Indigenous Carbon Research Articles

Assessing the survival of carbonaceous chondrites impacting the lunar surface as a potential resource

The Moon offers a wide range of potential resources that may help sustain a future human presence, but it lacks indigenous carbon (C) and nitrogen (N). Fortunately, these elements will have been delivered to the Moon's surface by carbonaceous chondrite (CC) asteroid impactors. Here, we employ numerical modelling to assess the extent to which these materials may have sufficiently survived impact with the lunar surface to be viable sources of raw materials for future exploration. We modelled the impact of a 1 km diameter CC-like asteroid, considering impact velocities between 5 and 15 km s−1, and impact angles between 15 and 60° to the horizontal. The most favourable conditions for the survival of C-rich, and especially N-rich materials, are those with the lowest impact velocities (≤10 km s−1) and impact angles (≤15°). Impacts with velocities >10 km s−1 and angles >30° were found not to yield any significant amount of surviving solid material, where bulk survival is defined as material experiencing temperatures less than the impactor material's estimated melting temperature (∼2100 K, based on a commonly adopted Equation of State for serpentine). Importantly, oblique and low velocity impacts result in concentrations of unmelted projectile material down-range from the impact site. For the canonical 1 km-diameter CC impactor considered here, with an impact angle ≤15° and velocity ≤10 km s−1, this results in ∼109–1010 kg of C and ∼108–109 kg of N being deposited a few tens of km down-range from the impact crater, where it might be accessible as a potential resource. Such low-velocity and oblique impacts have a low probability - we estimate that only ∼5 such impacts may have occurred on the Moon in the last 3 billion years (the number of impacts of smaller impactors will have been higher, but they will concentrate lower masses of potential resources). As the estimated C and N concentrations from such impacts greatly exceed those expected for ices within individual permanently shadowed polar craters, searching for these rare impact sites may be worthwhile from a resource perspective. We briefly discuss how this might be achieved by means of orbital infra-red remote-sensing measurements.

Facile, Label‐Free, Non‐Enzymatic Electrochemical Nanobiosensor Platform as a Significant Step towards Continuous Glucose Monitoring

AbstractThe paper proposes a low‐cost, facile methodology to develop a non‐enzymatic glucose sensor by utilizing the inherent affinity of Boronic Acid moieties towards glucose along with the enhanced electrochemical activity of gold nanoparticles (AuNPs). The AuNPs were electrochemically deposited onto the surface of the indigenous carbon paste wire electrodes to enhance both the active area and the kinetics of the electrodes, thereby increasing the sensitivity of the detection. The sensitivity and limit of detection of the proposed biosensor, as established using Differential Pulse Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS), was found to be 0.0254 [(μA/(mg/dL))/mm2] and 0.085 mg/dL, respectively. The interference and selectivity studies with the most common interference species, such as acrylic acid, uric acid, and salicylic acid, plasma, NaCl, and KCl, carried out resulted in negligible interference. The bio‐electrodes also showed excellent stability and shelf‐life, making them a potential candidate for non‐enzymatic glucose monitoring.

KAGUYA observation of global emissions of indigenous carbon ions from the Moon.

Carbon is a volatile element that has a considerable influence on the formation and evolution of planetary bodies, although it was previously believed to be depleted in the Moon. We present observations by the lunar orbiter KAGUYA of carbon ions emitted from the Moon. These emissions were distributed over almost the total lunar surface, but amounts were differed with respect to lunar geographical areas. The estimated emission fluxes to space were ~5.0 × 104 per square centimeter per second, which is greater than possible ongoing supplies from the solar wind and micrometeoroids. Our estimates demonstrate that indigenous carbon exists over the entire Moon, supporting the hypothesis of a carbon-containing Moon, where the carbon was embedded at its formation and/or was transported billions of years ago.

Carbonaceous matter in the Sariçiçek meteorite

AbstractAs of today, the Sariçiçek (SC) meteorite is the newest howardite and the only confirmed fall among the 17 known howardites. In this study, we present isotopic, infrared, and Raman data on three distinct pieces of the SC meteorite. Our oxygen isotopic measurements show that Δ17O values of the pieces are close to each other, and are in good agreement with other howardites, eucrites, and diogenites. The carbon isotopic measurements, which were conducted by combusting terrestrial contamination selectively at temperatures lower than 500–600 °C, show the presence of indigenous carbon in the SC specimens. The matrix of these specimens, investigated via infrared microspectroscopy, appears to be dominated by clinopyroxene/orthopyroxene, forsterite, and fayalite, with minor contributions from ilmenite, plagioclase, and enstatite. Carbon‐rich regions were mapped and studied via Raman imaging microspectroscopy, which reveals that both amorphous and graphitic carbon exist in these samples. Synchrotron‐based infrared microspectroscopy data show the presence of very little aliphatic and aromatic hydrocarbons. The SC meteorite is suggested to be originating from the Antonia impact crater in the Rheasilvia impact basin on 4 Vesta (Unsalan et al. 2019). If this is in fact the case, then the carbon phases present in the SC samples might provide clues regarding the impactor material (e.g., carbonaceous chondrites).

