data analysis can be applied to enhance groundwater investigations and subsurface interpretations. Collecting reproducible and representative soil vapor data in a subsurface sampling project is critical in the soil vapor sampling planning phase. Soil vapor data can be collected using active or passive methods. Specific vapor sampling protocols have been developed by regulatory agencies and others over the past three decades. Once the soil vapor samples have been collected and analyzed in a laboratory, interpretation of the data is critical in understanding vapor migration as well as the potential for soil vapor intrusion into subsurface conduits and into structures. This article begins with an overview of the various applications of soil vapor surveys, a brief discussion of the various soil vapor methods, and then focuses on a number of specific issues relating to soil vapor surveys for groundwater investigations. The intent of this article is to guide professionals on when, why, and how soil vapor data can be useful for groundwater‐related investigations and how to interpret the results.
Lead in Water and Soil: Speciation, Toxicity, and Treatment Technologies
Authors: Manecki Maciej
Published: December 2019

Lead (Pb) is widely distributed in the environment and its negative health effects, especially to children, have been well documented. The aqueous species of Pb, in their form and concentration, strongly depend on mineral–water interaction processes in the environment. Lead exists in the environment mostly in the form of solid particles but bioavailable toxic Pb is absorbed by living organisms through solution. Therefore, our understanding of formation, transformation, dissolution, and precipitation of Pb‐bearing phases in aqueous solutions is critical for successful strategies to minimize Pb in drinking water or food and to prevent exposure and poisoning. This article summarizes our current understanding of processes governing the presence of Pb in waters and soils, briefly discusses Pb toxicity, and reviews some key technologies for immobilizing Pb and making it less bioavailable. Finally, the article ends with some suggestions for further research.
Hydrodynamics of Lakes
Authors: Boegman Leon
Published: December 2019

Lake hydrodynamics change seasonally in response to the net heat flux through the free surface. Heating during summer causes seasonal stratification to develop, where basin‐scale hydrodynamics occur under a balance between the surface wind force, which displaces the stratification, and the restoring gravitational force, which acts to bring isotherms back to the horizontal. As a result of wind forcing, turbulent mixing may be strong within the surface layer and the boundary layers at the lake perimeter, with the lake interior remaining comparatively quiescent due to the stabilizing effect of the thermocline. Ice and snow cover, in winter, shelter the lake from wind stress and reduce convective motions, resulting in a “reverse” winter stratification. During spring and fall, net heat flux through the free surface, erodes the strength of the stratification, allowing penetrative convection and wind‐driven mixing to turnover the water column. These brief mixing periods, therefore, have profound implications for vertical biogeochemical fluxes. The lake response to wind forcing can be classified according to an energy balance or the dimensionless Wedderburn (or Lake) Number, both of which show strong seasonal dependence in accordance with changes in the net surface heat flux.
Massively Parallel and Flexible Processing forMIMOSystems
Authors: Nikitopoulos Konstantinos
Published: December 2019

5G mobile systems and beyond are envisaged to provide very high throughput, to meet very strict requirements in terms of latency, and to support a very large number of devices in a very small area. Multiple‐input, multiple‐output (MIMO) systems can contribute to meeting these targets by enabling the concurrent transmission of a large number of information streams. In such MIMO systems, the choice of the corresponding required beamforming/precoding (in the downlink) and detection (in the uplink) algorithms can determine how much of the overall MIMO channel capacity and how much of MIMO's inherent capability to support multiple users we can exploit in practice. Linear beamforming and detection approaches are practical, but they highly underutilize the MIMO channel. Nonlinear methods can provide substantial gains, both in terms of throughput and connectivity, but their complexity increases exponentially with the number of concurrently transmitted information streams. This complexity, together with the soon‐to‐be‐reached plateau in the speed of processors, urges a paradigm shift toward massively parallel signal processing for wireless communications systems. Ideal parallelization methods should be scalable to any number of available processing elements, generic, adjustable to the transmission conditions, and transparent to the choice of the implementation platform. Promising parallelization algorithms in this direction enable up to 70% throughput gains without changing the number of base‐station antennas and RF chains, and can substantially increase the number of connected devices, with processing latency requirements similar to those of linear approaches.
Random Access for Machine‐Type Communications
Authors: Leyva‐Mayorga Israel , Stefanovic Cedomir , Popovski Petar , Pla Vicent , Martinez‐Bauset Jorge
Published: December 2019

