Browsing by Author "Zelazny, Lucian W."
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- Acid deposition effects on soil chemistry and forest growth on the Monongahela National ForestElias, Patricia Elena (Virginia Tech, 2008-07-28)Acid deposition (AD) results largely from the combustion of fossil fuels, and has been found to negatively impact forest ecosystems. AD may acidify soils through base cation leaching or Al mobilization, may cause accumulation of nitrates and sulfates in soils, and in some cases has been related to forest decline. The Monongahela National Forest (MNF) lies downwind from many sources of AD pollution, and average deposition pH is around 4.4. Therefore, managers are concerned about the possible deleterious effects of AD on the forest ecosystem. During the 2006 Forest Plan revision, evaluation of site sensitivity to acidification was specifically stated as a step in the Forest's adaptive management process. To meet this management objective, forest practitioners must understand the effects AD has on the forest, prescribe appropriate practices, and be able to monitor for future changes. To address the needs of MNF managers we used Forest Inventory and Analysis (FIA) sites to evaluate forest growth patterns on the Forest and determined the relationship between growth and key indicators of soil acidity. Furthermore, we used those relationships to create a map of site resistance to acidification across the MNF. To further develop a monitoring scheme we assessed two soil sampling protocols and two soil analysis methods for their suitability for monitoring AD-related changes in soil chemistry. Additionally, we evaluated the utility of dendrochronological and foliar sampling as AD-specific monitoring methods. Across all FIA sites on the MNF periodic mean annual volume increment (PMAVI) ranged from -9.5 m³ha⁻¹yr¹ to 11.8 m³ha⁻¹yr¹, suggesting lower-than-expected growth on two-thirds of the sites. Growth was compared to soil indicators of acidity on 30 FIA sites. In the surface horizon, effective base saturation (+), Ca concentration (+), base saturation (+), K concentration (+), Fe concentration (-), Ca/Al molar ratio (+), and Mg/Al molar ratio (+), were correlated with PMAVI (p ≤ 0.1). In the subsurface horizon pH(w) (+), effective base saturation (+), Al concentration (-), and K concentration (-) were correlated with PMAVI. Site resistance to acidification was mapped based on site parent material, aspect, elevation, soil depth, and soil texture. There was a significant (p ≤ 0.1) positive correlation between PMAVI and a resistance index developed using five soil and site factors. Resistance was also compared with key soil indicators of AD-induced decline on 28 sites across the forest, and pH, effective base saturation, and Al content were found to be the best indicators related to resistance index. Resistance index was used to create a map of the MNF, of which 14% was highly resistant (RI ≥ 0.7), 57% was moderately resistant (0.7 > RI > 0.45) and 29% was slightly resistant (RI ≤ 0.45). The first of our monitoring program evaluations compared soil sampling and analysis methods on 30 FIA plots. Analyses of variance showed that soil pH, effective base saturation, Ca/Al molar ratio, and sum of bases varied significantly with sampling protocol. We also compared lab analyses methods and found that if sampling by horizon, a linear relationship can be used to estimate Ca/AlSrCl₂ ratio using NH₄Cl extractions. The second monitoring approach evaluated the utility of a northern red oak (Quercus rubra L.) dendrochronology on two FIA plots. This analysis suggests that pollution on the MNF caused a decrease in growth rate during the 50-year period from 1940 to 1990. There were no differences among ring width increment and basal area increment between the two sites. From 1900 to 2007 the two sites showed 58.5% similarity in growth trends, but these could not be attributed to a dissimilar influence of AD. The third monitoring approach evaluated the relationship between foliar and soil chemical indicators. Across FIA plots, nutrient concentrations varied by tree species. The first year results from a potted-seedling study suggest that soil acidity influences growth, and foliar concentrations are related to growth rates. This evaluation of the effects of AD on the MNF can be used to develop adaptive management plans and a monitoring program that will meet the AD-related objectives of the 2006 Forest Management plan.
- Adsorption of sulfate and phosphate at the mineral-water interface: isotherm, stoichiometry, and modelsHe, Liming (Virginia Tech, 1995-10-15)Processes occurring at mineral-water interfaces play critical roles for regulating the composition of surface and groundwater, for soil development, and for the availability of plant nutrients. Sulfate adsorption at three pH levels was conducted on y-AI203 and kaolinite. The adsorption isotherms were described well by the simple Langmuir, two-site Langmuir, Freundlich, and Temkin equations. The capacity of SO42-adsorption for y-AI203 was five times greater than for kaolinite, indicating the difference in reactive site density between y-Ab03 and kaolinite. Mathematical analyses for the adsorption isothenns demonstrated that S042- may not be adsorbed on the d-plane, i.e., in the diffuse layer, whereas both outer- and inner-sphere complexation mechanisms predicted S042- adsorption equally well.
