Nitrate movement under simultaneous influence of hydraulic, electric and chemical gradients was investigated. A one-dimensional ion migration model was developed and compared with laboratory column experiments. Operation of subsurface drainage with an electrode was discussed as an application. The ion transport equation was developed utilizing non-equilibrium thermodynamics. Onsager's reciprocal relations were applied to reduce the number of linear phenomenological coefficients that relate flux to driving forces. Then phenomenological coefficients were expressed using known or measurable physical, chemical and electrical properties of solute and porous media. Developed equations were numerically solved by the Integral Finite Difference Method in one dimension. The numerical results were validated with analytical solutions of simple boundary conditions as well as the results obtained from laboratory column experiments for two or three applied gradients. Without water flow, nitrate concentration increased at the anode by 2.5 times after 100 hrs of 30 V application. Three initial concentrations, 10, 100 and 500 ppm NO₃-N, were tested. A log normal relation between elapsed time and relative concentration increase at the anode was obtained. Two flux rates (0.112 and 0.225 cm min⁻¹), and three inflow concentrations (100, 500 and 1000 ppm NO₃-N) were used to evaluate nitrate transport in the column. Nitrate concentration at the anode increased by 10 to 20% at the end of all experiments. However, the concentration in the column was same as inflow concentration. The application of electrokinetic nitrate removal by installed subsurface drainage with on-off (no flow then flush out) operation is recommended over a continuous flow approach. The numerical model results showed very low flux rates (i.e. 2.68 x 10⁻³ cm min⁻¹) are required for nitrate accumulation in a sand column, and the experimental results confirmed no accumulation at a flux rate of 0.112 cm min⁻¹.

Siderophores are low molecular weight organic compounds secreted into the environment by bacteria and fungi in response to iron stress. Significant levels of siderophores have been found in the rhizosphere of crop plants; however, their potential significance in terms of mobilizing iron and other micronutrient cations has been overlooked. This research project studied the occurrence of siderophores in some Saskatchewan soils, and their importance in complexing and increasing availability of Cu, Fe, Mn, and Zn. Twenty four soils were surveyed for siderophore levels using a bioassay which employed the siderophore-requiring bacterium, Arthrobacter jlavescens JG-9. Hydroxamate type siderophores (HS) in the range of 2.1 to 27.3 x 10-9 M deferrioxamine methane sulfonate (DFOM) equivalents were detected in these soils. There was no simple correlation between HS levels and soil pH, % organic carbon, % clay, or DTPA-extractable Cu, Fe, Mn, and Zn. A total of 210 bacteria were isolated from the rhizosphere of wheat roots grown in three soils (Medstead, Smeaton, and Choiceland), which contained the highest HS levels. Bacteria were screened for siderophore production using the Arthobacterjlavescens JG-9 bioassay and the Chrome Azurol-S chemical method. Out of the 210 isolates, 29 were found to be producing siderophore. The 29 siderophore-producing bacteria and 9 plant growth-promoting rhizobacteria (PGPR) were further screened for the most efficient siderophore-producing bacteria. Three bacterial strains, CH 16, R III and KC 21, were selected and identified as Pseudomonas fluorescens. The efficient strains were grown in broth culture and their siderophores extracted and purified by Bio-Gel P2 filtration. The purified siderophores were used to study the mechanisms by which siderophores could increase availability of micronutrient cations. It was shown that siderophores produced by these bacterial strains were able to complex not only with Fe, but also with Cu. Another way by which these siderophores increased the availability of micronutrient cations was through dissolution of iron-hydroxide, thereby releasing specifically adsorbed and coprecipitated Cu, Mn, and Zn. The qualitative characterization of bacterial siderophores indicated that some components of these compounds are heat labile, and have maximum absorbance between 375 to 425 nm. The scanning of these siderophores in the infrared region indicated the presence of carboxyl and amino groups. My research shows that Saskatchewan soils contain siderophore levels that are high enough to increase the availability of Cu, Fe, Mn, and Zn. However, the ability of siderophore-producing bacteria to colonize plant roots under field conditions may be limited. Therefore, the use of siderophore-producing bacteria as seed inoculants might increase the level of siderophores in the rhizosphere and facilitate micronutrient nutrition of crops.