Stimulation of Indigenous Carbonate Precipitating Bacteria for Ground Improvement

Calcite minerals are precipitated in soil through biomineralisation which can be either organic or inorganic in nature. Biomineralisation can be employed to improve ground conditions in its natural state. Usually, studies of applied biomineralisation are highly interdisciplinary involving expertise from engineers, chemists and microbiologists. In this paper, we study the potential of biomineralisation from indigenous bacteria present in soil. The soil samples were collected from a high permeable zone and the bacteria that inhabit the soil were stimulated at a temperature of 15°C. A cementation solution consisting of 500mM calcium chloride, urea and nutrient broth at a pH of 7.5 was added to the soil samples. Inorganic precipitation was found to be dominant and was more efficient when compared to organic precipitation. Carbonate precipitation data indicated that inorganic precipitation were 1.37 times better at carbonate formation in comparison to organic precipitation. Scanning Electron Microscopy analysis identified cementation bonds formed between soil particles. It was deducted that organic precipitation is dependent on temperature, and may take an extended time at such low temperature. The preliminary data presented in this paper suggests that the implementation of biomineralisation with in-situ microbes is promising but requires further laboratory and field investigation before being considered for engineering application.

Cultures of Carbon and the Logic of Care: The Possibilities for Carbon Enrichment and Its Cultural Signature

Climate change and the associated need to decarbonize pose not just risks to cultures but potential opportunities for cultural experimentation, renewal, and economic dynamism. An Australian case of carbon mitigation through carbon farming represents a discursive tool with which indigenous groups are seeking to leverage a very distinct conceptualization of payment for ecosystem services, one that values the labor and reciprocal relationships and logic of care required to abate or sequester carbon. Inscribed with an inalienable ancestral cultural signature, the indigenous produced carbon offsets being promoted by indigenous carbon market participants represent more than a mere carbon reduction; they initiate processes of potentially enduring exchange and engagement. This carbon signature works to enrich carbon as well as embed peoples' relations with it, with each other, and with the places from which the offset is generated. Contributing to emergent research into cultures of carbon, it is our conjecture that valorizing these relations in ethical exchanges is a potentially productive way of financing alternative approaches to environmental stewardship. The insights signal potential prospects for other marginalized cultures to appropriate, repurpose, and benefit from mainstream decarbonization strategies and participate in climate governance.

Loss and gain of carbon during char degradation

We report results of a study examining controls on the degradation of chars produced at 300, 400 and 500 °C from radiocarbon-free wood, deployed for three years in a humid tropical rainforest soil in north Queensland, Australia. The chars were subjected to four treatments (i) no litter (ii) covered by leaf litter, (iii) covered by limestone chips to alter local pH, and (iv) covered by limestone chips mixed with leaf litter. Radiocarbon, stable isotope and proximate analyses indicate significant ingress of exogenous (environmental) carbon and mineral material, strongly correlated with loss of indigenous (char) carbon from the samples. While indigenous carbon losses over three years were generally <8% for the char produced at 500 °C char under any treatment, chars formed at lower temperatures lost 5–22% of indigenous carbon accompanied by ingress of up to 7.5% modern exogenous carbon. The data provide clear evidence of a direct link between the ingress of exogenous carbon, likely at least partly due to microbial colonization, and the extent of char decomposition. Failure to account for the ingress of exogenous carbon will lead to a significant under-estimate of the rate of char degradation.

Indigenous benefits and carbon offset schemes: An Australian case study

The nexus between human rights and the environment is a key issue for climate policymakers and Indigenous peoples around the world. We combine national spatial, social and biological datasets from Australia to describe where Indigenous carbon projects are happening, why Indigenous people are participating, and how effective these schemes might be at marrying Indigenous co-benefit, biodiversity and carbon emission mitigation goals. Our study shows that many Indigenous people engage in carbon offset schemes as part of their broader cultural responsibility for landscapes, and that they seek to grow the relationship between social and ecological benefits. It also highlights the challenges associated with designing carbon offset schemes that address the impacts of climate change and respond to Indigenous peoples’ world views about what is required to sustain cultural-social-ecological systems.

