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The topic of per- and polyfluoroalkyl substances (PFAS) is a late-breaking issue due to its high environmental relevance (toxicity, persistence and bioaccumulation) and due to the detection of PFAS as contaminants in various environmental compartments including groundwater, surface water and soil. PFAS enter the environment for instance through industrial, agricultural, and house-hold activities. Restricted PFAS like PFOA by the Stockholm Convention 2019 have often been replaced by molecules of the same family with shorter carbon chains, and nowadays around 4000 different molecules of PFAS can be found in the environment. Although PFAS have been manufactured since the 1940s, the fate of these chemicals in soils was not studied until the late 1990s. These studies have shown that the retention of PFAS in soils depends on various factors such as the PFAS type (e.g. molecular structure and carbon chain length), the soil properties (e.g. amount of organic carbon, surface charge), and the pore water (e.g. degree of saturation, pH). Still, the retention – and release – mechanisms of PFAS on soil constituents are not completely elucidated, and a generic model able to predict the transport of PFAS in the subsoil is not available yet. We were already able to demonstrate that magnetic resonance imaging (19F - MRI) can be successfully used during PFAS transport experiments [1]. We obtained MRI profiles providing quantitative information of the spatial and temporal distribution of the fluorinated substance inside a non-reactive porous medium, which were then compared with the traditional breakthrough curve (BTC) and numerical simulations to validate the performance of our approach. Our results showed that MRI as a non-invasive and non-destructive instrument is a meaningful tool for the measurement of PFAS inside porous media during flow-through experiments, and therefore for the interpretation as well as the modeling of BTCs compared to common transport experiments only measured with BTCs. In our latest experiments with 19F – MRI and PFAS, we studied the interactions of PFAS in chemically reactive porous media, which helps us to improve our understanding and modeling capability of PFAS in porous media. These results pave the way for the application of our innovative 19F – MRI / modeling approach of PFAS fate in natural soil. [1] Fries, E., Courtier-Murias, D., Gil Roca, J., Peyneau, P.-E., Michel, E., and Béchet, B.: 19F-MRI and numerical modeling as a combined method for the measurement and prediction of fluorinated substances (e.g. PFASs) transport in porous media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1288, https://doi.org/10.5194/egusphere-egu22-1288, 2022

International audience; There is an increasing interest on wood as it is an environmentally sustainable product (e.g. biodegradable and renewable). Thus, an accurate characterisation of wood properties is of extreme importance as they define the kind of application for which each type of wood can be used. For instance, dry mass of wood is a key parameter itself and is needed to calculate Moisture Content (MC) of wood, which is correlated to its physical properties. Due to the limitations of commonly used drying methods, preliminary work has shown the potential of 1H NMR to measure dry mass of wood but it has never been validated. Here, we performed a critical analysis of 1D and 2D 1H NMR relaxometry methods for obtaining the dry mass of wood and we compared their performance to three commonly used drying methods. This showed that commonly used drying methods do not remove all water from wood. Moreover, we are able to classify them accordingly to their performance. In addition, we showed that MC values obtained by 1H NMR relaxometry methods are higher (up to 20%) than values from commonly used drying methods. This empathizes the importance of accurate values of dry mass of wood and the utility of 1H NMR relaxometry on wood sciences. When comparing both NMR relaxometry methods, 2D should provide the more accurate results but 1D measurements would also be a recommended choice as they are faster than 2D and their results clearly overcome commonly used drying methods in a non-invasive and non-destructive manner.

The topic of per- and polyfluoroalkyl substances (PFASs) is a late-breaking issue due to its high environmental relevance (toxicity, persistence and bio accumulation) and due to the detection of PFASs as contaminants in various environmental compartments including groundwater, surface water and soil. PFASs enter the environment for instance through industrial, agricultural, and house-hold activities. Restricted PFASs like PFOA by the Stockholm Convention 2019 have often been replaced by molecules of the same family with shorter carbon chains, and nowadays around 4000 different molecules of PFASs can be found in the environment. Although PFASs have been manufactured since the 1940s, the fate of these chemicals in soils was not studied until the late 1990s.These studies have shown that the retention of PFASs in soils depends on various factors such as the PFASs type (e.g. molecular structure and carbon chain length), the soil properties (e.g. amount of organic carbon), and the pore water (e.g. degree of saturation, pH). Still, the retention – and release – mechanisms of PFASs on soil constituents are not completely elucidated, and a generic model able to predict the transport of PFASs in the subsoil is not available yet.In this work, building on a recently developed approach coupling nuclear magnetic resonance (19F - NMR) and modeling [1], we used magnetic resonance imaging (19F - MRI) to obtain quantitative information of the spatial and temporal distribution of a fluorinated substance inside a porous medium during transport experiments. We validated the performance of our approach by comparing MRI profiles obtained during flow-through experiments in sand columns tracing the transport of sodium fluoride (NaF) – a fluorinated non-reactive tracer – with traditional breakthrough curve and numerical simulations. These results pave the way for the application of this innovative MRI/modeling approach PFASs and conclusively to improve our understanding and modeling capability of PFASs fate in porous media.[1] Courtier-Murias, D., Michel, E., Rodts, S., & Lafolie, F. (2017). Novel Experimental-Modeling Approach for Characterizing Perfluorinated Surfactants in Soils. Environmental Science and Technology, 51(5), 2602–2610. https://doi.org/10.1021/acs.est.6b05671

Biochar aging may affect the interactions of biochar with water and thus its performance as soil amendment; yet the specific mechanisms underlying these effects are poorly understood. By means of FTIR, N adsorption, Hg intrusion porosimetry, thermogravimetric analysis, C solid state nuclear magnetic resonance (NMR) and H NMR relaxometry, we investigated changes in the chemistry and structure of biochar as well as its interaction with water after biochar aging, both physical (simulated by ball-milling) and biochemical (simulated by co-composting). Three different porosities of biochar were examined, This study was financially supported by the Comunidad de Madrid (Spain) and the Spanish National Research Council (CSIC) research grant Atracci ́on de Talento [grant number 2019T1/AMB14503]. The authors acknowledge the funding received from the Spanish National Research Council and the French National Centre for Scientific Research through the cooperation projects PICS [grant number 018FR0044] and IEA (ex-PICS) [grant number 203026]. This work was also partially funded by the Spanish Ministerio de Ciencia e Innovaci ́on (PTA 2018- 015282-I and PID 2020-119047RB-I00) and Comunidad de Madrid (PEJ-2018-TL/IND-11075). The authors want to thank the analytical services for the 1H relaxometry NMR at ICTP-CSIC, for the solid state 13C NMR at IRNAS-CSIC and for FT-IR, TGA and porosimetry analyses at ICA-CSIC. Technical support provided by Mr. H ́ector Fritis, Ms. Cristina G ́omez Ruano, Mr. David Mabilais, Mr. Fernando Martín Salamanca and Dr. Rebeca Herrero is gratefully acknowledged.

