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Salt marsh

A salt marsh, saltmarsh or salting, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.

Salt marshes have historically been endangered by poorly implemented coastal management practices, with land reclaimed for human uses or polluted by upstream agriculture or other industrial coastal uses. Additionally, sea level rise caused by climate change is endangering other marshes, through erosion and submersion of otherwise tidal marshes. However, recent acknowledgment by both environmentalists and larger society for the importance of saltwater marshes for biodiversity, ecological productivity and other ecosystem services, such as carbon sequestration, have led to an increase in salt marsh restoration and management since the 1980s.

Basic information

Salt marshes occur on low-energy shorelines in temperate and high-latitudes which can be stable, emerging, or submerging depending if the sedimentation is greater, equal to, or lower than relative sea level rise (subsidence rate plus sea level change), respectively. Commonly these shorelines consist of mud or sand flats (known also as tidal flats or abbreviated to mudflats) which are nourished with sediment from inflowing rivers and streams. These typically include sheltered environments such as embankments, estuaries and the leeward side of barrier islands and spits. In the tropics and sub-tropics they are replaced by mangroves; an area that differs from a salt marsh in that instead of herbaceous plants, they are dominated by salt-tolerant trees.

Most salt marshes have a low topography with low elevations but a vast wide area, making them hugely popular for human populations. Salt marshes are located among different landforms based on their physical and geomorphological settings. Such marsh landforms include deltaic marshes, estuarine, back-barrier, open coast, embayments and drowned-valley marshes. Deltaic marshes are associated with large rivers where many occur in Southern Europe such as the Camargue, France in the Rhône delta or the Ebro delta in Spain. They are also extensive within the rivers of the Mississippi Delta in the United States. In New Zealand, most salt marshes occur at the head of estuaries in areas where there is little wave action and high sedimentation. Such marshes are located in Awhitu Regional Park in Auckland, the Manawatū Estuary, and the Avon Heathcote Estuary / Ihutai in Christchurch. Back-barrier marshes are sensitive to the reshaping of barriers in the landward side of which they have been formed. They are common along much of the eastern coast of the United States and the Frisian Islands. Large, shallow coastal embayments can hold salt marshes with examples including Morecambe Bay and Portsmouth in Britain and the Bay of Fundy in North America.

Salt marshes are sometimes included in lagoons, and the difference is not very marked; the Venetian Lagoon in Italy, for example, is made up of these sorts of animals and or living organisms belonging to this ecosystem. They have a big impact on the biodiversity of the area. Salt marsh ecology involves complex food webs which include primary producers (vascular plants, macroalgae, diatoms, epiphytes, and phytoplankton), primary consumers (zooplankton, macrozoa, molluscs, insects), and secondary consumers.

The low physical energy and high grasses provide a refuge for animals. Many marine fish use salt marshes as nursery grounds for their young before they move to open waters. Birds may raise their young among the high grasses, because the marsh provides both sanctuary from predators and abundant food sources which include fish trapped in pools, insects, shellfish, and worms.

Worldwide occurrence
Saltmarshes across 99 countries (essentially worldwide) were mapped by Mcowen et al. 2017. A total of 5,495,089 hectares of mapped saltmarsh across 43 countries and territories are represented in a Geographic Information Systems polygon shapefile. This estimate is at the relatively low end of previous estimates (2.2–40 Mha). A later study conservatively estimated global saltmarsh extent as 90,800 km2 (9,080,000 hectares). The most extensive saltmarshes worldwide are found outside the tropics, notably including the low-lying, ice-free coasts, bays and estuaries of the North Atlantic which are well represented in their global polygon dataset.

Formation
The formation begins as tidal flats gain elevation relative to sea level by sediment accretion, and subsequently the rate and duration of tidal flooding decreases so that vegetation can colonize on the exposed surface. The arrival of propagules of pioneer species such as seeds or rhizome portions are combined with the development of suitable conditions for their germination and establishment in the process of colonisation. When rivers and streams arrive at the low gradient of the tidal flats, the discharge rate reduces and suspended sediment settles onto the tidal flat surface, helped by the backwater effect of the rising tide. Mats of filamentous blue-green algae can fix silt and clay sized sediment particles to their sticky sheaths on contact which can also increase the erosion resistance of the sediments. This assists the process of sediment accretion to allow colonising species (e.g., Salicornia spp.) to grow. These species retain sediment washed in from the rising tide around their stems and leaves and form low muddy mounds which eventually coalesce to form depositional terraces, whose upward growth is aided by a sub-surface root network which binds the sediment. Once vegetation is established on depositional terraces further sediment trapping and accretion can allow rapid upward growth of the marsh surface such that there is an associated rapid decrease in the depth and duration of tidal flooding. As a result, competitive species that prefer higher elevations relative to sea level can inhabit the area and often a succession of plant communities develops.

Tidal flooding and vegetation zonation
Coastal salt marshes can be distinguished from terrestrial habitats by the daily tidal flow that occurs and continuously floods the area. It is an important process in delivering sediments, nutrients and plant water supply to the marsh. At higher elevations in the upper marsh zone, there is much less tidal inflow, resulting in lower salinity levels. Soil salinity in the lower marsh zone is fairly constant due to everyday annual tidal flow. However, in the upper marsh, variability in salinity is shown as a result of less frequent flooding and climate variations. Rainfall can reduce salinity and evapotranspiration can increase levels during dry periods. As a result, there are microhabitats populated by different species of flora and fauna dependent on their physiological abilities. The flora of a salt marsh is differentiated into levels according to the plants' individual tolerance of salinity and water table levels. Vegetation found at the water must be able to survive high salt concentrations, periodical submersion, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower marsh zones are determined through the ability of plants to tolerate physiological stresses such as salinity, water submergence and low oxygen levels. The New England salt marsh is subject to strong tidal influences and shows distinct patterns of zonation. In low marsh areas with high tidal flooding, a monoculture of the smooth cordgrass, Spartina alterniflora dominate, then heading landwards, zones of the salt hay, Spartina patens, black rush, Juncus gerardii and the shrub Iva frutescens are seen respectively. These species all have different tolerances that make the different zones along the marsh best suited for each individual.

Plant species diversity is relatively low, since the flora must be tolerant of salt, complete or partial submersion, and anoxic mud substrate. The most common salt marsh plants are glassworts (Salicornia spp.) and the cordgrass (Spartina spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat and begin its ecological succession into a salt marsh. Their shoots lift the main flow of the tide above the mud surface while their roots spread into the substrate and stabilize the sticky mud and carry oxygen into it so that other plants can establish themselves as well. Plants such as sea lavenders (Limonium spp.), plantains (Plantago spp.), and varied sedges and rushes grow once the mud has been vegetated by the pioneer species.

Salt marshes are quite photosynthetically active and are extremely productive habitats. They serve as depositories for a large amount of organic matter and are full of decomposition, which feeds a broad food chain of organisms from bacteria to mammals. Many of the halophytic plants such as cordgrass are not grazed at all by higher animals but die off and decompose to become food for micro-organisms, which in turn become food for fish and birds.

Sediment trapping, accretion, and the role of tidal creeks

The factors and processes that influence the rate and spatial distribution of sediment accretion within the salt marsh are numerous. Sediment deposition can occur when marsh species provide a surface for the sediment to adhere to, followed by deposition onto the marsh surface when the sediment flakes off at low tide. The amount of sediment adhering to salt marsh species is dependent on the type of marsh species, the proximity of the species to the sediment supply, the amount of plant biomass, and the elevation of the species. For example, in a study of the Eastern Chongming Island and Jiuduansha Island tidal marshes at the mouth of the Yangtze River, China, the amount of sediment adhering to the species Spartina alterniflora, Phragmites australis, and Scirpus mariqueter decreased with distance from the highest levels of suspended sediment concentrations (found at the marsh edge bordering tidal creeks or the mudflats); decreased with those species at the highest elevations, which experienced the lowest frequency and depth of tidal inundations; and increased with increasing plant biomass. Spartina alterniflora, which had the most sediment adhering to it, may contribute >10% of the total marsh surface sediment accretion by this process.

Salt marsh species also facilitate sediment accretion by decreasing current velocities and encouraging sediment to settle out of suspension. Current velocities can be reduced as the stems of tall marsh species induce hydraulic drag, with the effect of minimising re-suspension of sediment and encouraging deposition. Measured concentrations of suspended sediment in the water column have been shown to decrease from the open water or tidal creeks adjacent to the marsh edge, to the marsh interior, probably as a result of direct settling to the marsh surface by the influence of the marsh canopy.

Inundation and sediment deposition on the marsh surface is also assisted by tidal creeks which are a common feature of salt marshes. Their typically dendritic and meandering forms provide avenues for the tide to rise and flood the marsh surface, as well as to drain water, and they may facilitate higher amounts of sediment deposition than salt marsh bordering open ocean. Sediment deposition is correlated with sediment size: coarser sediments will deposit at higher elevations (closer to the creek) than finer sediments (further from the creek). Sediment size is also often correlated with particular trace metals, and thus tidal creeks can affect metal distributions and concentrations in salt marshes, in turn affecting the biota. Salt marshes do not however require tidal creeks to facilitate sediment flux over their surface although salt marshes with this morphology seem to be rarely studied.

The elevation of marsh species is important; those species at lower elevations experience longer and more frequent tidal floods and therefore have the opportunity for more sediment deposition to occur. Species at higher elevations can benefit from a greater chance of inundation at the highest tides when increased water depths and marsh surface flows can penetrate into the marsh interior.

