Sulfur isotope biogeochemistry

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Sulfur_isotope_biogeochemistry

Sulfur isotope biogeochemistry is the study of the distribution of sulfur isotopes in biological and geological materials. In addition to its common isotope, ³²S, sulfur has three rare stable isotopes: ³⁴S, ³⁶S, and ³³S. The distribution of these isotopes in the environment is controlled by many biochemical and physical processes, including biological metabolisms, mineral formation processes, and atmospheric chemistry. Measuring the abundance of sulfur stable isotopes in natural materials, like bacterial cultures, minerals, or seawater, can reveal information about these processes both in the modern environment and over Earth history.

Background

Natural abundance of sulfur isotopes

Bar chart depicting the natural abundance of ³²S, ³³S, ³⁴S, and ³⁶S on Earth.

Sulfur has 24 known isotopes, 4 of which are stable (meaning that they do not undergo radioactive decay). ³²S, the common isotope of sulfur, makes up 95.0% of the natural sulfur on Earth. In the atomic symbol of ³²S, the number 32 refers to the mass of each sulfur atom in Daltons, the result of the 16 protons and 16 neutrons of 1 Dalton each that make up the sulfur nucleus. The three rare stable isotopes of sulfur are ³⁴S (4.2% of natural sulfur), ³³S (0.75%), and ³⁶S (0.015%). These isotopes differ from ³²S in the number of neutrons in each atom, but not the number of protons or electrons; as a result, each isotope has a slightly different mass, but has nearly identical chemical properties.

Physical chemistry

Small differences in mass between stable isotopes of the same element can lead to a phenomenon called an "isotope effect," where heavier or lighter isotopes are preferentially incorporated into different natural materials depending on the materials' chemical composition or physical state. Isotope effects are divided into two main groups: kinetic isotope effects and equilibrium isotope effects. A kinetic isotope effect occurs when a reaction is irreversible, meaning that the reaction only proceeds in the direction from reactants to products. Kinetic isotope effects cause isotopic fractionation—meaning that they affect the isotopic composition of reactant and product compounds—because the mass differences between stable isotopes can affect the rate of chemical reactions. It takes more energy to reach the transition state of a reaction if the compound has bonds with a heavier isotope, which causes the compound with heavier isotopes to react more slowly. Normal kinetic isotope effects cause the lighter isotope (or isotopes) to be preferentially included in a reaction's product. The products are then said to be "depleted" in the heavy isotope relative to the reactant. Rarely, inverse kinetic isotope effects may occur, where the heavier isotope is preferentially included in a reaction's product.

Equilibrium isotope effects cause fractionation because it is more chemically favorable for heavy isotopes to take part in stronger bonds. An equilibrium isotope effect occurs when a reaction is at equilibrium, meaning that the reaction is able to occur in both directions simultaneously. When a reaction is at equilibrium, heavy isotopes will preferentially accumulate where they can form the strongest bonds. For example, when the water in a sealed, half-full bottle is in equilibrium with the vapor above it, the heavier isotopes ²H and ¹⁸O will accumulate in the liquid, where they form stronger bonds, while the lighter isotopes ¹H and ¹⁶O will accumulate in the vapor. The liquid is then said to be "enriched" in the heavy isotope relative to the vapor.

Calculations

Delta notation

Differences in the abundance of stable isotopes among natural materials are usually very small (natural differences in the ratio of rare to common isotope are almost always below 0.1%, and sometimes much smaller). Nevertheless, these very small differences can record meaningful biological and geological processes. To facilitate comparison of these small but meaningful differences, isotope abundances in natural materials are often reported relative to isotope abundances in designated standards. The convention for reporting the measured difference between a sample and a standard is called "delta notation." For example, imagine an element X for which we wish to compare the rare, heavy stable isotope with atomic mass A (^AX) to the light, common isotope with atomic mass B (^BX). The abundance of ^AX and ^BX in any given material is reported with the notation δ^AX. δ^AX for the sample material is calculated as follows:

^AR = (total amount of ^AX)/(total amount of ^BX)

δ^AX_sample = (^AR_sample - ^AR_standard)/^AR_standard

δ values are most commonly reported in parts per thousand, commonly referred to in isotope chemistry as per mille and represented by the symbol ‰. To report δ values in per mille, the δ value as calculated above should be multiplied by 1000:

δ^AX_sample (‰) = ((^AR_sample - ^AR_standard)/^AR_standard) * 1000

Fractionation factors

While an isotope effect is the physical tendency for stable isotopes to distribute in a particular way, the isotopic fractionation is the measurable result of this tendency. The isotopic fractionation of a natural process can be calculated from measured isotope abundances. The calculated value is called a "fractionation factor," and allows the effect of different processes on isotope distributions to be mathematically compared. For example, imagine a chemical reaction Reactant → Product. Reactant and Product are materials that both contain the element X, and X has two stable isotopes, ^AX (the heavy isotope, with a mass of A) and ^BX (the light isotope, with a mass of B). The fractionation factor for the element X in the reaction Reactant → Product is represented by the notation ^Aα_{Product/Reactant}. ^Aα_{Product/Reactant} is calculated as follows:

^Aα_{Product/Reactant} = (δ^AX_Product + 1)/(δ^AX_Reactant + 1)

Fractionation factors can also be reported using the notation ^Aε_{Product/Reactant}, which is sometimes called the "enrichment factor" and is calculated as follows:

^Aε_{Product/Reactant} = ^Aα_{Product/Reactant} - 1

Like δ values, ε values can be reported in per mille by multiplying by 1000.

Δ³³S and Δ³⁶S notation

All kinetic and equilibrium isotope effects result from differences in atomic mass. As a result, a reaction that fractionates ³⁴S will also fractionate ³³S and ³⁶S, and the fractionation factor for each isotope will be mathematically proportional to its mass. Because of the mathematical relationships of their masses, the observed relationships between δ³⁴S, δ³³S, and δ³⁶S in most natural materials are approximately δ³³S = 0.515 × δ³⁴S and δ³⁶S = 1.90 × δ³⁴S. Rarely, natural processes can create deviations from this relationship, and these deviations are reported as Δ³³S and Δ³⁶S values, usually pronounced as "cap delta." These values are typically calculated as follows:

Δ³³S = 1000 × [(1 + δ³³S/1000) - (1 + δ³⁴S 1000)^0.518 - 1]

Δ³⁶S = 1000 × [(1 + δ³⁶S/1000) − (1 + δ³⁴S/1000)^1.91 − 1]

However, the method for calculating Δ³³S and Δ³⁶S values is not standardized, and can differ among publications.

A Canyon Diablo meteorite sample. The original reference standard for measuring δ³⁴S was the mineral troilite (FeS) recovered from the Canyon Diablo meteorite.

Reference materials

Agreed-upon reference materials are required so that reported δ values are comparable among studies. For the sulfur isotope system, δ³⁴S values are reported on the Vienna-Cañon Diablo Troilite (VCDT) scale. The original CDT scale was based on a sample of the mineral troilite recovered from the Canyon Diablo meteorite at Meteor Crater, Arizona, US. The Cañon Diablo Troilite was assigned a δ³⁴S value of 0‰. However, troilite from the Canyon Diablo meteorite was later discovered to have variable sulfur isotope composition. As a result, VCDT was established as a hypothetical sulfur isotope reference with a ³⁴R value of 0.044151 and δ³⁴S of 0‰, but no physical sample of VCDT exists. Samples are now measured in comparison to International Atomic Energy Agency (IAEA) reference materials, which are well-characterized, lab-prepared compounds with known δ³⁴S values. A commonly-used IAEA reference material is IAEA-S-1, a silver sulfide reference material with a δ³⁴S value of -0.30‰ VCDT. ³³S and ³⁶S abundance can also be measured relative to IAEA reference materials and reported on the VCDT scale. For these isotopes, too, VCDT is established as having δ³³S and δ³⁶S values of 0‰. The ³³R value of VCDT is 0.007877 and the ³⁶R value is 0.0002. IAEA-S-1 has a ³³R value of 0.0007878 and a δ³³S value of -0.05‰ VCDT; it has a δ³⁶S value of -0.6‰ VCDT.