- An approach to studying soil-landscape relationships in VirginiaStolt, Mark H. (Virginia Tech, 1990)Various methods and techniques were used to examine soil-landscape relationships for residual and colluvial soils of Virginia. Soil micromorphology indicated that although some BC and C horizons in the field appeared structureless, evidence of pedogenic process was observed. These were designated as either BCt, BC, or CB horizons depending on the amount of oriented clay and the rates of change with depth of clay, DCB extractable Fe, and sand contents. Soil variability was examined for the overall study, as well as within toposequences, pedons, and individual horizons. Most of the overall variability was attributed to differences between study sites or between horizons, with minimal amounts due to landscape position. Substantial lateral variability occurred within horizons indicating a strong need for subsampling within horizons of the same pedon. Lithologic discontinuities were found to be difficult to recognize without obvious field evidence. Reconstruction analysis was used to examine soil and saprolite formation. Summit and backslope soils were found to be essentially the same in both morphology and degree of profile development. Sand weathering and clay eluviation/illuviation were the major soil forming processes occurring within these soils. Footslope soils were less developed than associated summit and backslope soils, with both depositional and pedologic processes contributing to soil formation and development. Thickness of saprolite was found to decrease. from the summit to the footslope. Thicker saprolite at the summit was apparently related to the greater stability of the summit position compared to the backslope and footslopes. A bucket auger was modified to obtain undisturbed samples of deep saprolite for reconstruction analysis. Saprolite reconstruction indicated that between 20 and 36 % of the mass of the partially weathered rock, which is the precursor to saprolite, is lost during saprolite formation. Most of these losses were either Al or Si. Initial soil formation was shown to occur at a faster rate than saprolite formation, but after substantial profile development, soil formation is reduced to a rate below that of saprolite formation, and saprolite accumulates below the solum. Reconstruction analysis was found to be a valuable tool in studying soil-landscape relationships.
- Arsenic Adsorption on Iron Oxides in the Presence of Soluble Organic Carbon and the Influence of Arsenic on Radish and Lettuce DevelopmentGrafe, Markus (Virginia Tech, 2000-12-12)Chapter 2: Germination and Growth of Radish (Raphanus sativus) and Lettuce (Lactuca sativus) Exposed to Arsenite and Arsenate in Hydroponic Growth Solution Little information is available on the survival, uptake, and dry mass production of vegetable seedlings and maturing plants in arsenic enriched environments. Such information is however very important to many vegetable growers in areas of subsistent agricultural like Bangladesh or home-gardeners in closer proximity of As sources such as metal smelters. Accordingly we conducted research investigating (i) the germination and radical formation of radish and lettuce seeds at varying As (V) and As (III) concentrations and (ii) radish and lettuce plants in solution culture. Seed germination studies demonstrated that 0.1mM and 0.025mM are toxic threshold levels of As (III and V) for radishes and lettuce, respectively, while As (V) is more toxic to radish seeds than As (III). Arsenic (III and V) impacted both germination and radical development in radish seeds. For lettuce we observed that As had no impact on germination but reduced radical length significantly (p < 0.01). At most equimolar concentrations, As (III) was more toxic than As (V) in lettuce seeds (0.025 - 0.10mM As), a result contrary to those obtained in radish seeds (0.05 - 0.5mM As). The hydroponic growth studies showed that losses and increases in dry weight are a function of absorbed As and are dependent on the source of As: As (V) or As (III). Moreover, the effect of absorbed As (V) or As (III) on dry weight reductions and increases differed between root and shoot portions of the plants and are crop dependent. Tissue-As (originally solution As (V)) was more toxic at the radish root level and tissue-As (originally solution As (III)) was more toxic at the radish shoot level. Conversely for lettuce, As (III) caused reductions in dry weight, while As (V) had a stimulating effect on biomass production. Lower As (V) concentrations in plant tissue throughout the lettuce study and at low As (V) concentrations (0.02mM) in the radish study may be explained by the molar ratio of P:As of approximately 5. From a food nutrition safety standpoint, studies need to concentrate on sub-lethal levels in order to ensure the proper formation of the harvestable portion of the plant. Chapter 3: Adsorption of Arsenate (V) and Arsenite (III) on Goethite in the Presence and Absence of Soluble Organic Carbon The environmental fate of arsenic is of utmost importance as the U.S. EPA has recently proposed to tighten the arsenic drinking water standard from 50 ppb to 5 ppb. In natural systems the presence of dissolved organic carbon (DOC) may compete with As for adsorption to mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of arsenate As (V) and As (III) on goethite (α-FeOOH) was investigated in the presence of either a peat humic acid (Hap), a Suwannee River Fulvic Acid (FA) (IHSS) or citric acid (CA). Adsorption edges and kinetic experiments were used to examine the effects of equimolar concentrations of organic adsorbates on arsenic adsorption. Adsorption envelopes were conducted over a pH range of 11 to 3, while the kinetic studies were conducted at pH 6.5 for As (V) and pH 5.0 for As (III). Arsenate adsorption was inhibited in the order of Hap > FA > CA while arsenite adsorption was inhibited in the order of CA > FA > Hap. Humic acid reduces As V adsorption starting at pH 9, with a maximum reduction at pH 6.5. Fulvic acid slightly inhibited As (V) adsorption starting at pH 5, and this inhibition increased with a decrease in pH. No effect