Differentiating between physical and chemical constraints on pesticide and water movement into and out of soil aggregates

Johnson, Andrew C.; Bettinson, Robert J; Williams, Richard J.

doi:10.1002/(sici)1096-9063(199905)55:5<524::aid-ps937>3.0.co;2-#

Cited by 16 publications

(9 citation statements)

References 10 publications

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“…Natural soils are exposed to dynamic variations in temperature and moisture. Changes in moisture status may affect soil properties like water content or volumetric swelling of soil organic matter (SOM) [1,2] or sorbent properties [2][3][4][5]. Furthermore, the extractability of organic pollutants was found to be affected by the hydration time of soils indicating physical and physicochemical changes of SOM upon swelling [2].…”

Section: Introductionmentioning

confidence: 99%

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Jaegera¹

2010

TOMRJ

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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 1 H 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 H 2 O molecules by using 1 H 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 H 2 O 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 soils.

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Section: Introductionmentioning

confidence: 99%

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Jaegera¹

2010

TOMRJ

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“…In the last few years, an increasing number of studies have shown that the water content, the hydration time and drying-remoistening cycles affect sorption parameters of organic pollutants: High soil moisture enhanced sorption velocity for diuron and isoproturon and increased the final sorption for diuron (Gaillardon 1996). The release of isoproturon from soil samples was probably controlled by non-equilibrium sorption/desorption from air-dry aggregates, while a combination of nonequilibrium sorption/desorption and diffusion was needed to describe the release from wet aggregates (Johnson et al, 1999). Effects of the water status on the sorption mechanism of chlortoluron were found within up to three weeks of hydration (e.g.…”

Section: Introductionmentioning

confidence: 99%

H-NMR Relaxometry to Monitor Wetting and Swelling Kinetics in High-organic Matter Soils

et al. 2005

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Variations of soil moisture conditions affect sorption properties of soil organic matter and the pore size distribution of the soils and thus are expected to have an impact on the availability of pollutants and nutrients in soils. At least two principal processes that occur when a soil-water contact is established, are involved. Wetting, which is the very first step, is governed by the interactions of water with the surface of soil organic matter (SOM). The wettability of the pore walls determines the pore accessibility for water. Only in wettable soils, water will occupy the smallest pores first. In the course of wetting, the wettability of the pore walls increases, leading to water redistribution. Swelling of SOM is accompanied by an increase of volume due to the water uptake of the solid SOM phase and will change the SOM polarity. Swelling will thus affect sorption processes in the bulk SOM phase and is expected to change the pore sizes. In this contribution, we investigated swelling and wetting kinetics of soil samples by H-NMR-Relaxometry. We found different effects of wetting and swelling on the development of relaxation time distribution and thus of the pore size distribution. Both swelling and wetting can be slow processes, lasting for up to some weeks. During this time, we found changes in the pore size distribution. For swelling phenomena, we observed a continuous change of the effective pore size, and for wetting phenomena, we found a change in water distribution in a probably rigid pore system. Thus, during swelling and wetting, neither pore size distribution nor sorbent properties of SOM nor hydraulic properties remain constant. Due to the slow kinetics, both processes play an important role in sorption, transport and accessibility for water in hydrophobic areas within a time scale of weeks after e.g. a rainfall event. This will affect the environmental availability and the transport of pollutants and nutrients in the field.Abbreviations: SOM -Soil Organic Matter; DOM -Dissolved Organic Matter; T (T 2 ) -Relaxation Time (Transversal Relaxation Time); S -Surface of the pore walls occupied with water; V -Volume of the water filled pores; T S -Relaxation time of the water protons at the surface; k -Thickness of the layer within which surface relaxation can take place; q -Surface relaxivity, a parameter combined of T S and k: q ¼ k T S ; T B -Bulk relaxation time: relaxation time of the water protons at infinite distance from the pore walls; DPore diameter; r -Grain size (radius); t -Hydration time; Q -Time constant of the first order hydration process; Y, Y 0 , Y ¥ -Y acts as replacement character and is used for the parameters A PT)X , A P)X and TP X (see below), which are the Parameters for the evaluation of the hydration kinetics (Relaxation time or proportion of water). Y 0 values the parameter at the beginning of hydration (t = 0), and Y ¥ values the parameter at infinite hydration time (t fi ¥).; A P)X -Proportion of water assigned to the peak 'X' in the relaxation time distribution; T P)X -Relaxa...

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“…Hydration-induced changes in the macromolecules' mobility (Schaumann and LeBoeuf, 2005) may affect the retention of nutrients and pollutants by minerals coated with organic matter. The ability of soils and soil organic matter to sorb or release organic pollutants has been shown to depend on the state of hydration, hydration time, wetting and drying cycles, and the water content of the samples (Gaillardon, 1996;Altfelder et al, 1999;Johnson et al, 1999;Schaumann et al, 2004). In addition, the structure of organic matter can be affected by the dehydration technique applied in the laboratory, e.g., prior to sorption experiments (Altfelder et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

Restructuring of polygalacturonate on alumina upon hydration—Effect on phosphate sorption kinetics

Mikutta

Krüger

Schaumann

et al. 2006

Geochimica et Cosmochimica Acta

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Differentiating between physical and chemical constraints on pesticide and water movement into and out of soil aggregates

Cited by 16 publications

References 10 publications

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

H-NMR Relaxometry to Monitor Wetting and Swelling Kinetics in High-organic Matter Soils

Restructuring of polygalacturonate on alumina upon hydration—Effect on phosphate sorption kinetics

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