Analytical methods and instrumentation

The sulfur isotopic composition of natural samples can be determined by Elemental Analysis-Isotope Ratio Mass Spectrometry (EA-IRMS), by Dual Inlet-Isotope Ratio Mass Spectrometry (DI-IRMS), by Multi-Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS), by Secondary Ion Mass Spectrometry (SIMS), or by Nanoscale secondary ion mass spectrometry (NanoSIMS). MC-ICPMS can be paired with gas chromatography (GC-MC-ICPMS) to separate certain volatile compounds in a sample and measure the sulfur isotopic composition of individual compounds.

Natural variations in sulfur isotope abundance

Sulfur in natural materials

An illustration of some common processes in the biogeochemical sulfur cycle.

Sulfur is present in the environment in solids, gases, and aqueous species. Sulfur-containing solids on Earth include the common minerals pyrite (FeS₂), galena (PbS), and gypsum (CaSO₄•2H₂O). Sulfur is also an important component of biological material, including in the essential amino acids cysteine and methionine, the B vitamins thiamine and biotin, and the ubiquitous substrate coenzyme A. In the ocean and other natural waters, sulfur is abundant as dissolved sulfate. Hydrogen sulfide is also present in some parts of the deep ocean where it is released from hydrothermal vents. Both sulfate and sulfide can be used by specialized microbes to obtain energy or to grow. Gases including sulfur dioxide and carbonyl sulfide make up the atmospheric component of the sulfur cycle. Any process that transports or chemically transforms sulfur between these many natural materials also has the potential to fractionate sulfur isotopes.

Sulfur isotopic abundance in natural materials

Natural range of sulfur isotopic composition on Earth, modified and simplified from Meija et al. (2013).

Sulfur in natural materials can vary widely in isotopic composition: compilations of the δ³⁴S values of natural sulfur-containing materials include values ranging from -55‰ to 135‰ VCDT. The ranges of δ³⁴S values vary across sulfur-containing materials: for example, the sulfur in animal tissue ranges from ~ -10 to +20‰ VCDT, while the sulfate in natural waters ranges from ~ -20 to +135‰ VCDT. The range of sulfur isotope abundances in different natural materials results from the isotope fractionation associated with natural processes like the formation and modification of those materials, discussed in the next section.

Processes that fractionate sulfur isotopes

Numerous natural processes are capable of fractionating sulfur isotopes. Microbes are capable of a wide variety of sulfur metabolisms, including the oxidation, reduction, and disproportionation (or simultaneous oxidation and reduction) of sulfur compounds. The effect of these metabolisms on sulfur isotopic composition of the reactants and products is also highly variable, depending on the rate of relevant reactions, availability of nutrients, and other biological and environmental parameters. As an example, the microbial reduction of sulfate to sulfide generally results in a ³⁴S-depleted product, but the strength of this fractionation has been shown to range from 0 to 65.6‰ VCDT.

Many abiotic processes also fractionate sulfur isotopes. Small fractionations with ε values from 0-5‰ have been observed in the formation of the mineral gypsum, an evaporite mineral produced through the evaporation of seawater. Some sulfide minerals, including pyrite and galena, can form through thermochemical sulfate reduction, a process in which seawater sulfate trapped in seafloor rock is reduced to sulfide by geological heat as the rock is buried; this process generally fractionates sulfur more strongly than gypsum formation.

Prior to the rise of oxygen in Earth's atmosphere (referred to as the Great Oxidation Event), additional sulfur-fractionating processes referred to as mass-anomalous or mass-independent fractionation uniquely affected the abundance of ³³S and ³⁶S in the rock record. Mass-anomalous fractionations are rare, but they can occur through certain photochemical reactions of gases in the atmosphere. Studies have shown that photochemical reactions of atmospheric sulfur dioxide can cause substantial mass-anomalous fractionation of sulfur isotopes.

Observed ³⁴ε values for some common natural processes.

Process	Range of observed 34ε (‰ VCDT)
Assimilatory sulfate reduction	-0.9 to -2.8
Dissimilatory sulfate reduction	0 to -65.6
Sulfite reduction	+0.3 to -41
Sulfide oxidation	+3 to -18.0
Sulfur disproportionation	Sulfate: -0.6 to +20.2 Sulfide: -5.5 to -8.6
Thermochemical sulfate reduction	+10 to +25
Gypsum formation	0 to +4.2

Biological processes that intake sulfur

All organisms metabolize sulfur, and it is incorporated into the structure of proteins, polysaccharides, steroids, and many coenzymes. The biological pathway by which an organism intakes and/or removes sulfur can have significant impacts on the sulfur isotope composition of the organism and its environment.

The assimilatory sulfate reduction pathway as used by E. coli.

Some organisms take in relatively small amounts of sulfate in a process called assimilatory sulfate reduction, for the purpose of synthesizing compounds that contain sulfur, such as the amino acids methionine and cysteine that can then be used to make proteins. In phytoplankton, most of the sulfur taken in by this process is incorporated into biomass as proteins (~35%), sulfate esters (~20%), and low-weight sulfur-containing compounds (~40%). Literature on the isotopic fractionation effects of the assimilatory sulfate reduction pathway are noticeably less robust than those discussing other microbial sulfur pathways, but some sources believe there to be only very slight isotopic variations (δ³⁴S = -4.4‰ to +0.5‰) in the resulting organic sulfur relative to the surrounding sulfate.

A general dissimilatory sulfate reduction pathway as used by sulfate-reducing bacteria.

There is also another common pathway by which organisms intake sulfur. These microorganisms, which consume and reduce sulfate in relatively large quantities, are said to perform dissimilatory sulfate reduction. These organisms use sulfate reduction as an energy source as opposed to a way to synthesize new cell components, and remove the resulting sulfide as a waste product. Microbial sulfate reduction has been demonstrated to fractionate sulfur isotopes in bacteria, with some studies showing a dependence upon sulfate concentration and/or temperature. Studies examining dozens of species of dissimilatory sulfate reducing microbes have observed sulfur isotope fractionations ranging from -70‰ to +42.0‰.

While dissimilatory sulfate reduction and assimilatory sulfate reduction are two of the most common pathways by which organisms uptake and utilize sulfate, there are many other pathways by which living things intake sulfur. For example, sulfur oxidation of compounds like hydrogen sulfide and elemental sulfur is performed by lithotrophic bacteria and chemosynthetic archaea. Most animals obtain sulfur directly from the methionine and cysteine in the protein they consume.

Stable Isotopes in Plants

Methods of detection

Previous efforts to understand how sulfur metabolism and biosynthetic pathways relied on expensive labeling experiments using radioactive ³⁵S. By leveraging natural assimilatory processes, stable isotopes ratios can be used to track what are the sources of sulfur for plants, what organs plants utilize in sulfur acquisition and how sulfur moves through plants.