was observed in the presence of CA. Arsenite adsorption is inhibited by HA starting a pH 7 and increases with a decrease in pH, while FA and CA reduce As (III) adsorption beginning at pH 8, with a continuous reduction as the pH decreases. The differential extent of As V adsorption in the presence of the organic acids suggests that the distribution and the respective densities of the abundant functional groups (phenol/ catechol OH or COO⁻) are significant in the adsorption of As (V). Furthermore, larger organic acids may hydrophobically partition to surfaces via a more favorable entropy driven reaction mechanism which may influence As (V) diffusion and its subsequent adsorption to surfaces. The decrease in As (III) adsorption is caused by its reduced affinity for the surface at pH values lower than 9, and the simultaneous increase in surface activity by the organic substances' via their COO⁻ functional groups. The results of these experiments suggests that dissolved organic carbon substances are capable of increasing the bioavailability of As in soil and water systems in which the dominant solid phase is a crystalline iron oxide. Chapter 4: Adsorption of Arsenate and Arsenite on Ferrihydrite in the Presence and Absence of Dissolved Organic Carbon (DOC) The adsorption of As (V) and As (III) on synthetic 2-line ferrihydrite in the presence and absence of a peat humic acid (Hap), Suwannee River Fulvic Acid (FA) or citric acid (CA) was investigated. Previous work with goethite has demonstrated the ability of DOC materials to reduce As (V) and As (III) adsorption. In this study, a batch technique was used to examine the adsorption of arsenic (III and V) and DOCs on ferrihydrite in the pH range from 3 to 11. The results obtained demonstrated that As (V) adsorption on ferrihydrite was reduced only in the presence of CA. Arsenate reduced the adsorption of all organic acids except Hap. Both FA and CA reduced As (III) adsorption on ferrihydrite, while Hap had no effect. Fulvic and citric acid adsorption on ferrihydrite was reduced in the presence of As (III), however, adsorption increases of FA and CA were observed at lower pH, which is consistent with a decrease in As(III) adsorption. The peat humic acid had no effect on As (III) adsorption, and we believe that the adsorption process of Hap and As (III and V) on ferrihydrite are independent of each other. The observed differences between this study and the study on goethite are believed to be an intricate function of ferrihydrite's surface characteristics, which affects the mechanisms of surface adsorption and hence the affinity of organic acids such as Hap, FA, and CA for the ferrihydrite surface. As such, the adsorption of DOCs to ferrihydrite are assumed to be energetically less favorable and to occur with a fewer number of ligands, resulting in lower surface coverage of weaker bond strength. Additional factors for the observed differences are discussed. This work demonstrates the importance of the solid phase in adsorption processes and functional group composition, as noticeable differences are observed in comparison to a crystalline Fe-oxide solid phase.
- Atomic Force Microscopy Study of Clay Mineral DissolutionBickmore, Barry Robert (Virginia Tech, 1999-12-09)An integrated program has been developed to explore the reactivity of 2:1 phyllosilicates (biotite and the clays montmorillonite, hectorite, and nontronite) with respect to acid dissolution using in situ atomic force microscopy (AFM). Three techniques are described which make it possible to fix these minerals and other small particles to a suitable substrate for examination in the fluid cell of the atomic force microscope. A suite of macros has also been developed for the Image SXM image analysis environment which make possible the accurate and consistent measurement of the dimensions of clay particles in a series of AFM images, so that dissolution rates can be measured during a fluid cell experiment. Particles of biotite and montmorillonite were dissolved, and their dissolution rates normalized to their reactive surface area, which corresponds to the area of their edge surfaces (Ae). The Ae-normalized rates for these minerals between pH 1-2 are all ~10E-8 mol/m2*s, and compare very well to other Ae-normalized dissolution rates in the literature. Differences between the Ae-normalized rates for biotite and the BET-normalized rates (derived from solution chemical studies) found in the literature can be easily explained in terms of the proportion of edge surface area and the formation of leached layers. However, the differences between the Ae-normalized montmorillonite rates and the literature values cannot be explained the same way. Rather, it is demonstrated that rates derived from solution studies of montmorillonite dissolution have been affected by the colloidal behavior of the mineral particles. Finally, the dissolution behavior of hectorite (a trioctahedral smectite) and nontronite ( a dioctahedral smectite) were compared. Based on the differential reactivity of their crystal faces, a model of their surface atomic structures is formulated using Hartman-Perdock crystal growth theory, which explains the observed data if it is assumed that the rate-determining step of the dissolution mechanism is the breaking of connecting bonds between the octahedral and tetrahedral sheets of the mineral structure.
- Biodegradability of dicamba and 2,4-D in riparian wetland soilsLopez, Alfredo R. (Virginia Tech, 1995-06-05)A general review of soils in Virginia counties bordering the Chesapeake Bay reveals that coastal plain soils, especially those most agriculturally productive, are dominantly sandy texture in the subsurface horizon, and have shallow water tables. Considering the high amounts of pesticides used in the coastal plain region and the porous nature of sandy texture soils, there is a great potential for pesticide leaching and subsequent contamination of surface and groundwater sources. This is of great concern because of the potential detrimental effects these agrochemicals represent on aquatic and animal life in the Chesapeake Bay, the largest and most productive estuary in the United States.
