Browsing by Author "William Showers, Committee Member"

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Hydrologic Effects on Subsurface Fates and Transport of Contaminants
(2009-06-19) Abit, Sergio Manacpo, Jr.; Aziz Amoozegar, Committee Co-Chair; Michael Vepraskas, Committee Co-Chair; Wei Shi, Committee Member; Owen Duckworth, Committee Member; William Showers, Committee Member
Concerns over contamination of ground water (GW) and its subsequent effect on surface water quality underscore the need for an improved understanding of the fate and transport of the contaminants in the subsurface. Among the contaminants that are harmful to humans and the environment are nutrient pollutants [e.g., nitrogen (N) and phosphorus (P)] and microbes. The general goal of this research was to evaluate the subsurface fates and transport of contaminants in a vadose zone-GW continuum under various simulated hydrologic conditions through a series of laboratory-scale studies. The first study, which aimed to visually evaluate the effects of GW velocity and water table (WT) fluctuation on the fate and extent of horizontal transport of solutes and microbes in the capillary fringe (CF) and GW, was conducted in a sand-packed flow cell. Subsurface transport of surface-applied solutes and microbes tended to be isolated in the CF at a higher pore-water velocity. A rise in WT resulting from surface recharge of contaminated water occurred without the contaminants reaching the GW. Subsequent drainage did not effectively leach contaminants that were initially in the CF into the GW. The second study assessed the effect of pore-water velocity on the development of reduced conditions in a vadose zone-GW continuum. Reduction potential (Eh) was monitored at various locations in flow cells packed with Ponzer (Terric Haplosaprists), Lynchburg (Aeric Paleaquult), and Leon (Aeric Alaquod) soil materials that were subjected to different lateral pore-water velocities. Regardless of organic carbon (OC) content of the soil materials (12.4 to 195 g kg-1), locations close to the WT became reduced within 14 days. In contrast, the upper portions of the CF remained oxic. Increasing the pore-water velocity also slowed the development of reducing conditions especially in soils with low OC content. The third study was conducted to evaluate the effect of pore-water velocity on the fate and transport of nitrate (NO3-) in a simulated vadose zone-GW continuum. This was conducted in flow cells packed with soils of various OC content (0.3 to 35 g kg-1) that were subjected to different horizontal-water velocities. Nitrate and bromide (Br) concentrations as well as Eh at various locations along the flow path of an applied NO3- and Br- solution were monitored. Results show that in the presence of sufficient OC, NO3- was lost under reducing conditions below the WT but persisted while in transport in aerobic regions in the CF. Increasing GW flow pore-water velocity from 3.5 to 28 cm d-1 reduced the degree of NO3- removal from solution. High flow velocity also tended to limit the horizontal transport of surface-applied NO3- only in the upper regions of the CF. The fourth study was conducted to evaluate the dissolution of phosphorus (P) in pore-water flowing through the vadose zone-GW continuum. Distilled water was allowed to flow horizontally at different pore-water velocities through flow cells packed with an organic soil material (from Ponzer series). Extensive P dissolution was detected below and just above the WT. Phosphorus dissolution at the upper portion of the CF was relatively limited. These results suggest the following: a) the non-detection of contaminants below the WT down-gradient from a source does not definitively indicate that contaminants are not being transported horizontally in the subsurface as they can be transported in the CF, b) collection of samples from the CF should be considered when monitoring the subsurface transport of contaminants, and c) the hydrology of a system could be managed to improve nitrate removal from solution or to limit P dissolution.