Elemental Analysis-Isotope Ratio Mass Spectrometer (EA-IRMS)

Sulfur (S) stable isotope composition measurements are often done using an Elemental Analysis-Isotope Ratio Mass Spectrometer, (EA-IRMS) in which organic sulfur from biological samples is oxidized to sulfur dioxide (SO₂) and analysed on a mass spectrometer. The gas is then analyzed for the ratio of the lighter (³²S¹⁶O₂) to the heavier (³⁴S¹⁶O₂) isotopologue and this ratio is then compared to sulfur isotope standards in order to calculate relative fractionations. In biological materials, sulfur is particularly scarce, making the abundance of S isotopes difficult to measure. The elemental S composition of plant matter is ≈0.2%, accounting for approximately 2 mmol/m² in most leaf tissue. In order to reach detectable levels of 30 ng to 3 µg of elemental S to calculate reliable δ³⁴S values, leaf tissue samples need to be between 2–5 mg.

Improvements in detection have been made in recent years in the utilization of gas chromatography coupled with multicollector ICP-MS (GC/MC-ICP-MS) to be able to measure pmol quantities of organic S.Additionally, ICP-MS has been used to measure nanomolar quantities of dissolved sulfate. Most studies have focused on measuring the bulk δ³⁴S of plant tissues and few studies have been performed on measuring the δ³⁴S of individual S-containing compounds. The coupling of high-performance liquid chromatography (HPLC) with ICP-MS has been proposed as a way to test individual S-containing compounds.

Sources

Each year, approximately 0.3 gigatons of elemental sulfur is converted into organic matter by photosynthetic organisms. This organic sulfur is allocated into a diversity of compounds such as amino acids – namely cysteine (Cys) and methionine (Met) – proteins, cofactors, antioxidants, sulfate groups, Fe-S centers and secondary metabolites. The three main sources of sulfur are atmospheric, soil, and aquatic.

Most vegetation can acquire sulfur from gaseous atmospheric compounds or various ions either in soil solutions or water bodies. Uptake of gaseous and dissolved sulfur compounds apparently occurs with little accompanying isotopic selectivity. Dissolved sulfate (SO₄^2-) is considered to be the central pool which is metabolized by microorganisms and plants as most forms of atmospheric sulfur is oxidized into sulfate. Atmospheric sulfur is eventually returned to the soil when it is scrubbed from the atmosphere during precipitation or through dryfall.

Atmosphere

Many plants acquire sulfur through gaseous atmospheric compounds. Leaves of trees have δ³⁴S values lying between those of air and soil, suggesting that there is uptake occurring from atmospheric and soil sources. The δ³⁴S values of trees has also been demonstrated to be height dependent with the foliage at the tops of conifers, bull rushes and deciduous trees having δ³⁴S values more reflective of the atmosphere and lower foliage having δ³⁴S values closer to that of soil. It has been proposed that this is due to upper foliage exerting a canopy action on the lower branches, taking up atmospheric sulfur before it can reach lower levels. This is further supported with the epiphytic lichens and mosses having δ³⁴S values close to atmospheric S compounds. This occurs due lichen and mosses having no access to soil and relying on the direct uptake of gaseous sulfur, dissolved sulfur through rainfall and dry fall accumulation, providing a cumulative record of atmospheric sulfur isotope composition.

Main forms of atmospheric sulfur come from the natural sulfur emissions formed biologically and emitted as H₂S or organic sulfur gases such as DMS (dimethyl sulfide), COS (carbonyl sulfide), and CS₂ (carbon disulfide). These gases are predominantly formed over oceans, wetlands, salt marshes, and estuaries by algae and bacteria. Anthropogenic emissions have increased the concentration of sulfur in the atmosphere mainly through emissions of SO₂, from coal, oil, industrial processes, and biomass burning. In 2000, global anthropogenic emission of sulfur was estimated of 55.2-68 Tg S per year, which is much higher than the natural sulfur emissions estimated to be 34 Tg S per year. In the event of excess sulfur in plant tissue it has been demonstrated that when exposed to high doses of sulfur dioxide, plants emit hydrogen sulfide (H₂S) and possibly other reduced sulfur compounds in response to high sulfur loading

Soil

This is a simplified model of how sulfur is taken up by plants and how sulfur moves through the environment

If soil sulfur is derived consistently from one source, the water-soluble and insoluble organic S fractions acquire similar isotopic compositions. In the case that there are two or more sources and/or if the isotopic composition of atmospheric or groundwater sulfate fluctuates, there may not be sufficient time for isotopic homogenization among the various forms of sulfur. The primary form of sulfur in soil is sulfate, which is transported upwards through the root system with minimal δ³⁴S fractionation by 1-2‰. In contrast to higher canopy plants reflecting atmospheric δ³⁴S, protected understory plants tend to reflect soil sulfur.

Aquatic

The forms of sulfur available in aquatic environments depends on whether it is a marine or freshwater environment. In marine environments, the main forms of sulfur available is in sulfate at ~29mM and a δ³⁴S of 21‰ in the surface. This excess in sulfur is subsequently converted into dimethylsulfoniopropionate (DMSP) by algae as an osmolyte and a repellent against grazing. DMSP also accounts for 50-100% of bacterial sulfur demand making it the most important source of reduced sulfur for marine bacteria. DMSPs cleavage product dimethyl sulfide (DMS) is highly volatile escaping the ocean into the atmosphere with emissions ranging between 15 and 33 Tg S year⁻¹  and accounting for 50-60% of the total natural reduced sulfur flux to the atmosphere.

Freshwater environments are more varied and depend on a multitude of factors, such as atmospheric deposition, runoff, diagenesis of bedrock and the presence of microbial sulfate reducers (MSR). Overall, the main sources of sulfur in freshwater environments are hydrogen sulfide and sulfate. In estuaries, plant roots extend into sulfide rich δ³⁴S depleted sediments, created by MSR, and incorporate that into their biomass. Though levels of sulfide produced by MSR can be toxic and it has been proposed that these plants pump oxygen into their roots to oxidize sulfide into the less toxic sulfate. In these environments algaes will preferentially acquire the δ³⁴S of HS⁻ if present rather than the more abundant sulfate, as these sulfides can be readily incorporated into the direct formation of cysteine. This is consistent with cyanobacteria being able to carry out anoxygenic photosynthesis using sulfide.

Biochemistry

~90% of the organic-S in plants is concentrated in the amino acids cysteine and methionine. Cysteine acts as the direct or indirect precursor to any other organic-S compounds in plants such as coenzyme-A, methionine, biotin, lipoic acid and glutathione. The carbon skeleton necessary for S assimilation are provided by glycolysis (acetyl-CoA), respiration (aspartic acid, Asp, which derives from oxaloacetate) and photorespiration (serine, Ser). Because cysteine is a direct precursor to methionine, methionine is naturally ³⁴S depleted in comparison to cysteine. The majority of sulfur is generally in the organic form but, when excess sulphur is available in the environment, inorganic sulfate becomes the major sulphur form. In most plants, ³⁴S discrimination is minimal and in a study of rice plants it was observed that discrimination takes place in the uptake stage, depleting imported sulfate by 1-2‰ from the source. This effect is through the expression of SO₄^2- transporter genes (SULTR), 14 of which have been identified – which are expressed dependent on the availability of sulfate in the environment. When sulfate is plentiful low affinity transporters are expressed and when sulfate is scarce high affinity genes with greater ³⁴S discrimination.