- Biodegradation of pesticide and indolic compounds under methanogenic conditionsGu, Ji-Dong (Virginia Tech, 1991-10-15)Degradability of atrazine, cyanazine, and dicamba under methanogenic conditions was evaluated using serum bottle microcosms containing wetland soil inocula obtained from three different sites. Pesticides were monitored by high-performance liquid chromatography (HPLC) and the production of methane was measured with a gas chromatograph (GC). Dicamba was the most susceptible to degradation in the microcosms, followed by cyanazine. Atrazine was not degraded in the wetland soils. A dicamba-degrading methanogenic consortium was enriched from one of the initial wetland soil microcosms (Lawnes). Dicamba degradation was further examined using this consortium. Net methane production suggested that the aromatic ring was not degraded. Rates of dicamba degradation were enhanced with addition of 0.2 % yeast extract. Dicamba degradation was accomplished within 4 days compared to 22 days without yeast extract addition. The inability of the consortium to degrade the benzenoid ring was confirmed when no ¹⁴CO₂ was produced upon addition of [U-¹⁴C]dicamba to the cultures. Analysis of culture filtrate by HPLC revealed the presence of a possible metabolite that was aromatic in character.
- Biogeochemistry of Carbon on Disturbed Forest LandscapesAmichev, Beyhan Y. (Virginia Tech, 2007-04-11)Carbon accreditation of forest development projects is essential for sequestering atmospheric CO2 under the provisions of the Kyoto Protocol. The carbon sequestration potential of surface coal-mined lands is not well known. The purpose of this work was to determine how to measure carbon sequestration and estimate the additional amount that could be sequestered using different reforestation methods compared to the common practice of establishing grasslands. I developed a thermal oxidation technique for differentiating sequestered soil carbon from inorganic and fossilized carbon found at high levels in mine soils along with a geospatial and statistical protocol for carbon monitoring and accounting. I used existing tree, litter, and soil carbon data for 14 mined and 8 adjacent, non-mined forests in the Midwestern and Eastern coal regions to determine, and model sequestered carbon across the spectrum of site index and stand age in pine, mixed, and hardwood forest stands. Finally, I developed the framework of a decision support system consisting of the first iteration of a dynamic model to predict carbon sequestration for a 60-year period for three forest types (white pine, hybrid poplar, and native hardwoods) at three levels of management intensity: low (weed control), medium (weed control and tillage) and high (weed control, tillage, and fertilization). On average, the highest amount of ecosystem carbon on mined land was sequestered by pine stands (148 Mg ha-1), followed by hardwood (130 Mg ha-1) and mixed stands (118 Mg ha-1). Non-mined hardwood stands contained 210 Mg C ha-1, which was about 62% higher than the average of all mined stands. After 60 years, the net carbon in ecosystem components, wood products, and landfills ranged from 20 to 235 Mg ha-1 among all scenarios. The highest net amount of carbon was estimated under mixed hardwood vegetation established by the highest intensity treatment. Under this scenario, a surface-mined land of average site quality would sequester net carbon stock at 235 Mg C ha-1, at a rate of 3.9 Mg C ha-1 yr-1, which was 100% greater than a grassland scenario. Reforestation is a logical choice for mined land reclamation if carbon sequestration is a management objective.
- Bioremediation of Pcb Contaminated Surface Soil: A Microcosm StudyDas, Swati Jr. (Virginia Tech, 1997-02-12)This feasibility study was performed at Virginia Polytechnic Institute and State University (Blacksburg, VA) in collaboration with BioSystems Technology, Inc. (Blacksburg, VA). In this study, degradability of PCBs (Aroclor 1242) from an aged surface soil was evaluated using serum bottle microcosms containing aceticlastic methanogenic consortium, enriched from a municipal anaerobic digester. Two different experiments, "intermediate feed" and "starve and feed" were conducted by manipulating the methanogenic consortium with different amounts of acetate feeding, during 30 days of incubation. Disappearance of Aroclor 1242 in the microcosms was quantified using gas chromatography (GC). Significant differences in Aroclor 1242 removal between inoculated and uninoculated (control) microcosms were observed suggesting that the methanogenic consortium was responsible for Aroclor 1242 disappearance. However, GC-mass spectrometry (GC-MS) results could not confirm that disappearance of Aroclor 1242 was due to anaerobic dehalogenation. From another experiment, it was confirmed that removal of Aroclor 1242 was not due to evaporation losses during sample extraction. Toxicity of an aged Aroclor 1242 contaminated surface soil was evaluated on an aceticlastic methanogenic consortium, enriched from a municipal anaerobic digester. Microcosms were set up using different amounts of soil and inoculum. Total gas production in the microcosms was monitored during 30 days of incubation, using a glass syringe. Total methane production in the microcosms was quantitated using GC. Toxicity of the soil on the methanogenic inoculum was determined based on the decreased rate of methane production in the microcosms relative to non- soil containing controls. Compared to the control, there was reduction in total methane production in soil containing microcosms. Between 3-27% reduction in total methane production was noticed in microcosms containing different amounts of soil and consortium. Reduction in methane production seemed to increase with increasing amount of soil. Whether this decrease in methane production was due to toxicity of Aroclor 1242 on the methanogenic consortium or due possibly to the toxicity of trapped oxygen in the soil could not be determined. The rate of gas production in the soil microcosm was linear.