Preferential flow is quite usual in natural environments. Non-uniform and preferential flows co-exist or alternate, impacting water transport and contaminant transfer through the vadose zone. In this study, we investigated how macropore-induced flow affects manufactured nanoparticles, as emerging contaminants reactive transfer. Previous studies showed that the presence of a macropore into water-saturated soil columns can foster preferential water flow within the macropore. One could expect that this preferential flow may increase contaminant transfer and reduce retention by the matrix in the case of contaminant, as previously reported. In this study, we injected pulses of silver nanoparticles to assess their transfer through sand columns with and without a macropore. Both systems (with and without macropore) were studied under similar conditions. An unexpected result was obtained: more nanoparticles were retained in the system with a macropore, i.e., with a preferential flow. This result is quite counter-intuitive. It appears that the relation between flow homogeneity and contaminant retention is not straightforward. Some possible explanations, related to chemical and physical kinetics, are put forward to explain the experimental results.

This study aims at identifying the mechanisms of oil and water imbibition in heartwood and sapwood of Douglas-fir through a combination of original experiments with magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) relaxation measurements for oil and free water, and deformation measurements for bound water. Experiments by weighing are performed to verify whether the imbibition process is also consistent with Washburn law. All the results are discussed taking into account the structure of wood (tubular tracheids closed at their tips, but possibly connected to each other via open pits on the side faces) and the preparation of samples. The observation of relatively fast oil flow imbibition confirms that sapwood exhibits a connected hydraulic network through which a liquid can a priori flow and climb along the structure. However, the spontaneous water imbibition is strongly damped by its very poor wetting when in contact with cell-walls only partially saturated with bound water, so that the diffusion of bound water control the uptake dynamics. However, due to preferentially closed pits, the heartwood does not exhibit a continuous hydraulic network and water essentially penetrates into wood by diffusion through the cell walls.

The effect of macropore flow on solute transport has spurred much research over the last forty years. In this study, non-reactive solute transport in columns filled by macropored porous media was experimentally and numerically investigated, and the emphasis was put on the study of exit effects, whose very existence is inherent to the finite size of any experimental column. We specifically investigated the impact of the presence of a filter at the column outlet on water flow and solute transport in macropored systems. Experiments involving breakthrough measurements and magnetic resonance imaging (MRI) showed that solute transport displayed some significant non-unidirectional features, with a strong mass exchange at the interface between the macropore and the matrix. Fluid dynamics and transport simulations indicated that this was due to the non-unidirectional nature of the flow field close to the outlet filter. The flow near the exit of the column was shown to be strongly impacted by the presence of the outlet filter, which acts as a barrier and redistributes water from the macropore to the matrix. This impact was apparent on the breakthrough curves and the MRI images. It was also confirmed by computer simulations and could, if not properly taken into account, impede the accurate inference of the transport properties of macropored porous media from breakthrough experiments.

Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated with wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is also discussed taking into account the effect of aging methods on the two bound water components. The obtained results confirm the ability of 2D 1H NMR relaxometry to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material.

In natural systems, preferential flow is the rule rather than the exception. Non-uniform and preferential flows significantly impact mass transport, and by this way most of geochemical processes and pollutant dispersion in the environment. Laboratory columns are experimental devices used for the monitoring of solute transfer through porous. In particular, several studies used such experimental devices for characterizing mass transfer through heterogeneous systems and macropored systems. However, the design of these devices and its impacts on the experimental results has never been investigated in depth so far. In particular, the edge effect is rarely questioned and the transfer is always hypothesized to correspond to a fully developed flow (i.e., flow in an equivalent infinite system). In this study, we question this hypothesis both experimentally and numerically for the case of a macropored system. Tracer elutions, magnetic resonance imaging (MRI), and modeling using multiphysics approaches (Comsol) are conducted to demonstrate that flow is affected by edge effects close to the inlet and the outlet of the column, and that the presence of filters (used to prevent particles from exiting the system and clogging the outlet) do impact the flow and transfer breakthrough. Consequently, these edge effects should be considered when analyzing the results and concluding on the involved processes, in particular for the case of soils and systems with macropores.

Biochar application is now considered to be one of the most promising agricultural practices to mitigate climate change. However, to fully assess the benefits of biochar, we still need to better understand its effects on soil properties, and particularly on native soil organic matter (SOM) dynamics.In this work, we investigated soil respiration and changes in SOM pools (mineral-free, intra-aggregate, and mineral-associated SOM) as affected by the application of 20 t / ha per year of biochar alone or combined with mineral fertilizer, municipal solid waste compost, or sewage sludge. The experiment was run for 7 years in a semiarid agricultural soil. We found that biochar had no effect on soil respiration with respect to mineral fertilization and no amendment (control), and tended to decrease CO2 emissions from soils amended with municipal solid waste compost and sewage sludge. Biochar accumulated mainly in the mineral-free SOM fraction and its addition, especially in combination with municipal solid waste compost, promoted the amount of SOM occluded with aggregates and associated to mineral surfaces.Acknowledgments: to the Spanish MICINN (MINECO, AEI, FEDER, EU) for supporting the research project AGL2016-75762-R.

For most wood-based product uses it is essential to remove a large part of the water content from wet or green (fresh-cut) wood, to reduce further dimensional variations under varying humidity conditions, improve its mechanical characteristics, and protect it from biological attacks. However, the internal mechanisms of drying are not fully described. Here we observe drying at different scales using macroscopic measurements (weighing), nuclear magnetic resonance measurements allowing to distinguish bound- and free-water contents, and x-ray computed tomography images of air-liquid interfaces at the smallest pore scale (wood lumens). We show that during wood drying, even well above the fiber saturation point, bound-water diffusion in cell walls (instead of capillary effects) ensures the extraction of liquid water from pores and its transport towards the surface of evaporation, and thus controls the drying rate. The distribution of bound-water content (uniform or heterogeneous) along the main sample axis and the drying-rate evolution depend on the competition between the external conditions and a characteristic rate of transport due to bound-water diffusion. For sufficiently slow drying this distribution remains homogenous until free water is fully extracted. An original physical phenomenon is thus at work, which plays a major role in regulating water extraction, in that it maintains a constant drying rate and a homogeneous distribution of the (mean) water content throughout the material. These results provide sound concepts for modeling and controlling drying properties of wood materials. They open the way to the understanding or control of the properties of many other materials containing two water types in food or civil-engineering applications. Our results complete recent observations that bound-water diffusion also controls imbibition in hardwood and finally show that transfers between bound and free water play a major role in the interaction of plantlike systems with water.