Experimental investigation on the role of indigenous carbon nanotube emulsified fuel in a four-stroke diesel engine

Effect of carbon nanotube emulsified fuel in a single-cylinder water-cooled four-stroke diesel engine was studied. CNT were produced by indigenous flame synthesis method. Water diesel emulsion was prepared in the proportion of 78% diesel, 20% water, and 2% surfactant with a HLB balance of 8. Tween 80 and Span 80 were used as surfactants. CNT in the mass fraction of 50 ppm, 100 ppm, and 150 ppm were blended in the water–diesel emulsion. CNT were dispersed in the water for 35 min with the help of ultrasonicator set at frequency of 40 kHz and ultrasonic power of 120 W, subsequently added in diesel, surfactant mixture to produce CNT blended water diesel emulsion. A mechanical homogenizer was used to produce emulsion at the speed of 3000 r/min for 25 min. The experimental investigation was carried out using single-cylinder diesel engine coupled with eddy current dynamometer and equipped with data acquisition system. An AVL Di-gas analyzer and AVL smoke opacity meter has been used to measure the exhaust emissions. Experiment was conducted at a constant speed of 1500 r/min from no load to full load for all fuel specimens. A comparative study involving combustion characteristics, brake specific fuel consumption, brake thermal efficiency, NOx, CO, HC, CO2 were recorded for pure diesel, water diesel emulsion and CNT-emulsified fuel. The results have shown significant improvement in engine performance, combustions attributes and reduction in emissions using CNT-emulsified fuel.

The use of chlorate, nitrate, and perchlorate to promote crude oil mineralization in salt marsh sediments.

Due to the high volume of crude oil released by the Deepwater Horizon oil spill, the salt marshes along the gulf coast were contaminated with crude oil. Biodegradation of crude oil in salt marshes is primarily limited by oxygen availability due to the high organic carbon content of the soil, high flux rate of S(2-), and saturated conditions. Chlorate, nitrate, and perchlorate were evaluated for use as electron acceptors in comparison to oxygen by comparing oil transformation and mineralization in mesocosms consisting of oiled salt marsh sediment from an area impacted by the BP Horizon oil spill. Mineralization rates were determined by measuring CO2 production and δ (13)C of the produced CO2 and compared to transformation evaluated by measuring the alkane/hopane ratios over a 4-month period. Total alkane/hopane ratios decreased (~55-70 %) for all treatments in the following relative order: aerated ≈ chlorate > nitrate > perchlorate. Total CO2 produced was similar between treatments ranging from 550-700 mg CO2-C. The δ (13)C-CO2 values generally ranged between the indigenous carbon and oil values (-17 and -27‰, respectively). Oil mineralization was greatest for the aerated treatments and least for the perchlorate amended. Our results indicate that chlorate has a similar potential as oxygen to support oil mineralization in contaminated salt marshes, but nitrate and perchlorate were less effective. The use of chlorate as a means to promote oil mineralization in situ may be a promising means to remediate contaminated salt marshes while preventing unwanted secondary impacts related to nutrient management as in the case of nitrate amendments.

Perchlorate‐induced combustion of organic matter with variable molecular weights: Implications for Mars missions

AbstractInstruments on the Viking landers and Curiosity rover analyzed samples of Mars and detected carbon dioxide and organic compounds of uncertain origin. Mineral‐assisted reactions are leading to uncertainty, particularly those involving perchlorate minerals which thermally decompose to produce chlorine and oxygen which can then react with organic matter to generate organochlorine compounds and carbon dioxide. Although generally considered a problem for interpretation, the release profiles of generated gases can indicate the type of organic matter present. We have performed a set of experiments with perchlorate and organic matter of variable molecular weights. Results indicate that organic susceptibility to thermal degradation and mineral‐assisted reactions is related to molecular weight. Low molecular weight organic matter reacts at lower temperatures than its high molecular weight counterparts. The natural occurrence and association of organic matter with differing molecular weights helps to discriminate between contamination (usually low molecular weight organic matter only) and indigenous carbon (commonly low and high molecular weight organic matter together). Our results can be used to provide insights into data returning from Mars.

