225 research outputs found
Water and chemical transport in limestone: Merging measurement and modelling concepts at different scales
No full textThis master thesis analyses the hydrogeological properties that are determining the transport of water and solutes in a limestone aquifer. A closer look is been taken at the hydraulic conductivity and effective porosity of the limestone aquifer through experiments on small scale samples and an iterative process of in situ tests and numerical modelling.This thesis provides a toolbox to investigate and describe the architecture of the dual porosity system in limestone by gas diffusion through small scale samples. The hydraulic conductivity and effective porosity of small scale samples are determined through indirect and direct measurement methods and visualisation techniques. These hydrogeological parameters are also defined for a limestone aquifer through an iterative process of in situ tests and modelling. These parameters for both scales are compared and connected to each other to conclude this thesis.<br/
Effect of long-term irrigation and cultivation practices on X-ray CT and gas transport derived pore-network characteristics
No full textStochastic analyses of field‐scale pesticide leaching risk as influenced by spatial variability in physical and biochemical parameters
No full textModelling fungal growth in heterogeneous soil:analyses of the effect of soil physical structure on water distribution and fungal colonisation
No full textFungi play a pivital role in soil ecosystems contributing to plant productivity. The underlying soil physical and biological processes responsible for fungal colonistaion are interrelated and, at present, poorly understood. If these complex processes can be understood then this knowledge can be managed with an aim to providing more sustainable agriculture. Our understanding of microbial dynamics in soil has long been hampered by a lack of a theoretical framework and difficulties in observation and quantification. We will demonstrate how the spatial and temporal dynamics of fungi in soil can be understood by linking mathematical modelling with novel techniques that visualise the complex structure of the soil. The combination of these techniques and mathematical models opens up new possibilities to understand how the physical structure of soil affects water distribution which subsequently impacts on fungal colony dynamics. We will quantify, using X ray tomography, soil structure for a range of artificially prepared microcosms. We characterise the soil structures using soil metrics such as porosity, pore size distribution, and the connectivity of the pore volume. We use Lattice Boltzmann methods to predict the distribution of water in these soil microcosms. Furthermore we will use the individual based fungal colony growth model of Falconer et al. 2005, which is based on the physiological processes of fungi, to assess the effect of soil structure on water dynamics and microbial dynamics by qualifying biomass distributions. We demonstrate how soil structure can critically affect fungal colony growth and species interactions and how the distribution of water also effects this with consequences for biological control and fungal biodiversity
4.3 Gas Diffusivity
No full textIn general, the diffusion velocities of gas mixtures in porous media are related to each other in a complex manner dependent upon the mole fraction of each gas, the molar fluxes of each gas, and the binary diffusion coefficient of each gas pair. Soil-type effects on gas diffusivity in sieved and repacked soils appear to be minor and can probably be neglected. The adaption of the solution to measurement of the soil gas diffusion coefficient has been made by D.S. Mclntyre and J.R. Philip. The equations of Currie and Taylor will give the same values of the soil gas diffusion coefficient for t >> 0 when the linear part of the curve is attained if the correction due to change in storage is made. Undisturbed soil cores can be taken from the field with samplers. The two-chamber laboratory method is based upon an experimental apparatus consisting of two air chambers separated by a soil chamber.</p
Modelling fungal growth in heterogeneous soil:analyses of the effect of soil physical structure on water distribution and fungal colonisation