Distribution through plant organs

Sulfate transported through the roots and SO₂ diffusing into leaves becomes the pool for plants to assimilate sulfur throughout their tissues. Though there is minimal fractionation from the source sulfur of the total plant organic matter, in wheat, roots and stems are depleted from soil by 2‰ and leaves and grain are 2‰ enriched. The ³⁴S enrichment in leaf whole matter is not caused by ³⁴S-enriched sulfate present in the leaf, but is the result of the ³⁴S-enrichment arriving at sink organs causing proteins in the leaves to be ³⁴S-enriched. In rice, translocation from root to shoot does not discriminate S isotopes, however, the sulfate pools of the shoot are significantly ³⁴S-enriched with respect to the sulfate pools of both root and sap. As sulfate, moves through the plant system and is incorporated into biomass, the pool becomes enriched, giving organs such as leaves and grains a higher δ³⁴S than earlier tissues.

Applications

Rise of atmospheric oxygen

Signatures of mass-anomalous sulfur isotope fractionation preserved in the rock record have been an important piece of evidence for understanding the Great Oxidation Event, the sudden rise of oxygen on the ancient Earth. Nonzero values of Δ³³S and Δ³⁶S are present in the sulfur-bearing minerals of Precambrian rock formed greater than 2.45 billion years ago, but completely absent from rock less than 2.09 billion years old. Multiple mechanisms have been proposed for how oxygen prevents the fingerprints of mass-anomalous fractionation from being created and preserved; nevertheless, all studies of Δ³³S and Δ³⁶S records conclude that oxygen was essentially absent from Earth's atmosphere prior to 2.45 billion years ago.

Paleobiology and paleoclimate

A number of microbial metabolisms fractionate sulfur isotopes in distinctive ways, and the sulfur isotopic fingerprints of these metabolisms can be preserved in minerals and ancient organic matter. By measuring the sulfur isotopic composition of these preserved materials, scientists can reconstruct ancient biological processes and the environments where they occurred. δ³⁴S values in the geologic record have been inferred to reveal the history of microbial sulfate reduction and sulfide oxidation. Paired δ³⁴S and Δ³³S records have also been used to show ancient microbial sulfur disproportionation.

Pyrite, a sulfur-bearing mineral that forms in some ocean sediments, usually has relatively low δ³⁴S values due to the indirect role of biology in its formation.

Microbial dissimilatory sulfate reduction (MSR), an energy-yielding metabolism performed by bacteria in anoxic environments, is associated with an especially large fractionation factor. The observed ³⁴ε_MSR values range from 0 to -65.6‰. Many factors influence the size of this fractionation, including sulfate reduction rate, sulfate concentration and transport, availability of electron donors and other nutrients, and physiological differences like protein expression. Sulfide produced through MSR may then go on to form the mineral pyrite, preserving the ³⁴S-depleted fingerprint of MSR in sedimentary rocks. Many studies have investigated the δ³⁴S values of ancient pyrite in order to understand past biological and environmental conditions. For example, pyrite δ³⁴S records have been used to reconstruct shifts in primary productivity levels, changing ocean oxygen content, and glacial-interglacial changes in sea level and weathering. Some studies compare sulfur isotopes in pyrite to a second sulfur-containing material, like sulfate or preserved organic matter. Comparing pyrite to another material gives a fuller picture of how sulfur moved through ancient environments: it provides clues about the size of ancient ³⁴ε_MSR values and the environmental conditions controlling MSR fractionation of sulfur isotopes.

Paleoceanography

δ³⁴S records have been used to infer changes in seawater sulfate concentrations. Because the δ³⁴S values of carbonate-associated sulfate are thought to be sensitive to seawater sulfate levels, these measurements have been used to reconstruct the history of seawater sulfate. δ³⁴S values of pyrite have also been applied to reconstruct the concentration of seawater sulfate, based on expected biological fractionations at low sulfate concentrations. Both of these methods rely on assumptions about the depositional environment or the biological community, creating some uncertainty in the resulting reconstructions.

Isotope-ratio mass spectrometry

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Isotope-ratio_mass_spectrometry

Isotope-ratio mass spectrometry

Magnetic sector mass spectrometer used in isotope ratio analysis, through thermal ionization.
Acronym	IRMS
Classification	mass spectrometry

Isotope-ratio mass spectrometry (IRMS) is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample.

This technique has two different applications in the earth and environmental sciences. The analysis of 'stable isotopes' is normally concerned with measuring isotopic variations arising from mass-dependent isotopic fractionation in natural systems. On the other hand, radiogenic isotope analysis involves measuring the abundances of decay-products of natural radioactivity, and is used in most long-lived radiometric dating methods.

Introduction

Schematic of an isotope-ratio mass spectrometer for measuring CO₂

The isotope-ratio mass spectrometer (IRMS) allows the precise measurement of mixtures of naturally occurring isotopes. Most instruments used for precise determination of isotope ratios are of the magnetic sector type. This type of analyzer is superior to the quadrupole type in this field of research for two reasons. First, it can be set up for multiple-collector analysis, and second, it gives high-quality 'peak shapes'. Both of these considerations are important for isotope-ratio analysis at very high precision and accuracy.

The sector-type instrument designed by Alfred Nier was such an advance in mass spectrometer design that this type of instrument is often called the 'Nier type'. In the most general terms the instrument operates by ionizing the sample of interest, accelerating it over a potential in the kilo-volt range, and separating the resulting stream of ions according to their mass-to-charge ratio (m/z). Beams with lighter ions bend at a smaller radius than beams with heavier ions. The current of each ion beam is then measured using a 'Faraday cup' or multiplier detector.

Many radiogenic isotope measurements are made by ionization of a solid source, whereas stable isotope measurements of light elements (e.g. H, C, O) are usually made in an instrument with a gas source. In a "multicollector" instrument, the ion collector typically has an array of Faraday cups, which allows the simultaneous detection of multiple isotopes.

Gas source mass spectrometry

Measurement of natural variations in the abundances of stable isotopes of the same element is normally referred to as stable isotope analysis. This field is of interest because the differences in mass between different isotopes leads to isotope fractionation, causing measurable effects on the isotopic composition of samples, characteristic of their biological or physical history.

As a specific example, the hydrogen isotope deuterium (heavy hydrogen) is almost double the mass of the common hydrogen isotope. Water molecules containing the common hydrogen isotope (and the common oxygen isotope, mass 16) have a mass of 18. Water incorporating a deuterium atom has a mass of 19, over 5% heavier. The energy to vaporise the heavy water molecule is higher than that to vaporize the normal water so isotope fractionation occurs during the process of evaporation. Thus a sample of sea water will exhibit a quite detectable isotopic-ratio difference when compared to Antarctic snowfall.

Samples must be introduced to the mass spectrometer as pure gases, achieved through combustion, gas chromatographic feeds, or chemical trapping. By comparing the detected isotopic ratios to a measured standard, an accurate determination of the isotopic make up of the sample is obtained. For example, carbon isotope ratios are measured relative to the international standard for C. The C standard is produced from a fossil belemnite found in the Peedee Formation, which is a limestone formed in the Cretaceous period in South Carolina, U.S.A. The fossil is referred to as VPDB (Vienna Pee Dee Belemnite) and has ¹³C:¹²C ratio of 0.0112372. Oxygen isotope ratios are measured relative the standard, V-SMOW (Vienna Standard Mean Ocean Water).

