Browsing by Author "Michael Vepraskas, Committee Member"

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Dissolution of Phosphate in Mixed Fe- and Al-oxide Mineral Suspensions as Influenced by Reducing Conditions.
(2005-03-13) Murray, Gary Christopher; Philip Westerman, Committee Member; Dr. Dean Hesterberg, Committee Chair; Michael Vepraskas, Committee Member
The loss of soil phosphorus (P) to surface waters poses a threat to water quality. Research evaluating P dissolution and transfer among sorbents in pure mineral systems can provide basic knowledge useful for the environmental management of P. The objective of this research was to evaluate the effect of Al-oxides on the reductive dissolution of orthophosphate sorbed to Fe-oxides. Redox reactor systems containing 0.5 g ferrihydrite [Fe(OH)3] kg-1 suspension and 0.002 to 0.7 g boehmite (α-AlOOH) kg-1 suspension were equilibrated with 750 mmol P kg-1 of ferrihydrite, and abiotically reduced for 72 h with 0.5% H2 (g) in the presence of a catalyst of 10 % Pt on activated C. The kinetics of reductive dissolution of ferrihydrite, as indicated by dissolved Fe(II), followed a linear (zero-order) model. The rate coefficient showed a sharp, linear decrease (R2 = 0.61) with minor additions of boehmite (0 to 0.008 g kg-1), and net Fe(II) dissolution was essentially null for boehmite additions ≥ 0.02 g. Uptake of dissolved P occurred over time during reduction of mixed ferrihydrite-boehmite suspensions. XANES spectroscopy of samples collected during reduction of a 1:1 ferrihydrite: boehmite mixture did not detect a net transfer of P from ferrihydrite to boehmite over 168 h. Supporting experiments suggested that Al(III) dissolved from poorly crystalline boehmite caused the observed decrease in Fe(II) dissolution rate in the reduction reactors, either by sorbing to the ferrihydrite surface and blocking electron transfer, or by sorbing to Pt/C catalyst and inhibiting its catalytic activity. The results suggest that Al-oxides may affect net phosphate dissolution in soils undergoing reduction by taking up dissolved P or by inhibiting the reductive dissolution of iron oxides if Al(III) is sorbed to Fe(III)-oxide surfaces.
Hydrologic Evaluation of a Restored Wetland in Eastern North Carolina
(2009-06-18) Jarzemsky, Robert David; Michael Burchell, Committee Chair; Gregory Jennings, Committee Member; Michael Vepraskas, Committee Member
A prior-converted wetland in coastal North Carolina was restored in an attempt to re-establish a non-riverine hardwood wet forest Community. Topography was restored using three surface techniques to determine the effect surface topography had on wetland hydrology in coastal areas. The three treatments were: plugging field ditches without altering the surface (PLUG), plugging the field ditches and contouring the surface (CONT), and plugging the field ditches and removing the field crown (CR). The treatments were replicated three times forming a randomized complete block design. It was hypothesized that CR would produce the wettest site followed by CONT and then PLUG. Water table response and surface outflow was evaluated for 2006-2008. Few significant differences were found between the water tables of each treatment; however CR and PLUG appeared wetter than CONT. Surveying of the restoration revealed that the as-built topography of the PLUG and CONT treatments in block 3 were different than their intended design causing PLUG to produce wetter conditions and CR to produce drier conditions than intended. Based on these observations, the treatments were re-evaluated using only blocks 1 and 2, and using all three blocks with block 3 PLUG