- Changes in Streambank Erodibility and Critical Shear Stress Due to Surface Subaerial ProcessesHenderson, Marc Bryson (Virginia Tech, 2006-05-11)Previous studies have shown that soil erodibility and critical shear stress are highly influenced by weathering processes such as freeze-thaw cycling and wet-dry cycling. Despite over forty years of research attributing changes in soil properties over time to climate-dependent variables, little quantitative information is available on the relationships between streambank erodibility and critical shear stress and environmental conditions and processes that enhance streambank erosion potential. The goal of this study was to investigate temporal changes in streambank erodibility and critical shear stress due to surface weathering. Soil erodibility and critical shear stress were measured monthly in situ using a multi-angle submerged jet test device. Environmental and soil data were also collected directly at the streambank surface to determine freeze-thaw cycles, soil moisture, soil temperature, bulk density, soil erodibility, critical shear stress, and other atmospheric conditions that could impact bank erosion potential. Statistical tests, including a nonparametric alternative to ANOVA and multiple comparison tests, were used to determine if temporal changes in soil erosion potential were greater than spatial differences. Regression analyses were also utilized to identify the factors contributing to possible changes in soil erodibility, critical shear stress, and bulk density. The nonparametric alternative to ANOVA in combination with Dunn's nonparametric multiple comparison test showed soil erodibility was significantly higher (p=0.024) during the winter (November - March) and the spring/fall (April - May, September - October). Regression analyses showed 70 percent of soil erodibility variance was attributed to freeze-thaw cycling alone. Study results also indicated that bulk density is highly influenced by climate changes since gravimetric water content and freeze-thaw cycles combined explain as much as 86 percent of the variance in bulk density measurements. Results of this study show significant amounts of variation in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes, specifically changes in soil moisture and temperature. These results have potential implications for streambank modeling and restoration projects that assume constant values for soil erodibility. Watershed models and restoration designs should consider the implications of changing soil erodibility during the year in model development and stream restoration designs.
- Characterization of water distribution in sludgesPramanik, Amit (Virginia Tech, 1994)Knowledge of water distribution in sludges is important in developing a better understanding of the mechanisms by which various fractions of water are bound to the sludge matrix as well as the extent to which sludges may be dewatered in an economic manner. Various models have been proposed in the literature to describe the types or fractions of water present in sludges, both before and after dewatering. Likewise, there exist a variety of measurement techniques to quantify the fractions of water believed to be present in sludges. The major objective of the research reported herein was an attempt to develop a more rational basis for defining the various fractions of water present in sludges, as well as to apply and develop feasible analytical techniques to characterize moisture distribution in sludges and determine if there was any correlation between these techniques. Secondary objectives included investigation of polymer addition, mechanical dewatering, and the effect of freeze-thaw cycles to different water fractions in sludge samples, and measuring or estimating various densities (bulk, floc, dry) and specific surface areas of sludge particles in an attempt to predict the dewatering performance of various sludge samples. The matrix of sludges included various water treatment plant/inorganic chemical sludges and biosolids. The sludge moisture characterization techniques used or developed in this study were the thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dilatometric methods. The TGA method developed used the drying curve rate technique whereby changes in the drying (water removal) rates would provide information on moisture distribution in sludges. The DSC and dilatometric methods used the property of the free water fraction to freeze by -20° C, as compared to the bound water fraction that is thought not to freeze until well below -20°C. It was found that there were uncertainties in the determination of different sub-fractions of sludge water. In an effort to better rationalize these various subfractions, it has been proposed in this study that water in sludges be considered to be in two major fractions: bound and unbound. For the TGA, the demarcation point between these two fractions was indicated by the onset of the first critical/inflection point on the drying rate curve. The DSC and dilatometric methods determined the amount of bound water by first measuring the amount of unbound water that froze by -20°C, and subtracting this value from the total water present in the dry solids analysis. While the DSC measured the calorimetric (enthalpic) changes, the dilatometer measured the expansion of the unbound water. The three DSC instruments evaluated in this study were not able to measure the rapid exothermic change of the freezing of unbound water, but was able to measure the amount of unbound water that melted. Freezing point depression (supercooling) phenomena was also observed for various samples using this technique. Due to these effects, the sludge moisture characterization method developed for the DSC measured the amount of unbound water from the endothermic changes upon melting. The three different analytical techniques used to determine moisture in sludges were found to provide different quantities of the bound water fraction. Other sludge characteristics evaluated included the bulk, floc, and dry density values, as well as the specific surface area of dry sludge particles. Correlations were attempted to determine if there were any meaningful relationships in the results obtained.