Isotope-ratio mass spectrometer used to measure stable isotope ratios, with gas bench in foreground

It is critical that the sample be processed before entering the mass spectrometer so that only a single chemical species enters at a given time. Generally, samples are combusted or pyrolyzed and the desired gas species (usually hydrogen (H₂), nitrogen (N₂), carbon dioxide (CO₂), or sulfur dioxide (SO₂)) is purified by means of traps, filters, catalysts and/or chromatography.

The two most common types of IRMS instruments are continuous flow and dual inlet. In dual inlet IRMS, purified gas obtained from a sample is alternated rapidly with a standard gas (of known isotopic composition) by means of a system of valves, so that a number of comparison measurements are made of both gases. In continuous flow IRMS, sample preparation occurs immediately before introduction to the IRMS, and the purified gas produced from the sample is measured just once. The standard gas may be measured before and after the sample or after a series of sample measurements. While continuous-flow IRMS instruments can achieve higher sample throughput and are more convenient to use than dual inlet instruments, the yielded data is of approximately 10-fold lower precision.

Static gas mass spectrometry

A static gas mass spectrometer is one in which a gaseous sample for analysis is fed into the source of the instrument and then left in the source without further supply or pumping throughout the analysis. This method can be used for 'stable isotope' analysis of light gases (as above), but it is particularly used in the isotopic analysis of noble gases (rare or inert gases) for radiometric dating or isotope geochemistry. Important examples are argon–argon dating and helium isotope analysis.

Thermal ionization mass spectrometry

Several of the isotope systems involved in radiometric dating depend on IRMS using thermal ionization of a solid sample loaded into the source of the mass spectrometer (hence thermal ionization mass spectrometry, TIMS). These methods include rubidium–strontium dating, uranium–lead dating, lead–lead dating and samarium–neodymium dating.

When these isotope ratios are measured by TIMS, mass-dependent fractionation occurs as species are emitted by the hot filament. Fractionation occurs due to the excitation of the sample and therefore must be corrected for accurate measurement of the isotope ratio.

There are several advantages of the TIMS method. It has a simple design, is less expensive than other mass spectrometers, and produces stable ion emissions. It requires a stable power supply, and is suitable for species with a low ionization potential, such as Strontium (Sr), and Lead (Pb).

The disadvantages of this method stem from the maximum temperature achieved in thermal ionization. The hot filament reaches a temperature of less than 2500 degrees Celsius, leading to the inability to create atomic ions of species with a high ionization potential, such as Osmium (Os), and Tungsten (Hf-W). Although the TIMS method can create molecular ions instead in this case, species with high ionization potential can be analyzed more effectively with MC-ICP-MS.

Secondary-ion mass spectrometry

Schematic diagram of a SHRIMP instrument illustrating the ion beam path. After Figure 4, Williams, 1998.

An alternative approach used to measure the relative abundance of radiogenic isotopes when working with a solid surface is secondary-ion mass spectrometry (SIMS). This type of ion-microprobe analysis normally works by focusing a primary (oxygen) ion beam on a sample in order to generate a series of secondary positive ions that can be focused and measured based on their mass/charge ratios.

SIMS is a common method used in U-Pb analysis, as the primary ion beam is used to bombard the surface of a single zircon grain in order to yield a secondary beam of Pb ions. The Pb ions are analyzed using a double focusing mass spectrometer that comprises both an electrostatic and magnetic analyzer. This assembly allows the secondary ions to be focused based on their kinetic energy and mass-charge ratio in order to be accurately collected using a series of Faraday cups.

A major issue that arises in SIMS analysis is the generation of isobaric interference between sputtered molecular ions and the ions of interest. This issue occurs with U–Pb dating as Pb ions have essentially the same mass as HfO₂⁺. In order to overcome this problem, a sensitive high-resolution ion microprobe (SHRIMP) can be used. A SHRIMP is a double-focusing mass spectrometer that allows for a large spatial separation between different ion masses based on its relatively large size. For U-Pb analysis, the SHRIMP allows for the separation of Pb from other interfering molecular ions, such as HfO₂⁺.

Multiple collector inductively coupled plasma mass spectrometry

An MC-ICP-MS instrument is a multiple collector mass spectrometer with a plasma source. MC-ICP-MS was developed to improve the precision achievable by ICP-MS during isotope-ratio measurements. Conventional ICP-MS analysis uses a quadrupole analyser, which only allows single-collector analysis. Due to the inherent instability of the plasma, this limits the precision of ICP-MS with a quadrupole analyzer to around 1%, which is insufficient for most radiogenic isotope systems.

Isotope-ratio analysis for radiometric dating has normally been determined by TIMS. However, some systems (e.g. Hf-W and Lu-Hf) are difficult or impossible to analyse by TIMS, due to the high ionization potential of the elements involved. Therefore, these methods can now be analysed using MC-ICP-MS.

The Ar-ICP produces an ion-beam with a large inherent kinetic energy distribution, which makes the design of the mass-spectrometer somewhat more complex than it is the case for conventional TIMS instruments. First, different from Quadrupole ICP-MS systems, magnetic sector instruments have to operate with a higher acceleration potential (several 1000 V) in order to minimize the energy distribution of the ion beam. Modern instruments operate at 6-10kV. The radius of deflection of an ion within a magnetic field depends on the kinetic energy and the mass/charge ratio of the ion (strictly, the magnet is a momentum analyzer not just a mass analyzer). Because of the large energy distribution, ions with similar mass/charge ratio can have very different kinetic energies and will thus experience different deflection for the same magnetic field. In practical terms one would see that ions with the same mass/charge ratio focus at different points in space. However, in a mass-spectrometer one wants ions with the same mass/charge ratio to focus at the same point, e.g. where the detector is located. In order to overcome these limitations, commercial MC-ICP-MS are double-focusing instruments. In a double-focusing mass-spectrometer ions are focused due to kinetic energy by the ESA (electro-static-analyzer) and kinetic energy + mass/charge (momentum) in the magnetic field. Magnet and ESA are carefully chosen to match the energy focusing properties of one another and are arranged so that the direction of energy focusing is in opposite directions. To simplify, two components have an energy focus term, when arranged properly, the energy term cancels out and ions with the same mass/charge ratio focus at the same point in space. It is important to note, double-focusing does not reduce the kinetic energy distribution and different kinetic energies are not filtered or homogenized. Double-focusing works for single as well as multi-collector instruments. In single collector instruments ESA and magnet can be arranged in either forward geometry (first ESA then magnet) or reversed geometry (magnet first then ESA), as only point-to-point focusing is required. In multi-collector instruments, only forward geometry (ESA then magnet) is possible due to the array of detectors and the requirements of a focal plane rather than a focal point.

Accelerator mass spectrometry

Accelerator mass spectrometry

Accelerator mass spectrometer at Lawrence Livermore National Laboratory
Acronym	AMS
Classification	Mass spectrometry
Analytes	Organic molecules Biomolecules
Other techniques
Related	Particle accelerator

For isotopes occurring at extremely low levels, accelerator mass spectrometry (AMS) can be used. For example, the decay rate of the radioisotope ¹⁴C is widely used to date organic materials, but this approach was once limited to relatively large samples no more than a few thousand years old. AMS extended the range of ¹⁴C dating to about 60,000 years BP, and is about 10⁶ times more sensitive than conventional IRMS.

AMS works by accelerating negative ions through a large (mega-volt) potential, followed by charge exchange and acceleration back to ground. During charge exchange, interfering species can be effectively removed. In addition, the high energy of the beam allows the use of energy-loss detectors, that can distinguish between species with the same mass/charge ratio. Together, these processes allow the analysis of extreme isotope ratios above 10¹².

