Interactions Of Clay Minerals Research Articles

Organic-inorganic interactions of clay minerals and organic matter: Action mechanism and analysis techniques

Organic-inorganic interactions of clay minerals and organic matter: Action mechanism and analysis techniques

Interactions of Clay Minerals with Biomolecules and Protocells Complex Structures in the Origin of Life: A Review

AbstractThe origin of life (OoL) has always been a mysterious and challenging topic that puzzles human beings. Clay minerals have unique properties and wide distribution in early Earth environments. They can not only adsorb biological small molecules to catalyze their polymerization, but play an active role in the formation and evolution of protocells. In this review, the research progress on the interactions of clay minerals with biomolecules and protocells complex structures in the field of the OoL based on chemical evolution theory is summarized. The types, structures and properties of clay minerals, biological molecules and protocell models related to the OoL are introduced in detail. The mechanism of interaction between clay minerals and biological molecules, the construction of protocells and the role of clay minerals in the formation, structure and stability of protocells are systematically described. Finally, the future research priorities and challenges in the field of OoL based on clay minerals, biomolecules and protocells are discussed. It is aspired that this review can further advance the exploration of the OoL from a new perspective, and can also bring some interesting findings and ideas to the interdisciplinary research of materials, biology, chemistry and other related disciplines.Clay minerals have a variety of interactions with small biomolecules, which can be used as structural and functional templates to promote the organic synthesis of biomolecules and the formation and evolution of protocells, playing a non‐negligible role in the field of the OoL.

Biochemically induced diagenesis of Jurassic micrite: evidence from phase analysis, carbon, oxygen, and strontium isotopes (Franconian Alb, Germany)

The marine Upper Jurassic rocks of the Franconian Alb consist largely of micritic carbonate of partly dolomitized reef mounds and bedded basinal limestone. All carbonates were lithified in the shallow (centimeters, meters) subsurface and have a wide range of ∂13C (≤ + 3‰ to − 10‰VPDB) but always negative ∂18O (− 1 to − 6‰VPDB). Dolomite and reef limestone show the highest ∂18O and ∂13C values. The most negative ∂13C (≥ − 10‰) occurs mainly as cement in dolomite of a basinal, partly dolomitic, biostrome interval. Basinal limestone shows intermediate ∂13C values. Because freshwater diagenesis and elevated temperatures cannot explain the observed isotope values, pH is here considered a major factor influencing the isotope signal of micritic limestone. The bulk sediment isotope signal was reset to lower values, from an original lime mud with ∂13C ≥ 3‰ and a ∂18O of ≥ + 1‰, as a result of biochemically induced diagenesis. Carbonate, probably mostly aragonite but occasionally including dolomite, was dissolved in a zone where low pH developed as a result of organic matter degradation. Dissolved carbonate was translocated by diffusion and re-precipitated as cement (ca. 50vol%) in a zone with elevated pH where all in situ lime mud ∂18O was reset. Imported cement carbonate precipitated in equilibrium with the pore fluid with negative isotope values, whereas ∂13C of the in situ lime mud remained unmodified. The negative shift of the bulk ∂13C and ∂18O is variable and depends on pH and the contribution of 12C from anaerobic sulfate reduction in the zone of cement precipitation. This produced an ubiquitous covariance of ∂18O and ∂13C. Incorporation of seawater-derived Mg2+ during recrystallization of carbonate can account for the local dolomitization. Elevated 87Sr/86Sr ratios are explained as a result of interaction of clay minerals with the stationary pore fluids. This study shows that the isotopic signal produced by biochemically induced shallow submarine subsurface carbonate diagenesis can be indistinguishable from freshwater diagenesis, that ∂18O and ∂13C of the bulk rock are always reset, and that carbonates can show, in the presence of clay minerals, elevated 87Sr/86Sr ratios even when the pore fluids were never exchanged.Graphical

