Three goals of this research were: (1) to study the movement of a non-reactive tracer (bromide) and of water through non-aggregated fine sand, with low clay (1.2%) and organic matter content (<1%); 2) to develop an inverse method for estimating the hydraulic properties of unsaturated soil from intermediate- and field-scale infiltration data; and (3) to develop a transient in-situ method for calibrating the neutron probe. All three goals of this research are crucial for understanding and determining water and solute transport at the intermediate to field scale. The field research was conducted in a field-scale research facility--the University of Arizona Superfund lysimeter (400-cm deep and 250-cm in diameter). We found equilibrium conditions, as evidenced by symmetrical bromide breakthrough curves (BTCs), from data collected during an unsaturated infiltration experiment in the lysimeter. Breakthrough of bromide, however, occurred sooner than was expected based on water arrival, and this observation is inconsistent with previous observations of other investigators. About 21% of the pore water (corresponding to approximately 0.03 cm³ cm⁻³) was found to be isolated from the bromide transport. We postulate that this inaccessible water partly existed as very thin films, adsorbed onto soil particle surfaces, and did not participate in anion transport. The combined effect of these films and of anion exclusion caused the bromide tracer to travel faster than the wetting front in this initially dry soil, because the excluded water fraction was larger than the initial water content. The soil hydraulic properties were estimated by an inverse method using in-situ data collected from this deep infiltration experiment. Soil hydraulic properties determined from laboratory experiments often are non-representative of field conditions. The inverse method developed in this study uses transient tension data during wetting of the profile, and the steady state water content found behind the wetting front. The results indicate that the method is fast and yields a unique estimate of the in-situ hydraulic properties at the field scale, without the need to collect excessive amounts of data. The neutron moisture meter used to determine the soil water content was calibrated using a newly developed transient mass balance method. The method was tested in the field scale lysimeter, and at a field site at the Agriculture Center, Maricopa, AZ. Water content errors using this method were less than 0.01 cm³ cm⁻³ for both sites. Application of the method to the lysimeter data showed excellent agreement between the soil water storage obtained using the calibration curve, and the actual volume of soil water added into the system.

The objective of this research was to evaluate the impact of bioaugmentation of soil with microorganisms harboring plasmid pJP4 on remediation, plasmid transfer, and plasmid dispersal. Divided into three sections, this research showed that use of microbial inocula harboring self-transmissible plasmids holds promise as an applicable bioremediation approach. In the first study, a pJP4 donor that could readily be counter-selected due to a lack of chromosomal genes necessary for 2,4-dichlorophenoxyacetic acid (2,4-D) mineralization was generated to allow detection of transconjugants in soil. Plasmid pJP4 was introduced into Escherichia coli (ATCC 15224), via plate mating with Ralstonia eutropha JMP134 to create such a donor (E. coli D11). Transfer of Plasmid pJP4 to diverse indigenous populations was detected in soils, and under conditions, where it had not been observed previously. Plexiglass columns were used in the second study to evaluate dissemination of plasmid pJP4 under unsaturated or saturated flow conditions in a 2,4-D contaminated soil. In unsaturated soil, pJP4 was detected in both culturable donor and transconjugant cells extending to 10.5 cm from the inoculated layer. In soil subjected to saturated flow conditions, no transconjugants were detected; however, donors were found throughout the entire length of the column (30.5 cm). Thus, donor transport in conjunction with plasmid transfer to indigenous recipients allowed for significant dissemination of introduced genes through contaminated soil. The last study was conducted using soil contaminated with 2,4-D alone or co-contaminated with 2,4-D and cadmium (Cd). This study assessed the impact of introduction of the pJP4 genes via cell bioaugmentation (R. eutropha JMP134 donor), or via gene augmentation (E. coli D11 donor). Both introduced donors remained culturable and transferred plasmid pJP4 to diverse indigenous recipients. Cell bioaugmentation resulted in the most rapid 2,4-D degradation; however, upon a second exposure to 2,4-D, gene augmentation of indigenous populations was more successful. The presence of Cd (100 μg g dry soil⁻¹) had a minimal impact on 2,4-D degradation and transconjugant formation. The establishment of an array of stable indigenous plasmid hosts may be particularly useful in sites with potential for re-exposure or extensive, and thus, long term contamination.

Forty percent of hazardous waste sites on the U.S. Environmental Protection Agency's National Priority List (NPL) are cocontaminated with organic and metal pollutants. Conventional approaches to remediating these sites are costly and often ineffective. Bioremediation is a promising, cost-effective alternative but metal toxicity at cocontaminated sites may limit its efficacy. The research described in this dissertation provides two new possible approaches to enhance the bioremediation of cocontaminated environments and sheds light on the relationship between metal concentration and inhibition of organic pollutant biodegradation. In Objective 1, a rhamnolipid biosurfactant was employed to increase naphthalene biodegradation in the presence of cadmium. The biosurfactant reduced bioavailable cadmium concentrations and increased naphthalene bioavailability. Neither of these phenomena, however, fully accounted for the ability of rhamnolipid to reduce cadmium toxicity. The ability of rhamnolipid to alter the cell surface appeared critical to its ability to mitigate toxicity. In Objective 2, pH was lowered to increase naphthalene biodegradation in the presence of cadmium. Reductions in pH had previously been reported to mitigate metal toxicity, but the mechanism of such reductions warranted elucidation. Previous studies implicated the formation of monovalent hydroxylated metal in the mechanism by which pH mediates toxicity. Results of this study, however, suggest that the importance of such species in determining toxicity may be much less than that of the increased competition between hydrogen and metal ions for binding sites on the cell surface at reduced pH. An indirect relationship between metal concentration and inhibition of organic biodegradation was revealed in Objective 3. Naphthalene biodegradation was more sensitive to cadmium concentrations of 10 and 37.5 mg/L than 100 mg/L. For this reason, we investigated whether naphthalene biodegradation could be increased in the presence of a toxic concentration of cadmium by raising the total metal concentration to a higher, but relatively less toxic concentration. Only elevated concentrations of zinc reduced cadmium toxicity. High but less toxic levels of metal may more rapidly induce the transcription of a gene(s) important in metal efflux than lower more toxic concentrations.