Two refractory Wild 2 terminal particles from a carrot‐shaped track characterized combining MIR/FIR/Raman microspectroscopy and FE‐SEM/EDS analyses

AbstractWe present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter‐family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE‐SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca‐free and low‐Ca, Mg‐rich, Mg,Fe‐olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni‐free and low‐Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE‐SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE‐SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.

The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments – ABOX, ABA and hypy

Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ∼1 pMC after one year (apparent age of ∼40,000 yrs BP) and ∼5 pMC after three years (apparent age of ∼25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ∼350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique.

Australia's Indigenous Carbon Economy: A National Snapshot

AbstractMany Indigenous communities in Australia are well situated to provide greenhouse gas abatement and carbon sequestration benefits, but little is known about the factors affecting the capability of Australia's Indigenous organisations to participate in climate change mitigation strategies. This paper provides a ‘snapshot’ summary of certain aspects of Australia's Indigenous organisations' participation in carbon offset schemes. The snapshot provides insight into the degree to which Indigenous organisations are aware of carbon market opportunities in Australia, the level that these Indigenous organisations participate in or engage with carbon‐based economic enterprises, and the key pathways through which Indigenous carbon market opportunities are pursued. Analysis of data collected from a national survey conducted between 2011 and 2012 show that most obstacles to Indigenous participation in carbon offset schemes relate to land tenure arrangements; geographic and biophysical factors; low levels of requisite technical, human and financial resources; and appropriate recognition of Indigenous knowledge and cultural responsibilities. The snapshot also highlights the value of supporting regionally specific capacity‐building strategies to enable Indigenous people to participate in emerging carbon offset activities and the generation of associated ecosystem services. Cultural, socio‐economic or demographic factors that are also likely to influence the ability of many Indigenous communities to participate in carbon market opportunities are identified as important areas for further research.

Stable isotope analysis of carbon and nitrogen in angrites

AbstractAngrites are a small group of ancient basaltic achondrites, notable for their unusual chemistry and extreme volatile depletion. No comprehensive study of indigenous light elements currently exists for the group. Measurement of the abundances and isotopic composition of carbon and nitrogen could provide information pertaining to the evolution of the angrite parent body. Bulk‐sample stepped combustion analyses of five angrites and a glass separate from D'Orbigny were combined with earlier data and acid dissolution experiments of carbonates found in D'Orbigny to compile an inventory of indigenous carbon and nitrogen. Indigenous carbon combusted between 700 °C and 1200 °C, with abundances of 10–140 ppm and a mass‐weighted δ13C of −25 to −20‰ with the exception of D'Orbigny (δ13C approximately −5‰). Nitrogen was released at 850–1200 ºC, 1–20 ppm with a δ15N −3‰ to +4‰; again, D'Orbigny (δ15N approximately +20 to +25‰) was an exception. We interpret these components as largely indigenous and decoupled; the carbon in graphitic or amorphous form, while the nitrogen is present as a dissolved component in the silicates. No relationship with the textural sub‐classification of angrites is apparent. We suggest that the angrite parent body contains a reservoir of reduced carbon and thus may have undergone a change in redox conditions, although the timing and mechanism for this remain unclear.

Effect of corn cobs concentration on xylanase biosynthesis by Aspergillus niger

Corn cobs, an indigenous carbon source, were tested as substrate by Aspergillus niger for optimum synthesis of xylanase using the submerged fermentation technique. The trials for xylanase production were conducted at three concentration levels (2.5, 3.0 and 3.5%) of corn cobs, four different fermentation temperatures (25.0, 27.5, 30.0 and 32.5°C) and four various initial pH levels (5.0, 5.5, 6.0 and 6.5) of the culture medium for a period of 96 h. It was deduced from the study that the organism exhibited maximum enzyme activity (60.03 ± 1.83) at 3.0% corn cobs concentration, followed by 52.03 ± 1.21 and 50.07 ± 2.14 at 2.5 and 3.5% concentration, respectively at 30°C and 5.5 pH after a period 72 h of incubation. The comparison of the effect of various pH levels of culture medium showed that pH 5.5 had enhanced role in xylanase synthesis, as compared to other pH levels investigated in the study. Time scale analysis also revealed that a fermentation period of 72 h was best suitable for obtaining maximum yields of xylanase. Moreover, a temperature of 30°C was found to be optimum for higher yields of xylanase exhibiting the mesophillic behavior of the organism.