Human impacts
The coast is a highly attractive natural feature to humans through its beauty, resources, and accessibility. As of 2002, over half of the world's population was estimated to being living within 60 km of the coastal shoreline, making coastlines highly vulnerable to human impacts from daily activities that put pressure on these surrounding natural environments. In the past, salt marshes were perceived as coastal 'wastelands,' causing considerable loss and change of these ecosystems through land reclamation for agriculture, urban development, salt production and recreation. The indirect effects of human activities such as nitrogen loading also play a major role in the salt marsh area. Salt marshes can suffer from dieback in the high marsh and die-off in the low marsh. A study published in 2022 estimates that 22% of saltmarsh loss from 1999-2019 was due to direct human drivers, defined as observable activities occurring at the location of the detected change, such as conversion to aquaculture, agriculture, coastal development, or other physical structures. Additionally, 30% of saltmarsh gain over this same time period were also due to direct drivers, such as restoration activities or coastal modifications to promote tidal exchange.

Land reclamation
Reclamation of land for agriculture by converting marshland to upland was historically a common practice. Dikes were often built to allow for this shift in land change and to provide flood protection further inland. In recent times intertidal flats have also been reclaimed. For centuries, livestock such as sheep and cattle grazed on the highly fertile salt marsh land. Land reclamation for agriculture has resulted in many changes such as shifts in vegetation structure, sedimentation, salinity, water flow, biodiversity loss and high nutrient inputs. There have been many attempts made to eradicate these problems for example, in New Zealand, the cordgrass Spartina anglica was introduced from England into the Manawatu River mouth in 1913 to try and reclaim the estuary land for farming. A shift in structure from bare tidal flat to pastureland resulted from increased sedimentation and the cordgrass extended out into other estuaries around New Zealand. Native plants and animals struggled to survive as non-natives out competed them. Efforts are now being made to remove these cordgrass species, as the damages are slowly being recognized.

In the Blyth estuary in Suffolk in eastern England, the mid-estuary reclamations (Angel and Bulcamp marshes) that were abandoned in the 1940s have been replaced by tidal flats with compacted soils from agricultural use overlain with a thin veneer of mud. Little vegetation colonisation has occurred in the last 60–75 years and has been attributed to a combination of surface elevations too low for pioneer species to develop, and poor drainage from the compacted agricultural soils acting as an aquiclude. Terrestrial soils of this nature need to adjust from fresh to saline interstitial water by a change in the chemistry and the structure of the soil, accompanied with fresh deposition of estuarine sediment, before salt marsh vegetation can establish. The vegetation structure, species richness, and plant community composition of salt marshes naturally regenerated on reclaimed agricultural land can be compared to adjacent reference salt marshes to assess the success of marsh regeneration.

Upstream agriculture
Cultivation of land upstream from the salt marsh can introduce increased silt inputs and raise the rate of primary sediment accretion on the tidal flats, so that pioneer species can spread further onto the flats and grow rapidly upwards out of the level of tidal inundation. As a result, marsh surfaces in this regime may have an extensive cliff at their seaward edge. At the Plum Island estuary, Massachusetts (U.S.), stratigraphic cores revealed that during the 18th and 19th century the marsh prograded over subtidal and mudflat environments to increase in area from 6 km2 to 9 km2 after European settlers deforested the land upstream and increased the rate of sediment supply.

Urban development and nitrogen loading
The conversion of marshland to upland for agriculture has in the past century been overshadowed by conversion for urban development. Coastal cities worldwide have encroached onto former salt marshes and in the U.S. the growth of cities looked to salt marshes for waste disposal sites. Estuarine pollution from organic, inorganic, and toxic substances from urban development or industrialisation is a worldwide problem and the sediment in salt marshes may entrain this pollution with toxic effects on floral and faunal species. Urban development of salt marshes has slowed since about 1970 owing to growing awareness by environmental groups that they provide beneficial ecosystem services. They are highly productive ecosystems, and when net productivity is measured in g m−2 yr−1 they are equalled only by tropical rainforests. Additionally, they can help reduce wave erosion on sea walls designed to protect low-lying areas of land from wave erosion.

De-naturalisation of the landward boundaries of salt marshes from urban or industrial encroachment can have negative effects. In the Avon-Heathcote estuary/Ihutai, New Zealand, species abundance and the physical properties of the surrounding margins were strongly linked, and the majority of salt marsh was found to be living along areas with natural margins in the Avon / Ōtākaro and Ōpāwaho / Heathcote river outlets; conversely, artificial margins contained little marsh vegetation and restricted landward retreat. The remaining marshes surrounding these urban areas are also under immense pressure from the human population as human-induced nitrogen enrichment enters these habitats. Nitrogen loading through human-use indirectly affects salt marshes causing shifts in vegetation structure and the invasion of non-native species.

Human impacts such as sewage, urban run-off, agricultural and industrial wastes are running into the marshes from nearby sources. Salt marshes are nitrogen limited and with an increasing level of nutrients entering the system from anthropogenic effects, the plant species associated with salt marshes are being restructured through change in competition. For example, the New England salt marsh is experiencing a shift in vegetation structure where S. alterniflora is spreading from the lower marsh where it predominately resides up into the upper marsh zone. Additionally, in the same marshes, the reed Phragmites australis has been invading the area expanding to lower marshes and becoming a dominant species. P. australis is an aggressive halophyte that can invade disturbed areas in large numbers outcompeting native plants. This loss in biodiversity is not only seen in flora assemblages but also in many animals such as insects and birds as their habitat and food resources are altered.

Sea level rise
Due to the melting of Arctic sea ice and thermal expansion of the oceans, as a result of global warming, sea levels have begun to rise. As with all coastlines, this rise in water levels is predicted to negatively affect salt marshes, by flooding and eroding them. The sea level rise causes more open water zones within the salt marsh. These zones cause erosion along their edges, further eroding the marsh into open water until the whole marsh disintegrates.

While salt marshes are susceptible to threats concerning sea level rise, they are also an extremely dynamic coastal ecosystem. Salt marshes may in fact have the capability to keep pace with a rising sea level, by 2100, mean sea level could see increases between 0.6m to 1.1m. Marshes are susceptible to both erosion and accretion, which play a role in a what is called a bio-geomorphic feedback. Salt marsh vegetation captures sediment to stay in the system which in turn allows for the plants to grow better and thus the plants are better at trapping sediment and accumulate more organic matter. This positive feedback loop potentially allows for salt marsh bed level rates to keep pace with rising sea level rates. However, this feedback is also dependent on other factors like productivity of the vegetation, sediment supply, land subsidence, biomass accumulation, and magnitude and frequency of storms. In a study published by Ü. S. N. Best in 2018, they found that bioaccumulation was the number one factor in a salt marsh's ability to keep up with SLR rates. The salt marsh's resilience depends upon its increase in bed level rate being greater than that of sea levels' increasing rate, otherwise the marsh will be overtaken and drowned.

Biomass accumulation can be measured in the form of above-ground organic biomass accumulation, and below-ground inorganic accumulation by means of sediment trapping and sediment settling from suspension. Salt marsh vegetation helps to increase sediment settling because it slows current velocities, disrupts turbulent eddies, and helps to dissipate wave energy. Marsh plant species are known for their tolerance to increased salt exposure due to the common inundation of marshlands. These types of plants are called halophytes. Halophytes are a crucial part of salt marsh biodiversity and their potential to adjust to elevated sea levels. With elevated sea levels, salt marsh vegetation would likely be more exposed to more frequent inundation rates and it must be adaptable or tolerant to the consequential increased salinity levels and anaerobic conditions. There is a common elevation (above the sea level) limit for these plants to survive, where anywhere below the optimal line would lead to anoxic soils due to constant submergence and too high above this line would mean harmful soil salinity levels due to the high rate of evapotranspiration as a result of decreased submergence. Along with the vertical accretion of sediment and biomass, the accommodation space for marsh land growth must also be considered. Accommodation space is the land available for additional sediments to accumulate and marsh vegetation to colonize laterally. This lateral accommodation space is often limited by anthropogenic structures such as coastal roads, sea walls and other forms of development of coastal lands. A study by Lisa M. Schile, published in 2014, found that across a range of sea level rise rates, marshlands with high plant productivity were resistant against sea level rises but all reached a pinnacle point where accommodation space was necessary for continued survival. The presence of accommodation space allows for new mid/high habitats to form, and for marshes to escape complete inundation.

Mosquito control
Earlier in the 20th century, it was believed that draining salt marshes would help reduce mosquito populations, such as Aedes taeniorhynchus, the black salt marsh mosquito. In many locations, particularly in the northeastern United States, residents and local and state agencies dug straight-lined ditches deep into the marsh flats. The end result, however, was a depletion of killifish habitat. The killifish is a mosquito predator, so the loss of habitat actually led to higher mosquito populations, and adversely affected wading birds that preyed on the killifish. These ditches can still be seen, despite some efforts to refill the ditches.

Crab herbivory and bioturbation
Increased nitrogen uptake by marsh species into their leaves can prompt greater rates of length-specific leaf growth, and increase the herbivory rates of crabs. The burrowing crab Neohelice granulata frequents SW Atlantic salt marshes where high density populations can be found among populations of the marsh species Spartina densiflora and Sarcocornia perennis. In Mar Chiquita lagoon, north of Mar del Plata, Argentina, Neohelice granulata herbivory increased as a likely response to the increased nutrient value of the leaves of fertilised Spartina densiflora plots, compared to non-fertilised plots. Regardless of whether the plots were fertilised or not, grazing by Neohelice granulata also reduced the length specific leaf growth rates of the leaves in summer, while increasing their length-specific senescence rates. This may have been assisted by the increased fungal effectiveness on the wounds left by the crabs.

