Proton NMR relaxometry as a useful tool to evaluate swelling processes in peat soils

Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H2O molecules by using 1H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 – T2 and T2 – D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H2O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 – 50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soil

MRI in soils: determination of water concent changes due to root water uptake by means of a multi-slice-multi-echo sequence (MSME)

Root water uptake by ricinus communis (castor bean) in fine sand was investigated using MRI with multiecho sampling. Before starting the experiments the plants germinated and grew for 3 weeks in a cylindrical container with a diameter of 9 cm. Immediately before the MRI experiments started, the containers were water-saturated and sealed, so water content changes were only caused by root water uptake. In continuation of a preceding work, where we applied SPRITE we tested a multi-echo multi-slice sequence (MSME). In this approach, the water content was imaged by setting TE = 6.76 ms and nE = 128 with an isotropic resolution of 3.1mm. We calculated the water content maps by biexponential fitting of the multi-slice echo train data and normalisation on reference cuvettes filled with glass beads and 1 mM NiCl2 solution. The water content determination was validated by comparing to mean gravimetric water content measurements. By coregistration with the root architecture, visualised by a 3D fast spin echo sequence (RARE), we conclude that the largest water content changes occurred in the neighbourhood of the roots and in the upper layers of the soil

Functional imaging of plants: A nuclear magnetic resonance study of a cucumber plant

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water los

Fine‐scale measurement of diffusivity in a microbial mat with nuclear magnetic resonance imaging

Noninvasive 1H‐nuclear magnetic resonance (NMR) imaging was used to investigate the diffusive properties of microbial mats in two dimensions. Pulsed field gradient NMR was used to acquire images of the H2O diffusion coefficient, Ds, and multiecho imaging NMR was used to obtain images of the water density in two structurally different microbial mats sampled from Solar Lake (Egypt). We found a pronounced lateral and vertical variability of both water density and water diffusion coefficient, correlated with the laminated and heterogeneous distribution of microbial cells and exopolymers within the mats. The average water density varied from 0.5 to 0.9, whereas the average water diffusion coefficient ranged from 0.4 to 0.9 relative to the values obtained in the stagnant water above the mat samples. The apparent water diffusivities estimated from NMR imaging compared well to apparent O2 diffusivities measured with a diffusivity microsensor. Analysis of measured O2 concentration profiles with a diffusion‐reaction model showed that both the magnitude of calculated rates and the depth distribution of calculated O2 consumption/production zones changed when the observed variations of diffusivity were taken into account. With NMR imaging, diffusivity can be determined at high spatial resolution, which can resolve inherent lateral and vertical heterogeneities found in most natural benthic systems

Quantitative NME microscopy of iron transport in methanogenic aggregates

Transport of micronutrients (iron, cobalt, nickel, etc.) within biofilms matrixes such as methanogenic granules is of high importance, because these are either essential or toxic for the microorganisms living inside the biofilm. The present study demonstrates quantitative measurements of metal transport inside these biofilms using T1 weighted 3D RARE. It is shown that iron(II)-EDTA diffusion within the granule is independent of direction or the inner structure of the granules. Assuming position dependence of the spin-lattice relaxivity, Fick’s law for diffusion in a sphere can be applied to simulate the diffusion within the methanogenic granules under investigation. A relatively low diffusion coefficient of 2.5*10-11 m2·s-1 was obtained for iron diffusion within the methanogenic granul

When the Office of Health Standards Compliance inspector knocks: What do I do

Inspectors and health officers attached to the Office of Health Standards Compliance (OHSC) may inspect or investigate premises where health services are provided, and may then perform a number of actions, including questioning people, taking samples, requesting documents, and conducting inspections and investigations. The outcomes of these activities may result in a number of sanctions, some of which may seriously impact health establishments and practitioners. This article aims to review the rights that health establishments, healthcare providers and health workers have when subjected to inspections or investigations by the OHSC. It also recommends a number of steps that may be taken when an inspector arrives at an establishment

When the Office of Health Standards Compliance inspector knocks: What do I do?