A potentially new type of nonchondritic interplanetary dust particle with hematite, organic carbon, amorphous Na,Ca‐aluminosilicate, and FeO‐spheres

Abstract– We used a combination of different analytical techniques to study particle W7190‐D12 using microinfrared spectroscopy, micro‐Raman spectroscopy, and field emission scanning electron microscopy (FESEM) energy dispersive X‐ray spectroscopy (EDS). The particle consists mainly of hematite (α‐Fe2O3) with considerable variations in structural disorder. It further contains amorphous (Na,K)‐bearing Ca,Al‐silicate and organic carbon. Iron‐bearing spherules (&lt;150 nm in diameter) cover the surface of this particle. At local sites of structural disorder at the hematite surface, the hematite spheres were reduced to FeO in the presence of organic carbons forming FeO‐spheres. However, metallic Fe spheres cannot be excluded based on the available data. To the best of our knowledge, this particle is the first detection of such spherules at the surface of a stratospheric dust particle. Although there is no definitive evidence for an extraterrestrial origin of particle W7190‐D12, we suggest that it could be an IDP that had moved away from the asteroid‐forming region of the early solar system into the outer solar system of the accreting Kuiper Belt objects. After it was released from a Jupiter family comet, this particle became part of the zodiacal cloud. Atmospheric entry flash‐heating caused (1) the formation of microenvironments of reduced iron oxide when indigenous carbon materials reacted with hematite covering its surface resulting in the formation of FeO‐spheres and (2) Na‐loss from Na,Al‐plagioclase. The particle of this study, and other similar particles on this collector, may represent a potentially new type of nonchondritic IDPs associated with Jupiter family comets, although an origin in the asteroid belt cannot be ignored.

Addressing the Challenges of Ammonia Loss from Poultry Droppings through Indigenous Carbon Wastes

Laboratory experiment was conducted to screen the carbonaceous wastes suitable for making poultry droppings compost. Carbon-rich waste materials namely, coir pith, sawdust, paper wastes, leaf litter and paddy straw were evaluated for their efficacy in reducing the ammonia volatilization from poultry droppings. Among the carbon wastes tested, coir pith, saw dust and paddy straw were found to be efficient in reducing the ammonia loss by 31 to 48 per cent. In the compost mix, major nutrients like nitrogen, phosphorus and potassium were increased with the advancement of composting. The coir pith mixed poultry compost recorded high nitrogen (19.7 g kg -1 ) and potassium content (13.9 g kg -1 ), whereas, coir pith and rock phosphate (RP) mixed poultry compost recorded high phosphorus content (20.1 g kg -1 ). When poultry waste was composted without mixing any carbon wastes, it recorded high conductivity (EC) (3.63 dS m -1 ), whereas the poultry waste mixed with coir pith and paddy straw recorded low conductivity value. The carbon and C/N ratio of the compost got reduced with the advancement of composting. The cumulative loss of ammonia was more when poultry manure composted without carbon wastes (1125.8 mg kg -1 ). Mixing of poultry wastes with coir pith reduced the ammonia loss by 57.7 percent.

Column experiments to assess the effects of electron donors on the efficiency of in situ precipitation of Zn, Cd, Co and Ni in contaminated groundwater applying the biological sulfate removal technology