Reactivity and bioconcentration of stable cesium in a hyperturbid fluvial-estuarine continuum: A combination of field observations and geochemical modeling

Effective, post-accidental management needs an accurate understanding of the biogeochemical behavior of radionuclides in surface environments at a regional scale. Studies on stable isotopes (element homologs) can improve this knowledge. This work focuses on the biogeochemical behavior of stable cesium (Cs) along a major European fluvial-estuarine system, the Gironde Estuary (SW France). We present results obtained from (i) a long-term monitoring (2014–2017) of dissolved (Csd) and particulate (Csp) Cs concentrations at five sites along the freshwater continuum of the Garonne watershed, (ii) Csd and Csp concentrations during four oceanographic campaigns at contrasting hydrological conditions along longitudinal profiles of the estuarine system, (iii) a 24 h cycle of Csp at the estuary mouth, and (iv) a historical trend of Cs bioconcentration in wild oysters at the estuary mouth (RNO/ROCCH, 1984–2017). In addition, we model the partitioning of Cs within the estuarine environment for clay mineral interactions via PhreeqC. At fluvial sites, we observe a geogenic dependence of the Csp and a seasonal variability of Csd, with a downstream increase of the solid-liquid partitioning (log10 Kd values from 3.64 to 6.75 L kg−1) for suspended particulate matter (SPM) < 200 mg L−1. Along the estuarine salinity gradients, Cs shows a non-conservative behavior where fresh SPM (defined as Cs-depleted particles recently put in contact with Csd) act as a Cs sink during both flood and low discharge (drought) conditions. This sorption behavior was explained by the geochemical model, highlighting the relevance of ionic strength, water and SPM residence times. However, at high salinities, the overall log10 Kd value decreases from 6.02 to 5.20 for SPM ∼300–350 mg L−1 due to the Csd oceanic endmember. Despite wild oysters showing low bioconcentration factors (∼1220 L kg−1) at the estuary mouth, they are sensitive organisms to Cs fluxes.

Asymmetric response of transition metal cationic orbitals to applied electric field

Understanding the quantum mechanical mechanisms underlying atomic/ionic interfacial processes and phenomena, particularly their dependence on the electronic orbital rearrangement of atoms/ions in an external electric field, remains a significant challenge. This study investigated the asymmetric response of transition metal (TM) cationic orbitals when subjected to an applied electric field. Quantum mechanical calculations were employed to quantify the newly formed hybrid orbitals and evaluate the corresponding orbital energies of the TM cations. Analysis of the quantitative contribution of asymmetric orbital hybridization to TM–surface interactions showed a significant change in orbital energy and increased effective charges of TM cations at the charged surface. This asymmetric response, induced by a negative external electric field generated from the structural charges of clay minerals (e.g., montmorillonite), repels electrons from the outer-shell orbital. This repulsion consequently increases the electron binding energy of the inner-shell orbitals, leading to new surface reactions, polarization-enhanced induction force, and polarization-induced covalent bonding between the TM cations and the charged surface. Our theoretical predictions regarding TM–clay mineral interactions are consistent with the experimental observations of TM cation adsorption. This finding has significant implications for the adsorptive removal of TM cations from wastewaters and for enhancing the catalytic efficiency of TM–surface catalysts. The unique physical and chemical characteristics exhibited by TMs at charged particle surfaces, resulting from their asymmetric response, can play pivotal roles in environmental and chemical engineering.