<p> Tillage is the common practice for seedbed preparation prior to early spring vegetables. To investigate the possibility of eliminating the need for spring tillage through the use of cover crops, spring seedbed characteristics after winterkilled cover crops forage radish (Raphanus sativus L.) and oat (Avena sativa L.) were monitored prior to and during growth of no-till and rototilled plantings of spinach (Spinacia oleracea var. Tyee) over four site years in Maryland's Coastal Plain and Piedmont regions. Results indicate that forage radish can facilitate no-till planting of spring vegetables in the mid-Atlantic without herbicides or fertilizer. Forage radish increases soil nitrate and sulfate in early spring and is best suited as a cover crop before the earliest planted main crops.</p>

Discrepancies in ecotoxicity effects data derived from soils amended with dissolved metals in the laboratory and soils from historically aged metal-contaminated sites pose a challenge in deriving environmentally relevant soil quality criteria. In this thesis, the chemical artefacts produced by dissolved metal additions and the subsequent effects on metal bioavailability, toxicity and bioaccumulation are examined. The overall goal of this research is to advance the understanding of soil trace metal bioavailability mechanisms and improve current methods for ecotoxicity testing and bioavailability modeling. / The first objective was to develop a leaching method which would minimize the "salt-effect" commonly observed in freshly-spiked soil samples. This was achieved by adapting a column leaching procedure in order to spike and leach larger volumes of test soil as a preparatory step prior to ecotoxicity assays. An experiment was set up to observe changes to leachate chemistry resulting from the dissolved Cu additions and subsequent leaching with two weak electrolyte solutions. Results showed that leaching removed the excess dissolved Cu as well as the excess acidity and base cations that were solubilized during the Cu additions. Differences between control and spiked samples of some key soil solution parameters (e.g. pH, DOC and total dissolved Ca, Mg, Al, Fe) were reduced thereby resulting in a set of spiked samples more conducive to deriving causal dose-response relationships. / A second experiment compared soil and soil solution properties of samples which underwent the spike/leach procedure to those of freshly spiked samples. Lower soil pH (up to 0.81 pH units) and DOC concentrations were observed in non-leached samples as well as up to 35-fold and 55-fold increases of dissolved Ca and Mg concentrations, typical of the salt-effect. It was estimated that the non-leached samples contained up to 100-fold greater Cu2+ and 50-fold greater Al3+ activities which, I hypothesized, could result in greater phytotoxicity of non-leached samples. Bioassays were conducted wherein Hordeum vulgare (barley) seedlings were exposed to the leached and non-leached Cu-spiked soil samples for 14 days. The leached samples were less toxic to barley and showed significant increases (up to 1.7-fold) in median inhibitory concentrations (i.e. IC50) for root elongation in two of the three test soils. The Cu2+ fraction was able to explain much of the variability in toxicity between leached and non-leached samples, as well as among the different test soils. One exception was the most acidic test soil for which plants in the leached samples showed up to 10-fold greater toxicity than plants in the non-leached samples, when exposed to similar Cu2+ activities. Soil speciation and bioaccumulation data for Cu, Al and Ca were used to deduce that Ca deficiency and possibly Al toxicity contributed to the toxicity observed in this sample set. / In a modeling exercise, the concepts of the terrestrial biotic ligand model (TBLM), which take into account ion competition at the soil solution/root interface, to describe toxic response in our samples. Results showed that the additive effects of Cu and Al toxicity estimated from the Cu-root ligand complex (Cu-BL+) and Al-root ligand complex (Al-BL2+ ) accounted for more of the variability in toxic response data than did the Cu2+ fraction or the Cu-BL+ fraction alone. The model however, could not account for the effects of the Cu-induced Ca deficiency in the most acidic test soil, thus highlighting one of the limitations of the TBLM. This thesis has contributed to the understanding of metal bioavailability mechanisms affected by soil spiking procedures and highlights the benefits of soil leaching in preparing soil samples for ecotoxicity assays which should improve trace metal risk assessment in the future.