The wetting properties of a liquid along cell-walls of plant-like systems or in porous hydrogels change from poor to good wetting when the walls are saturated with bound water, which then allows liquid displacement. As a consequence, the dynamics of capillary imbibition of free water in hygroscopic systems may be strongly damped (by several orders of magnitude) although water can freely climb over significant heights. This process might contribute to the regulation of water absorption in unsaturated wood and could be explored to design porous materials with tunable liquid adsorption.

Soil contamination is still poorly understood and modeled in part because of the difficulties of looking inside the “black box” constituted by soils. Here, we investigated the application of a recently developed 1H NMR technique to 19F NMR relaxometry experiments and utilized the results as inputs for an existing model. This novel approach yields 19F T2 NMR relaxation values of any fluorinated contaminant, which are among the most dangerous contaminants, allowing us to noninvasively and directly monitor their fate in soils. Using this protocol, we quantified the amount of a fluorinated xenobiotic (heptafluorobutyric acid, HFBA) in three different environments in soil aggregate packings and monitored contaminant exchange dynamics between these compartments. A model computing HFBA partition dynamics between different soil compartments showed that these three environments corresponded to HFBA in solution (i) between and (ii) inside the soil aggregates and (iii) to HFBA adsorbed to (or strongly interacting wi...

National audience; Le séchage du bois représente une dépense énergétique importante qui va s’amplifier avec le développement du bois dans la construction. L’enjeu de ce projet est de réaliser une étude sur l’utilisation du bois vert, c’est à dire jamais séché, dans la construction. Les bâtiments en bois datant du Moyen Age, basés sur ce procédé, nous prouvent la longévité des structures mises en œuvre à partir du bois vert. La problématique réside dans le respect des déformations admissibles des poutres de bois vert soumises à des chargements mécaniques et climatiques variables ainsi que dans les techniques d’assemblage pertinentes pour les structures. Une meilleure connaissance du comportement hygro-mécanique du bois vert pourrait permettre de proposer des innovations constructives.

Nuclear magnetic resonance (NMR) spectroscopy is arguably one the most powerful tools to study the interactions and molecular structure within plants. Traditionally, however, NMR has developed as two separate fields, one dealing with liquids and the other dealing with solids. Plants in their native state contain components that are soluble, swollen, and true solids. Here, a new form of NMR spectroscopy, developed in 2012, termed comprehensive multiphase (CMP)-NMR is applied for plant analysis. The technology composes all aspects of solution, gel, and solid-state NMR into a single NMR probe such that all components in all phases in native unaltered samples can be studied and differentiated in situ. The technology is evaluated using wild-type Arabidopsis thaliana and the cellulose-deficient mutant ectopic lignification1 (eli1) as examples. Using CMP-NMR to study intact samples eliminated the bias introduced by extraction methods and enabled the acquisition of a more complete structural and metabolic profile; thus, CMP-NMR revealed molecular differences between wild type (WT) and eli1 that could be overlooked by conventional methods. Methanol, fatty acids and/or lipids, glutamine, phenylalanine, starch, and nucleic acids were more abundant in eli1 than in WT. Pentaglycine was present in A. thaliana seedlings and more abundant in eli1 than in WT. Copyright © 2015 John Wiley & Sons, Ltd.

International audience; Imbibition in poplar wood is studied from macroscopic measurements (mass and deformation) along with Magnetic Resonance Imaging (MRI) experiments allowing to observe bound and free water dynamics. Additional experiments with silicone oil allow to compare the characteristics of water imbibition with those of a liquid not hygroscopically adsorbed in wood. It was shown that, in contrast to porous media with an impermeable solid structure, the water imbibition in the hydraulic conduits of hardwood is not simply driven by the standard capillary effects associated with a good wetting of the solid surface, but it is in fact strongly affected by the adsorption of bound water in cell walls. More precisely bound water appears to progress far beyond the front of free water, and the free water penetration along the sample axis apparently coincides with the development of a region saturated with bound water. This likely explains that water imbibition is about three orders of magnitude slower than expected from standard Washburn imbibition process.

Soil organic matter (SOM) is one of the earth’s largest reservoirs of actively cycled carbon and plays a critical role in various ecosystem functions. In this study, mineral soils with the same parent material and of similar approximate age were sampled from the same climatic region in Halsey, Nebraska to determine the relationship between overlying vegetation inputs to SOM composition using complementary molecular level methods (biomarker analyses and solid state 13 C nuclear magnetic resonance (NMR) spectroscopy). Soil samples were collected from a native prairie and cedar and pine sites planted on the native prairie. Free and bound lipids isolated from the pine soil were more enriched in aliphatic and cutinderived compounds than the other two soils. Cinnamyl type lignin-derived phenols were more abundant in the grassland soil than in the pine and cedar soils. Acid to aldehyde ratios (Ad/Al) for vanillyl and syringyl type phenols were higher for the pine soil indicating a more advanced stage of lignin oxidation (also observed by 13 C NMR) in the soil that has also been reported to have accelerated carbon loss. In

International audience; The microbial contribution to soil organic matter (SOM) has recently been shown to be much larger than previously thought and thus its role in carbon sequestration may also be underestimated. In this study we employ 13C (13CO2) to assess the potential CO2 sequestration capacity of soil chemoautotrophic bacteria and combine nuclear magnetic resonance (NMR) with stable isotope probing (SIP), techniques that independently make use of the isotopic enrichment of soil microbial biomass. In this way molecular information generated from NMR is linked with identification of microbes responsible for carbon capture. A mathematical model is developed to determine real-time CO2 flux so that net sequestration can be calculated. Twenty-eight groups of bacteria showing close homologies with existing species were identified. Surprisingly, Ralstonia eutropha was the dominant group. Through NMR we observed the formation of lipids, carbohydrates, and proteins produced directly from CO2 utilized by microbial biomass. The component of SOM directly associated with CO2 capture was calculated at 2.86 mg C (89.21 mg kg-1) after 48 h. This approach can differentiate between SOM derived through microbial uptake of CO2 and other SOM constituents and represents a first step in tracking the fate and dynamics of microbial biomass in soil.