Microbial weathering of montmorillonite and its implication for Cd(II) immobilization

Interactions between silicate bacteria and silicates are very common in nature and hold great potential in altering their mutual physicochemical properties. But their interactions in regulating contaminants remediation involving performance and mechanisms are often overlooked. Here, we focused on the interactions between silicate bacteria (Paenibacillus polymyxa, PP; Bacillus circulans, BC) and a soil silicate montmorillonite (Mt), and their impact on Cd(II) immobilization. The obtained results showed that Mt greatly promoted the growth of the bacteria, resulting in a maximum 10.31 times increase in biomass production. In return, the bacteria strongly enhanced the Cd(II) adsorption on Mt, with adsorption capacities increased by 80.61%–104.45% in comparison to the raw Mt. Additionally, the bacteria-Mt interaction changed Cd(II) to a more stabilized state with a maximum reduction of 38.90%/g Mt in bioavailability. The enhancement of Cd(II) adsorption and immobilization on the bacterial modified Mt was caused by the following aspects: (1) the bacteria activities altered the aggregation state of Mt and made it better dispersed, thus more active sites were exposed; (2) the microbial activities brought about more rough and crumpled surface, as well as smaller Mt fragments; (3) a variety of microbial-derived functional groups were introduced onto the Mt surface, increasing its affinity for heavy metals; (4) the main Cd(II) immobilization mechanism was changed from ion exchange to the combination of ion exchange and functional groups induced adsorption. This work elucidates the potential ecological and evolutionary processes of silicate bacteria-soil clay mineral interactions, and bears direct implications for the clay-mediated bioremediation of heavy metals in natural environments.

Application of molecular dynamics simulations in interface interaction of clay: Current status and perspectives

AbstractTo understand the research progress of molecular dynamics (MD) method in the field of clay minerals, the application of MD in the interface interaction of clay minerals is reviewed in this paper. MD simulations have become the indispensable means to study mineral interface effects. Clay minerals are common associated minerals with hydrophilic surface, the ease of argillization, negative electricity, and the ability of forming impurities and defects. They are widely concerned in the fields of mine wastewater treatment, fine clay mineral flotation, shale oil and gas exploitation, and so forth. In addition, clay minerals are considered as natural adsorbents due to their large specific surface area, but their complex interface interactions hinder their effective utilization. Therefore, it is particularly important to reveal the interaction mechanism of clay interface at the atomic/molecular level by means of software simulation technology. In this review, our focus is on the applications of MD method in the field of clay mineral interface interaction, such as clay/gas interface, clay/water interface, agents and clay/water interface, and mineral particle and clay/water interface. Furthermore, the history and shortcomings of MD simulation are summarized. The research and effective utilization of clay interface are summarized and prospected as well.

Understanding the rheology of kaolinite clay suspensions using Bayesian inference

Mud is a suspension of fine-grained particles (sand, silt, and clay) in water. The interaction of clay minerals in mud gives rise to complex rheological behaviors, such as yield stress, thixotropy, and viscoelasticity. Here, we experimentally examine the flow behaviors of kaolinite clay suspensions, a model mud, using steady shear rheometry. The flow curves exhibit both yield stress and rheological hysteresis behaviors for various kaolinite volume fractions (ϕk). Further understanding of these behaviors requires fitting to existing constitutive models, which is challenging due to numerous fitting parameters. To this end, we employ a Bayesian inference method, Markov chain Monte Carlo, to fit the experimental flow curves to a microstructural viscoelastic model. The method allows us to estimate the rheological properties of the clay suspensions, such as viscosity, yield stress, and relaxation time scales. The comparison of the inherent relaxation time scales suggests that kaolinite clay suspensions are strongly viscoelastic and weakly thixotropic at relatively low ϕk, while being almost inelastic and purely thixotropic at high ϕk. Overall, our results provide a framework for predictive model fitting to elucidate the rheological behaviors of natural materials and other structured fluids.

Comprehensive Review on the Interactions of Clay Minerals With Animal Physiology and Production.