- Clay mineralogy and soil classification of alluvial and upland soils associated with Blackwater and Nottoway rivers in southeastern VirginiaAl-Hawas, Ibrahim A. M. (Virginia Tech, 1989-10-06)Because the Coastal Plain of southeastern Virginia has not been extensively studied, thirty random samples associated with Blackwater and Nottoway rivers were collected in the spring of 1987 from Surry, Sussex, and Southampton counties. Soil classification as well as mineralogical, chemical, and physical analysis were conducted for all samples. The purposes of this investigation were to: (1)classify the soils in this area, (2) determine the distribution of sand and clay minerals, (3) examine the weathering effect on clay minerals on different position of the landscape for different parent material sources. The soils examined classified as follow: Aquic Hapludults 43% > Typic Hapludults 26.6% > Ultic Hapludalfs 10% > Humic Hapludults 3% = Typic Rhodudlts 3% = Aquic Hapludalfs 3% = Typic Udipsamment 3% = Typic Quartzpsamment 3% = Psammentic Hapludalfs. Qualitative analysis of clay minerals revealed that kaolinite and hydroxy interlayer vermiculite were the dominant clay minerals; that montmorillonite, mica, gibbsite quartz, and vermiculite were of lesser quantities; that chlorite, feldspar and interstratified minerals were of trace amounts. Kaolinite represents about 21-70%, HlV 11-60%, montmorillonite 0-20%, mica 0-16%, gibbsite 0-13%, quartz 1-12%, and vermiculite 0-10%. The presence of these minerals were mainly related to the acid reaction of the soil media, which was essentially attributed to Al and H ions in soil solution. From the past history and geological composition of the Piedmont it is assumed that kaolinitic minerals were transported and sedimented in the Coastal Plain. Hydroxy-interlayer vermiculite minerals was weathering from vermiculite because most of the Al was adsorbed by vermiculite to form HIV. Therfore, gibbsite was not precipitated. Montmorillonite was assumed to have formed from mica minerals. That was substantiated by statistical analysis which showed a high negative correlation between gibbsite and vermiculite (r=0.46, n=30) and between montmorillonite and mica (r=-0.6, n=10).
- Competitive Adsorption of Arsenite and Silicic Acid on GoethiteLuxton, Todd Peter (Virginia Tech, 2002-12-12)The adsorption behavior of silicic acid and arsenite alone and competitively on goethite over a broad pH range (3-11) at environmentally relevant concentrations was investigated utilizing pH adsorption data and zeta potential measurements. Both addition scenarios (Si before As(III) and As(III) before Si) were examined. The results of the adsorption experiments and zeta potential measurements were then used to model the single ion and competitive ion adsorption on goethite with the CD-MUSIC model implemented in the FITEQL 4.0 computer program. Silicic acid adsorption was reduced by the presence of arsenite for all but one of the adsorption scenarios examined, while in contrast silicic acid had little effect upon arsenite adsorption. However, the presence of silicic acid, regardless of the addition scenario, dramatically increased the arsenite equilibrium solution concentration over the entire pH range investigated. The CD-MUSIC model was able to predict the single ion adsorption behavior of silicic acid and arsenite on goethite. The modeled zeta potential data provided further evidence of the CD-MUSIC model's ability to describe the single anion adsorption on goethite. Our model was also able to collectively describe adsorption and zeta potential data for the low Si-arsenite adsorption scenario quite well however, our model under-predicted silicic acid adsorption for the high Si-arsenite competitive scenario.
- Continuous No-till Management: Implications for Soil Quality, Carbon Sequestration, and Nitrogen ConservationSpargo, John T. (Virginia Tech, 2008-02-01)No-till management for agronomic crop production is recognized as an effective practice to regain a portion of soil organic matter lost following decades of cultivation. Increasing soil organic matter sequesters C, conserves organic N and concomitantly improves soil quality. Objectives of this research were to: i) quantify C sequestration rate and N conservation with duration of continuous no-till; ii) measure C stratification with continuous no-till as an indicator of soil quality; and iii) evaluate the Illinois soil N test (ISNT) for its value to predict fertilizer N needs of corn in Virginia. Objectives i and ii were achieved by collecting soil samples from 63 production fields in the Virginia Coastal Plain that were managed using continuous no-till from 0 to 14 yrs. No-till management resulted in sequestration of 0.308 ± 0.280 Mg C ha⁻¹ y⁻¹ and conservation of 22.2 ± 21.2 kg N ha⁻¹ yr⁻¹ (0-15 cm). The C stratification ratio (0-2.5 cm: 7.5-15 cm) increased with increasing duration of continuous no-till (0.133 ± 0.056 yr⁻¹) due to the accumulation of organic matter at the soil surface indicating improved soil quality with continuous no-till management. Objective iii was addressed by conducting 29 on-farm fertilizer N response trials in major corn producing areas of Virginia with the duration of continuous no-till management ranging from 0 to 25 yrs. The ISNT values were significantly related to yield without fertilizer N (r² = 0.57; p<0.001) and relative yield (r² = 0.64; p<0.0001). We also found that the ISNT extracted a relatively consistent percentage of total soil N (16.3 ± 0.73 %) suggesting it is a poor indicator of labile N. Total soil N values did almost as well as the ISNT in predicting yield without fertilizer N (r² = 0.53; p = 0.0002), and equally well predicting relative yield (r² = 0.64; p<0.0001). Results do not suggest the ISNT is useful for measuring mineralizalbe N or improving fertilizer N recommendations in Virginia cropping systems.