Earlywood (EW) and latewood (LW) have different hygromechanical behaviors, if subjected to relative humidity (RH) variations. To understand this effect better, the adsorption mechanisms of EW and LW of Douglas fir were studied by 2D 1H NMR relaxometry under conditions of equilibrium moisture content (EMC) at 20°C. Two bound water components were detected with relaxation times T1 and T2 indicating that they are located in distinct environments but these are similar in EW and LW. Sorption isotherms were calculated and analyzed based on the sorption model of Dent. A difference of sorption energy between the two water components is in agreement with their mobility difference observed on T1−T2 correlation spectra. Moreover, for the two bound water components, EW and LW exhibit different sorption isotherms at high RH. This may be attributed to a difference of adsorption capacity. Based on the macrofibril models provided by the literature, the following hypothesis is proposed: bound water components are located in lamellar and lenticular areas, both leading to possible deformations.

The sorption of anthropogenic compounds on clay minerals is a complex molecular process with important implications for the fate of agrochemicals and organic pollutants in the environment. The present study illustrates the use of a water-mediated NOE approach to study clay binding interactions. This method exploits the interfacial water layer on clay surfaces as a hydrogen reservoir for magnetization transfer. The interactions of four different xenobiotics with clay suspension were investigated through this method to demonstrate its capability to screen for the clay–xenobiotic molecular affinity. Further, based on the NOE build-up rates, epitope map of clay–xenobiotic interactions can be generated, explaining the orientation and mechanism of the interactions. The water-mediated NOE approach has the potential to reveal key insights into the role that interfacial water plays in the binding process, providing a better understanding of the partitioning of anthropogenic compounds from bulk water into aqueous clay suspensions.

We use magnetic resonance imaging to follow the adsorption of colloids during their transport through a porous medium (grain packing). We injected successive pulses of a suspension of nanoparticles able to adsorb onto the grains. To get quantitative information we carry out 2D imaging and 1D measurements of the evolution in time of the distribution profile of all particles (suspended or adsorbed) in cross-sectional layers along the sample axis during the flow. For the first injections we observe the 1D profile amplitude progressively damping as particles advance through the sample, due to their adsorption. 2D imaging shows that successive injections finally result in a coverage of grains by adsorbed particles regularly progressing along the sample. The analysis of the results makes it possible to get a clear description of the adsorption process. In our specific case (particle charged oppositely to the adsorption sites) it appears that the particles rapidly explore the pores and adsorb as soon as they encounter available sites on grains, and the surplus of particles goes on advancing in the sample. A further analysis of the profiles makes it possible to distinguish the respective concentration distribution of suspended and adsorbed particles over time at each step of the process.

Colloidal particles can act as vectors of adsorbed pollutants in the subsurface, or be themselves pollutants. They can reach the aquifer and impair groundwater quality. The mechanisms of colloid transport and deposition are often studied in columns filled with saturated porous media. Time-lapse profiles of colloid concentration inside the columns have occasionally been derived from magnetic resonance imaging (MRI) data recorded in transport experiments. These profiles are valuable, in addition to particle breakthrough curves (BTCs), for testing and improving colloid transport models. We show that concentrations could not be simply computed from MRI data when both deposited and suspended colloids contributed to the signal. We propose a generic method whereby these data can still be used to quantitatively appraise colloid transport models. It uses the modeled suspended and deposited particle concentrations to compute modeled MRI data that are compared to the experimental data. We tested this method by performing transport experiments with sorbing colloids in sand, and assessed for the first time the capacity of the model calibrated from BTCs to reproduce the MRI data. Interestingly, the dispersion coefficient and deposition rate calibrated from the BTC were respectively overestimated and underestimated compared with those calibrated from the MRI data, suggesting that these quantities, when determined from BTCs, need to be interpreted with care. In a broader perspective, we consider that combining MRI and modeling offers great potential for the quantitative analysis of complex MRI data recorded during transport experiments in complex environmentally relevant porous media, and can help improve our understanding of the fate of colloids and solutes, first in these media, and later in soils.

A method is presented that combines Carr–Purcell–Meiboom–Gill (CPMG) during acquisition with either selective or nonselective excitation to produce a considerable intensity enhancement and a simultaneous loss in chemical shift information. A range of parameters can theoretically be optimized very rapidly on the basis of the signal from the entire sample (hard excitation) or spectral subregion (soft excitation) and should prove useful for biological, environmental, and polymer samples that often exhibit highly dispersed and broad spectral profiles. To demonstrate the concept, we focus on the application of our method to T1 determination, specifically for the slowest relaxing components in a sample, which ultimately determines the optimal recycle delay in quantitative NMR. The traditional inversion recovery (IR) pulse program is combined with a CPMG sequence during acquisition. The slowest relaxing components are selected with a shaped pulse, and then, low-power CPMG echoes are applied during acquisition with intervals shorter than chemical shift evolution (RCPMG) thus producing a single peak with an SNR commensurate with the sum of the signal integrals in the selected region. A traditional 13C IR experiment is compared with the selective 13C IR-RCPMG sequence and yields the same T1 values for samples of lysozyme and riverine dissolved organic matter within error. For lysozyme, the RCPMG approach is ~70 times faster, and in the case of dissolved organic matter is over 600 times faster. This approach can be adapted for the optimization of a host of parameters where chemical shift information is not necessary, such as cross-polarization/mixing times and pulse lengths. Copyright © 2013 John Wiley & Sons, Ltd.

We measure the dispersion coefficient through homogeneous bead or sand packings at different flow rates from direct magnetic resonance imaging (MRI) visualizations of the transport characteristics of a pulse of paramagnetic nanoparticles. Through two-dimensional imaging we observe homogeneous dispersion inside the sample, but we show that entrance effects may induce significant radial heterogeneities, which would affect the interpretation of the breakthrough curve. Another MRI approach then provides quantitative measurements of the evolution in time of the longitudinal particle distribution in the sample. These data can be analyzed to deduce the coefficient of dispersion independently of entrance effects. The values obtained for this ``effective'' dispersion coefficient are almost ten times lower than the commonly accepted values.