Clay minerals are naturally occurring rock and soil materials primarily composed of fine-grained aluminosilicate minerals, characterized by high hygroscopicity. In animal production, clays are often mixed with feed and, due to their high binding capacity towards organic molecules, used to limit animal absorption of feed contaminants, such as mycotoxins and other toxicants. Binding capacity of clays is not specific and these minerals can form complexes with different compounds, such as nutrients and pharmaceuticals, thus possibly affecting the intestinal absorption of important substances. Indeed, clays cannot be considered a completely inert feed additive, as they can interfere with gastro-intestinal (GI) metabolism, with possible consequences on animal physiology. Moreover, clays may contain impurities, constituted of inorganic micronutrients and/or toxic trace elements, and their ingestion can affect animal health. Furthermore, clays may also have effects on the GI mucosa, possibly modifying nutrient digestibility and animal microbiome. Finally, clays may directly interact with GI cells and, depending on their mineral grain size, shape, superficial charge and hydrophilicity, can elicit an inflammatory response. As in the near future due to climate change the presence of mycotoxins in feedstuffs will probably become a major problem, the use of clays in feedstuff, given their physico-chemical properties, low cost, apparent low toxicity and eco-compatibility, is expected to increase. The present review focuses on the characteristics and properties of clays as feed additives, evidencing pros and cons. Aims of future studies are suggested, evidencing that, in particular, possible interferences of these minerals with animal microbiome, nutrient absorption and drug delivery should be assessed. Finally, the fate of clay particles during their transit within the GI system and their long-term administration/accumulation should be clarified.

Generalized effective stress concept for saturated active clays

Experimental evidence shows that changes in pore-water chemistry can significantly affect the mechanical behavior of saturated active clays. Despite this evidence, how the chemical composition of the pore water can be considered in effective stress definition is questionable. This paper develops the concept of generalized effective stress for active clays. To this end, physicochemical studies on water–clay mineral interactions are used to clearly define the different types of ions and water present in an active clay. In particular, the presence of both movable and non-movable ions within the liquid water is highlighted. Taking this into account, thermodynamic and geochemistry principles are applied to the representative elementary volume scale for determining the pore-water pressure and redefine the effective stress accordingly. The theoretical development results in the dependence of the effective stress on the pore-water chemistry through the effective solute suction variable. Equations for the determination of this chemical variable are developed. The implications of the use of the proposed effective stress concept are investigated using experimental results taken from the literature. The results show advantages both in the interpretation of shear strength and volumetric data, and all support the theoretical explanation underlying the proposed concept.

Microbial Interaction with Clay Minerals and Its Environmental and Biotechnological Implications

Clay minerals are very common in nature and highly reactive minerals which are typical products of the weathering of the most abundant silicate minerals on the planet. Over recent decades there has been growing appreciation that the prime involvement of clay minerals in the geochemical cycling of elements and pedosphere genesis should take into account the biogeochemical activity of microorganisms. Microbial intimate interaction with clay minerals, that has taken place on Earth’s surface in a geological time-scale, represents a complex co-evolving system which is challenging to comprehend because of fragmented information and requires coordinated efforts from both clay scientists and microbiologists. This review covers some important aspects of the interactions of clay minerals with microorganisms at the different levels of complexity, starting from organic molecules, individual and aggregated microbial cells, fungal and bacterial symbioses with photosynthetic organisms, pedosphere, up to environmental and biotechnological implications. The review attempts to systematize our current general understanding of the processes of biogeochemical transformation of clay minerals by microorganisms. This paper also highlights some microbiological and biotechnological perspectives of the practical application of clay minerals–microbes interactions not only in microbial bioremediation and biodegradation of pollutants but also in areas related to agronomy and human and animal health.