Inspectors and health officers attached to the Office of Health Standards Compliance (OHSC) may inspect or investigate premises where health services are provided, and may then perform a number of actions, including questioning people, taking samples, requesting documents, and conducting inspections and investigations. The outcomes of these activities may result in a number of sanctions, some of which may seriously impact health establishments and practitioners. This article aims to review the rights that health establishments, healthcare providers and health workers have when subjected to inspections or investigations by the OHSC. It also recommends a number of steps that may be taken when an inspector arrives at an establishment

NMR, water and plants

This Thesis describes the application of a non-destructive pulsed proton NMR method mainly to measure water transport in the xylem vessels of plant stems and in some model systems. The results are equally well applicable to liquid flow in other biological objects than plants, e.g. flow of blood and other body fluids in human and animals (Chapter 8). The method is based on a pulse sequence of equidistant πpulses in combination with a linear magnetic field gradient G.Following a general introduction and a survey of the properties of water in plants (Chapters 1 and 2), the basic NMR theory as well as reviews on the application of pulsed NMR to the determination of flow, diffusion and water content are presented in chapter 3.A mathematical treatment has produced analytical expressions for the shape of the signal S(t), based on a model in which the flowing fluid is thought to receive a ½π-τ-(π-τ-) n pulse train: a ½πpulse upon entering the r.f. coil followed by a sequence of equidistant πpulses until the fluid leaves the coil; simultaneously, this movement. of the fluid along a magnetic field gradient applied in the direction of flow produces a phase shift of the nuclear magnetization with respect to the rotating frame of reference (Chapter 4). Although this model does not lead to perfect agreement between the experimental and theoretical signal shape S(t), it correctly predicts the effects of experimental parameters on S(t) via analytical expressions. The main results from this theoretical treatment in combination with computer simulations, which have been experimentally verified in glass capillary systems, are:- as long as T 2≥ ½T 1 , the mean linear flow velocity v can be found from the time t max at which a maximum appears in the signal shape: v=C/t max , where C is a calibration constant, depending on G, τand the flow profile. If T 2 <½T 1 v can only be reliably determined when both T 1 and T 2 of the flowing fluid are known.- T 2 and the amount of flowing water in the coil V, and consequently the volume flowrate Q, can be determined from the height of the maximum S(t max ) and t max . Depending on the value of T 2 and the value of the ratio T 1 /T 2 , T 2 and V are found from a semilog plot of either S(t max ) vs. t max (T 1 >>T 2 ) or ∂[S(t max ) . t max ]/∂t max vs. t max (T 1≈ T 2 ).Based on flow measurements in plant stem segments (Chapter 5) it has been suggested that T 2 strongly depends on the vessel diameter for the narrow xylem capillaries. This behaviour of T 2 can explain negative results in plant stems with small vessel diameter. Under the present experimental conditions the method has been successfully applied to Cucurbitaceae (cucumber, gherkin, pumpkin) and tomato plants.T 2 measurements in wheat leaves have been shown to be insensitive to the presence of cell-bound paramagnetic ions (Chapter 7). The magnitude of T 2 of two separate water fractions (covering -90% of the total water content) has been found to be inversely proportional to water content. Measurements of flow and water content have been combined for an intact gherkin plant (Chapter 5), demonstrating that the combination of both NMR methods results in a powerful non-invasive method to study important parts of the plant water balance simultaneously. The results strongly suggest that the method can be used as an early warning for development of stress phenomena in plants, due to drought and other factors. From the flow measurements it has been shown how in a plant system the values of T 2 and T 1 of the water in the xylem vessels can be determined and estimated, respectively.A comparison between the results obtained with NMR, heat pulse and weight balance flow measurements is presented in Chapter 6. A linear relationship between the linear flow velocity obtained by NMR and the volume flowrate determined by the balance method yields an effective cross-sectional area available for flow of ~50% of the cross-sectional area of the xylem vessels measured by using a microscope. NMR measurements alone yield a slightly lower value of the effective cross-sectional area. Compared with the NMR method, the heat pulse method monitors only relative changes in the flow velocity. A plot of the flow velocity obtained by the heat pulse method versus the volume flowrate obtained by the balance method exhibits some unwanted experimental scatter.Chapter 8 suggests some applications of the pulsed NMR flow method, also to other systems than plants, and defines important instrumental requirements for these applications