Nuclear magnetic resonance (NMR) spectroscopy is an essential tool for studying environmental samples but is often hindered by low sensitivity, especially for the direct detection of nuclei such as13C. In very heterogeneous samples with NMR nuclei at low abundance, such as soils, sediments, and air particulates, it can take days to acquire a conventional13C spectrum. The present study describes a prescreening method that permits the rapid prediction of experimental run time in natural samples. The approach focuses the NMR chemical shift dispersion into a single spike, and, even in samples with extremely low carbon content, the spike can be observed in two to three minutes, or less. The intensity of the spike is directly proportional to the total concentration of nuclei of interest in the sample. Consequently, the spike intensity can be used as a powerful prescreening method that answers two key questions: (1) Will this sample produce a conventional NMR spectrum? (2) How much instrument time is required to record a spectrum with a specific signal-to-noise (S/N) ratio? The approach identifies samples to avoid (or pretreat) and permits additional NMR experiments to be performed on samples producing high-quality NMR data. Applications in solid- and liquid-state13C NMR are demonstrated, and it is shown that the technique is applicable to a range of nuclei. Environ. Toxicol. Chem. 2013;32:129–136. © 2012 SETAC

Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate (1)H and (13)C spectra for the different phases. In addition, (19)F performance is also addressed. To illustrate the capability of (19)F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state.

Selective examples of OH...arene, NH2...arene and C-HN[triple bond, length as m-dash]C weak interactions are presented using a flexible dibenzobicyclo[3.2.2]nonane scaffold for detection and comparative characterisation of non-covalent interactions in solution and solid states.

A linear scaling of the calculated chemical shifts is used in order to improve the accuracy of the DFT predicted C-13 NMR chemical shifts, The widely applied method of GIAO B3LYP/6-311+G(2d,p) using the B3LYP/6-3G(d) optimized geometries is chosen, which allows cost-effective calculations of the 13C chemical shifts in the molecular systems with 100 and more atoms. A set of 27 13C NMR chemical shifts determined experimentally for 22 simple molecules with various functional groups is used in order to determine scaling factors for reproducing experimentally measured values of C-13 chemical shifts. The results show that the use of a simple relationship (delta(scale) = 0.95 delta(calc) + 0.30, where delta(calc) and 5(scalc) are the C-13 calculated and the linearly scaled values of the chemical shifts, respectively) allows to achieve a three-fold improvement in mean absolute deviations for 27 chemical shifts considered. To test the universal applicability of the scaling factors derived, we have used complex organic molecules such as taxol and a steroid to demonstrate the significantly improved accuracy of the DFT predicted chemical shifts. This approach also outperforms the recently recommended usage of the Hartree-Fock optimized geometries for the GIAO B3LYP/6-311+G(2d,p) calculations of the C-13 chemical shifts. (C) 2008 Elsevier B.V. All rights reserved.

Since the isolation of soil organic matter in 1786, tens of thousands of publications have searched for its structure. Nuclear magnetic resonance (NMR) spectroscopy has played a critical role in defining soil organic matter but traditional approaches remove key information such as the distribution of components at the soil-water interface and conformational information. Here a novel form of NMR with capabilities to study all physical phases termed Comprehensive Multiphase NMR, is applied to analyze soil in its natural swollen-state. The key structural components in soil organic matter are identified to be largely composed of macromolecular inputs from degrading biomass. Polar lipid heads and carbohydrates dominate the soil-water interface while lignin and microbes are arranged in a more hydrophobic interior. Lignin domains cannot be penetrated by aqueous solvents even at extreme pH indicating they are the most hydrophobic environment in soil and are ideal for sequestering hydrophobic contaminants. Here, for the first time, a complete range of physical states of a whole soil can be studied. This provides a more detailed understanding of soil organic matter at the molecular level itself key to develop the most efficient soil remediation and agricultural techniques, and better predict carbon sequestration and climate change.

The results of the ring conformational analysis of L-proline, N-acetyl-L-proline, and trans-4-hydroxy-L-proline by NMR combined with calculations using density functional theory (DFT) and molecular dynamics (MD) are reported. Accurate values of 1H-1H J-couplings in water and other solvents have been determined. Using a two-site equilibrium model, the Cgamma-endo conformer of L-proline in water has been identified as intermediate between gammaTdelta [twist(Cgamma-endo, Cdelta-exo)] and gammaE [envelope(Cgamma-endo)] and the Cgamma-exo conformer as betaTgamma. Both conformers were equally populated at room temperature. The N-acetyl [cis-rotamer gammaTbeta(80%)/gammaE(20%) and trans-rotamer gammaTbeta(61%)/gammaE(39%)] and 4-hydroxy (gammaEpsilon) derivatives showed significant changes in both the population and the geometries of the preferred ring conformers. The combination of NMR predicted populations with the DFT B3LYP/6-311+G(2d,p)/IEFPCM calculations proved successful, resulting in fairly accurate predictions of J-couplings. Simulations using MD were mostly in favor of the two-site equilibrium model between Cgamma-endo and Cgamma-exo conformers, similar to that used for the analysis of NMR J-couplings. Various force fields examined for MD simulations failed to reproduce the ring conformational geometries and populations of L-proline in water accurately, while significantly better agreement with NMR was found for trans-N-acetyl-L-proline using GROMOS and AMBER force fields.

Comprehensive multiphase NMR is a novel NMR technique that permits all components (solutions, gels, and solids) to be studied in unaltered natural samples. In this study a wide range of CMP-NMR interaction and editing-based experiments are combined to follow contaminants (pentafluorophenol (PFP) and perfluorooctanoic acid (PFOA)) from the solution state (after a spill) through the gel-state and finally into the true solid-state (sequestered) in an intact water-swollen soil. Kinetics experiments monitoring each phase illustrate PFOA rapidly transfers from solution to the solid phase while for PFP the process is slower with longer residence times in the solution and gel phase. Interaction-based experiments reveal that PFOA enters the soil via its hydrophobic tails and selectively binds to soil microbial protein. PFP sorption shows less specificity exhibiting interactions with a range of gel and solid soil components with a preference toward aromatics (mainly lignin). The results indicate that in addition to more traditional measurements such as Koc, other factors including the influence of the contaminant on the soil-water interface, specific biological interactions, soil composition (content of lignin, protein, etc.) and physical accessibility/swellability of soil organic components will likely be central to better explaining and predicting the true behavior of contaminants in soil.