The salt marshes of Cape Cod, Massachusetts (US), are experiencing creek bank die-offs of Spartina spp. (cordgrass) that has been attributed to herbivory by the crab Sesarma reticulatum. At 12 surveyed Cape Cod salt marsh sites, 10% – 90% of creek banks experienced die-off of cordgrass in association with a highly denuded substrate and high density of crab burrows. Populations of Sesarma reticulatum are increasing, possibly as a result of the degradation of the coastal food web in the region. The bare areas left by the intense grazing of cordgrass by Sesarma reticulatum at Cape Cod are suitable for occupation by another burrowing crab, Uca pugnax, which are not known to consume live macrophytes. The intense bioturbation of salt marsh sediments from this crab's burrowing activity has been shown to dramatically reduce the success of Spartina alterniflora and Suaeda maritima seed germination and established seedling survival, either by burial or exposure of seeds, or uprooting or burial of established seedlings. However, bioturbation by crabs may also have a positive effect. In New Zealand, the tunnelling mud crab Helice crassa has been given the stately name of an 'ecosystem engineer' for its ability to construct new habitats and alter the access of nutrients to other species. Their burrows provide an avenue for the transport of dissolved oxygen in the burrow water through the oxic sediment of the burrow walls and into the surrounding anoxic sediment, which creates the perfect habitat for special nitrogen cycling bacteria. These nitrate reducing (denitrifying) bacteria quickly consume the dissolved oxygen entering into the burrow walls to create the oxic mud layer that is thinner than that at the mud surface. This allows a more direct diffusion path for the export of nitrogen (in the form of gaseous nitrogen (N2)) into the flushing tidal water.

Microbial life in salt marshes
The variable salinity, climate, nutrient levels and anaerobic conditions of salt marshes provide strong selective pressures on the microorganisms inhabiting them. In salt marshes, microbes play the main role in nutrient cycling and biogeochemical processing. To date, the microbial community of salt marshes has not been found to change drastically due to human impacts, but the research is still ongoing. Because of the major role of microbes in these environments, it is critical to understand the different processes performed and different microbial players present in salt marshes. Salt marshes provide habitat for chemo(litho)autotrophs, heterotrophs, and photoautotrophs alike. These organisms contribute diverse environmental services such as sulfate reduction, nitrification, decomposition and rhizosphere interactions.

Chemo(litho)autotrophs in salt marshes
Chemoautotrophs, also known as chemolithoautotrophs, are organisms capable of creating their own energy, from the use of inorganic molecules, and are able to thrive in harsh environments, such as deep sea vents or salt marshes, due to not depending upon external organic carbon sources for their growth and survival. Some Chemoautotrophic bacterial microorganisms found in salt marshes include Betaproteobacteria and Gammaproteobacteria, both classes including sulfate-reducing bacteria (SRB), sulfur-oxidizing bacteria (SOB), and ammonia-oxidizing bacteria (AOB) which play crucial roles in nutrient cycling and ecosystem functioning.

Abundance and diversity of sulfate-reducing chemolithoautotrophs
Bacterial chemolithoautotrophs in salt marshes include sulfate-reducing bacteria. In these ecosystems, up to 50% of sedimentary remineralization can be attributed to sulfate reduction. The dominant class of sulfate-reducing bacteria in salt marshes tends to be Deltaproteobacteria. Some examples of deltaproteobacteria that are found in salt marshes are species of genera Desulfobulbus, Desulfuromonas, and Desulfovibrio.

The abundance and diversity of chemolithoautotrophs in salt marshes is largely determined by the composition of plant species in the salt marsh ecosystem. Each type of salt-marsh plant has varying lengths of growing seasons, varying photosynthetic rates, and they all lose varying amounts of organic matter to the ocean, resulting in varying carbon-inputs to the ecosystem. The results from an experiment that was done in a salt marsh in the Yangtze estuary in China, suggested that both the species richness and total abundance of sulfate-reducing bacterial communities increased when a new plant, S. alterniflora, with a higher C-input to the ecosystem was introduced. Although chemolithotrophs produce their own carbon, they still depend on the C-input from salt marshes because of the indirect impact it has on the amount of viable electron donors, such as reduced sulfur compounds. The concentration of reduced sulfur compounds, as well as other possible electron donors, increases with more organic-matter decomposition (by other organisms). Therefore if the ecosystem contains more decomposing organic matter, as with plants with high photosynthetic and littering rates, there will be more electron donors available to the bacteria, and thus more sulfate reduction is possible. As a result, the abundance of sulfate-reducing bacteria increases. The high-photosynthetic-rate, high-litter-rate salt marsh plant, S. alterniflora, was discovered to withstand high sulfur concentrations in the soil, which would normally be somewhat toxic to plants.

The abundance of chemolithoautotrophs in salt marshes also varies temporally as a result of being somewhat dependent on the organic C-input from plants in the ecosystem. Since plants grow most throughout the summer, and usually begin to lose biomass around fall during their late stage, the highest input of decomposing organic matter is in the fall. Thus seasonally, the abundance of chemolithotrophs in salt marshes is highest in autumn.

Why are sulfate-reducing bacteria in salt marshes?
Salt marshes are the ideal environment for sulfate-reducing bacteria. The sulfate-reducing bacteria tend to live in anoxic conditions, such as in salt marshes, because they require reduced compounds to produce their energy. Since there is a high sedimentation rate and a high amount of organic matter, the conditions of the sediment are usually dependably anoxic. However, the conditions all across the salt marsh (above the sediment) are not completely anoxic, which means the organisms living here must have some level of tolerance to oxygen. Many of the chemolithoautotrophs living outside or at the surface of the sediment also exhibit this characteristic.

Significance of sulfate-reducing bacteria
Sulfate-reducing bacteria play a significant role in nutrient recycling and in reducing nitrate pollution levels. Since humans have been adding disproportionate amounts of nitrates to coastal waters, salt marshes are one of the ecosystems where nitrate pollution remains an issue. The enrichment of nitrates in the water increases denitrification, as well as microbial decomposition and primary productivity. Sulfate-reducing and oxidizing bacteria, however, play a role in removing the excess nitrates from the water to prevent eutrophication. Since the sulfate-reducing bacteria is in the water and sediment, reduced sulfur molecules are usually in abundance. These reduced sulfates then react with excess nitrate in the water, reducing nitrate and oxidizing the reduced sulfur. As a result of human nitrate enrichment, it is predicted that sulfur-oxidizing bacteria which also reduce nitrates will increase in relative abundance to sulfur-reducing bacteria.

Abundance and significance of chemolithoautotroph nitrifiers within salt marshes
Within salt marshes, chemolithoautotrophic nitrifying bacteria are also frequently identified, including Betaproteobacteria ammonia oxidizers such as Nitrosomonas and Nitrosospira. Although ammonia-oxidizing Archaea (AOA) are found to be more prevalent than ammonium-oxidizing Bacteria (AOB) within salt marsh environments, predominantly from the Crenarchaeota group, AOB play a critical role within the salt marsh environment too. Increases in marsh salinity tend to favor AOB, while higher oxygen levels and lower carbon-to-nitrogen ratios favor AOA. These AOB are important in catalyzing the rate-limiting step within the nitrification process, by using ammonium monooxygenase (AMO), produced from amoA, to convert ammonium (NH4+) into nitrite (NO2-). Specifically, within the class of Betaproteobacteria, Nitrosomonas aestuarii, Nitrosomonas marina, and Nitrosospira ureae are highly prevalent within the salt marsh environment; similarly, within the class of Gammaproteobacteria, Nitrosococcus spp. are key AOB in the marshes.

The abundance of these chemolithoautotrophs varies along the salinity gradients present within salt marshes: Nitrosomonas are more prevalent within lower salinity or freshwater regions, while Nitrosospira are found to dominate in higher saline environments. In addition, the abundance of fixed-nitrogen in these environments critically influences the distribution of the betaproteobacteria within the salt marsh: Nitrosomonas are more found to be in greater abundance within high N and C environments, whereas Nitrosospira are found to be more abundant in lower N and C regions. Further, factors such as temperature, pH, net primary productivity, and regions of anoxia may limit nitrification, and thus critically influence nitrifier distribution.

The role of nitrification by AOB in salt marshes critically links ammonia, produced from the mineralization of organic nitrogen compounds, to the process of nitrogen oxidation. Further, nitrogen oxidation is important for the downstream removal of nitrates into nitrogen gas, catalyzed by denitrifiers, from the marsh environment. Hence, AOB play an indirect role in nitrogen removal into the atmosphere.

Photoautotrophic bacteria
The bacterial photoautotroph community of salt marshes primarily consists of cyanobacteria, purple bacteria, and green sulfur bacteria.

Cyanobacteria in salt marshes
Cyanobacteria are important nitrogen fixers in salt marshes, and provide nitrogen to organisms like diatoms and microalgae.

Purple bacteria
Oxygen inhibits photosynthesis in purple bacteria, which makes estuaries a favorable habitat for them due to the low oxygen content and high levels of light present, optimizing their photosynthesis. In anoxic environments, like salt marshes, many microbes have to use sulfate as an electron acceptor during cellular respiration instead of oxygen, producing lots of hydrogen sulfide as a byproduct. While hydrogen sulfide is toxic to most organisms, purple bacteria require it to grow and will metabolize it to either sulfate or sulfur, and by doing so allowing other organisms to inhabit the toxic environment. Purple bacteria can be further classified as either purple sulphur bacteria, or purple non-sulfur bacteria. Purple sulphur bacteria are more tolerant to sulfide and store the sulfur they create intracellularly, while purple non-sulfur bacteria excrete any sulfur they produce.

Green bacteria
Green sulfur bacteria (Chlorobiaceae) are photoautotrophic bacteria that utilize sulfide and thiosulfate for their growth, producing sulfate in the process. They are very adapted to photosynthesizing in low light environments with bacteriochlorophyll pigments a, c, d, and e, to help them absorb wavelengths of light that other organisms cannot. When co-existing with purple bacteria, they often occupy lower depths as they are less tolerant to oxygen, but more photosynthetically adept.

Fungi
Some mycorrhizal fungi, like arbuscular mycorrhiza are widely associated with salt marsh plants and may even help plants grow in salt marsh soil rich in heavy metals by reducing their uptake into the plant, although the exact mechanism has yet to be determined.