Nitrate Isotopic Composition in Rainfall and Fine Particulate Matter: Back Trajectory, Meteorology, and Source - Receptor Relationship Analysis
(2006-08-22) Occhipinti, Christopher Olovson; William Showers, Committee Member; Dev Niyogi, Committee Co-Chair; Viney Aneja, Committee Chair
The southeastern portion of North Carolina is a dense crop and animal (swine) agricultural region which previous research suggests emits a significant portion of the state's nitrogen emissions. These findings indicated that transporting air over this region can effect nitrogen concentrations in precipitation at sites at least 50 miles away. The present study was able to combine isotope compositional information with the concept of back trajectory analysis to examine the relationship between this regional nitrogen emission source and receptors independent of pollutant concentration information. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to determine potential sources of nitrogen in rainwater collected at an urban receptor site in Raleigh, North Carolina, during the first three quarters of 2004. The delta 15N isotope ratio signatures of each sample were used to further differentiate between sources of the rainwater nitrogen. This study examined the importance of pollutant sources such as animal agricultural activity and meteorology on rainfall chemistry as well as their implications on fine particulate matter formation. Additionally, meteorological conditions associated with anomalous springtime fine particulate matter concentrations found in coastal New Hanover County, North Carolina were investigated. Samples that transited the dense crop and animal (swine) agricultural region of east-southeastern North Carolina (i.e. the source region) had lower delta 15N isotope ratios in the nitrate ion (average = -2.1 ± 1.7 per mil) than those from a counterpart nonagricultural region (average = 0.1 ± 3.0 per mil.) However, the limited data set does not offer any conclusive evidence of similar patterns in ammonium ions. An increase in PM fine mass concentrations in the urban receptor site (yearly average = 15.1 ± 5.8 μg/m3) was also found to correspond to air transport over the dense agricultural region relative to air which was not (yearly average = 11.7 ± 5.8 μg/m3). Fine particulate matter concentrations over the course of four years in four counties around the state were examined, and peak levels of PM2.5 were found in the summer at 3 of the 4 sites. The fourth site, located in costal New Hanover County had a fine particulate matter peak in the spring, which appeared to be unusual as most literature indicates that conditions for high PM2.5 levels are generally found in the summer. Investigation of the phenomenon revealed that historically, meteorological conditions including relative humidity, temperature, and wind direction allow for a peak to exist much earlier in the year at such a location. Transport of pollutants from the dense swine region to the Northwest of New Hanover County is more common in the springtime, along with relative humidity that is in a range witch allows an increase in particulate matter to occur.
Nonlethal Health Assessment of the Freshwater Mussel Elliptio complanata
(2006-02-04) Gustafson, Laura L; Richard Linnehan, Committee Member; Jay Levine, Committee Co-Chair; Michael Stoskopf, Committee Co-Chair; Tom Kwak, Committee Member; William Showers, Committee Member
Freshwater mussels are in decline, with over 70% of North American species categorized as endangered, threatened or of special concern. In an effort to create a nonlethal protocol for health evaluation of freshwater mussels we conducted a series of investigations on wild and captive populations of Elliptio complanata. We tested a method for nonlethal hemolymph collection and found no growth or survival effects in 30 sampled animals relative to 30 controls. We surveyed unionid populations from 19 different stream reaches from a rural region of North Carolina to provide a set of baseline ranges for hemolymph composition in healthy populations. These parameters included hemolymph calcium, magnesium, phosphorus, cell count, glucose, aspartate aminotransferase (AST), ammonia and protein. We tested these parameters in a captive population held under relatively uniform conditions and found most stable over time. Delta 15N declined substantially over time in captivity, likely in response to a large change in environmental _15N signatures. We tested health parameters in three groups of Elliptio complanata after three months under low, moderate or high feed conditions. The treatment groups varied in hemolymph glycogen, magnesium, calcium and phosphorus concentrations and in foot tissue _15N and _13C, providing possible indicators of subtle change in nutritional condition. We also transplanted Elliptio complanata from a stream enriched in _15N-N03 to a relatively depleted stream and evaluated the lag time required for mussel nitrogen isotope signatures to reflect new environmental signatures. We found a slow turnover time but relatively little variability compared to water signatures, suggesting that bivalves may be useful indicators of chronic nutrient loading in rivers and streams. We conclude that, with further research, hemolymph can be a valuable and safe tool for assessment of freshwater mussel population and habitat health.
Three-Dimensional Microphysical and Dynamical Structures of Winter Storms in the U.S. Pacific Northwest
(2007-12-30) Payne, Matthew J; Sankar Arumugam, Committee Member; Sandra Yuter, Committee Chair; William Showers, Committee Member