Caveats of using fractal analysis for clay rich pore systems

The conventional techniques cannot accurately predict the multiphase flow behaviour in clay rich low permeability rocks. This is particularly important in applications such as hydraulic fracturing where fluid uptake into low permeability rocks is of interest. This inability has given rise to the use of fractal-based estimation of petrophysical properties of such rocks. The concept of fractal theory revolves around the fractal dimension (Df) representing the entire pore structure which is often estimated using the mercury-intrusion capillary pressure (MICP) data among other techniques. However, rocks containing high clay content often exhibit higher capillary pressures than those based on MICP. This is due to interaction of clay minerals with external fluids such as hydraulic fracturing fluid and subsequent transient change in pore structure. This also in turn causes the Df value to vary thus leading to errors and uncertainties in fractal-estimated petrophysical properties of clay rich rocks. This transient aspect of clay rich rocks’ pore network is not yet fully understood nor systematically investigated or incorporated in current fractal methods. We have therefore conducted a comprehensive study to narrate a cautionary tale on the use of MICP-based fractal methods in clay rich tight rocks analyses. We first highlighted the uncertainty in the MICP-based Df value by comparing experimental and simulated oil recoveries from three clay-rich low permeability sandstone samples. We then developed, for the first time, a new set of physical equations to describe the transient pore network based on MICP-based fractal theory in order to partially overcome these uncertainties. We next compared the new theoretical model with experimental oil-water capillary pressure data. Through such rigorous analyses, it was concluded that MICP-based fractal theory relying on an unchanging pore structure is not accurate in its current form. Although our new approach can address the issue with the transient nature of clay rich pore network, there is yet immense space for improvement to overcome the limitations associated with fractal based petrophysical property estimation.

Способность смектитовой компоненты бентонитовой глины к интеркаляции глицина

The availability, environmental friendliness and unique properties of bentonite clays determine their wide application in various industries. The mechanisms of interaction of clay minerals with organic matter arise more interest of scientists. This article presents the results of study of the possibility of glycine penetration into the interlayer space of the smectite component of bentonite clay based on x-ray diffraction and thermal analyzes.

Physical, mechanical, and microstructure investigation of tropical clayey soils stabilised with desulfurisation slag for pavement application

This study aims to perform a chemical, physical, mechanical, and microstructural characterisation of Kambara Reactor Slag (KRS) and to evaluate its potential to stabilise residual clay-type soils for roadway application. In addition to KRS characterisation, physical and mechanical properties of soil-KRS mixtures are also obtained and compared. Also, microstructural and chemical investigation based on Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were performed in selected mixtures to infer about the KRS stabilisation process. Results show that KRS was able to stabilise the two different soils selected in this study, but the efficiency is dependent on the type of soil used. The chemical stabilisation seems to be the main mechanism to promote soil mixture resistance gain, and it might occur due to KRS compounds and clay mineral interactions. KRS could be a promising alternative to stabilise low quality clay soils for roadway application, bringing significant environmental and economic gains.

Control of Soil Extracellular Enzyme Activities by Clay Minerals—Perspectives on Microbial Responses

Knowledge of how interactions of clay minerals and extracellular enzymes (EEs) influence organic matter turnover in soils are still under discussion. We studied the effect of different montmorillonite contents on EE activities, using two experiments—(1) an adsorption experiment with a commercially available enzyme (α-glucosidase) and (2) an incubation experiment (10 days) where microorganisms were stimulated to produce enzymes through organic carbon (OC) addition (starch and cellulose). Soil mixtures with different montmorillonite contents were created in four levels to a sandy soil: +0% (control), +0.1%, +1%, and +10%. The potential enzyme activity (pEA) of four enzymes, α-glucosidase, β-glucosidase, cellobiohydrolase, and aminopeptidase, involved in the soil carbon and nitrogen cycle were analysed. The adsorption experiment revealed a reduction in the catalytic activity of α-glucosidase by up to 76% with increasing montmorillonite contents. However, the incubation experiment showed an inhibitory effect on pEA only directly after the stimulation of in-situ EE production by OC addition. At later incubation stages, higher pEA was found in soils with higher montmorillonite contents. This mismatch between both experiments, with a transient reduction in catalytic activity for the incubation experiments, points to the continuous production of enzymes by soil microorganisms. It is conceivable that microbial adaptation is characterized by higher investment in EEs production induced by increasing clay contents and a stabilisation of the EEs by clay minerals. Our results point to the need to better understand EE-clay mineral-OC interactions regarding potential microbial adaptations and EE stabilisation with potentially prolonged activities.