and CR data switched. These evaluations found CR produced the wettest hydrology followed by CONT then PLUG, which matched the original hypothesis. Based on the alternate evaluations, CR produced wetter conditions than the reference (3 of 4 hydrologic criteria were significantly wetter) while PLUG produced drier conditions than the reference (3 of 4 hydrologic criteria were drier). CONT matched reference hydrology the closest but only one hydrologic criteria was not significantly different than the reference (ÃŽÂ± = 0.05). All three treatments produced significantly more surface inundation than the reference likely due to pre-restoration surface compaction by farming equipment. Surface outflow evaluation found that CONT produced significantly more outflow than PLUG and CR. PLUG was hypothesized to produce the most outflow, but that CONT produced the most outflow likely due to unintended conveyance pathways created during construction. A second study, evaluated the hydrology of the restored wetland during tropical weather. Three periods were evaluated from 2004 Ã¢â‚¬â€œ 2007. In 2004, a 34 day period of tropical weather including, Hurricane Alex and Tropical Storm Charley produced 41 cm of rainfall and 21 cm of outflow. In 2005, a 15 day period including Hurricane Ophelia produced 33 cm of rainfall and 11 cm of outflow, and in 2007, an 11 day period including Tropical Storm Gabrielle produced 21 cm of rainfall and 7.5 cm of outflow. The restored wetland performed similarly during 2005 and 2007, retaining 67% and 64% of the rainfall. During 2004, the restored wetland retained only 49% of the rainfall. It performed less efficiently due to lower antecedent soil moisture condition and increased rainfall. Soil moisture conditions were high prior to both Alex and Charley which limited the wetlands ability to store water. Prior to Ophelia and Gabrielle, soil moisture conditions were low which provided large amounts of water-free pore space in the soil for storage. DRAINMOD was used to simulate pre-restoration, agricultural hydrology. DRAINMOD predicted the restoration reduced peak daily outflow during all three storm periods by at least 70%. Total outflow reduction was found to be dependent on soil moisture conditions. In 2005 and 2007 antecedent soil moisture conditions were low; the simulation predicted the restoration reduced total outflow by 44% and 29%. In 2004, soil moisture conditions were high prior to Hurricane Alex and Tropical Storm Charley and the simulation predicted the restoration did not reduce total outflow. The modeling predicted the restoration reduced annual outflow by 6 Ã¢â‚¬â€œ 31% depending on the year.
Isovolumetric Weathering of Granite in Wake County, North Carolina
(2004-07-15) Witanachchi, Channa Devinda; Aziz Amoozegar, Committee Member; Edward Stoddard, Committee Member; Stanley W Buol, Committee Chair; Michael Vepraskas, Committee Member
Saprolite, formed by chemical weathering of rocks near the earth's surface, holds water, serves as a parent material of soils, and is a medium for waste disposal. Saprolite formation consumes CO₂ and may stabilize atmospheric CO₂ levels. This dissertation examined the influence of joint orientation on isovolumetric weathering of saprolite developed on the Rolesville granitic batholith at Knightdale, North Carolina. Rock density (ρ[subscript s]) (μ α[subscript 0.05]) was 2.62±0.01 g cm⁻³. Mass altered per unit volume (m[subscript A/V[subscript T]) of saprolite was taken as the difference between rock density (ρ[subscript s]) and primary mineral mass remaining per unit volume (m1⁰[subscript R]/V[subscript T]). Altered mass lost per unit volume (m[subscript