Moving wire IRMS

Moving wire IRMS is useful for analyzing carbon-13 ratios of compounds in a solution, such as after purification by liquid chromatography. The solution (or outflow from the chromatography) is dried onto a nickel or stainless steel wire. After the residue is deposited on the wire, it enters a furnace where the sample is converted to CO₂ and water by combustion. The gas stream finally enters a capillary, is dried, ionized, and analyzed. This process allows a mixture of compounds to be purified and analyzed continuously, which can decrease the analysis time by a factor of four. Moving wire IRMS is quite sensitive, and samples containing as little as 1 nanomole of carbon can yield precise (within 1‰) results.

Public awareness of science

From Wikipedia, the free encyclopedia

Public awareness of science (PAwS) is everything relating to the awareness, attitudes, behaviors, opinions, and activities that comprise the relations between the general public or lay society as a whole to scientific knowledge and organization. This concept is also known as public understanding of science (PUS), or more recently, public engagement with science and technology (PEST). It is a comparatively new approach to the task of exploring the multitude of relations and linkages science, technology, and innovation have among the general public. While early work in the discipline focused on increasing or augmenting the public's knowledge of scientific topics, in line with the information deficit model of science communication, the deficit model has largely been abandoned by science communication researchers. Instead, there is an increasing emphasis on understanding how the public chooses to use scientific knowledge and on the development of interfaces to mediate between expert and lay understandings of an issue. Newer frameworks of communicating science include the dialogue and the participation models. The dialogue model aims to create spaces for conversations between scientists and non-scientists to occur while the participation model aims to include non-scientists in the process of science.

Major themes

Photo taken during a Citizen Science Bioblitz

The area integrates a series of fields and themes such as:

• Citizen science
• Consumer education
• Fixed and mobile science exhibits
• Media and science (medialisation of science)
• Public controversies over science and technology
• Public tours of research and development (R&D) parks, manufacturing companies, etc.
• Science and art
• Science communication in the mass media, Internet, radio, films and television programs
• Science education for adults
• Science fairs in schools and social groups
• Science festivals
• Science in popular culture
• Science in text books and classrooms
• Science museums, aquaria, planetaria, zoological parks, botanical gardens, etc.
• Science social movements

Important lines of research are how to raise public awareness and public understanding of science and technology. Also, learning how the public feels and knows about science generally as well as individual subjects, such as genetic engineering, or bioethics. Research by Matthew Nisbet highlights several challenges in science communication, including the paradox that scientific success can create either trust or distrust in experts in different populations and that attitudes of trust are shaped by mostly socioeconomic rather than religious or ideological differences. A 2020 survey by the Pew Research Center found varying levels of trust in science by country, political leanings, and other factors.

The Bodmer report

The publication of the Royal Society's' report The Public Understanding of Science (or Bodmer Report) in 1985 is widely held to be the birth of the Public Understanding of Science movement in Britain. The report led to the foundation of the Committee on the Public Understanding of Science and a cultural change in the attitude of scientists to outreach activities.

Models of engagement

The Contextualist Model

In the 1990s, a new perspective emerged in the field with the classic study of Cumbrian Sheep Farmers' interaction with the Nuclear scientists in England. Brian Wynne demonstrated how the experts were ignorant or disinterested in taking into account the lay knowledge of the sheep farmers while conducting field experiments on the impact of the Chernobyl nuclear fallout on the sheep in the region. Because of this shortcoming from the side of the scientists, local farmers lost their trust in them. The experts were unaware of the local environmental conditions and the behaviour of sheep and this has eventually led to the failure of their experimental models. Following this study, scholars have studies similar micro-sociological contexts of expert-lay interaction and proposed that the context of knowledge communication is important to understand public engagement with science. Instead of large scale public opinion surveys, researchers proposed studies informed by sociology of scientific knowledge (SSK). The contextualist model focuses on the social impediments in the bidirectional flow of scientific knowledge between experts and laypersons/communities.

Deliberative Model

Scholars like Sheila Jasanoff have advanced the debate around public engagement with science by leveraging the theory of deliberative democracy to analyze the public deliberation of and participation in science through various institutional forms. Proponents of greater public deliberation argue it is a basic condition for decision making in democratic societies, even on science and technology issues. There are also attempts to develop more inclusive participatory models of technological governance in the form of consensus conferences, citizen juries, extended peer reviews, and deliberative mapping.

Civic Science Model

Some scholars have identified a new era of "post-normal science" (PNS) in which many scientific discoveries carry high stakes if risks are estimated incorrectly within a broader social context that has a high degree of uncertainty. This PNS era requires a new approach to public engagement efforts and requires a reevaluation of the underlying assumptions of "public engagement", especially with emerging science and technology issues, like CRISPR gene editing, that have the potential to become "wicked problems". These "wicked" issues often require regulatory and policy decisions that have no single correct solution and often involve numerous interest groups – none of whom are clearly positioned to decide and resolve the problem. Policy and regulatory decisions around these scientific issues are inherently political and must balance trade-offs between the scientific research, perceptions of risk, societal needs, and ethical values. While scientists can provide factual answers to research questions and mathematical estimates of risk, many considerations surrounding these wicked science and technology issues have no factual answer. The unidirectional deficit model of simply educating the public on theses issues is insufficient to address these complex questions, and some scholars have proposed scientists adopt a culture of civic science: "broad public engagement with issues that arise at the many intersections between science and society." An emphasis is placed on developing an iterative engagement model that actively seeks to incorporate groups who stand to be adversely effected by a new technology and conducting this engagement away from universities so that it can be done on the public's terms with the public's terms. Other scholars have emphasized that this model of public engagement requires that the public be able to influence science, not merely be engaged by it, up to the point of being able to say "no" to research that does not align with the broader public's values. Under the civic science model, there are five key lessons for scientists committed to public engagement:

1. Establish why you want to engage with the public and clearly identify your goals.
2. Seek out and engage with a broad, diverse range of groups and perspectives and center engagement on listening to these groups.
3. Work cooperatively with groups to establish common definitions to avoid the perception that researchers are being disingenuous by relying on semantic differences between expert and lay interpretations of vocabulary to ensure the public "supports" their position.
4. Working to tilt public debates in favor of the priorities and values of researchers will not lead to consistent "best" decisions because wicked science and technology problems will have different considerations and perspectives depending on the application and cultural context.
5. Meaningfully engage as early as possible; engagement must begin early enough in the research process that the public's views can shape both the research and implementation of findings

Measuring public understanding of science

Social scientists use various metrics to measure public understanding of science, including:

1. Factual knowledge

The Key assumptions is that the more individual pieces of information a person is able to retrieve, the more that person is considered to have learned.

Examples of measurement

• Recognition: Answering a specific question by selecting the correct answer out a list
• Cued Recall: Answering a specific question without a list of choices
• Free Recall: After exposure to information, the study participant produces a list of as much of the information as they can remember

2. Self-reported knowledge, perceived knowledge, or perceived familiarity

The key assumption is that emphasizes the value of knowledge of one's knowledge.

Examples of measurement

• Scaled survey responses to questions such as, "How well informed you would say you are about this topic?", this can be also used to assess perceived knowledge before and after events

3. Structural knowledge

The nature of connections among different pieces of information in memory. The key assumption is that the use of elaboration increases the likelihood of remembering information.