International audience; Direct observations of the surface and shape of model nano-colloidal gels associated with measurements of the spatial distribution of water content during drying show that air starts to significantly penetrate the sample when the material stops shrinking. We show that whether the material fractures or not during desiccation, as air penetrates the porous body, the water saturation decreases but remains almost homogeneous throughout the sample. This air-invasion is at the origin of another type of fracture due to capillary effects; these results provide a new insight in the liquid dynamics at the nano-scale. PACS number(s): 47.56.+r, 68.03.Fg, 81.40.Np

A quantitative understanding of the dynamics of the interactions between organofluorine compounds and humic acids will contribute to an improved understanding of the role that Natural Organic Matter plays as a mediator in the fate, transport and distribution of these contaminants in the environment. Here, Nuclear Magnetic Resonance (NMR) spectroscopy-based diffusion measurements are used to estimate the association dynamics between dissolved humic acid and selected organofluorine compounds: pentafluoroaniline, pentafluorophenol, potassium perfluorooctane sulfonate, and perfluorooctanoic acid. Under the conditions used here, the strength of the association with humic acid increases linearly as temperature decreases for all compounds except for perfluorooctanoic acid, which exhibits divergent behavior with a non-linear decrease in the extent of interaction as temperature decreases. A general interaction mechanism controlled largely by desolvation effects is suggested for all compounds examined here except for perfluorooctanoic acid, which exhibits a specific mode of interaction consistent with a proteinaceous binding site. Reverse Heteronuclear Saturation Transfer Difference NMR is used to confirm the identity and nature of the humic acid binding sites.

Nuclear magnetic resonance (NMR) spectroscopy is arguably one the most powerful tools to study the interactions and molecular structure within plants. Traditionally, however, NMR has developed as two separate fields, one dealing with liquids and the other dealing with solids. Plants in their native state contain components that are soluble, swollen, and true solids. Here, a new form of NMR spectroscopy, developed in 2012, termed comprehensive multiphase (CMP)-NMR is applied for plant analysis. The technology composes all aspects of solution, gel, and solid-state NMR into a single NMR probe such that all components in all phases in native unaltered samples can be studied and differentiated in situ. The technology is evaluated using wild-type Arabidopsis thaliana and the cellulose-deficient mutant ectopic lignification1 (eli1) as examples. Using CMP-NMR to study intact samples eliminated the bias introduced by extraction methods and enabled the acquisition of a more complete structural and metabolic profile; thus, CMP-NMR revealed molecular differences between wild type (WT) and eli1 that could be overlooked by conventional methods. Methanol, fatty acids and/or lipids, glutamine, phenylalanine, starch, and nucleic acids were more abundant in eli1 than in WT. Pentaglycine was present in A. thaliana seedlings and more abundant in eli1 than in WT.

International audience; Soils are amongst the largest organic carbon reservoirs on earth containing approximately three times the carbon contained in all living systems and roughly double the amount present in the atmosphere. Soil organic matter is central to agriculture, carbon cycling, and contaminant sequestration, but due to its extreme heterogeneity it is challenging to study with most modern analytical approaches. As such 13C NMR spectroscopy has emerged as an indispensable technique for the characterization of soil organic matter in the solid-state. Single pulse (SP) 13C NMR approaches theoretically provide the highest level of quantitation for soil organic matter, however, due to its relative insensitivity, sample analysis can take a prohibitively long time. Consequently, for routine studies the more sensitive approach of cross-polarization under magic angle spinning conditions (CP/MAS) is more commonly utilized. In particular, 13C CP is extremely useful when low organic carbon content samples are compared and is normally used to reveal the nature, transformations and fate of organic matter in soils. Here, the performance of a novel NMR scheme, which so far has not yet been applied to soils samples, is investigated. The ramp-CPSP scheme adds a SP block to a ramp-CP scheme, taking advantage of both techniques without extending the experimental time. This method shows enhancements higher than 100% for key regions of the 13C spectra and also provides 13C profiles that are closer to quantitative when compared to the widely used ramp-CP scheme. In addition, a critical analysis of these enhancements is presented. Even under the worst case scenario, when the SP element adds little additional signal, the result still reflects the conventional ramp-CP experiment. As such the ramp-CPSP approach can be implemented in a routine fashion without drawback. The results shown here suggest replacing conventional ramp-CP with the ramp-CPSP sequence for routine soil analysis in the solid-state since it can save considerable experimental time and provide a more representative 13C spectrum of the soil in general.

A combined experimental-computational method is reported for structure and dynamics elucidations of highly flexible open chain molecules in the solution state.

International audience; High Resolution Magic Angle Spinning (HR-MAS) NMR spectroscopy is a versatile technique that provides high resolution NMR data on samples containing solutions, gels and swellable solids. In addition to providing structural information HR-MAS can also be used to investigate interfaces (for example organic structures at the solid-aqueous soil interface), processes such as swelling/flocculation, kinetic transfer between gel/liquid phases, as well as conformation and molecular interactions in situ. As such, HRMAS has potential in a diversity of fields including organic, biological, environmental, and medical research. This manuscript focuses on the application of HR-MAS to intact natural samples. A range of 1D and 2D NMR experiments are reviewed and compared in terms of general performance on a range of samples. Therefore, this practical guide and review should be a useful reference and starting point for those wishing to apply HR-MAS NMR. While this article focuses on natural samples, common key 1D and 2D experiments are considered which may be of interest to readers with diverse research interests.

Molecular dynamics characterisations in solids can be carried out selectively using dipolar-dephasing experiments. Here we show that the introduction of a sum of Lorentzian and Gaussian functions greatly improve fittings of the "intensity versus time" data for protonated carbons in dipolar-dephasing experiments. The Lorentzian term accounts for remote intra- and intermolecular (1)H-(13)C dipole-dipole interactions, which vary from one molecule to another or for different carbons within the same molecule. Thus, by separating contributions from weak remote interactions, more accurate Gaussian decay constants, T(dd), can be extracted for directly bonded (1)H-(13)C dipole-dipole interactions. Reorientations of the (1)H-(13)C bonds lead to the increase of T(dd), and by measuring dipolar-dephasing constants, insight can be gained into dynamics in solids. We have demonstrated advantages of the method using comparative dynamics studies in the α and γ polymorphs of glycine, cyclic amino acids L-proline, DL-proline and trans-4-hydroxy-L-proline, the Ala residue in different dipeptides, as well as adamantane and hexamethylenetetramine. It was possible to distinguish subtle differences in dynamics of different carbon sites within a molecule in polymorphs and in L- and DL-forms. The presence of overall molecular motions is shown to lead to particularly large differences in dipolar-dephasing experiments. The differences in dynamics can be attributed to differences in noncovalent interactions. In the case of hexamethylenetetramine, for example, the presence of C-H···N interactions leads to nearly rigid molecules. Overall, the method allows one to gain insight into the role of noncovalent interactions in solids and their influence on the molecular dynamics.