AL/V[subscript T]) was taken as the difference between ρ[subscript s] and bulk density (ρ[subscript b]). Altered mass retained per unit volume (m[subscript AR/V[subscript T]) was taken as (m[subscript A]/V[subscript T]) - (m[subscript AL/V[subscript T]). Saprolite with steeply-dipping joints showed a uniformly sandy texture. The distribution (mass percent) of sand-, silt-, and clay-sized particles (μ α[subscript 0.05]) was 82.4±2.7, 10.3±1.8, and 2.3±2.5, respectively, on a whole saprolite basis, and ρ[subscript b] (μ α[subscript 0.05]) was 1.66±0.06 g cm⁻³. Saprolite with horizontally-oriented unloading joints was extensively altered and occurred between horizontal slabs of unweathered rock. The saprolite was composed of sandy layers alternating with clayey layers on the scale of approximately 1 to 2 cm. The distribution of sand-, silt-, and clay-sized particles (μ α[subscript 0.05]) in the saprolite was 50.1±10.4, 3.1±0.5, and 46.8±10.5, respectively, on a whole saprolite basis. Bulk density (μ α[subscript 0.05]) was 1.55±0.01 g cm⁻³. The mean content of sand-, silt-, and clay-sized particles in the two saprolites differed statistically at α = 0.001, and mean bulk density differed at α = 0.01. The fine-earth fraction of saprolite with steeply-dipping joints was characterized (μ α[subscript 0.05]) by pH of 5.8±0.2, mass percent Fe2O3 of 0.21±0.09, cation exchange capacity (CEC) at pH 7.0 of 3.95±0.88 cmol⁺kg⁻¹, and percent base saturation (% BS) of 36.66±9.93. The fine-earth fraction of saprolite with horizontal joints was characterized (μ α[subscript 0.05]) by pH of 5.1±0.2, mass percent Fe2O3 of 2.68±0.28, CEC (in cmol⁺[superscript kg]⁻¹) at pH 7.0 of 8.28±0.91 and % BS of 19.73±9.22. The means of pH, mass percent Fe2O3, and CEC in the two saprolites differed statistically at α = 0.01, and the means of % BS differed at α = 0.05. The differences in mean values of individual extractable bases are not significant at α = 0.05. Density of unweathered granite (μ α[subscript 0.05]) was 2.62±0.01 g cm⁻³. Calculated mean (μ α[subscript 0.05]) values of m[subscript A]/V[subscript T], m[subscript AL]/V[subscript T], and m[subscript AR]/V[subscript T] (all in g cm⁻³) in saprolite with steeply-dipping joints were 1.17±0.12, 0.96±0.06 and 0.21±0.05, respectively. Corresponding values in saprolite with horizontal joints were 1.85±0.15, 1.08±0.02 and 0.77±0.17, respectively. Calculated mean (μ α[subscript 0.05]) values of m[subscript AL]/m[subscript A] were 0.82±0.03 for the former saprolite and 0.58±0.06 for the latter, indicating greater leaching losses in the former. Differences in the calculated means of m[subscript A]/V[subscript T], m[subscript AR]/V[subscript T], m[subscript AR]/m[subscript A] and m[subscript AL]/m[subscript A] in the two saprolites are statistically significant at α = 0.001, and m[subscript AL]/V[subscript T] differed at α = 0.05. Saprolite with steeply dipping joints was composed predominantly of plagioclase and potassium feldspar. Saprolite with horizontal joints contained approximately equal proportions of potassium feldspar and kaolinite (or halloysite). Nordstrandite occurred in both types of saprolite. Saprolite was classified based on the relative proportions of (m1⁰[subscript R]/V[subscript T]) 100/ρ[subscript s], (m[subscript AR]/V[subscript T]) 100/ρ[subscript s], and (m[subscript AL]/V[subscript T]) 100/ρ[subscript s]. Saprolite with steeply-dipping joints classified as 'moderately altered, highly leached', and saprolite with horizontal joints classified as 'severely altered, moderately leached'. Joint orientation appears to be a significant variable in saprolite formation.