The goal of this study was to design, characterize and test a flow-through extraction cell for rapid determination of toxic metals present in soil and sediment samples. / Based on a design elaborated by Jean Bouffard, a Teflon cell was first machined, but it appeared to be leaky and hard to disassemble without breaking the fritted glass discs. To overcome these difficulties, a poly ether ether ketone (PEEK) cell was machined and several parts were modified. Even though the shape and seal of the components seemed to be affected when heated, the cell was working at room temperature and proved promising for future work. / Finally, the EPA (Environmental Protection Agency) method 1311 was applied on some real samples, and the extracts were analyzed in order to get reference results that could eventually be compared to results given by extracts obtained with the flow-through cell.* / *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.

<p> The quantification and prediction of soil properties is fundamental to further understanding the Critical Zone (CZ). In this study we aim to quantify and predict soil properties within a forested catchment, Marshall Gulch, AZ. Input layers of soil depth (modeled), slope, Saga wetness index, remotely sensed normalized difference vegetation index (NDVI) and national agriculture imagery program (NAIP) bands 3/2 were determined to account for 95% of landscape variance and used as model predictors. Target variables including soil depth (cm), carbon (kg/m²), clay (%), Na flux (kg/m²), pH, and strain are predicted using multivariate linear step-wise regression models. Our results show strong correlations of soil properties with the drainage systems in the MG catchment. We observe deeper soils, higher clay content, higher carbon content, and more Na loss within the drainages of the catchment in contrast to the adjacent slopes and ridgelines.</p>

<p> Carbon isotope studies are commonly used to provide a proxy for past vegetation communities and for evaluating environmental change. Original studies suggested carbon isotope ratios of soil organic matter (SOM) faithfully preserved the isotopic composition of standing vegetation with little or no modification in the pedogenic and shallow burial environment. Recent studies of modern soils and laboratory experiments suggest that this may not necessarily be the case and that degradation of SOM in the burial environment may alter the original C-isotope ratio of bulk SOM. A first step in addressing the issue is to begin to understand the transformations of SOM in the burial environment; of particular interest in this study are transformations involving microbial residues. Sedimentary sequences with stacked buried soils afford the opportunity to study the changes that may occur through time and are especially useful if numerical ages and other environmental proxies are present.</p><p> The objective of this study is to thoroughly investigate the composition and quantity of organic matter that has been preserved in the surface and buried soils at the Claussen site, using Fourier Transform Infrared Spectroscopy (FTIR), which provides an estimate for the abundance of organic matter components preserved in each paleosol's SOM. We can trace the fate of bioavailable OM and determine the magnitude of preferential decay of SOM with time by first comparing the composition of bulk SOM to the composition of physically protected carbon, located in soil microaggregates (Christensen, 1992) of the stacked buried soils. The results of this project suggest differences in the composition of paleosol and surface soil SOM that could impact paleovegetation interpretations derived from &delta;¹³C values.</p>

As very little detailed X-ray diffraction investigations have been carried out in South Africa on 2:1 phyllosi1icates in soils, the aim of the present study was to contribute to the knowledge of soil genesis, as well as K-fixation and swelling, by investigation of the clay fraction of selected soils known to be rich in these minerals. X-ray diffraction analysis has been used almost exclusively as the investigative technique. In Chapter 1 a literature review is presented on the reasons for X-ray diffraction peak broadening and the problems encountered in the identification of swelling clay minerals. For interstratifications, the concept of an ABAB layer sequence, considered as having suggested an abab that the inter1ayer space, X-ray diffraction is questioned. data from which It is the ABAB arrangement is inferred can as well be explained in terms of an alternative AAAB layer sequence, having an aabb interlayer arrangement. Chapters 2, 3 and 4 deal with layer silicate formation/alteration in the course of soil development in dolerite and shale-derived profiles. Dolerite-derived pedons could· be characterized by one of the following layer silicate suites : suite i : discrete smectite (Fe-containing beidellite-montmorillonite) with or without traces of kaolinite and talc (Vertisol) suite ii : smectite-kaolinite interstratification (Vertisol) suite iii : 14 ft minerals (vermiculite, beidellite, montmorillonite, chlorite) and 7 ft minerals (halloysite, kaolinite ) in about equal proportions (Vertisol and Mollisol) suite iv : kaolinite with subordinate chlorite and traces of talc (Oxisol, Ultisol). Eccashale-derived Vertisols are dominated by mica-smectite interstratifications. The occurrence of an iron-rich pedogenic talc is discussed in Chapter 4. X-ray and chemical data suggest 30 - 50 mole percent substitutions of iron for magnesium. The mineralogical basis for K-fixation has been established in Chapter 5. Two K-fixing components could be identified : dioctahedral high-charge vermiculite as a discrete mineral and random mica-smectite interstratifications with 20 - 60% mica. In Chapter 6, some of the most expansive soils in South Africa have been investigated. They can be subdivided into two groups denoted by the swelling component as follows : (a) smectite-dominated (the smectite species involved being most probably beidellite with a heterogeneous charge distribution); (b) mica-smectite interstratification with random or ordered stacking arrangement. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