Solid-state NMR studies of collagen samples of various origins confirm that the amplitude of collagen backbone and sidechain motions increases significantly on increasing the water content. This conclusion is supported by the changes observed in three different NMR observables: (i) the linewidth dependence on the 1H decoupling frequency; (ii) 13C CSA changes for the peptide carbonyl groups, and (iii) dephasing rates of 1H-13C dipolar couplings. In particular, a nearly threefold increase in motional amplitudes of the backbone librations about C-Cα or N-Cα bonds was found on increasing the added water content up to 47 wt%D2 O. On the basis of the frequencies of NMR observables involved, the timescale of the protein motions dependent on the added water content is estimated to be of the order of microseconds. This estimate agrees with that from wideline T2(1)H NMR measurements. Also, our wideline 1H NMR measurements revealed that the timescale of the microsecond motions in proteins reduces significantly on increasing the added water content, i.e., an ∼15-fold increase in protein motional frequencies is observed on increasing the added water content to 45 wt% D2 O. The observed changes in collagen dynamics is attributed to the increase in water translational diffusion on increasing the amount of added water, which leads to more frequent "bound water/free water" exchange on the protein surface, accompanied by the breakage and formation of new hydrogen bonds with polar functionalities of protein.

18 páginas, 6 figuras y 4 tablas, The fundamental mechanisms whereby organic inputs stabilize in soil are poorly resolved, which limits our current capacity to predict the dynamics of soil organic matter (OM)turnover and its influence on soil quality and functioning. Here we fractionated soil OM from long-term experimental field plots either unamended or amended with two organic materials of different quality (i.e., solid cattle manure and crop residues) for 44 years into five measurable and meaningful pools directly related to conceptual preservation mechanisms: dissolved OM, mineral-free particulate OM located outside aggregates (unprotected from decomposition), OM occluded within both macroaggregates and microaggregates(weakly and strongly protected by physical mechanisms, respectively), and OM intimately associated with soil mineral particles (protected by chemical mechanisms). Compared to the unamended soil, the application of cattle manure and crop residues increased total organic C content by 35 and 10%, respectively. Most of these increases (up to 60 and 72% for cattle manure and crop residues, respectively) were explained by the mineral-associated OM pool, followed by the intra-microaggregate OM fraction. In general, the distribution and dynamics of N content paralleled those of C content. As determined by a range of modern nuclear magnetic resonance (NMR) techniques, including 13C cross polarization magic angle spinning (MAS), 1H high resolution (HR)-MAS, and 1H 13C heteronuclear single quantum coherence HR-MAS NMR, the mineral-associated OM fraction was found to be predominately of microbial origin, unlike free and intra-aggregate OM pools, which were dominated by plant structures at different stages of decomposition. As a whole, our results indicate that the main mechanism by which organic inputs are stabilized and OM accrues in soils is not the physical and chemical protection of undecayed or partially degraded organic structures, but the adsorption on mineral surfaces of microbial biomass and microbial by-products resulting from microbial growth, transformation, and degradation processes. It is possible that organic amendments increase more than previously thought the microbial populations of the soil, which live, thrive, and die in close association with the mineral surfaces. This mechanism appears to be enhanced with the addition of stable organic materials., This work was partly supported by the Spanish Ministry of Science and Innovation (research grant AGL2009-09124). C. Plaza thanks the Spanish National Research Council (CSIC) for the travel grant (PA1003114) which made possible his visit to the University of Toronto. Andre Simpson thanks the NSERC Discovery and Strategic Programs for providing support.

The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental biogeochemistry. Interactions between xenobiotics and the naturally occurring organic constituents of soils are strongly correlated to environmental persistence, bioaccessibility, and ecotoxicity. Nevertheless, because of the complex structural and chemical heterogeneity of soils, studies of these interactions are most commonly performed indirectly, using correlative methods, fractionation, or chemical modification. Here we identify the organic components of an unmodified peat soil where some organofluorine xenobiotic compounds interact using direct molecular-level methods. Using (19)F→(1)H cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy, the (19)F nuclei of organofluorine compounds are used to induce observable transverse magnetization in the (1)H nuclei of organic components of the soil with which they interact after sorption. The observed (19)F→(1)H CP-MAS spectra and dynamics are compared to those produced using model soil organic compounds, lignin and albumin. It is found that lignin-like components can account for the interactions observed in this soil for heptafluoronaphthol (HFNap) while protein structures can account for the interactions observed for perfluorooctanoic acid (PFOA). This study employs novel comprehensive multi-phase (CMP) NMR technology that permits the application of solution-, gel-, and solid-state NMR experiments on intact soil samples in their swollen state.

Metabolic mixtures are often analyzed via NMR spectroscopy as it provides a metabolic profile without sample alteration in a noninvasive manner. These mixtures however tend to be very complex and demonstrate considerable spectral overlap resulting in assignments that are sometimes ambiguous given the range of current NMR methods available. De novo molecular identification in these mixtures is generally accomplished using chemical shift information and J-coupling based experiments to determine spin connectivity information, but these techniques fall short when a molecule of interest contains nonrelaying centers. A method is presented here that enhances intramolecular spatial interactions via supercooled water and uses the resulting spatial correlations to edit mixtures. This is accomplished by utilizing nuclear Overhauser effect spectroscopy (NOESY) at subzero temperatures in capillaries to enhance NOE and provide more complete spin systems. This technique is applied to a standard mixture of three known molecules in D(2)O with overlapping resonances and is further demonstrated to assign molecules in a worm tissue extract. The current method proves to be a powerful complement to existing methods such as total correlation spectroscopy (TOCSY) to expand the range of molecules that can be assigned in situ without physical separation of mixtures.