Surface and Substance Hydrology of a Drained Carolina Bay Prior to Restoration
(2004-05-21) Luginbuhl, Sarah C; James Gregory, Committee Chair; Rodney Huffman, Committee Member; Michael Vepraskas, Committee Member; David Genereux, Committee Member
Juniper Bay is a 330 ha Carolina Bay located 13 km southeast of Lumberton in Robeson County, North Carolina. Carolina Bays are elliptical depressions in the landscape primarily located in the Coastal Plain region of North and South Carolina and Georgia. They are oriented with major axes northwest to southeast and their origin is unknown. Juniper Bay was drained beginning in the 1970's for agriculture. In the year 2000 the North Carolina Department of Transportation bought the bay to restore to a wetland. North Carolina State University wrote a proposal to do research at Juniper Bay and the overall goal is to evaluate the strategy and performance of the restoration of wetland functions in Juniper Bay and to test alternative restoration methods. This research focuses on the hydrology of the bay prior to restoration. The objectives are the determination of the current ground water flow paths and the water table regime both inside and outside the bay, the identification of a strategy for hydrologic restoration, the documentation of the variability in the properties of the water table regime across Juniper Bay and the reference bays that will affect the success of the restoration, and the assessment of the usefulness of reference ecosystems for defining required hydrologic factors necessary for long-term restoration success. There are three reference Carolina Bays, located in neighboring Bladen County, North Carolina. The hydrologic properties of these bays is the hydrologic goal of Juniper Bay once restoration is complete. Twenty-nine water table monitoring wells were installed to a depth of 2.44 meters in and around Juniper Bay in early 2001, and four water table monitoring wells were installed in each of the reference bays. Seventeen piezometers equipped with pressure transducers were installed in and around Juniper Bay along two main transects, with depths ranging from 2.44 to 10.36 meters. The results from the water table wells show that 4% of Juniper Bay in 2001 and 22% in 2002 met wetland hydrology requirements, which are that the water table is within 30 cm of the soil surface continuously for 12.5% of the growing season in most years. The percentages of the reference bays that meet the wetland hydrology requirements range from 20% to 100%. Results show that ground water may be entering Juniper Bay from the northwest and southeast boundaries of the bay, which are higher in elevation, and exiting the bay through the northeast and southwest boundaries of the bay, which are lower in elevation. The ditches likely have a significant influence on the water table and the ground water, and the hydrology of the bay will likely be altered once they are plugged. The reference bays provide useful information in the determination of what conditions were probably like prior to disturbance and what the restoration effort in Juniper Bay should try to accomplish.
Surface Shading, Soil Temperature, and Soil Moisture Effects on C Loss in a Temperate Peatland
(2010-04-20) Taggart, Matthew J.; Michael Burchell, Committee Member; Joshua Heitman, Committee Chair; Michael Vepraskas, Committee Member
TAGGART, MATTHEW. Surface Shading, Soil Temperature, and Soil Moisture Effects on Soil C Loss in a Temperate Peatland. (Under the direction of Joshua Heitman). Histosols are a huge reservoir for C, covering < 1% of the worldâ€Ÿs land surface but holding up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from peatlands is critical for proper management of these C sinks. Three experiments evaluated how formerly cultivated, warm climate Histosols undergoing restoration efforts might respond to increasing water content via water table re-establishment and decreases in soil temperatures via vegetative shading. We compared temperature and soil CO2 efflux differences from intact soil cores, collected from Juniper bay, under three levels of light reduction in a greenhouse: 0%, 70%, and 90%. Soil in full sun was consistently warmer and showed higher efflux rates than 70% and 90% shade treatments: 4.132, 3.438, and 2.054 Î¼mol CO2 m-2 s-1, respectively. Shade treatments reached peak efflux rates at similar water potential, -2 to -4 kPa. A field experiment at Juniper bay subjected in-situ soil to full sun, 70% light reduction, and light reduction from naturally occurring herbaceous vegetation. Shade treatment effects on soil temperature and C mineralization were evident throughout the growing season. Vegetation shade effects on soil temperature were greatest in August and September when soil under vegetation was 5Â°-11Â°C cooler than unshaded soil. Soil CO2 efflux was correlated strongly with soil temperature; daily efflux rates were consistently highest from unshaded soil. Efflux across treatments showed a strong seasonal correlation to soil moisture, increasing as soil dried in response to water table decline. Soil water potential was unaffected by shade treatment, suggesting temperature effects were solely responsible for efflux differences between treatments. C mineralization response to temperature and moisture was verified with lab incubations of soil material at 25Â° and 37Â°C for three moisture ranges. Incubation showed a temperature/moisture interaction where Q10 was 2.55 under wet soil conditions (0.40 m3 m-3) and 1.64 when soil was driest (0.15-0.16 m3 m-3). All results confirm surface shading has a strong influence on soil temperatures and C mineralization rates. Thoughtful management of vegetation in mitigated peatlands may be an effective strategy for slowing soil C losses and promoting soil C sequestration.