Bacteria
Examining 16S ribosomal DNA found in Yangtze River Estuary, the most common bacteria in the rhizosphere were Proteobacteria such as Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria. One such widespread species had a similar ribotype to the animal pathogen S. marcescens, and may be beneficial for plants as the bacteria can break down chitin into available carbon and nitrogen for plants to use. Actinobacteria have also been found in plant rhizosphere in costal salt marshes and help plants grow through helping plants absorb more nutrients and secreting antimicrobial compounds. In Jiangsu, China, Actinobacteria from the suborders Pseudonocardineae, Corynebacterineae, Propionibacterineae, Streptomycineae, Micromonosporineae, Streptosporangineae and Micrococcineae were cultured and isolated from rhizosphere soil.

Microbial decomposition activity within salt marshes
Another key process among microbial salt marshes is microbial decomposition activity. Nutrient cycling in salt marshes is highly promoted by the resident community of bacteria and fungi involved in remineralizing organic matter. Studies on the decomposition of a salt marsh cordgrass, Spartina alterniflora, have shown that fungal colonization begins the degradation process, which is then finished by the bacterial community. The carbon from Spartina alterniflora is made accessible to the salt marsh food web largely through these bacterial communities which are then consumed by bacterivores. Bacteria are responsible for the degradation of up to 88% of lignocellulotic material in salt marshes. However, fungal populations have been found to dominate over bacterial populations in winter months.

The fungi that make up the decomposition community in salt marshes come from the phylum ascomycota, the two most prevalent species being Phaeosphaeria spartinicola and Mycosphaerella sp. strain 2. In terms of bacteria, the alphaproteobacteria class is the most prevalent class within the salt marsh environment involved in decomposition activity. The propagation of Phaeosphaeria spartinicola is through ascospores that are released when the host plant is wetted by high tides or rain.

Restoration and management
The perception of bay salt marshes as a coastal 'wasteland' has since changed, acknowledging that they are one of the most biologically productive habitats on earth, rivalling tropical rainforests. Salt marshes are ecologically important, providing habitats for native migratory fish and acting as sheltered feeding and nursery grounds. They are now protected by legislation in many countries to prevent the loss of these ecologically important habitats. In the United States and Europe, they are now accorded a high level of protection by the Clean Water Act and the Habitats Directive respectively. With the impacts of this habitats and their importance now realised, a growing interest in restoring salt marshes through managed retreat or the reclamation of land has been established. However, many Asian countries such as China still need to recognise the value of marshlands. With their ever-growing populations and intense development along the coast, the value of salt marshes tends to be ignored and the land continues to be reclaimed.

Bakker et al. (1997) suggests two options available for restoring salt marshes. The first is to abandon all human interference and leave the salt marsh to complete its natural development. These types of restoration projects are often unsuccessful as vegetation tends to struggle to revert to its original structure and the natural tidal cycles are shifted due to land changes. The second option suggested by Bakker et al. (1997) is to restore the destroyed habitat into its natural state either at the original site or as a replacement at a different site. Under natural conditions, recovery can take 2–10 years or even longer depending on the nature and degree of the disturbance and the relative maturity of the marsh involved. Marshes in their pioneer stages of development will recover more rapidly than mature marshes as they are often first to colonize the land. It is important to note that restoration can often be sped up through the replanting of native vegetation. This last approach is often the most practiced and generally more successful than allowing the area to naturally recover on its own. The salt marshes in the state of Connecticut in the United States have long been an area lost to fill and dredging. As of 1969, the Tidal Wetland Act was introduced that ceased this practice, but despite the introduction of the act, the system was still degrading due to alterations in tidal flow. One area in Connecticut is the marshes on Barn Island. These marshes were diked then impounded with salt and brackish marsh during 1946–1966. As a result, the marsh shifted to a freshwater state and became dominated by the invasive species P. australis, Typha angustifolia and T. latifolia that have little ecological connection to the area.

By 1980, a restoration programme was put in place that has now been running for over 20 years. This programme has aimed to reconnect the marshes by returning tidal flow along with the ecological functions and characteristics of the marshes back to their original state. In the case of Barn Island, reduction of the invasive species has been initiated, re-establishing the tidal-marsh vegetation along with animal species such as fish and insects. This example highlights that considerable time and effort is needed to effectively restore salt marsh systems. The timescale for salt marsh recovery is dependent on the development stage of the marsh, type and extent of the disturbance, geographical location and the environmental and physiological stress factors to the marsh-associated flora and fauna.

Although much effort has gone into restoring salt marshes worldwide, further research is needed. There are many setbacks and problems associated with marsh restoration that require careful long-term monitoring. Information on all components of the salt marsh ecosystem should be understood and monitored from sedimentation, nutrient, and tidal influences, to behaviour patterns and tolerances of both flora and fauna species. Once a better understanding of these processes is acquired, and not just locally, but over a global scale, then more sound and practical management and restoration efforts can be implemented to preserve these valuable marshes and restore them to their original state.

While humans are situated along coastlines, there will always be the possibility of human-induced disturbances despite the number of restoration efforts we plan to implement. Dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic spills or just plain carelessness are examples that will for some time now and into the future be the major influences of salt marsh degradation. In addition to restoring and managing salt marsh systems based on scientific principles, the opportunity should be taken to educate public audiences of their importance biologically and their purpose as serving as a natural buffer for flood protection. Because salt marshes are often located next to urban areas, they are likely to receive more visitors than remote wetlands. By physically seeing the marsh, people are more likely to take notice and be more aware of the environment around them. An example of public involvement occurred at the Famosa Slough State Marine Conservation Area in San Diego, where a "friends" group worked for over a decade in trying to prevent the area from being developed. Eventually, the 5 hectare site was bought by the city and the group worked together to restore the area. The project involved removing of invasive species and replanting with native ones, along with public talks to other locals, frequent bird walks and clean-up events.

Research methods
There is a diverse range and combination of methodologies employed to understand the hydrological dynamics in salt marshes and their ability to trap and accrete sediment. Sediment traps are often used to measure rates of marsh surface accretion when short term deployments (e.g. less than one month) are required. These circular traps consist of pre-weighed filters that are anchored to the marsh surface, then dried in a laboratory and re-weighed to determine the total deposited sediment.

For longer term studies (e.g. more than one year) researchers may prefer to measure sediment accretion with marker horizon plots. Marker horizons consist of a mineral such as feldspar that is buried at a known depth within wetland substrates to record the increase in overlying substrate over long time periods. In order to gauge the amount of sediment suspended in the water column, manual or automated samples of tidal water can be poured through pre-weighed filters in a laboratory then dried to determine the amount of sediment per volume of water.

Another method for estimating suspended sediment concentrations is by measuring the turbidity of the water using optical backscatter probes, which can be calibrated against water samples containing a known suspended sediment concentration to establish a regression relationship between the two. Marsh surface elevations may be measured with a stadia rod and transit, electronic theodolite, Real-Time Kinematic Global Positioning System, laser level or electronic distance meter (total station). Hydrological dynamics include water depth, measured automatically with a pressure transducer,  or with a marked wooden stake, and water velocity, often using electromagnetic current meters.

title: Salt marsh


text:
Supercritical water oxidation

Supercritical water oxidation (SCWO) is a process that occurs in water at temperatures and pressures above a mixture's thermodynamic critical point. Under these conditions water becomes a fluid with unique properties that can be used to advantage in the destruction of recalcitrant and hazardous wastes such as polychlorinated biphenyls (PCB) or per- and polyfluoroalkyl substances (PFAS). Supercritical water has a density between that of water vapor and liquid at standard conditions, and exhibits high gas-like diffusion rates along with high liquid-like collision rates. In addition, the behavior of water as a solvent is altered (in comparison to that of subcritical liquid water) - it behaves much less like a polar solvent. As a result, the solubility behavior is "reversed" so that oxygen, and organics such as chlorinated hydrocarbons become soluble in the water, allowing single-phase reaction of aqueous waste with a dissolved oxidizer. The reversed solubility also causes salts to precipitate out of solution, meaning they can be treated using conventional methods for solid-waste residuals. Efficient oxidation reactions occur at low temperature (400-650 °C) with reduced NOx production.

SCWO can be classified as green chemistry or as a clean technology. The elevated pressures and temperatures required for SCWO are routinely encountered in industrial applications such as petroleum refining and chemical synthesis.

A unique addition (mostly of academic interest) to the world of supercritical water (SCW) oxidation is generating high-pressure flames inside the SCW medium. The pioneer works on high-pressure supercritical water flames were carried out by professor EU Franck at the German University of Karlsruhe in the late 80s. The works were mainly aimed at anticipating conditions which would cause spontaneous generation of non-desirable flames in the flameless SCW oxidation process. These flames would cause instabilities to the system and its components. ETH Zurich pursued the investigation of hydrothermal flames in continuously operated reactors. The rising needs for waste treatment and destruction methods motivated a Japanese Group in the Ebara Corporation to explore SCW flames as an environmental tool. Research on hydrothermal flames has also begun at NASA Glenn Research Center in Cleveland, Ohio.

Basic research
Basic research on supercritical water oxidation was undertaken in the 1990s at Sandia National Laboratory's Combustion Research Facility (CRF), in Livermore, CA. Originally proposed as a hazardous waste destruction technology in response to the Kyoto protocol, multiple waste streams were studied by Steven F. Rice and Russ Hanush, and hydrothermal (supercritical water) flames were investigated by Richard R. Steeper and Jason D. Aiken. Among the waste streams studied were military dyes and pyrotechnics, methanol,  and isopropyl alcohol. Hydrogen peroxide was used as an oxidizing agent, and Eric Croiset was tasked with detailed measurements of the decomposition of hydrogen peroxide at supercritical water conditions.

In mid-1992, Thomas G. McGuinness, PE invented what is now known as the "transpiring-wall SCWO reactor" (TWR) while seconded to Los Alamos National Laboratory on behalf of Summit Research Corporation. McGuinness subsequently received the first US patent for a TWR in early 1995. The TWR was designed to mitigate problems of salt/solids deposition, corrosion and thermal limitations occurring in other SCWO reactor designs (eg. tubular & vat-type reactors) at the time. The upper part of the vertical reactor incorporates a permeable liner through which a clean fluid permeates to help prevent salts and other solids from accumulating at the inner surface of the liner. The liner also insulates the outer pressure containment vessel from high temperatures within the reaction zone. The liner can be manufactured from a variety of materials resistant to corrosion and high reaction temperatures. The bottom end of the TWR incorporates a "quench cooler" for cooling the reaction byproducts while neutralizing any components that might form acids during transition to subcritical temperature. Proof-of-concept and performance advantages of the TWR for a variety of feedstocks was demonstrated by Eckhard Dinjus and Johannes Abeln at Forschungszentrum Karlsruhe (FZK), via direct comparison between a TWR and an adjacent tubular reactor.