<p> We investigated the agricultural use of locally produced biosolids compost, the fate of the antibiotic ciprofloxacin during the composting process, community perceptions about biosolids, and sociological factors of community involvement in waste management research and decision-making. </p><p> Two biological assays were used to determine if the antibiotic ciprofloxacin selects for and amplifies ciprofloxacin-resistant bacteria during composting. A third biological assay measured the capacity of compost to adsorb ciprofloxacin from solution. Our results show that the ciprofloxacin had no selective effect on resistant populations of bacteria during composting and that the compost was capable of adsorbing and effectively neutralizing this antibiotic. </p><p> A two-year field trial was conducted to evaluate the potential of biosolids compost as a high-carbon soil amendment in local agriculture. Potatoes and small grains were grown with biosolids compost and/or synthetic fertilizer and effects on crop yield, soil fertility, and soil quality were measured. Biosolids compost increased potato tuber and grain yield in the second year, demonstrating cumulative effects of repeated compost applications. In this study, the value of biosolids compost was primarily as a source of nitrogen, plant available phosphorus, and soil organic matter. </p><p> A mail survey of 1,374 Skagit County households was conducted to gain insight into community perceptions about the use of biosolids in local agriculture, interest in using biosolids compost as a soil amendment, and desire to participate in local waste management decision-making processes. Mail survey results and participant observation were used to develop a case study of community involvement in waste management research and decision-making in the town of La Conner. </p><p> This project addressed challenges inherent in conducting research on a controversial topic while developing a new collaborative research model for the region. Scientists, public planners and biosolids managers may be able to build and improve upon what was learned here in their efforts to develop effective regional waste management solutions.</p>

<p> ¹⁰Be_met, or cosmogenic beryllium, has a long half-life of 1.4 million years and quick adsorption on soil particles, which may make it ideal for dating soil erosion in historical context. However, there are questions on about the fundamental assumptions of the retentivity of ¹⁰Be_met. This manuscript explores these assumptions and the context of nutrient cycling in a natural forest setting. </p><p> To see if ¹⁰Be_met was being cycled through the trees, and at what rate, we looked at the[¹⁰Be_met] in the soil, 4 species of trees, and their leaves. The isotopic ratio¹⁰Be/⁹Be in all four tree species was comparable to the soil on which they grow, ranging from 6-8 x 10 ^-9. However, there was one exception with hickory (<i>Carya spp.</i>) which strongly bioaccumulate beryllium with an average of 0.38 ppm dry weight in the wood. Abscised hickory leaves have a higher [Be] of 2.0 ppm, over 10 times higher than in the soil. </p><p> Using standard allometric equations relating tree biomass to trunk diameter, and assuming that belowground biomass has the same [Be] as aboveground, we calculate that hickory trees at our site contain approximately 1% of the total ¹⁰Be_met under their canopy and that ~10% of this Be is cycled annually by leaf abscission. It is not clear at this point what fraction of litterfall Be is recycled into the plant, returned to the soil, or carried to groundwater as organic chelates. </p><p> Hickory trees occupy an average of ~10% of the oak-hickory forest area. Assuming that trees are randomly distributed, that litterfall Be is returned to the soil, and maintaining a constant ¹⁰Be_met budget over time for simplicity, then more than half of all ¹⁰Be_met in the forest soil will have passed through a hickory tree over the past 10 ky. Fully 90% of all ¹⁰Be_met will pass through a hickory tree over a period of ~25 ky. It is clear that hickory trees can transport a sizable fraction of the total ¹⁰Be_met in their nutrient cycle, and that they may be responsible for landscape-scale Be mobility.</p>