In a previous study, we explored the use of acetate, lactate, molasses, Hydrogen Release Compound (HRC, which is based on a biodegradable poly-lactate ester), methanol and ethanol as carbon source and electron donor to promote bacterial sulfate reduction in batch experiments, this with regards to applying an in situ metal precipitation (ISMP) process as a remediation tool to treat heavy metal contaminated groundwater at the site of a nonferrous metal work company. Based on the results of these batch tests, column experiments were conducted with lactate, molasses and HRCI as the next step in our preliminary study for a go-no go decision for dimensioning an on site application of the ISMP process that applies the activity of the endogenous population of sulfate-reducing bacteria (SRB). Special attention was given to the sustainability of the metal precipitation process under circumstances of changing chemical oxygen demand (COD) to [SO4(2-)] ratios or disrupted substrate supply. To optimize the ISMP process, an insight is needed in the composition and activity of the indigenous SRB community, as well as information on the way its composition and activity are affected by process conditions such as the added type of C-source/ electron donor, or the presence of other prokaryotes (e.g. fermenting bacteria, methane producing Archaea, acetogens). Therefore, the biological sulfate reduction process in the column experiments was evaluated by combining classical analytical methods [measuring heavy metal concentration, SO4(2-)-concentration, pH, dissolved organic carbon (DOC)] with molecular methods [denaturing gradient gel electrophoresis (DGGE) fingerprinting and phylogenetic sequence analysis] based on either the 16S rRNA-gene or the dsr (dissimilatory sulfite reductase) gene, the latter being a specific biomarker for SRB. All carbon sources tested promoted SRB activity, which resulted within 8 weeks in a drastic reduction of the sulfate and heavy metal contents in the column effluents. However, unexpected temporal decreases in the efficiency of the ISMP process, accompanied by the release of precipitated metals, were observed for most conditions tested. The most dramatic observation of the failing ISMP process was observed within 12 weeks for the molasses amended column. Subsequent lowering the COD/ SO4(2-) ratio from 1.9 to 0.4 did not alter the outcome of sulfate reduction and metal precipitation efficiency in this set-up. Remarkably, after 6 months of inactivity, bacterial sulfate reduction was recovered in the molasses set up when the original COD/ SO4(2-) ratio of 1.9 was applied again. Intentional disruption of the lactate and HRC supplies resulted in an immediate stagnation of the ISMP processes and in a rapid release of precipitated metals into the column effluents. However, the ISMP process could be restored after substrate amendment. 16S rDNA-based DGGE analysis revealed that the SRB population, in accordance with the results of the previously performed batch experiments, consisted exclusively of members of the genus Desulfosporosinus. The community of Archaea was characterized by sequencing amplicons of archaeal and methanogen-specific PCR reactions. This approach only revealed the presence of non-thermophilic Crenarchaeota, a novel group of organisms which is only distantly related to methane producing Euryarchaeota. DGGE on the dsrB genes was successfully used to link the results of the ISMP process to the community composition of the sulfate reducing bacteria. In the case of an intentional disruption of substrate supply, the ISMP process failed most likely because the growth and activity of the indigenous SRB community stopped due to a lack of a carbon and electron donor. On the other hand, the cause of the sudden temporal shortcomings of the ISMP process in the presence of different substrates was not immediately clear. It was first thought to be the result of competition between methanogenic prokaryotes (MP) and sulfate reducers, since the formation of small amounts of CH4 (0.01-0.03 ppm ml(-1) was detected. However, the results of molecular analyzes indicate that methanogens do not constitute a major fraction of the microbial communities that were enriched in the column experiments. Therefore, we postulate that the SRB population becomes inhibited by the formed metal sulfides. Our results indicate that the ISMP process is highly dependent on SRB-stimulation by substrate amendments and suggest that this remedial approach might not be viable for long-term application unless substrate amendments are continued and environmental conditions are strictly controlled. This will include the removal of affected aquifer material from the metal precipitation zone at the end of the remediation process, or removal of metal precipitates when the microbial activity decreases. Additional tests are necessary to investigate what will happen when clear groundwater passes through the reactive zone while no more C-sources are amended and all indigenous carbon is consumed. Also, the effects of dramatic increases in sulfate- or HM-concentrations on the SRB-community and the concomitant ISMP process need to be studied in more detail.

Halite and stable chlorine isotopes in the Zag H3–6 breccia

Abstract— Zag is an H3‐6 chondrite regolith breccia within which we have studied 14 halite grains ≤3 mm. The purity of the associated NaCl‐H2O brine is implied by freezing characteristics of fluid inclusions in the halite and EPMA analyses together with a lack of other evaporite‐like phases in the Zag H3–6 component. This is inconsistent with multi‐stage evolution of the fluid involving scavenging of cations in the Zag region of the parent body. We suggest that the halite grains are clastic and did not crystallize in situ. Halite and water‐soluble extracts from Zag have light Cl isotopic compositions, δ37Cl = −1.4 to −2.8%. Previously reported bulk carbonaceous chondrite values are approximately δ37Cl = +3 to +4%. This difference is too great to be the result of fractionation during evaporation, and instead, we suggest that Cl isotopes in chondrites are fractionated between a light reservoir associated with fluids and a heavier reservoir associated with higher temperature phases such as phosphates and silicates. Extraterrestrial carbon released at 600 °C from the H3–4 matrix has δ13C = −20%, consistent with poorly graphitized material being introduced into the matrix rather than indigenous carbonate derived from a brine. We have also examined 28 other H chondrite falls to ascertain how widespread halite or evaporite‐like mineral assemblages are in ordinary chondrites. We did not find any more to add to Zag (H3‐6) and Monahans (H5), which suggests that such highly soluble phases were not usually preserved on the parent bodies.