- Copper adsorption/desorption characteristics on copper amended soilsReed, Stewart T. (Virginia Tech, 1993)Laboratory tests were conducted to determine Cu availability of three Virginia soils amended with Cu as either Cu-rich pig manure or CuSO₄ with the same Cu content as that in manure. The study also assessed the capability of Mehlich-3 to estimate deficient and toxic Cu levels in soil. Application of Cu as manure or CuSO₄ did not affect grain yield or grain Cu concentration in corn grown at each site. Young corn plant height was reduced by CuSO₄ application on the Bertie sandy loam, an indication of greater toxicity from inorganic than organic Cu. Very little exchangeable or solution Cu was present in any of the three soils. The vast majority of Cu was distributed between the organic and soil oxide fractions. The ratio of soil oxide to organic matter determines the relative distribution of Cu among these fractions. Most organically bound Cu was held by specific adsorption mechanisms and Mehlich-3 strongly extracts this fraction. Mehlich-3 extraction patterns were indicative of Cu binding strength in the different soils. Since Mehlich-3 strongly extracts specifically bound Cu and only poorly removes oxide Cu, this test may underestimate Cu availability on sandy soils with low organic matter content. However, Mehlich-3 provides an acceptable test for soil Cu. Soil sorption characteristics were studied for Cu, Pb, and Zn added, both alone and simultaneously. Copper sorption energy was higher than both Pb or Zn, however, sorption capacity followed the order Pb > Zn > Cu. High Pb and Zn sorption was in part due to precipitation reactions especially at high initial solution concentrations. Zinc was bound to soil mostly by weak electrostatic forces. Copper and Pb were bound at specific sorption sites and by complex multi-site bonding mechanisms possibly involving organic substances. These specific and multi-site mechanisms account for metal ions removed from solution at low concentration. Even at low metal concentration, Cu and Pb sorption results in concurrent release of H⁺ and Ca²⁺ at a greater than one to one charge basis. Soils adjusted to various pH levels were equilibrated with Cu solution and then extracted with a series of dilute acid extractions to determine Cu adsorption and fixation capacities. Copper adsorption and more importantly Cu fixation increased with an increase in soil pH. Soil with a high organic matter content as a result of manure applications adsorbed and fixed more Cu at all pH levels than the control and CuSO₄ soil. The presence of organic matter may have a greater effect on metal sorption characteristics than maintenance of pH ≥ 6.5. Heavy metal sorption was accompanied by concurrent release of H⁺ and Ca²⁺ which represents exchangeable and specifically bound cation nutrients. Soils which receive heavy metal applications from sewage sludge or animal manure would have a short-term increase in plant available nutrients at the expense of long-term reserve capacity. Soil tests for cation nutrient availability on soils receiving heavy metal applications should be adopted to account for these responses.
- Cotton Yield as Related to Selected Physical and Chemical Properties of Soils of the Coastal Plain of Virginia and North CarolinaAdcock, Clyde Wesley (Virginia Tech, 1998-08-28)Cotton (Gossipium hiristum, L) is a warm season perennial with indeterminant growth habit. In 1995, 42,500 and 300,000 hectares were grown in Virginia and North Carolina, respectively. Soil physical and chemical properties may limit cotton yields. The objective of this study was to; 1) determine influences of soil physical and chemical properties on yield, 2) validate existing preharvest yield estimators, and 3) determine the effect of subsoiling and/or subsurface liming on cotton development and root growth. Two hundred sites were sampled across the Coastal Plain of Virginia and North Carolina to a depth of 92 cm representing 5 major soil series. Soil samples were analyzed for selected physical and chemical properties from each horizon. Boll and plant counts were obtained while harvesting a 3-meter length of row at each site to determine yield for the 1996 and 1997 growing season. Cotton was grown in the greenhouse on 30 cm diameter cores of a soil with low subsoil pH and a hard pan to determine the effects of subsoiling and/or subsurface liming. Ninety days after planting, the cotton plants were harvested and the above ground biomass and rootmass were analyzed. Physical and chemical properties explained 52% of yield variability in 1996 and 27% in 1997. Physical and chemical properties that were significant to yield were surface bulk density, available water holding capacity, depth of the water table and Bt horizon, Mg, K, Ca, and Al content. Soil analysis for nutrient status at depths up to 45 cm were better indicators of cotton yield. Subsoiling with or without subsurface liming increased rooting depth over the untreated check. The subsurface liming reached first flower 11 days prior to the other treatments. The additional period for flowering and boll set in Virginia and North Carolina could increase potential yield.
- Describing and Predicting Breakthrough Curves for non-Reactive Solute Transport in Statistically Homogeneous Porous MediaWang, Huaguo (Virginia Tech, 2002-11-18)The applicability and adequacy of three modeling approaches to describe and predict breakthough curves (BTCs) for non-reactive solutes in statistically homogeneous porous media were numerically and experimentally investigated. Modeling approaches were: the convection-dispersion equation (CDE) with scale-dependent dispersivity, mobile-immobile model (MIM), and the fractional convection-dispersion equation (FCDE). In order to test these modeling approaches, a prototype laboratory column system was designed for conducting miscible displacement experiments with a free-inlet boundary. Its performance and operating conditions were rigorously evaluated. When the CDE with scale-dependent dispersivity is solved numerically for generating a BTC at a given location, the scale-dependent dispersivity can be specified in several ways namely, local time-dependent dispersivity, average time-dependent dispersivity, apparent time-dependent dispersivity, apparent distance-dependent dispersivity, and local distance-dependent dispersivity. Theoretical analysis showed that, when dispersion was assumed to be a diffusion-like process, the scale-dependent dispersivity was locally time-dependent. In this case, definitions of the other dispersivities and relationships between them were directly or indirectly derived from local time-dependent dispersivity. Making choice between these dispersivities and relationships depended on the solute transport problem, solute transport conditions, level of accuracy of the calculated BTC, and computational efficiency The distribution of these scale-dependent dispersivities over scales could be described as either as a power-law function, hyperbolic function, log-power function, or as a new scale-dependent dispersivity function (termed as the LIC). The hyperbolic function and the LIC were two potentially applicable functions to adequately describe the scale dependent dispersivity distribution in statistically homogeneous porous media. All of the three modeling approaches described observed BTCs very well. The MIM was the only model that could explain the tailing phenomenon in the experimental BTCs. However, all of them could not accurately predict BTCs at other scales using parameters determined at one observed scale. For the MIM and the FCDE, the predictions might be acceptable only when the scale for prediction was very close to the observed scale. When the distribution of the dispersivity over a range of scales could be reasonably well-defined by observations, the CDE might be the best choice for predicting non-reactive solute transport in statistically homogeneous porous media.