Major engineering challenges were associated with the deposition of salts and chemical corrosion in these supercritical water reactors. Anthony Lajeunesse led the team investigating these issues. To address these issues Lajeunesse designed a transpiring wall reactor which introduced a pressure differential through the walls of an inner sleeve filled with pores to continuously rinse the inner walls of the reactor with fresh water. Russ Hanush was charged with the construction and operation of the supercritical fluids reactor (SFR) used for these studies. Among its design intricacies were the Inconel 625 alloy necessary for operation at such extreme temperatures and pressures, and the design of the high-pressure, high-temperature optical cells used for photometric access to the reacting flows which incorporated 24 carat gold pressure seals and sapphire windows.

Commercial applications
Several companies in the United States are now working to commercialize supercritical reactors to destroy hazardous wastes. Widespread commercial application of SCWO technology requires a reactor design capable of resisting fouling and corrosion under supercritical conditions.

In Japan a number of commercial SCWO applications exist, among them one unit for treatment of halogenated waste built by Organo. In Korea two commercial size units have been built by Hanwha.

In Europe, Chematur Engineering AB of Sweden commercialized the SCWO technology for treatment of spent chemical catalysts to recover the precious metal, the AquaCat process. The unit has been built for Johnson Matthey in the UK. It is the only commercial SCWO unit in Europe and with its capacity of 3000l/h it is the largest SCWO unit in the world. Chematur's Super Critical Fluids technology was acquired by SCFI Group (Cork, Ireland) who are actively commercializing the Aqua Critox SCWO process for treatment of sludge, e.g. de-inking sludge and sewage sludge. Many long duration trials on these applications have been made and thanks to the high destruction efficiency of 99.9%+ the solid residue after the SCWO process is well suited for recycling – in the case of de-inking sludge as paper filler and in the case of sewage sludge as phosphorus and coagulant. SCFI Group operate a 250l/h Aqua Critox demonstration plant in Cork, Ireland.

Turbosystems Engineering (California, USA) is actively commercializing their patented transpiring wall SCWO reactor ("TWR") with a focus on renewable energy applications.

374Water Inc. is a company offering commercial SCWO systems that convert organic wastes to clean water, energy and minerals. It is spun out after more than seven years of research and development funded by the Bill & Melinda Gates Foundation to Prof. Deshusses laboratory based at Duke University. The founders of 374Water, Prof. Marc Deshusses and Kobe Nagar, possess the waste processing reactor patent relevant to SCWO. 374Water is actively commercializing its AirSCWO systems for the treatment of biosolids and wastewater sludges, organic chemical wastes, and PFAS wastes including unspent Aqueous Film Forming Foams (AFFFs), rinsates or spent resins and adsorption media. The first commercial sale was announced in February 2022.

Aquarden Technologies (Skaevinge, Denmark) provides modular SCWO plants for the destruction of hazardous pollutants such as PFAS, pesticides, and other problematic hydrocarbons in industrial wastestreams. Aquarden is also providing remediation of hazardous energetic wastes and chemical warfare agents with SCWO, where a full-scale SCWO system has been operating for some years in France for the Defense Industry.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Supercritical water oxidation


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Talk:Drakar och Demoner

What is T20? Also, I changed "edition five" to "version five". Is this misleading? - Molinari 06:59 11 Jul 2003 (UTC)
 * Sorry about that, it should be D20 (T stands for "tärning" (Just as in D20, where D stands for dice)). // Liftarn

I reorganized the text, correcting a few small errors, but mostly lifting out "campaign worlds" into its own section. Hope you find it to be more clear.213.112.249.111 09:30, 9 September 2006 (UTC)

DoD picture
Shouldn't a game line be represented by its latest, current, edition? In that case, we should feature a picture of Riotmind's latest edition (titled "Drakar och Demoner Trudvang" if you wanna google), and not nostalgia.213.112.249.111 09:37, 9 September 2006 (UTC)
 * Riotmind haven't sold 100 000 copies of their game to the best of my knowledge. Perhaps their game should have it's own article.--Sus scrofa 17:09, 9 September 2006 (UTC)

100 000 editions or not, the game stil carries the original name and features an evolution of the original system. The new picture should beon the front. Unfortunately the new edition doesnt really have a cover picture, but it does have a logo (the malicious green imp/troll thingy with the axe) which should be displayed.Temple83 15:11, 16 May 2007 (UTC)

title: Talk:Drakar och Demoner


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Mexicali

Mexicali  is the capital city of the Mexican state of Baja California. The city, which is the seat of the Mexicali Municipality, has a population of 689,775, according to the 2010 census, while the Calexico–Mexicali metropolitan area is home to 1,000,000 inhabitants on both sides of the Mexico–United States border. Mexicali is a regional economic and cultural hub for the border region of The Californias.

Mexicali was founded at the turn of the 20th century, when the region's agricultural economy experienced a period of boom. The city rapidly expanded throughout the 20th century, owing to the proliferation of maquiladoras in the city, making the Mexicali economy more interconnected with businesses from across the border. Today, Mexicali is a major manufacturing center and an emerging tourist destination.

History
The Spaniards arrived in the area after crossing the Sonoran Desert's "Camino del Diablo" or Devil's Road. This led to the evangelization of the area by Catholic missionaries and also to the reduction of native populations in the region. Nowadays, indigenous Cocopah people still inhabit a small government-protected corner of the Colorado River delta near the junction of the Hardy and the Colorado. The Cocopah mostly work on agricultural ejidos or fishing.

The early European presence in this area was limited to Anza's and subsequent Spanish expeditions across the Colorado Desert and subsequent travelers on the Sonora Road opened by them. Also the presence of the Jesuits who attempted to establish a mission in what is now Fort Yuma. They left after a revolt by the Yuma in 1781. After this, the Spanish had little to do with the northeastern corner of the Baja California Peninsula, perceiving it as an untamable, flood-prone desert delta. Later in the 1820s, the Mexican authorities reopened the Sonoran Road and restored peaceful relations with the Yuma People.

19th century
In the mid-19th century, a geologist working for the Southern Pacific Railroad came to the delta area, discovering what the native Yumans had known for centuries: that the thick river sediment deposits made the area prime farming land. These sediments extended far to the west of the river itself, accumulating in a shallow basin below the Sierra de Cucapá. However, from this time period until the 1880s, the area was almost completely unpopulated, mostly due to its harsh climate. In 1888, the federal government granted a large part of northern Baja California state, including Mexicali, to Guillermo Andrade, with the purpose of colonizing the area on the recently created border with the United States. However, around 1900, the only area with any real population, aside from the Cocopah, were concentrated in Los Algodones, to the east of Mexicali.

20th century
In 1900, the U.S.-based California Development Company received permission from the government of Díaz to cut a canal through the delta's Arroyo Alamo, to link the dry basin with the Colorado River. To attract farmers to the area, the developers named it the "Imperial Valley". In 1903, the first 500 farmers arrived; by late 1904, 405 km2 (100,000 acres) of valley were irrigated, with 10,000 people settled on the land harvesting cotton, fruits, and vegetables. The concentration of small housing units that straddled the border was called Calexico on the U.S. side and Mexicali on the Mexican side. Led by Los Angeles Times publisher Harry Chandler, one company controlled 800,000 hectares of land in northern Baja California by 1905, and began to build the irrigation system for the Valley. However, instead of using Mexican labor to dig the ditches, Chandler brought in thousands of Chinese laborers. Mexicali became culturally Chinese influenced.

The Mexican side was named Mexicali (a portmanteau composed of "Mexico" and "California") by Coronel Agustín Sanguinéz. Initially the area belonged to the municipality of Ensenada. The town of Mexicali was officially created on 14 March 1903 when Manuel Vizcarra was named as the town's first authority and Assistant Judge (juez auxiliar). On January 29, 1911, Mexicali was briefly "liberated" by the Liberal Party of Mexico during the Mexican Revolution. Mayor Baltazar Aviléz declared the municipality of Mexicali on November 4, 1914, and called for elections to creation of the first ayuntamiento or municipality, which was then headed by Francisco L. Montejano.

In the 20th century, the Colorado Riverland Company, a U.S.-based company, was dedicated to renting Mexican land to farmers; however, these farmers were almost always foreigners, such as Chinese, East Indians and Japanese. Mexicans were employed only as seasonal laborers. This situation led to the agrarian conflict known as the "El Asalto a las Tierras" (Assault on the Lands) in 1937. in which Mexican land was taken by Mexicans. Agricultural production continued to increase during the 20th century. Cotton became the most important crop and helped develop the textile industry. In the early 1950s, the Mexicali Valley became the biggest cotton-producing zone in the country and in the 1960s, production reached more than half a million parcels a year.

The first factories appeared in the 1960s with the end of the Bracero program. A 1988 study found 100 factories in the city, including 10 electronics manufacturers, 25 auto parts manufacturers, 27 textile plants and nine plastics companies. Most maquiladoras are run by US companies, followed by Mexican, South Korean, and Japanese companies.

21st century
Today Mexicali is an important center for maquiladora (assembly plant) production in the automotive, aerospace, telecommunications, metallurgical, and health items as well as manufacturing and exporting products to various countries.

The 2010 Baja California earthquake occurred on Easter Sunday about 60 km south-southeast of Mexicali. This very large magnitude 7.2 earthquake occurred at 15:40:40 local time (UTC−8) according to the U.S. Geological Survey. With a maximum Mercalli intensity of VII (Very strong), it was felt in northern Baja California near the United States–Mexico border, and was also felt in western cities such as Tijuana, San Diego, Los Angeles and parts of Arizona.