Attachment of cerium oxide nanoparticles of different surface charges to kaolinite: Molecular and atomic mechanisms

Sustainable applications of nanotechnology in agriculture require insights into the interactions between engineered nanoparticles (ENPs) and clay minerals, a key component in soil that governs the soil properties and functions. This study investigated the charge-dependent interactions of cerium oxide nanoparticles (CeO2NPs) with kaolinite at atomic level with several complementary surface characterization techniques. High resolution transmission electron microscope (HRTEM) and atomic force microscope (AFM) images showed strong attachment of positively charged and neutral CeO2NPs to the surface of kaolinite while the negatively charged CeO2NPs demonstrated low affinity to the surface of kaolinite, indicating strong electrostatic interactions between CeO2NPs and kaolinite surface. Attached CeO2NPs on kaolinite surface displayed charge-dependent aggregation, with neutral CeO2NPs showing the most substantial aggregation on kaolinite surface. The variation in hydrodynamic size and surface charge of kaolinite with the charge on CeO2NPs was observed. The attachment of CeO2NPs also changed the surface charge density distribution on the surface of kaolinite, converting a relatively homogenously charged basal plane into a heterogeneously charged plate. The change on kaolinite surface charge density may markedly affect the interactions of clay minerals with surrounding macro- and micro-nutrients in soil pore water and affect their bioavailability to plants.

THE ECOLOGICAL ROLE OF CLAYS AND CLAY MINERALS

The article considers the ecological role played by clays and clay minerals in the ecosystem and the biosphere as a whole. The value of clays and clay minerals in the origin of life on Earth and the formation of RNA are analyzed, due to the periodicity of the microstructure of these minerals, their physicochemical activity and sorption capacity with respect to amino acids, nucleotides, proteins and RNA. The processes of interaction of clay minerals with organic matter are considered, including under conditions of hydrothermal conditions, which have specific features that contribute to the origin of life. In addition, the ecological functions of the lithosphere due to clays and clay minerals were analyzed. It is shown that clays and clay minerals perform the most important ecological resource function, being a valuable mineral resource and mineral, participating in providing biota (including humans) with various mineral and energy resources of minerals, in providing biophilic resources, in providing renewable resources (water, oil and gas), in providing resources of the geological space, etc. Also, the clays perform an important ecological geochemical function, which consists in their participation in the geochemistry processes of the lithosphere and the formation of specific geochemical barriers that perform protective ecological functions on the migration routes of various contaminants. The ecological geodynamic function of clays consists in their influence on the development of endogenous and exogenous geological processes affecting the state and functioning of ecosystems. Finally, the participation of clays in ensuring the geophysical ecological function of the lithosphere consists in their influence on the formation of both natural and man-made geophysical fields in ecological-geological systems. Thus, clays and clay minerals have a great influence on ecological and geological systems, they are involved in the formation of all the most important ecological functions of the lithosphere: resource, geochemical, geodynamic and geophysical. Among them, the most significant is the role of clays and clay minerals in ensuring the resource ecological function of the lithosphere.

Spectroscopic evidence and molecular simulation investigation of the bonding interaction between lysine and montmorillonite: Implications for the distribution of soil organic nitrogen

Abstract Clay minerals, widespread in natural soil environment, play important roles in the distribution of organics and their utilization by plants and microorganisms. Interface interactions of clay minerals and amino acids are essential for soil and life sciences. The bonding interaction between montmorillonite and lysine was studied systematically and comprehensively in this paper. The montmorillonite-lysine complexes were characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier-transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and molecular simulation investigation. The results of XRD showed that interlayer spacing of montmorillonite increased or decreased with different amounts of lysine indicating two different bonding interactions. Amino acids adsorbed onto montmorillonite through the bonding interaction of electrostatic attraction between negatively charged surface of montmorillonite and NH3+ at the end of lysine on interlayer adsorption aspect as confirmed by XPS and ATR-FTIR spectroscopy. For edge adsorption aspect, the adsorption was through the bonding interaction between COO– group and > AlOH2+/>SiOH2+ groups. Electron localization function calculations for O, Si and Al atoms further demonstrated the bonding interaction of NH3+ groups and the Si O– groups intuitively. These findings give more understandings on the adsorption and distribution of amino acids in different sites of clay minerals.