Examples of measurement

• Asking study participants to assess relationships among concepts. For example, participants free recall concepts onto the first row and column of a matrix, then indicate whether the concepts are related to each other by placing an "X" in the cell if they are not. Participants then rank the remaining open cells by their relatedness from 1 (only very weakly) to 7 (very strongly related)
• Study participants answer questions designed to measure elaboration involved in a task, such as, "I tried to relate the ideas I read about to my own past experiences"

Mixed use of the three measures

• While some studies purport that factual and perceived knowledge can be viewed as the same construct, a 2012 study investigating public knowledge of nanotechnology supports separating their use in communications research, as they "do not reflect the same underlying knowledge structures." Correlations between them were found to be low and they were not predicted by the same factors. For example different types of science media use, television versus online, predicted different constructs
• Factual knowledge has been shown to be empirically distinct from structural knowledge

Project examples

Government and private-led campaigns and events, such as Dana Foundation's "Brain Awareness Week", are becoming a strong focus of programmes which try to promote public awareness of science.

The UK PAWS Foundation dramatically went as far as establishing a Drama Fund with the BBC in 1994. The purpose was to encourage and support the creation of new drama for television, drawing on the world of science and technology.

The Vega Science Trust was set up in 1994 to promote science through the media of television and the internet with the aim of giving scientists a platform from which to communicate to the general public.

The Simonyi Professorship for the Public Understanding of Science chair at The University of Oxford was established in 1995 for the ethologist Richard Dawkins by an endowment from Charles Simonyi. Mathematician Marcus du Sautoy has held the chair since Dawkins' retirement in 2008. Similar professorships have since been created at other British universities. Professorships in the field have been held by well-known academics including Richard Fortey and Kathy Sykes at the University of Bristol, Brian Cox at Manchester University, Tanya Byron at Edge Hill University, Jim Al-Khalili at the University of Surrey, and Alice Roberts at the University of Birmingham.

Public participation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Public_participation 

Public participation, also known as citizen participation or patient and public involvement, is the inclusion of the public in the activities of any organization or project. Public participation is similar to but more inclusive than stakeholder engagement.

Generally public participation seeks and facilitates the involvement of those potentially affected by or interested in a decision. This can be in relation to individuals, governments, institutions, companies or any other entities that affect public interests. The principle of public participation holds that those who are affected by a decision have a right to be involved in the decision-making process. Public participation implies that the public's contribution will influence the decision. Public participation may be regarded as a form of empowerment and as vital part of democratic governance. In the context of knowledge management the establishment of ongoing participatory processes is seen by some in the facilitator of collective intelligence and inclusiveness, shaped by the desire for the participation of the whole community or society.

Public participation is part of "people centred" or "human centric" principles, which have emerged in Western culture over the last thirty years, and has had some bearings of education, business, public policy and international relief and development programs. Public participation is advanced by the humanist movements. Public participation may be advanced as part of a "people first" paradigm shift. In this respect public participation may challenge the concept that "big is better" and the logic of centralized hierarchies, advancing alternative concepts of "more heads are better than one" and arguing that public participation can sustain productive and durable change.

Some legal and other frameworks have developed a human rights approach to public participation. For example, the right to public participation in economic and human development was enshrined in the 1990 African Charter for Popular Participation in Development and Transformation. Similarly major environmental and sustainability mechanisms have enshrined a right to public participation, such as the Rio Declaration.

By field

Art

See also: Participatory art, Participatory cinema, and Participatory theatre

Budgeting

Main article: Participatory budgeting

Participatory budgeting is a process of democratic deliberation and decision-making, in which ordinary city residents decide how to allocate part of a municipal or public budget. Participatory budgeting is usually characterized by several basic design features: identification of spending priorities by community members, election of budget delegates to represent different communities, facilitation and technical assistance by public employees, local and higher level assemblies to deliberate and vote on spending priorities, and the implementation of local direct-impact community projects. Participatory budgeting may be used by towns and cities around the world, and has been widely publicised in Porto Alegre, Brazil, were the first full participatory budgeting process was developed starting in 1989.

Development

Main articles: Participatory development, Participatory planning, and Participatory rural appraisal

In economic development theory, there is a school of participatory development. The desire to increase public participation in humanitarian aid and development has led to the establishment of a numerous context-specific, formal methodologies, matrices, pedagogies and ad hoc approaches. These include conscientization and praxis; Participatory action research (PAR), rapid rural appraisal (RRA) and participatory rural appraisal (PRA); appreciation influence control analysis (AIC); "open space" approaches; Objectives Oriented Project Planning (ZOPP); vulnerability analysis and capacity analysis.

Environment and sustainable development

Further information: right to public participation

In recent years public participation has become to be seen as a vital part of addressing environmental problems and bringing about sustainable development. In this context the limits of solely relying on technocratic bureaucratic monopoly of decision making, and it is argued that public participation allows governments to adopt policies and enact laws that are relevant to communities and take into account their needs.

Public participation is recognised as an environmental principle, see Environmental Principles and Policies, and has been enshrined in the Rio Declaration.

Heritage

Around the globe experts work closely with local communities. Local communities are crucial stakeholders for heritage.

Consultation with local communities is acknowledged formally in cultural management processes. They are necessary for defining the significance of a cultural place/site, otherwise you run the risk to oversee many values, focusing on “experts’” views. This has been the case in heritage management until the end of the 20th century. A paradigm shift started with the Burra Charter by ICOMOS Australia in 1979 and was later developed by the work of the GCI around 2000. Today, so called “value-led conservation” is at the base of heritage management for WH sites: establishing stakeholders and associated values is a fundamental step in creating a Management Plan for such sites.

The concept of stakeholders has widened to include local communities.

Various levels of local government, research institutions, enterprises, charitable organisations, and communities are all important parties. Activities such as knowledge exchange, education, consultation, exhibitions, academic events, publicity campaigns, among others are all effective means for local participation.

For instance, local charities in Homs, Syria have been undertaking several projects with local communities to protect their heritage.

A conservation programme in Dangeil, Sudan, has used social and economic relationship with the community to make the project sustainable over the long term.

In Australia, Indigenous communities increasingly have stewardship of conservation and management programs to care for, monitor and maintain their cultural heritage places and landscapes, particularly those containing rock art.

Media

Main articles: Participatory media and Participatory video

Public policy

See also: Participatory democracy

In some countries public participation has become a central principle of public policy making.Within democratic bodies, policies are rendered legitimate when citizens have the opportunity to influence the politicians and parties involved. In the UK and Canada it has been observed that all levels of government have started to build citizen and stakeholder engagement into their policy-making processes. Situating citizens as active actors in policy-making can work to offset government failures by allowing for reform that will better emulate the needs of citizens. By incorporating citizens, policies will reflect everyday needs and realities, and not the machinations of politicians and political parties. This may involve large-scale consultations, focus group research, online discussion forums, or deliberative citizens' juries. There are many different public participation mechanisms, although these often share common features (for a list over 100, and a typology of mechanisms, see Rowe and Frewer, 2005).

Public participation is viewed as a tool, intended to inform planning, organising or funding of activities. Public participation may also be used to measure attainable objectives, evaluate impact, and identify lessons for future practice. In Brazil's housing councils, mandated in 2005, citizen engagement in policy drafting increased effectiveness and responsiveness of government public service delivery. All modern constitutions and fundamental laws contain and declare the concept and principle of popular sovereignty, which essentially means that the people are the ultimate source of public power or government authority. The concept of popular sovereignty holds simply that in a society organized for political action, the will of the people as a whole is the only right standard of political action. It can be regarded as an important element in the system of the checks and balances, and representative democracy. Therefore, the people are implicitly entitled even to directly participate in the process of public policy and law making.