Geography
The Mexicali Valley is one of the largest and most fertile valleys in Mexico. Over fifty different crops are grown in the valley, which is similar in production to the Imperial Valley. National and international industries have invested in Mexicali and surrounding cities to take advantage of its tax-free status given to industry. The Mexicali Valley is a primary source of water for the region, which is the largest irrigation district in Mexico.

A study by Instituto Mexicano de la Competitividad has listed Mexicali as Mexico's most polluted air of large cities, with a PM10 rating of 137 for the year 2010. It is thought that the reason is lack of pavement (dust) and lack of wind, especially in summer. The city is grappling with huge amounts of trash "from old appliances, to electronic waste and used tires, some of which comes from the United States." Mexican government agencies in the border region have not made pollution a priority, and weak enforcement of environmental standards is considered a reason that multinationals locate factories there, along with low wages. In general, maquiladoras are supposed to return any toxic waste to its country of origin, but in some cases it can be handled in Mexico.

Ecology
Despite its arid desert location, Mexicali is watered through a system of aquifers in the valley. Under a 1944 water treaty, the city is "guaranteed an annual quantity of 1,500,000 acre.ft [of water] to be delivered" from the Colorado River. However, a proposed concrete lining in the United States on the All-American Canal would cut off billions of leaked gallons of water, which is used to irrigate onions, alfalfa, asparagus, squash and other crops in Mexicali.

The nearby Cerro Prieto volcano is adjacent to the Cerro Prieto Geothermal Power Station, which creates high volumes of pollutants including mercury. As of 2014, the government are creating a zone of exclusion, due to the alarming amount of pollutants and contamination that has permeated throughout miles around the geothermal plant of Cerro Prieto.

Climate
Because of its low annual precipitation, Mexicali has an arid climate (BWh), featuring long, extremely hot summers and mild to warm winters. Under the criteria for the Köppen climate classification, Mexicali maintains desert weather temperatures every year, receiving only 70.9 mm of precipitation annually over 16 precipitation days on average. On December 12, 1932, the city experienced snowfall. Rainfall usually occurs in the winter months of December, January and February. Summer rainfall in the city is infrequent, although in some years thunderstorms and the remnants of tropical storms and hurricanes passing over Baja California from the Pacific can sometimes drop heavy rainfall (most likely in August and September). A notable example was Hurricane Kathleen in 1976, which dropped several inches of rain in the area. During winter time, Mexicali is affected by the snow storms that pass by the town of La Rumorosa located in the Sierra de Juárez, about 45 minutes west of the city, causing a decrease in temperature that lasts from two days to one week. July is the hottest month with a mean at 33.9 C and an average high at 42.3 C, while January is the coolest month with a mean at 13.1 C and an average low at 5.8 C.

On 28 July 1995, the Mexicali area recorded a temperature of 52.0 C, which is the highest temperature ever recorded in Mexico.

Demographics

As of 2020, the city of Mexicali had a population of 854,186.

The city itself had a 2005 census population of 653,046, whereas the municipality's population was 895,962. It is the 13th largest municipality in Mexico as of the Census 2005 with population estimates exceeding one million alone.

The population is constantly growing due to the number of maquiladoras in the area, lack of urban planning, and migrational aspects, like seasonal labor and the constant in-and-out flow of immigrants to the U.S. or into Mexico.

Economy
Mexicali's economy has been historically based on agricultural products, and they remain a large sector of the economy. However, its economy has gradually gone from being agricultural to include industry, mainly maquiladoras—duty-free factories in which parts from the United States are imported, assembled, and then returned to the United States as finished products. Currently, the Mexicali Valley still is one of Mexico's most productive agricultural regions, mostly producing wheat, cotton and vegetables. The city is one of Mexico's most important exporters of asparagus, broccoli, carrots, green onions, lettuce, peas, peppers, radishes and tomatoes to the world. In its beginnings Mexicali was an important center for cotton production for export, until synthetic fabrics reduced the worldwide demand for the fiber. Currently, horticulture is the most successful agricultural activity with scallion (green onion), and asparagus being among the most important crops. Cotton and wheat are still grown, but low government price guarantees and subsidies make wheat farmer protests an annual event. There is an annual agri-business fair, which if unfunded by the government, would have been dead a decade ago, named AGROBAJA, Agrobaja in March of every year, drawing people by the thousands, from all over Mexico and before the crisis, from the United States.

The current prospects for economic growth in Mexicali rely on in-bond and assembly plants (maquiladoras), which come due to low wages and loose worker right laws, include companies like, Selther, Daewoo Electronics, Mitsubishi, Honeywell, Paccar, Vitro, Skyworks Solutions, CareFusion, Bosch, Price Pfister, Gulfstream, United Technologies Corporation, Kenworth, Kwikset and Collins Aerospace. Mexicali is also home to many food processing plants such as Nestlé, Jumex, Bimbo, Coca-Cola, Kellogg's, and Sabritas. In December 2018 there were 180 in all, employing 70,000 people.

Mexicali became the national center for the aerospace industry in Mexico when Rockwell Collins established an operation there in 1966. Rockwell Collins is the oldest company under the maquiladora program nationwide.

Silicon Border

Silicon Border is an empty 40 km2 development supposedly tailored to the specific needs of high-technology manufacturing and is situated in the outskirts of Mexicali, along the western border of the U.S. and Mexico. The aim of the empty manufacturing park, which began in 2004, was to transform Mexicali into the world's next semiconductor manufacturing center, if the world economy was fine. The Mexican federal and Baja California state governments have given away $2 million of public money to private hands, without a referendum for the design of the project and the laying of a few streets and lamp posts that can be seen on the premises as the only work done. Neither authorities nor the private frontmen of the project have given the public any account on what the public money was spent on. Former president Vicente Fox offered ten years of a tax rate as low as 3% to foreign-owned factories.

The premises sit empty as of October 2022.

Tourism
Mexicali also relies on tourism as a medium to generate revenue, and visitors cross by foot or by car from Calexico, United States, every day. Tourists are mainly attracted to local taco stands, restaurants, pharmacies, bars and dance clubs. Near the border, in walking distance, there are many shops and stalls selling Mexican curios and souvenirs. Arizona and Nevada residents look for medical and dental services in Mexicali, since they tend to be less expensive than in the United States. Pharmacies sell some drugs without a prescription and at much lower cost than in the US, but some medications still require a doctor's prescription, although several accessible doctor offices are located near the border as well.

Mexico's drinking age is 18 years old (vs. 21 in the United States) which makes it a common weekend destination for many high school and college students from Southern California.

Mexicali hosts Baja Prog, one of the world's most important events in progressive rock. Mexicali hosts four main shopping malls, the most visited being Plaza La Cachanilla, located a mile away from the US border. The mall hosts a variety of shops, which sell a wide array of items, ranging from cheap Mexican curios to expensive imports. The Plaza La Cachanilla also represents a common place for people to socialize, especially during summer days when the weather reaches high temperatures, many families come and spend the day inside the air-conditioned mall.

For recreation, Mexicali has bath halls, bowling alleys, traditional cantinas, car clubs, strip clubs, movie theaters, museums, a zoo, a convention center, supermarkets, and fast food restaurants for every choice of food.

Galerias del Valle, holds a WalMart Supercenter, a twelve-screen Cinepolis movie theater, two casinos, a food court, and a large array of stores that sell many items needed for daily living. It is located on Boulevard Lázaro Cárdenas at Calle 11.

Education
According to a previous census conducted by the National Institute of Statistics and Geography (INEGI) in 2008, the number of students who have graduated from Mexicali's public and private schools are as follows:

Pre-scholar students: 18,648 Primary school students: 17,272 Secondary school students: 12,337 Technical education students: 531 Baccalaureate students: 6,152

Some public universities in the city include Autonomous University of Baja California, Mexicali, Universidad Politécnica de Baja California and the Mexicali Institute of Technology. Private universities include Centro de Enseñanza Técnica y Superior, University of the Valley of Mexico and Xochicalco University.

Culture
The residents of Mexicali (Mexicalenses) call themselves "Cachanillas" (due to a local plant, the cachanilla, used by the Cucapah tribe to build shacks) and are from culturally diverse backgrounds. It is among the most ethnically diverse cities in Mexico, with people from various Native American, European, African, East Asian, and Middle Eastern origins.

There is a very popular song called "Puro Cachanilla" also known as "El Cachanilla" that identifies people from Mexicali. In 2004, there were 8 theaters in the city: Teatro del Estado, Teatro de Casa de Cultura de Mexicali. Idem, Teatro del CREA, Teatro Universitario de Mexicali, Teatro al Aire Libre de Rectoría, Teatro del Seguro Social, and Centro Estatal de las Artes.

Mexicali also has the Baja Prog festival, a series of progressive rock concerts that take place during four consecutive days in springtime. It is hosted by CAST, a progressive rock band from Mexicali.

La Chinesca
The city claimed to have the largest per capita concentration of residents of Chinese origin in Mexico, around 5,000 until 2012 when the Tijuana La Mesa District surpassed that number at 15,000 Chinese immigrants. The Chinese immigrants came to the area as laborers for the Colorado River Land Company, an American enterprise which designed and built an extensive irrigation system in the Valley of Mexicali. Some immigrants came from the United States, often fleeing anti-Chinese policies there, while others sailed directly from China. Thousands of Chinese were lured to the area by the promise of high wages, but that never materialized.

Since 2000, new migrants from China to Mexicali come from many of the same areas as before 1960, with perhaps 90% from Guangdong or Hong Kong.

Sports
Mexicali has many sites visited by people from across the country, as well as by visitors from the U.S. and Canada, such as the bullfighting arena, Plaza Calafia, where one or two bullfights are held yearly. Mexicali also has a professional 18-hole golf course, Club Campestre, where both national and international championships have taken place.