No full textFungi play a pivital role in soil ecosystems contributing to plant productivity. The underlying soil physical and biological processes responsible for fungal colonistaion are interrelated and, at present, poorly understood. If these complex processes can be understood then this knowledge can be managed with an aim to providing more sustainable agriculture. Our understanding of microbial dynamics in soil has long been hampered by a lack of a theoretical framework and difficulties in observation and quantification. We will demonstrate how the spatial and temporal dynamics of fungi in soil can be understood by linking mathematical modelling with novel techniques that visualise the complex structure of the soil. The combination of these techniques and mathematical models opens up new possibilities to understand how the physical structure of soil affects water distribution which subsequently impacts on fungal colony dynamics. We will quantify, using X ray tomography, soil structure for a range of artificially prepared microcosms. We characterise the soil structures using soil metrics such as porosity, pore size distribution, and the connectivity of the pore volume. We use Lattice Boltzmann methods to predict the distribution of water in these soil microcosms. Furthermore we will use the individual based fungal colony growth model of Falconer et al. 2005, which is based on the physiological processes of fungi, to assess the effect of soil structure on water dynamics and microbial dynamics by qualifying biomass distributions. We demonstrate how soil structure can critically affect fungal colony growth and species interactions and how the distribution of water also effects this with consequences for biological control and fungal biodiversity
Effect of long-term irrigation and tillage practices on X-ray CT and gas transport derived pore-network characteristics
No full textThe gas transport parameters, diffusivity and air-filled porosity are crucial for soil aeration, microbial activity and greenhouse gas emission, and directly depend on soil structure. In this study, we analysed the effect of long-term tillage and irrigation practices on the surface structure of an arable soil in New Zealand. Our hypothesis was that topsoil structure would change under intensification of arable production, affecting gas exchange. Intact soil cores were collected from plots under intensive tillage (IT) and direct drill (DD), irrigated or rainfed. In total, 32 cores were scanned by X-ray computed tomography (CT) to derive the pore network >30 μm. The cores were then used to measure soil-gas diffusivity, air-permeability and air-filled porosity of pores close to the resolution of the X-ray CT scans, namely ≥30 μm. The gas measurements allow the calculation of pore-network connectivity and tortuosity parameters, which were compared with the CT-derived structural characteristics. Long-term irrigation had little effect on any of the parameters analysed. Total porosity tended to be lower under IT than DD, whereas the CT-derived porosity was comparable. Both the CT-derived mean pore diameter (MPD) and other morphological parameters, as well as gas measurement-derived parameters, highlighted a less developed structure under IT. The differences in the functional pore-network structure were attributed to SOC depletion and the mechanical disturbance through IT. Significant correlations between CT-derived parameters and functional gas transport parameters such as tortuosity and MPD were found, which suggest that X-ray CT could be useful in the prediction of gas transport
Closure to discussion of “Pore network structure linked by X-ray CT to particle characteristics and transport parameters” by Hamamoto S., Moldrup P., Kawamoto K., Sakaki T., Nishimura T., and Komtatsu, T
No full textInteraction between Mesodinium rubrum and its prey: importance of prey concentration, irradiance and pH
No full textABSTRACT: The functional and numerical responses for the marine obligate mixotrophic ciliate Mesodinium rubrum Lohmann, 1908 (=Myrionecta rubra Jankowsky, 1976) were studied at 2 irradiances (20 and 100 µE m2 s-1). Furthermore, its tolerance to high pH levels and response to starvation were studied in mixed cultures of M. rubrum and Teleaulax sp. The functional and numerical response study showed that the threshold concentration of the cryptophyte Teleaulax sp. was 50 cells ml-1 and the maximum growth of M. rubrum was 0.23 and 0.49 d-1 for 20 and 100 µE m2 s-1, respectively. Calculation of ingestion rates revealed that ~1 Teleaulax sp. cell M. rubrum-1 d-1 was sufficient to maintain the maximum growth rate. Maximum ingestion rates were independent of light and saturated at ~6 Teleaulax sp. cells M. rubrum-1 d-1. A heterotrophic carbon uptake of from 2 to 4% of M. rubrum carbon content was sufficient for maximum growth, but carbon contributions as high as 22% were observed to have no effect on growth. The pH experiments revealed that the growth of M. rubrum and Teleaulax sp. was impeded at pH levels in excess of 8.5 and 8.8, respectively. Experiments to reveal M. rubrum's response to starvation showed that M. rubrum could survive for around 50 d without prey. These results are all discussed with respect to M. rubrum's adaptation to its environment
GAS CHROMATOGRAPHY MICRO-COLUMN METHOD FOR MEASURING RETARDATION OF VOLATILE ORGANIC CHEMICAL GAS TRANSPORT IN SOILS
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