In this study we explore the relationship between solution pH and the distribution of the binding interactions at different domains of a dissolved humic acid (HA) for three xenobiotics: pentafluoroaniline (PFA), pentafluorophenol (PFP), and hexafluorobenzene (HFB). The components of HA where xenobiotic interactions occur are identified using the 1 H{ 19 F} Reverse Heteronuclear Saturation Transfer Difference (RHSTD) Nuclear Magnetic Resonance (NMR) spectroscopy experiment. At low pH, PFA and PFP interact preferentially with aromatic components of HA. Increasing pH reduces this preference. Conversely, HFB interacts with all components of HA equally, across the entire pH range. The possible roles of both aromatic-specific interactions and conformational changes of HA behind these observations are explored. It is shown that T-oriented π–π interactions at π-electron accepting HA structures are slightly stronger for PFA and PFP than for HFB. Using DOSY NMR it is shown that the pH-dependence of the interactions is correlated with changes in the conformation of the carbohydrate components of HA rather than with the aromatic components. It is argued that the observed preference for aromatic HA is caused by restricted access to the non-aromatic components of HA at low pH. These HA components form tightly bound hydrophobic domains due to strong inter- and intra-molecular hydrogen bonds. At high pH, these structures open up, making them more available for interactions with polar compounds.

A method is presented that combines Carr-Purcell-Meiboom-Gill (CPMG) during acquisition with either selective or nonselective excitation to produce a considerable intensity enhancement and a simultaneous loss in chemical shift information. A range of parameters can theoretically be optimized very rapidly on the basis of the signal from the entire sample (hard excitation) or spectral subregion (soft excitation) and should prove useful for biological, environmental, and polymer samples that often exhibit highly dispersed and broad spectral profiles. To demonstrate the concept, we focus on the application of our method to T(1) determination, specifically for the slowest relaxing components in a sample, which ultimately determines the optimal recycle delay in quantitative NMR. The traditional inversion recovery (IR) pulse program is combined with a CPMG sequence during acquisition. The slowest relaxing components are selected with a shaped pulse, and then, low-power CPMG echoes are applied during acquisition with intervals shorter than chemical shift evolution (RCPMG) thus producing a single peak with an SNR commensurate with the sum of the signal integrals in the selected region. A traditional (13)C IR experiment is compared with the selective (13)C IR-RCPMG sequence and yields the same T(1) values for samples of lysozyme and riverine dissolved organic matter within error. For lysozyme, the RCPMG approach is ~70 times faster, and in the case of dissolved organic matter is over 600 times faster. This approach can be adapted for the optimization of a host of parameters where chemical shift information is not necessary, such as cross-polarization/mixing times and pulse lengths.

11 páginas, 6 figuras, 1 tabla, Conservation tillage practices that entail no or reduced soil disturbance are known to help preserve or accumulate soil organic matter (OM). However, the underlying mechanisms especially at the molecular level are not well understood. In this study soil samples from 25-year-old experimental plots continuously cropped with barley (Hordeum vulgare L.) under no-tillage (NT) and chisel tillage (CT) were subjected to a new physical fractionation method to isolate dissolved OM, mineral-free particulate OM located outside aggregates (physically and chemically unprotected), OM occluded within both macroaggregates and microaggregates (weakly and strongly protected by physical mechanisms, respectively), and OM in intimate association with minerals (protected by chemical mechanisms). The whole soils and OM fractions were analyzed for organic C and N content and by modern nuclear magnetic resonance (NMR) techniques. The soil under NT stored 16% more organic C and 5% more N than the soil under CT. Compared to CT, NT increased free organic C content by 7%, intra-macroaggregate organic C content by 20%, intra-microaggregate organic C content by 63%, and mineral-associated organic C content by 16% and decreased dissolved organic C content by 11%. The mineral-associated OM pool accounted for 65% of the difference in total organic C content between NT and CT, whereas the intra-microaggregate OM only explained 18%, intra-macroaggregate OM 14%, and free OM 11%. The NMR experiments revealed that the free and intra-aggregate OM fractions were dominated by crop-derived materials at different stages of decomposition, whereas the mineral-associated OM pool was predominately of microbial origin. Overall, our results indicate that microbes and microbial by-products associated with mineral surfaces and likely physically protected by entrapment within very small microaggregates constitute the most important pool of OM stabilization and C sequestration in soils under NT. Most probably the slower macroaggregate turnover in NT relative to CT boosts not only the formation of microaggregates and thereby the physical protection of crop-derived particulate OM, but more importantly the interaction between mineral particles and microbial material that results in the formation of very stable organo-mineral complexes., This research was partly supported by the Spanish Ministry of Science and Innovation (grant AGL2009-09124). C. Plaza is grateful to the Spanish National Research Council (CSIC) for having supplied a research fellowship from the CSIC Mobility Program (grant PA1003114) that made possible his visit to the University of Toronto at Scarborough. J.M. Fernández is the recipient of a fellowship from the JAE-Doc subprogram financed by the CSIC and the European Social Fund. A.J. Simpson wishes to thank the Natural Sciences and Engineering Council of Canada (NSERC) (Discovery and Strategic Programs) for funding this research.

[1] Marine pockmarks are a specific type of seabed geological setting resembling craters or pits and are considered seabed surface expressions of fluid flow in the subsurface. A large composite pockmark on the Malin Shelf, off the northern coast of Ireland was surveyed and ground truthed to assess its activity and investigate fluid related processes in the subsurface. Geophysical (including acoustic and electromagnetic) data confirmed the subsurface presence of signatures typical of fluids within the sediment. Shallow seismic profiling revealed a large shallow gas pocket and typical gas related indicators such as acoustic blanking and enhanced reflectors present underneath and around the large pockmark. Sulphate profiles indicate that gas from the shallow reservoir has been migrating upwards, at least recently. However, there are no chimney structures observed in the sub-bottom data and the migration pathways are not apparent. Electromagnetic data show slightly elevated electrical conductivity on the edges of the pockmarks and a drop below regional levels within the confines of the pockmark, suggesting changes in physical properties of the sediment. Nuclear Magnetic Resonance (NMR) experiments were employed to characterize the organic component of sediments from selected depths. Very strong microbial signatures were evident in all NMR spectra but microbes outside the pockmark appear to be much more active than inside. These observations coincide with spikes in conductivity and the lateral gas bearing body suggesting that there is an increase in microbial activity and biomass when gas is present.