The success of 5G wireless networks (5G) substantially relies on efficiently embracing machine‐type communications (MTC), intended to support autonomous exchange of data between devices. Typical MTC applications include smart metering, e‐health care, environmental and structural monitoring, and asset tracking. Therefore, MTC is an essential component of smart cities and the Internet of Things (IoT). However, cellular networks have traditionally been designed to efficiently handle human‐to‐human (H2H) traffic, whose characteristics greatly differ from those of MTC traffic. Only recently the cellular networks started to be optimized for MTC and, in that sense, a special focus has been put on the random access (RA), which occurs whenever a device requests initial access to a base station (BS). Specifically, the RA mechanism of cellular networks is based on the slotted ALOHA protocol, whose efficiency degrades rapidly as the number of users increases, also presenting a large signaling overhead when short packets are transmitted. The RA channels are further challenged by massive machine‐type communications (mMTC) applications, where a great number of MTC devices attempt to access the BS, while the class of MTC applications with strict latency requirements is challenged by the signaling overhead. These problems have been inherited from the H2H‐oriented cellular systems and, while numerous solutions have been proposed, there is still no consensus on the MTC enhancements for the second phase of 5G standardization.
Full‐Duplex in Small‐Cell Networks
Authors: Hong Jun‐Pyo
Published: December 2019

Based on recent advances in analog/digital circuits for self‐interference cancellation, the use of full duplex (FD) in small‐cell networks has been receiving increasing attention as a promising solution to cope with explosive demand for wireless communications. FD operation has the potential to double the spectral efficiency of point‐to‐point communications by enabling concurrent transmission and reception over the same frequency band. However, the spectral efficiency gain of FD can be significantly limited in small‐cell networks if traditional strategies developed for half duplex (HD) are reused without careful consideration of cross‐mode interference. In this article, we look at some major issues in developing FD communication strategies for small‐cell networks and introduce recent results on spectral efficiency gains of FD over HD in various networks.

First, we focus on single‐antenna systems. To improve mitigate the cross‐mode interference, selection diversity is exploited by allocating the same channel to widely separated uplink/downlink users, opportunistically scheduling uplink/downlink user pair, and selecting FD/HD mode. In particular, the spectral efficiency gain of FD over HD can be at most about 20% in randomly deployed large networks. This low gain comes from the limited interference avoidance capability of single‐antenna systems. Second, we shift our focus to multi‐antenna systems. By means of multi‐antenna techniques, multi‐antenna system can effectively mitigate the aggregated network interference. In particular, the FD operation can asymptotically double the spectral in randomly deployed large networks with massive MIMO. Finally, we present challenges and opportunities in developing FD strategies for future small‐cell networks.
MassiveMIMO
Authors: Zhang Ticao , Mao Shiwen
Published: December 2019

Massive MIMO has been regarded as a promising technique for 5G wireless communication networks. It equips the base station (BS) with a large number of antennas to serve a set of user equipment (UEs) simultaneously. Due to channel hardening, the uncorrelated noise and the small‐scale fading can be eliminated. As a result, the transmitted signal can be directed into very focused areas, which brings orders‐of‐magnitude improvements in both spectral efficiency and energy efficiency with simple (linear) processing. In this chapter, we present a comprehensive overview of the state‐of‐the‐art research on massive MIMO. We begin with an information theoretic analysis to illustrate the advantages of massive MIMO. Then, we introduce both the physical layer and networking issues of massive MIMO. The integration of other 5G technologies with massive MIMO is also reviewed. Finally, we conclude this article with a discussion of challenges and future research topics.
Energy‐Efficient Offloading for Mobile Edge Computing
Authors: You Changsheng , Mao Yuyi , Zhang Jun , Huang Kaibin
Published: December 2019

