Movement of Nutrients to Plant Roots

Olsen, S. R.; Kemper, W. D.

doi:10.1016/s0065-2113(08)60855-x

Cited by 211 publications

(92 citation statements)

References 66 publications

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“…The diffusion flux of dissolved nutrients in porous media is described by Fick's law considering a tortuosity factor, n that accounts for constrained aqueous pathways in porous media that vary with saturation or matric potential [Olsen and Kemper, 1968]:…”

Section: Nutrient Diffusionmentioning

confidence: 99%

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

Ebrahimi

2014

Water Resources Research

110

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The dispersal rates of self-propelled microorganisms affect their spatial interactions and the ecological functioning of microbial communities. Microbial dispersal rates affect risk of contamination of water resources by soil-borne pathogens, the inoculation of plant roots, or the rates of spoilage of food products. In contrast with the wealth of information on microbial dispersal in water replete systems, very little is known about their dispersal rates in unsaturated porous media. The fragmented aqueous phase occupying complex soil pore spaces suppress motility and limits dispersal ranges in unsaturated soil. The primary objective of this study was to systematically evaluate key factors that shape microbial dispersal in model unsaturated porous media to quantify effects of saturation, pore space geometry, and chemotaxis on characteristics of principles that govern motile microbial dispersion in unsaturated soil. We constructed a novel 3-D angular pore network model (PNM) to mimic aqueous pathways in soil for different hydration conditions; within the PNM, we employed an individual-based model that considers physiological and biophysical properties of motile and chemotactic bacteria. The effects of hydration conditions on first passage times in different pore networks were studied showing that fragmentation of aquatic habitats under dry conditions sharply suppresses nutrient transport and microbial dispersal rates in good agreement with limited experimental data. Chemotactically biased mean travel speed of microbial cells across 9 mm saturated PNM was $3 mm/h decreasing exponentially to 0.45 mm/h for the PNM at matric potential of 215 kPa (for 235 kPa, dispersal practically ceases and the mean travel time to traverse the 9 mm PNM exceeds 1 year). Results indicate that chemotaxis enhances dispersal rates by orders of magnitude relative to random (diffusive) motions. Model predictions considering microbial cell sizes relative to available liquid pathways sizes were in good agreement with experimental results for unsaturated soils. The new modeling platform enables quantitative consideration of key biophysical factors (e.g., pore space heterogeneities and hydration conditions) governing microbial interactions in 3-D soil pore spaces.

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Section: Nutrient Diffusionmentioning

confidence: 99%

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

Ebrahimi

2014

Water Resources Research

110

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“…The three models are as follows. .98 model was actually taken from work by Kemper and Van Schaik [1966] and Olsen and Kemper [1968], but I will call it Wright's model for brevity. In Wright's model, a varies from 0.005 to 0.001, depending on soil type and texture.…”

Section: Tortuosity Modelsmentioning

confidence: 99%

Compliance Assessment Document for the Transuranic Wastes in the Greater Confinement Disposal Boreholes at the Nevada Test Site, Volume 2: Performance Assessment

Cochran¹,

Beyeler²,

Brosseau³

et al. 2001

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Intermediate depth disposal operations were conducted by the U.S. Department of Energy (DOE) at the DOE's Nevada Test Site (NTS) from 1984 through 1989. These operations emplaced highspecific activity low-level wastes (LLW) and limited quantities of classified, "special case" transuranic (TRU) wastes in 37 m (120-ft) deep, 3 m (10 ft) diameter Greater Confinement Disposal (GCD) boreholes.Four boreholes contain about 60,000 kg (132,000 lb.) of classified TRU waste packages, containing less than 330 curies of Plutonium-239. All of the TRU wastes emplaced in the GCD boreholes are classified for national security reasons and cannot be disposed of in the DOE's Waste Isolation Pilot Plant.The U.S. Environmental Protection Agency's (EPA's) 40 CFR 191 defines the requirements for protection of human health from disposed TRU wastes. This EPA standard sets a number of requirements, including probabilistic limits on the cumulative releases of radionuclides to the accessible environment for 10,000 years. This report presents the performance assessment (PA) that has been conducted to determine if disposal of TRU waste in the GCD boreholes complies with the EPA's 40 CFR 191 requirements.Sandia National Laboratories completed this PA using all available information and an Iterative PA Methodology, which focused work on uncertainty reduction in a cost-effective fashion that does not overestimate system performance and assured defensibility. The simplicity of the conceptual models of the GCD disposal system allowed them to be implemented in Microsoft ® Visual Basic™ macros in an Access™ database. This PA model is built from a mathematical expression for mass conservation that includes the operation of a number of transport processes, including dissolution, precipitation, reversible chemical sorption onto soil, advection, diffusion, dispersion, radioactive decay and ingrowth, plant uptake, and bioturbation. The mathematical model and implementing code was used to calculate a complementary cumulative distribution function of integrated normalized release to the accessible environment for 10,000 years and probability distributions of dose based on two exposure conditions for the 1,000 year individual protection requirements.The primary conclusions of this PA are that the disposal of TRU wastes in the GCD boreholes will, at most, result in minuscule doses to individuals, and that the GCD disposal system easily meets the EPA's 1985, 40 CFR 191 requirements for disposal of TRU waste. Further, there is a strong, reasonable expectation that actual system performance will be better than what is simulated in this PA.vi ACKNOWLEDGMENTS

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“…Moreover, if surface diffusion is important, diffusion coefficients should not decrease with decreasing volumetric moisture content of soil because the electrical double layer is not affected and only the pore water content decreases. However, diffusion coefficients in soils and clays generally decrease markedly with decreasing moisture content (Nye 1979;Olsen and Kemper 1968).…”

Section: Introductionmentioning

confidence: 99%

Surface Diffusion: Is It an Important Transport Mechanism in Compacted Clays?

Oscarson

1994

Clays and clay miner.

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Abstract--Surface diffusion, or migration within the electrical double layer next to mineral surfaces, is often invoked as a significant contributor to the overall diffusion coefficient in compacted clays, particularly where model predictions underestimate measured diffusion coefficients. The potential for surface diffusion of Sr 2 § Ca 2+ and Na + on three clays compacted to dry bulk densities of 1.25 and 1.60 Mg/m 3 was examined. The clays were a bentonite, an illite/smectite, and a glacial lake clay (composed mainly of smectite, illite, kaolinite and quartz). The clays were saturated with a Na-Ca-Cl-dominated synthetic groundwater solution with an effective ionic strength of 220 mol/m 3. Total intrinsic diffusion coefficients for the cations were determined from their steady-state flux through compacted clays, and apparent diffusion coefficients were obtained from the time-lag technique. Models of diffusive transport in compacted clays, based only on diffusion in the pore solution, adequately described the diffusion data for all clays and diffusants, and there was no need to invoke other transport mechanisms, like surface diffusion. The data indicate that surface diffusion is not a significant transport mechanism in compacted clays at least to a clay density of 1.60 Mg/m 3.

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Movement of Nutrients to Plant Roots

Cited by 211 publications

References 66 publications

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

Compliance Assessment Document for the Transuranic Wastes in the Greater Confinement Disposal Boreholes at the Nevada Test Site, Volume 2: Performance Assessment

Surface Diffusion: Is It an Important Transport Mechanism in Compacted Clays?

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