The city's professional basketball team is Soles de Mexicali of the Liga Nacional de Baloncesto Profesional (LNBP). Soles lifted the national trophy as the 2006–07, 2014–15, 2017–18, and 2019–20 LNBP Champions. Their stadium, the Auditorio del Estado, is located in Ciudad Deportiva de Mexicali. The Bomberos de Mexicali were founded in 2010 and participated in the Pacific Coast Basketball Circuit, CIBACOPA. Another defunct franchise, Calor de Mexicali (Mexicali Heat), participated in the 2007 edition of the league. They played their home games at the Gimnasio de Mexicali located on Avenida Reforma. Mexicali was also home to a 2006 American Basketball Association franchise, the Centinelas de Mexicali (The Sentinels).

Ciudad Deportiva houses a football stadium where Mexicali Fútbol Club in the Mexican Second Division and Cachanillas de Mexicali, a Mexican Third Division team plays. The home of the Pioneros del Valle, also a Mexican third division football team, is located in the Mexicali Valley.

In addition, Ciudad Deportiva is the location of Farmacias Sta Maria formally known as Estadio B'Air, where the Águilas de Mexicali play, competing in winter baseball's Mexican Pacific League (LMP). The Centinelas de Mexicali are a professional team which plays in the North Sonora League, the main development league for the LMP. Young Mexicali baseball players have played in the Little League World Series five times; first in 1985, with the Félix Arce Little League representing the United States West region, and then in 2005, 2007, 2011 and 2015 the Seguro Social Little League representing Mexicali.

Transportation
Mexicali is located at a Junction of major interstates and federal highways. These include Interstate 8, leading from San Diego to the Arizona Sun Corridor where the cities of Phoenix and Tucson dominate, Federal Highway 2, which leads east to San Luis Río Colorado and west to Tijuana, and Federal Highway 5 connecting San Felipe with Mexicali. Other roads lead southwest to Ensenada or north to the Imperial Valley.

The road system in the city of Mexicali and its conurbation is very complex. Over the urban area long boulevards are traversed from one end of which most are 6 lanes with a median of 2 lanes. The backbone of the city is the Lazaro Cardenas Boulevard extending from east to west. Other important boulevards include: Adolfo Lopez Mateos, Benito Juárez, Anáhuac, Justo Sierra, Venustiano Carranza, Manuel Gómez Morin, Francisco L. Montejano, Cetys, Héctor Terán Terán, Independencia and Heroico Colegio Militar, among others. There are two corridors within the city: New River Ecological Corridor, which is guided in the ancient New River bed, and the Palaco Industrial Corridor, this crosses the southern Industrial zone of Mexicali. There is also the beltway, located in the east of the city, connecting the Lazaro Cardenas Blvd. with Islas Agrarias Blvd. and the road to Colonia Abasolo, and this in turn with the Airport Road.

Airport
The city is linked to other Mexican cities by Mexicali International Airport, which serves the city and the surrounding towns.

Public transit
There are some bus routes across the city and its urban area, where companies like Atusa Plus, Cachanilla, Amarillo y Blanco, among others, offer this service.

Sister cities
Mexicali has the following sister cities:
 * 🇺🇸 San Bernardino, United States
 * Nanjing, China
 * Gumi, North Gyeongsang, South Korea
 * 🇺🇸 Sacramento, California, United States
 * 🇺🇸 Calexico, California, United States

title: Mexicali


text:
Talk:Periodic table (big)

Why do you keep removing the link to the wheel format of the periodic table without any explanation?

 * Becasue it is based on the pseudoscientific Reciprocal System of Theory and thus has no place on a page that deals with real science. --mav

Ahh - you don't like the pseudo-scientific view - well at least that is an explanation for your edits. However it seems to me that the wheel is an interesting alternative view of the table even if the explanation part of it is pseudo science. BLH

 * Interesting to look at maybe but fundamentally flawed as far as science is concerned. It has no place here next to valid scientifically-based representations of the periodic table. --mav

Is the current way of linking to it acceptable? I don't think that it is unreasonable to link to alternative views even if they aren't based on the same rigourous science. BLH

I see it's not acceptable to mav anyway.

 * I'm warming to the idea of a "see also" section but that implementation was sub-optimal. Perhaps we can have a section titled =="pseudoscientific"-based tables== and then explain that the following tables (we would have only one to begin with) are not accepted by the scientific community. Although I'm not really comfortable with the word "pseudoscientific"... Any other ideas? --mav

 * Duh. Why not ==Periodic tables not accepted by the scientific community==. But there should be no link to these crackpot tables at periodic table. --mav

I think there should be a link to them. There is always a danger in becoming too blinkered in our views of the scientific reality. As an example, I have just added a link to a Catalyst transcription on junk DNA. (Which you have nicely standised - thank you) For years scientists believed it had no purpose but now that is changing. Who knows what insight someone might have by looking at a different, even if non traditional and non accepted view of the periodic table? BLH

 * Who knows how many freshmen chemistry students we would flunk by giving a crackpot idea far more prominence that it deserves. Here in WikiLand we report the consensus view on subjects. That means we leave out a whole bunch of wild ideas in main articles (but they can be in their own articles since in their own smaller context they can still be written via a consensus view). In short, placing a link to the RST periodic table at periodic table would be like placing a link to the full RST article at physics. I hope you can understand how much of a grievous mistake that would be. --mav

title: Talk:Periodic table (big)


text:
Talk:Density functional theory

Wiki Education Foundation-supported course assignment
This article was the subject of a Wiki Education Foundation-supported course assignment, between 10 March 2020 and 30 April 2020. Further details are available on the course page. Student editor(s): Natefoulk4. Peer reviewers: Nduc5420.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 19:19, 16 January 2022 (UTC)

Comments
The page is inconsistent in whether "density-functional" is hyphenated or not. Perhaps most egregiously, the article title is not hyphenated but the bold term right below it that starts the article is hyphenated. I'm partial to hyphenating it, but I'd prefer to leave it to others more familiar with the field and how the term is generally used to make the decision. 172.92.14.139 (talk) 16:51, 26 October 2022 (UTC)

In my opinion, the explanation given for a functional in the second sentence is not complete, because by function of a function it is meant f(g(x)), while a functional can be whatever application defined on a space of functions. This definition includes functions of functions but also other kinds of application (a common one is the integral over an interval [a,b] of the function). Francesco.randi (talk) 15:36, 23 March 2012 (UTC)

Mott insulators are quite an important example of DFT not working as it could in strongly correlated electron systems. Do you think it's worth mentioning specifically. I don't know if it is comparable to the examples given in other fields. Grj23 (talk) 21:01, 1 April 2009 (UTC)

When discussing DFT and dispersion forces I would be more careful in saying that"Despite the improvements in DFT, there are still difficulties in using density functional theory to properly describe intermolecular interactions, especially van der Waals forces (dispersion)". In literature there are some examples of how to address this issue. In particular, it has been shown that the BHandH functional is able of reproducing with great accuracy correlated ab initio performances, see for instance "Hybrid density functional theory for pi-stacking interactions: application to benzenes, pyridines, and DNA bases", Robertazzi et al., Journal of Computional Chemistry, 2006 Mar;27(4):491-504.
 * Thank you for the reference! It seems however that they do not simply treat dispersion interactions, but the special case that is pi-pi stacking. A very interesting problem, of course, but still a special case. -- Mipmip 06:58, 15 November 2006 (UTC)
 * There are also some other derived or ad-hoc (see Grimme's B2PLYP) dispersion-cabable methods that include DFT. Nevertheless, a semi-local KS-DFT functional can, in principle, never describe dispersion interactions properly due to the simple fact that dispersion is intrinsically a non-local correlation effect.129.69.55.52 (talk) 13:35, 4 April 2008 (UTC)

I would explain the different opinions about DFT vs ab initio. While DFT is able to treat bigger, more complex systems, many scientists view it just as a good semiempyrical technique, not to be used if a "proper" ab initio calculation is possible.

True, also should be mentioned are techniques that are less accurate than DFT but can be used for bigger systems still.

DFT is not in itself semi-empirical (Hohenberg-Kohn is in itself just a reformulation of the Schrodinger equation.) LDA and LSDA are ab initio. Many popular functionals are however semi-empirical.

But the debate on true ab initio vs. hybrid DFT may be a bit too specific for a general article such as this though. Although DFT looks somewhat empirical in comparison to wave-based methods, by comparison to the very empirical methods such as MM, DFT looks very 'ab initio' indeed.

I made some changes to the introduction of the article. I felt some statements were incorrect, or at least very vague. For example, the sentence beginning with "Within the framework of DFT, the ..." actually describes Kohn-Sham theory. DFT, of course, can be done without Kohn-Sham (see the original Hohenberg-Kohn paper).

The same sentence says that DFT reduces the many body problem to a "solvable problem of a single electron moving in an averaged effective force field." Being picky and precise, I don't think this is true. DFT does not reduce the N-body problem to a single electron problem, Kohn-Sham reduces it to an effective non-interacting electron problem. Moreover, this is not always solvable: if you have $$10^{23}$$ electrons you still cannot solve the equivalent non-interacting problem. Where, by solve, I mean to numerically solve the problem.

I will probably make more modifications, further down the article, as time goes on. I know that some of the material in the introduction is now repeated later, but that shouldn't be a big deal. Please comment. WikipAcct 07:58, 2 Jan 2005 (UTC)

Also, I think the article needs to emphasize that KS-DFT is a groundstate theory. And it should mention the time-dependent generalization. I will add these to the to-do list.
 * Added TD-DFT to "see also" list Azo bob (talk) 12:59, 3 May 2009 (UTC)

The statement: DFT is an exact theory only for the free electron gas, while for the treatment of extended atomic systems various approximations have to be made, is slightly misleading.

The paradigm of DFT development, starting with Thomas-Fermi and Kohn-Sham has been to work as a series of corrections to the free electron gas model. All functionals I know of use that approach, and can thus be said to be 'exact for the free electron gas'. But this does not mean DFT by necessity is like that. DFT can in principle be exact for any potential fullfilling the criterium of the Hohenberg-Kohn proof.