Effects of exchangeable cations, mineralogy and clay content on the mineralization of plant residue carbon

Interactions of clay minerals with organic materials and the consequences of these interactions on dynamics of organic carbon (OC) have been reviewed in detail. However, the effects of exchangeable cations and clay types on the turnover rate of OC have not been given much attention. Appropriate amounts of homoionic Na-, Ca- and Al-clays from Georgia kaolinite, Illinois illite and Wyoming bentonite were mixed with pure sand to prepare artificial soils with different clay contents, exchange cations and clay types. Alfalfa plant residues were incorporated into the artificial soils and the soils were inoculated with microbes from a natural soil and incubated for 184days to study the effects of clay contents, exchangeable cations and clay types on the mineralization of OC and plant residue derived microbial biomass. Mineralization of plant residue carbon was significantly (⁎⁎p<0.01) more rapid in pure sand than in soils containing 5 and 10% clay, indicating that clay contents influence the capacity of soils to protect and store OC. The amounts of biomass carbon were lowest in pure sand and highest in soils with 10% clay. There was a significant influence (⁎⁎p<0.01) of exchangeable cations on microbial biomass and hence the mineralization of OC over a period of 184days. At 5 and 10% clay contents, the amounts of microbial biomass carbon and the mineralization of plant residue carbon were highest in Ca-soils and lowest in Al-soils. Statistical analysis of data showed a significant effect (⁎⁎p<0.01) of clay type on mineralization of plant residue carbon and microbial biomass. However, the effects of clay types on the mineralization of OC were much less than those of clay contents and exchangeable cations. The mineralization of plant residue carbon was highest in soils with Georgia kaolinite clay and lowest in soils with Wyoming bentonite clay. The amounts of biomass carbon were slightly lower in soils with Wyoming bentonite clay than soils with Georgia kaolinite and Illinois illite clay minerals. The results of this study indicate that OC and microbial biomass are stabilized in soils through the interaction with clay minerals and a small amount of clay (5%) slows OC decomposition significantly and reduces carbon dioxide emission from soils. Exchangeable cations exert their influence on microbial biomass and hence carbon dynamics by controlling the size and activity of the microbial population through modifying the physicochemical characteristics of microbial habitats.

Microbe-clay interactions as a mechanism for the preservation of organic matter and trace metal biosignatures in black shales

Organic-rich, fine-grained sedimentary rocks, such as black shales, are important geochemical archives providing information on the evolution of seawater composition and biological activity over the past 3billionyears. While biological productivity and sedimentation rates greatly affect the organic matter content in these rocks, mechanisms linking these two processes remain poorly resolved. Here, we examine the interactions of clay minerals with the marine planktonic cyanobacterium Synechococcus sp. PCC 7002. We suggest that clays settling through the water column could influence carbon and trace metal burial in three ways: (1) the interaction of reactive clay surfaces with the bacterial cells increases organic matter deposition via mass increase in a seawater growth medium by several orders of magnitude; (2) reactive bacterial cells become completely encased within a clay shroud, enhancing the preservation potential of this organic matter; and (3) the trace metal content of the biomass buried along with metals sorbed to the clay particles contributes to the trace metal concentrations of the black shale precursor sediments. Significantly, our findings imply that the chemical composition of ancient, organic-rich, fine-grained deposits are not only archives of ancient seawater composition and redox state, but they also provide a record of the degree of biological activity in the water column through geological time.