The visions of Internet of Things and 5G communications have driven the evolution of mobile computing paradigm, shifting from the centralized mobile cloud computing toward mobile edge computing (MEC). By pushing mobile computing, network control, and storage to the network edges (e.g. base stations and wireless access points), MEC is expected to enable computation‐intensive and latency‐critical applications at the resource‐limited mobile devices. MEC promises dramatic reduction in mobile energy consumption and latency, tackling the key challenges for realizing the 5G visions. The promised gains of MEC have motivated extensive research efforts in both academia and industry. A main thrust of MEC research is to seamlessly integrate the two disciplines of wireless communications and mobile computing, leading to a wide range of new designs ranging from techniques for energy‐efficient computation offloading to network architectures. This article first introduces the basic principles of computation offloading in MEC, and then provides a comprehensive survey of the state‐of‐the‐art MEC research with emphasis on energy‐efficient computation offloading and joint radio‐and‐computational resource management. Last, we introduce recent 5G standardization efforts on MEC as well as typical use scenarios.
An Introduction on Millimeter Wave Communications
Authors: He Shiwen , Huang Yongming
Published: December 2019

In the past few years, millimeter wave (mmWave) communication has attracted significant attention both from industry and academia, due to the large available spectrum at mmWave frequency bands. With the significantly increased communication bandwidth, mmWave communication is able to achieve tremendous data rate (e.g. on the order of dozens of Gbps) to satisfy the ever‐increasing traffic demand in 5G‐and‐beyond wireless networks. This article aims to give an introductory overview on the fundamentals of mmWave communication, including the general background of mmWave systems, the propagation characteristics of mmWave channels, followed by the design of hybrid antenna architecture to balance the trade‐off between the hardware cost and the system performance. The state of the art for the design of hybrid precoding/combining and channel acquisition for mmWave systems will be highlighted.
Network Economics of Spectrum Management
Authors: Jiang1 Changkun , Duan2 Lingjie
Published: December 2019

Providing economic incentives is essential for the success of sustainable spectrum management. There are two promising spectrum management schemes, namely, database‐assisted and cooperative spectrum sharing. In the former one, a spectrum database centrally identifies idle spectrum from primary users (PUs), and exclusively allocates the spectrum to secondary users (SUs). In the latter one, users trade spectrum in a distributed manner and SUs relay PU traffics in exchange for their own spectrum access. In this article, we present the economic design and analysis for (i) spectrum database management via centralized pricing and admission control, and (ii) cooperative peer‐to‐peer spectrum sharing via contract mechanism design. In part (i), we study how to maximize a database operator's revenue through joint pricing and admission control. We formulate the revenue maximization problem, considering the stochastic and heterogeneous SU demands. We study the optimal solutions under both static and dynamic pricing, showing that dynamic pricing can improve revenue by 30%. In part (ii), we study cooperative spectrum sharing under incomplete information, where SUs' wireless characteristics are private information and not known by PUs. We model the PU–SU interaction as a labor market using contract theory. We study the optimal contract design for both weakly and strongly incomplete information scenarios. In the former one, we show that the PU will optimally hire the most efficient SUs and the PU achieves the same maximum utility as in the complete information benchmark. In the latter one, however, the PU may conservatively hire less‐efficient SUs as well.
Aerial Networks
Authors: Kim Minsu , Kim Dongsun , Lee Jemin
Published: December 2019

On unmanned aerial vehicle (UAV) communications, we can obtain better communication performance due to line‐of‐sight (LoS) environments and flexible mobility. It also means that received signal power of the interference link increases as the interference link is in the LoS environment. Hence, we analyze the successful transmission probability (STP) of the aerial network in the presence of the interfering node by considering channel fadings and channel components, which are affected by the elevation angle of the communication link. We present the STP for noise‐limited environments and interference‐limited environments in closed‐form expressions. We also show the non‐line‐of‐sight (NLoS) environments for both main and interference links can be better than the LoS environments for both main and interference links if the effect of the interfering signal is more dominant than that of the transmitting signal. Furthermore, we present the aerial network with multiple interfering nodes and the multi‐layer aerial network, where various types of UAVs form aerial networks in different heights with different densities and transmission power, and show the existence of optimal height and density of the UAV that maximize the STP.