A series of three experiments were conducted to determine the diversity of indigenous chlorobenzoate (CB) degraders in soil and to investigate the use of different methods of bioaugmentation for remediation of contaminated soil. In the first study, soil was amended with either 500 or 1000 μg of 3-CB g⁻¹ and was either uninoculated or inoculated with the 3-CB degrader Comamonas testosteroni BR60. Bioaugmentation with C. testosteroni BR60 increased 3-CB degradation at both contaminant levels, and the increase was more pronounced at the higher level due to contaminant inhibition of indigenous 3-CB degraders. Bioaugmentation also appeared to reduce the deleterious effects that 3-CB contamination had on indigenous soil microbial populations as evidenced by changes in culturable heterotrophic bacterial populations. In the second study, two similar pristine soils were contaminated with 500 μg of 2-, 3-, or 4-CB g⁻¹ . The two soils differed in their ability to degrade the compounds with one degrading 2- and 4-CB and the other degrading 3- and 4-CB. Several hundred degraders were isolated, grouped according to DNA fingerprints, and selected degraders were identified by 16S rDNA sequences. The identity of the CB degraders differed between the two soils. The results indicated that the development of 2-, 3-, and 4-CB degrader populations was site-specific even for the soils that developed under similar soil-forming conditions. The third study also used the two soils from the second study. This project investigated the potential for use of activated soil, which contained an indigenous degrader population, as a bioaugmentation inoculant. An aliquot of a given soil that contained an indigenous 2-, 3-, or 4-CB degrader population was added to a soil that did not have an indigenous degrader population for the same contaminant. The study found that bioaugmentation with activated soil increased degradation of each 2-, 3-, and 4-CB but only if the activated soil was pre-exposed to the contaminant prior to use for bioaugmentation. The results from these three studies indicate that CB degrader populations are diverse and variable in pristine soils and, if not present in contaminated soils, appropriate degrader populations may be established via different bioaugmentation strategies.

The toppling of trees forms mounds of disturbed sediment and pits from which the mound removes sediment, rocks, and organic matter. Sites of uprooted trees in Puerto Rico and Colorado were examined (1) to compare areas and volumes of mounds and pits relative to tree size, (2) to compare areas and volumes of mounds and pits formed during catastrophic events at the landscape scale, and (3) to consider decay of mounds and pits after formation. For a given basal area, the analyses found no difference among sites in area and volume of freshly formed individual mounds and pits. For landscape-level catastrophic uprooting, the percent of toppled trees in a plot can explain 85% and 87% of the areas and volumes, respectively, of the quantity of soil uplifted. Exponential decay coefficients developed by monitoring mound/pit complexes indicate that mounds and pits at the humid tropical site in Puerto Rico decay in about 74% and 57% of the time, respectively, of mounds and pits at a temperate Colorado site. Decay coefficients developed for the Colorado site indicate that mounds and pits are reduced to 10% of their original volume within 30 and 78 years, respectively. Coefficients for Puerto Rico suggest that a similar reduction in volume requires 17 years, whereas pits generally fill within a decade.

The encroachment of deeply rooted woody plants into grasslands throughout the world has the potential to alter local, regional, and global water balance. The consequence of encroachment by woody plants on ecosystem water balance is, in part, related to the sensitivity of these plants to summer and winter precipitation pulses. This dissertation addresses the primary question: does pulse sensitivity of a dominant warm-desert woody plant, velvet mesquite (Prosopis velutina Woot.) vary across soil texture and water availability gradients? To address this question, sap flow and xylem anatomy and function were evaluated in mature velvet mesquite trees at two upland sites varying in soil texture at the Santa Rita Experimental Range (SRER), and one floodplain site along the San Pedro River National Conservation Area (SPRNCA). Experimental irrigation was used to assess the sensitivity of mesquite plants to small and large precipitation pulses. There was a moderate response to both small (10 mm) and large (35 mm) irrigation inputs by trees on sandy-loam soil, while trees on loamy-clay soil were only responsive to the large pulse. The differential response between sites was associated with differences in infiltration of the experimental pulses between the two soil types. Model predictions of the critical transpiration rate (Ecrit )--above which hydraulic conductivity through the soil-plant continuum falls to zero--showed that trees at the sandy-loam site operated well below their maximum transpiration rate before the onset of the monsoon. Conversely, plants on loamy-clay soils likely operate closer to their maximum permissible transpiration rates throughout the growing season. Hydraulic redistribution was observed and rates were tightly coupled to growing season and dormant season precipitation inputs. Hydraulic redistribution could enhance pulse sensitivity by transferring soil water to regions of the root zone that are otherwise dry, thereby allowing a greater proportion of the root system to participate in the extraction of pulse water during transpiration. Results from this research suggest that patterns of mesquite water relations are strongly mediated by soil texture. Nevertheless, once established, mesquite plants substantially modify ecosystem water balance, due to their responsiveness to growing season precipitation pulses, and their ability to withstand severe water deficits between precipitation pulses.

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.

<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.