- Desorption Kinetics of Lead from Goethite: Effect of Mixing and Sorption PeriodGarman, Stephanie Michelle (Virginia Tech, 2006-02-10)In natural systems, the solution concentration and hence, potential bioavailability of trace metals is primarily controlled by adsorption-desorption reactions at the mineral-water interface. While many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with no change in the quantity of lead adsorbed over the 6 month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first order equations. At all sorption densities, the desorption of lead followed the order Short-term (24 h) > Long-term non-stirred (6 months) > Long-term stirred (6 months). However, statistical analysis indicated that these differences were not statistically significant. Furthermore, the desorption rate coefficients were very similar for all the experiments indicating that there was no significant residence time effect in this study. However, a sample from a previous study that was allowed to age 5 years and then analyzed by the desorption procedure did have statistically significant differences between the long-term (5 years) and the short-term (5 months). These results suggest that longer adsorption periods, perhaps a number of years, may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period.
- Development of Nitrogen rate Recommendations for No-till Dryland Grain Sorghum in VirginiaKhosla, Rajiv (Virginia Tech, 1998-10-26)Little research has been done in the humid mid-Atlantic region to develop full-season N fertilizer recommendations for dryland no-tillage grain sorghum (Sorghum bicolor L. Moench) production. The objectives of this study were: (i) to determine the optimum rate of band-placed starter N fertilizer needed in combination with side-dress N applications to achieve economic grain yields, (ii) to investigate if pre-plant broadcast N applications are as efficient as band-placed plus side-dress N applications, (iii) to evaluate the response of grain sorghum yield to partitioned side-dress N applications, and (iv) to study the influence of residual soil profile mineral-N (nitrate and ammonium) on sorghum response to applied N fertilization. Multi-location field studies were conducted over three years. A range of N treatments of various starter-band and side-dress N rates were applied. The experimental data indicate that an optimum rate of N fertilization depends on residual soil mineral-N. Little or zero starter-band-N in conjunction with side-dress-N applications of 130 kg of N ha-1 for soils testing high in mineral-N ( 50 kg N ha-1 in the top 0.3m of surface soil) at planting, and a starter-band-N supplement of 40 kg N ha-1 in conjunction with 130 kg N ha-1 side-dress N for soils testing low in mineral-N at planting, optimized the grain sorghum yields in these experiments. Broadcast N applications were observed to be as efficient as band placed N applications when followed by rainfall soon after application. Grain sorghum yields did respond to the partitioned side-dress N applications. However, partitioning of side-dress N application again depends on the residual mineral-N level present in the soil. In order to consider residual soil mineral-N in making N fertilizer recommendations "Associated Nitrogen Fertilizer Equivalency" (ANFE) values were calculated. ANFE is the amount of applied N that has potential to produce the same yield as that produced by the residual soil mineral-N. The N fertilizer recommendations based on ANFE values were quite close for two out of four sites as compared to the N rates at which the maximum yields were obtained in this study.
- The dissolution rate of chrysotileHume, Lily Ann (Virginia Tech, 1991-05-05)Chrysotile can be linked to three diseases: lung cancer, asbestosis, and mesothelioma. The duration and intensity of exposure along with fiber size appear to play an important role in the development of the diseases. Chrysotile is part of the serpentine group which has the general composition of Mg₃Si₂O₅(OH)₄. The fluids in lung tissue contain very low concentrations of magnesium and silicon. As a result they are quite undersaturated with respect to chrysotile and chrysotile will dissolve. Its persistence in lung tissue is simply a result of its dissolution kinetics. The purpose of this study was to estimate the lifetime of a respirable size fiber of chrysotile in lung tissue. The dissolution reaction for chrysotile for pH's less than nine is: Mg₃Si₂O₅(OH)₄ + 6H⁺ = 3Mg²⁺+ 2H₄4SiO₄ + H₂0 This reaction proceeds in two steps. First, the magnesium hydroxide layer of the serpentine dissolves leaving behind the silica structure of the fiber. Then the silica dissolves. Therefore, the fiber lifetime depends upon the rate of silica release. Over the range of undersaturation expected for lung tissue, the rate of silica release was found to be independent of pH with the average rate being 5.94 (±3.05) x 10⁻¹⁰ moles m⁻² sec⁻¹. A shrinking fiber model was used to determine the relationship between dissolution time and fiber diameter. It was found that the most hazardous sized fiber of chrysotile (1 μm) would completely dissolve in about 9 months, consideration of one standard deviation above and below the mean of the rate constant gives estimates of the lifetime of a fiber ranging from 6 to 19 months.