In the United States public participation in administrative rulemaking refers to the process by which proposed rules are subject to public comment for a specified period of time. Public participation is typically mandatory for rules promulgated by executive agencies of the US government. Statutes or agency policies may mandate public hearings during this period.

Science

Main articles: Citizen science, Participatory monitoring, and Participatory action research

Other

• Participatory culture
• Participatory design
• Participatory economics
• Participatory ergonomics
• Participatory evaluation
• Participatory GIS
• Public participation geographic information system
• Participatory justice
• Participatory management
• Participatory modeling
• Participatory 3D modelling
• Participatory poverty assessment
• Participatory technology development
• Participatory organization
• Participatory sensing
• Public participation in patent examination

Public trust

In recent years loss of public trust in authorities and politicians has become a widespread concern in many democratic societies.The relationship between citizens and local governments has weakened over the past two decades due to shortcomings in public service delivery. Public participation is a regarded as one potential solution to the crisis in public trust and governance, particularly in the UK, Europe, and other democracies. Establishing direct citizen participation can increase governance's effectiveness, legitimacy, and social justice. The idea is that public should be involved more fully in the policy process in that authorities seek public views and participation, instead of treating the public as simply passive recipients of policy decisions.

The underlying assumption by political theorists, social commentators, and even politicians is that public participation increase public trust in authorities, improving citizen political efficacy, enhancing democratic ideals and even improving the quality of policy decisions. However, the assumed benefits of public participation in restoring public trust are yet to be confirmed. Citizen participation is only sustained if citizens support it and if their involvement is actively supported by the governing body.

Accountability and transparency

Main article: Radical transparency

Public participation may also be viewed as accountability enhancing. The argument being that public participation can be a means for the participating communities to hold public authorities accountable for implementation. In the United Kingdom citizens are used to ensure the fair and humane detention of prisoners. Volunteers comprise the Independent Monitoring Board that reports on the fair and humane detention of prisoners and detainees.

Many community organizations are composed of affluent middle-class citizens with the privilege and the time to participate. It is well documented that low-income citizens face difficulty organizing themselves and engaging in public issues. Obstacles like: finding affordable childcare, getting time off of work, and access to education in public matters exacerbate the lack of participation by low-income citizens. To foster greater participation of all social groups, vanguard privileged classes work to bring in low-income citizens through collaboration. The organizations establish an incentive for participation through accessible language and friendly environments. This allows for an atmosphere of consensus between middle and lower-income citizens.

Critical interpretations

The concept and practice of public participation has been critiqued, often using Foucauldian analytical frameworks. Such accounts detail how participation can be a method of capturing community activity into regimes of power and control although it has also been noted that capture and empowerment can co-exist.

In 1990 practitioners established the International Association for Public Practitioners in order to respond to the increasing interest in the practice, and in turn established the International Association for Public Participation (IAP2). The practice is well established globally and the International Association of Public Participation now has affiliate organizations across the globe.

Public participation in environmental governance

With growing complexities of the environmental issues, public participation has come to the fore in academic analysis concerning the contemporary debates about environmental governance.

There have emerged a number of arguments in favor of a more participatory approach, which stress that public participation is a crucial element in environmental governance that contributes to better decision making. It is recognised that environmental problems cannot be solved by government alone. Participation in environmental decision-making effectively links the public to environmental governance. By involving the public, who are at the root of both causes and solutions of environmental problems, in environmental discussions, transparency and accountability are more likely to be achieved, thus secures the democratic legitimacy of decision-making that good environmental governance depends on. Arguably, a strong public participation in environmental governance could increase the commitment among stockholders, which strengthens the compliance and enforcement of environmental laws. GIS can provide a valuable tool for such work (see GIS and environmental governance). In addition, some opponents argue that the right to participate in environmental decision-making is a procedural right that "can be seen as part of the fundamental right to environmental protection". From this ethical perspective, environmental governance is expected to operate within a framework coinciding the "constitutional principle of fairness (inclusive of equality)", which inevitably requires the fulfillment of "environmental rights" and ultimately calls for the engagement of public. Further, in the context of considerable scientific uncertainties surrounding environmental issues, public participation helps to counter such uncertainties and bridges the gap between scientifically-defined environmental problems and the experiences and values of stakeholders. Through joint effort of the government and scientists in collaboration with the public, better governance of environment is expected to be achieved by making the most appropriate decision possible.

Although broad agreements exist, the notion of public participation in environmental decision-making has been subject to a sustained critique concerning the real outcome of participatory environmental governance. Critics argue that public participation tends to focus on reaching a consensus between actors who share the same values and seek the same outcomes. However, the uncertain nature of many of the environmental issues would undermine the validity of public participation, given that in many cases the actors come to the table of discussion hold very different perceptions of the problem and solution which are unlikely to be welded into a consensus due to the incommensurability of different positions. This may run the risk of expert bias, which generates further exclusion as those who are antagonistic to the consensus would be marginalised in the environmental decision-making process, which violates the assumed advantage of participatory approach to produce democratic environmental decisions. This raises the further question of whether consensus should be the measure of a successful outcome of participation. As Davies suggests, participative democracy could not guarantee the substantive environmental benefits 'if there are competing views of what the environment should be like and what it is valuable for'. Consequently, who should be involved at what points in the process of environmental decision-making and what is the goal of this kind of participation become central to the debates on public participation as a key issue in environmental governance.

Citizen science

Main article: Citizen science

Citizen science is a coined term commonly used to describe the participation of non-scientists in scientific research.

Greater inclusion of non-professional scientists in policy research is important. It is academia's responsibly to facilitate the "democratization of policy research". This has several benefits: having citizens involved in not just the contribution of data, but also the framing and development of research itself.

The key to success in applying citizen science to policy development is data which is "suitable, robust, and of a known quality for evidence-based policy making". Barriers to applying citizen science to policy development include a lack of suitability between the data collected and the policy in question and skepticism regarding the data collected by non-experts.

Right to public participation

The right to public participation is a human right enshrined by some international and national legal systems that protects public participation in certain decision making processes. Article 21 of the Universal Declaration of Human Rights states the right of every person to participate in the affairs of his country, either directly or by selecting representatives. Likewise, the right to political participation means the right under which the ruling authority is committed to providing rights to citizens, including the right to nominate and elect representatives, to hold public office in accordance with the principle of equal opportunities, to participate in private and public meetings, and the right to form and join political parties. Articles 20 and 27 of the International Covenant on Civil and Political Rights make a similar declaration about the right to participate in the management of public affairs.

In some jurisdictions, the right to public participation is enshrined by law. The right to public participation may also be conceived of as human right, or as manifestation of the right to freedom of association and freedom of assembly. As such the Netherlands, Germany, Denmark and Sweden, have public participation and freedom of information provisions in their legal systems since before the Middle Ages. Democracy and public participation are closely connected democratic societies have incorporated public participation rights into their laws for centuries. For example, in the US the right to petition has been part of the First Amendment of the US constitution since 1791. More recently, since the 1970s in New Zealand numerous laws (e.g.: health, local government, environmental management) require government officials to "consult" those affected by a matter and take their views into consideration when making decisions.

Effective public participation depends on the public having accessing to accurate and comprehensive information. Hence laws regarding public participation often deal with the issue of the right to know, access of information and freedom of information. The right to participation may also be advanced in the context of equality and group rights, meant to ensure equal and full participation of a designated group in society. For example, in the context of disabled people.