 * Yes, I agree. To be precise, the sentence in the article refered to
 * by this person is incorrect. Feel free to fix it!  I just stumbled upon
 * the article yesterday. I thought about quickly fixing it to say
 * that "LDA is exact for theuniform gas", but that doesn't help
 * the article much. In fact, in my not so humble opinion, the article
 * needs some work. I'll try to add some improvements. WikipAcct 05:52, 4 Jan 2005 (UTC)

Some of the statements seemed to be still odd, and so i cleaned up some sections, and expanded some. I think it still needs a discussion of time-dependent DFT, as well as some more applications, and maybe some of the work on including dispersion into functionals. Salsb 18:30, 26 July 2005 (UTC)

If I may add something: The Spartan package distributed by Wavefunction, Inc. also supports DFT computations. The version we are running in our laboratory is properly cited as: Spartan'04 for Macintosh; Wavefunction, Inc.; Irvine, CA. Iamthealchemist 22:03, 6 December 2005 (UTC)

I think there needs to be more on the various exchange and correlation functions that are widely used, particularly in programs such as Gaussian. There is a mention of B3LYP without stating that it is a hybrid method and this needs defining as noted on the TODO list above. There is no mention of non-hybrid methods such as BLYP. Elsewhere there is an empty link to B3LYP, so perhaps we need a set of sections on different widely used methods, so they can be used as links for B3LYP and so on. I am rather busy at present with other pages and I am not a real expert on DFT. Anyone else want to do it? Bduke 01:02, 19 December 2005 (UTC)

Kohn-Sham functional
Which part of Kohn-Sham equations is the "Kohn-Sham functional"? --HappyCamper 14:14, 4 October 2006 (UTC)
 * E[ρ] WilliamDParker 15:15, 4 October 2006 (UTC)
 * Thanks. --HappyCamper 20:27, 4 October 2006 (UTC)

Software
I think it might be helpful to separate the list of software that supports DFT into programs available for free (including GPL'd software and proprietary software released gratis) and programs for which a paid site license is required. Does this make sense? --WilliamJenkins09 (talk) 14:02, 4 January 2008 (UTC)
 * It might be better to make it into a table, with columns for license (free etc as you suggest), methods (basis set KS or pure DFT, only DFT or DFT + HF etc) and perhaps other things. This would make it rather large and it might then have to become a separate article like Quantum chemistry computer programs. --Bduke (talk) 00:40, 5 January 2008 (UTC)
 * The section is only somewhat helpful, in that it only informs of the existence of all these programs. A separate article with a big table would allow more useful information to be included, as you have both noted. Also, it's becoming a bit of an eye saw, which is only going to grow with time. THEN WHO WAS PHONE? (talk) 19:43, 2 November 2008 (UTC)

Structuring
Seems like the section, Description of the theory, is out of place. It could be to merged with the lead (which needs beefing up anyway), placed above the Hohenberg-Kohn theorems section, or a bit of both. Part of the last paragraph in that section could be expanded in to a general overview of the issues that are still being worked out with DFT and placed in a section of its own lower down the article. Also the Thomas-Fermi model section could be expanded in to an article of its own having only a brief comment in this article. Any of these suggestions sound reasonable? THEN WHO WAS PHONE? (talk) 19:28, 2 November 2008 (UTC)

 * I basically agree with you. Here's some specific thoughts:
 * Re "Seems like the section, Description of the theory, is out of place." - I agree.
 * Re "It could be to merged with the lead (which needs beefing up anyway), placed above the Hohenberg-Kohn theorems section, or a bit of both." - We could start out by moving it above the Theorems section. Then we could extract some info from it to put in the lead.  However, I think we want to keep the lead relatively simple and not make it too big.
 * Re "Part of the last paragraph in that section could be expanded in to a general overview of the issues that are still being worked out with DFT and placed in a section of its own lower down the article." - Could you be more specific about what part and the place you had in mind for it?
 * Re "Also the Thomas-Fermi model section could be expanded in to an article of its own having only a brief comment in this article." - I've been thinking along similar lines and when I first saw it in the DFT article I was surprised that it wasn't in an article of its own.
 * --Bob K31416 (talk) 21:15, 2 November 2008 (UTC)

 * I moved part of the "Description of the theory" (DOTT) section that gives history, general info related to other subjects, etc., to the Intro where it is more appropriately placed. (For the most part, this is what THEN WHO WAS PHONE? suggested.) Now the DOTT section doesn't seem as much out of place since a disorienting part has been moved. Also, I'm looking into not having the HK theorems section as a section by itself but instead putting it into the DOTT section. --Bob K31416 (talk) 17:14, 5 November 2008 (UTC)

 * I like what you have done, it flows nicely and we just need some others to comment on re moving the Thomas-Fermi section. Your third point above now refers to what is the third paragraph of the lead. I think that it's nice to have a mention in the lead, as many people tend to think DFT (or rather DFA, density functional approximations) can do anything. We should also mention self-interaction error in this regard, but perhaps only in the body. I'll think about tweaking the Overview of the method section – especially the way it begins. THEN WHO WAS PHONE? (talk) 23:53, 9 November 2008 (UTC)

 * It might be better to create a Thomas-Fermi Model article before deciding related changes in this article. --Bob K31416 (talk) 18:03, 11 November 2008 (UTC)

 * It would be easiest for the creation to proceed by splitting the section off directly in to a new article. If nothing else, this provides (appreciative, and GFDL) recognition to all those people that have contributed to it. Doing so would need a commitment to expand the article beyond what is in that section though, since the issue is not that it's too big, but rather (IMO), too significant and too wide ranging to be hidden in a DFT article. I'll pull together something in my sandbox which would build on any split, if it were so to happen. THEN WHO WAS PHONE? (talk) 19:21, 11 November 2008 (UTC)

 * It doesn't seem like "split" is quite appropriate because the TF section in DFT isn't very large and thus doesn't fit into the motive for "split". How about just leaving the DFT article intact for now and starting a new article Thomas-Fermi Model by simply copying the TF section to it? The new TF article can be worked on at leisure and the DFT article can be edited with the new article in mind, just like regular editing.
 * As far as recognition is concerned, from what I've seen it is essentially nonexistent on Wikipedia. There are Barnstars but I don't think anyone keeps track of who did what when, except maybe a few people amongst themselves or on a very short term basis for the purpose of a good working atmosphere. There are no bylines.

 * I think what we want to do is simple and doesn't need to be complicated. Just copy the TF section to a new article and carry on with business-as-usual editing of DFT with the TF section still in it for now. I'm willing to make the new article in this way if you like or you can do it. Either way is fine with me. Or you can do what you suggested above. All these ways seem to end up in the same place so I'm flexible on this. --Bob K31416 (talk) 01:26, 12 November 2008 (UTC)

 * I think were pretty much suggesting the same thing :)

 * In the context of DFT and of this article, the section seems disproportionately large. In the context of itself, it seem too small. It's not that big of an issue, and certainly not something which needs to be dealt with in a hurry. There's no harm in it staying here even if duplicated, with recognition for GFDL, to some extent elsewhere. If you want to quasi-"split" (no hurry in doing so) without deleting I'll would certainly see what I can pull together to expand it. THEN WHO WAS PHONE? (talk) 03:19, 12 November 2008 (UTC)

 * I created the new Thomas-Fermi Model article by copying from DFT and mentioned that it was copied in the edit summary, as we discussed here and on our talk pages.
 * "For unto us a child is born..." Isaiah 9:6 --Bob K31416 (talk) 20:23, 13 November 2008 (UTC)

Text on calculating electron chemical potential within density functional theory
I'm in the process of deleting some text with mathematical details about how to calculate electron chemical potential within DFT. It is this section here. It is too specialized to keep within the general chemical potential article. If someone knows a good home for it, either this article or somewhere else, please feel free to put it there. Thanks! --Steve (talk) 14:13, 27 April 2012 (UTC)

the coordinate where the functional is evaluated
When the article is describing LDA, it says "the functional depends only on the density at the coordinate where the functional is evaluated". However, the functional isn't evaluated at a particular coordinate in space, r. The functional is an integral over all points in space. The "coordinate" of the functional is the density function, not a location, r.Mpalenik (talk) 02:11, 14 March 2013 (UTC)

Split classical Density Functional Theory?
This article is structurally weird, tacking on the whole classical DFT topic after what feels like the end of a complete article on quantum QFT. Plus, wading through all this quantum stuff is frustrating when searching for information on classical DFT. German wikipedia has two separate articles and I found it more readable. However, an ambitious undertaking and I'm personally struggling to understand either. CyreJ (talk) 10:41, 13 January 2022 (UTC)

 * I agree. I would prefer a separate article, too. From Mermin's proof analogous to Hohenberg-Kohn classical DFT has gone its own way. Then there is not even a mentioning of mean field approximations or Fundamental Measure Theory (a successful family of hard sphere fluid functionals) in the classical DFT text, which are discussed in review papers on classical DFT. FNGdM (talk) 18:57, 28 August 2023 (UTC)

Potential mistake in classical DFT section
The dimensions in the equation $$\frac{\delta^s\Omega}{\delta \mu(\boldsymbol{r}_1)\dots\delta \mu(\boldsymbol{r}_s)}=(-1)^sn_s(\boldsymbol{r}_1,\dots,\boldsymbol{r}_s)$$ do not add up.

Also, a clarification, that $$\mu(\boldsymbol{r})$$ is not the chemical potential in the sense of being the intensive variable $$\mu_{\mathrm{thermodynamics}}$$ to particle number, but that $$\mu(\boldsymbol{r})=\mu_{\mathrm{thermodynamics}}-v(\boldsymbol{r})$$, where $$v(\boldsymbol{r})$$ is the external potential, would in my opinion be an improvement. FNGdM (talk) 17:05, 31 August 2023 (UTC)

title: Talk:Density functional theory