No description available.

Snow and ice can significantly affect the environmental fate of contaminants. This thesis presents a laboratory technique for measuring mercury in metamorphosing snow, and a computer model for organic contaminants in a seasonally ice covered ocean. The laboratory method to study the fate of mercury in snow was developed using laboratory-made snow of controlled composition made in a cold room, aged and melted, with mercury quantified in air, snow, and dissolved and particulate fractions of the melt water. It was found that the method gave a mass balance for mercury, and can be used to look at mercury fate in snow representative of different environments. The fugacity based fate and transport model for organic contaminants in a seasonally ice-covered ocean was parameterized to Barrow Strait, and tested against environmentally derived net air to sea water fluxes. It was found that the model could reproduce these environmental data.

Snow and ice can significantly affect the environmental fate of contaminants. This thesis presents a laboratory technique for measuring mercury in metamorphosing snow, and a computer model for organic contaminants in a seasonally ice covered ocean. The laboratory method to study the fate of mercury in snow was developed using laboratory-made snow of controlled composition made in a cold room, aged and melted, with mercury quantified in air, snow, and dissolved and particulate fractions of the melt water. It was found that the method gave a mass balance for mercury, and can be used to look at mercury fate in snow representative of different environments. The fugacity based fate and transport model for organic contaminants in a seasonally ice-covered ocean was parameterized to Barrow Strait, and tested against environmentally derived net air to sea water fluxes. It was found that the model could reproduce these environmental data.

The increasing production and usage of engineered nanoparticles has raised concerns about potential ecological and human exposures and the risks these novel materials may pose. Nanoparticles are often manufactured with an organic macromolecular coating, and they will attain further coatings of adsorbed natural organic matter (NOM) in the environment. The overall objective of this thesis is to improve our ability to quantify the effects of adsorbed coatings on nanoparticle fate in the environment. The physicochemical properties of the coating or the adsorbing macromolecule are expected to strongly mediate the surface interactions, and hence the environmental fate, of coated nanoparticles. To this end, this research focuses on assessing a coating characterization method and applying extensive characterization of NOM coatings to enable the development of correlations to predict nanoparticle deposition onto model environmental surfaces and aggregation. The first objective is to assess the applicability of a soft particle electrokinetic modeling approach to characterize adsorbed layer thickness, which contributes to repulsive steric forces that will affect nanoparticle deposition. A statistical analysis determined that high uncertainty in fitted layer thicknesses will limit this approach to thin, low-charged coatings (for which it may be advantageous to typical sizing methods such as dynamic light scattering). Application of this method in experimental studies further confirmed the model limitations in estimating layer thicknesses and the inability of this measurement (and other commonly measured properties) to fully explain nanoparticle deposition behavior. These results demonstrated the need for improved detail and accuracy in coating characterization. The second objective is to correlate the properties of NOM to its effects on gold nanoparticle aggregation, with particular focus on the role of heterogeneity or polydispersity of the NOM molecular weight. Multiple types of NOM collected from representative water bodies and soils were used, both in whole and separated into molecular weight (MW) fractions, and characterized for chemical composition and MW distribution. While average MW of the NOM provided good correlation with aggregation rate, the highest MW components were found to contribute disproportionately in stabilizing nanoparticles against aggregation, highlighting the importance of measuring and accounting for high MW components to explain nanoparticle aggregation. However, an outlier from the MW trend was identified, emphasizing the need for additional characterization (e.g. of reduced sulfur content or the conformation of the adsorbed NOM) to fully explain the effects of NOM on nanoparticle aggregation. Altogether, this research provides novel knowledge that will guide future application of characterization methods to predict attachment processes for coated nanoparticles in the environment.

abstract: Nanotechnology is becoming increasingly present in our environment. Engineered nanoparticles (ENPs), defined as objects that measure less than 100 nanometers in at least one dimension, are being integrated into commercial products because of their small size, increased surface area, and quantum effects. These special properties have made ENPs antimicrobial agents in clothing and plastics, among other applications in industries such as pharmaceuticals, renewable energy, and prosthetics. This thesis incorporates investigations into both application of nanoparticles into polymers as well as implications of nanoparticle release into the environment. First, the integration of ENPs into polymer fibers via electrospinning was explored. Electrospinning uses an external electric field applied to a polymer solution to produce continuous fibers with large surface area and small volume, a quality which makes the fibers ideal for water and air purification purposes. Indium oxide and titanium dioxide nanoparticles were embedded in polyvinylpyrrolidone and polystyrene. Viscosity, critical voltage, and diameter of electrospun fibers were analyzed in order to determine the effects of nanoparticle integration into the polymers. Critical voltage and viscosity of solution increased at 5 wt% ENP concentration. Fiber morphology was not found to change significantly as a direct effect of ENP addition, but as an effect of increased viscosity and surface tension. These results indicate the possibility for seamless integration of ENPs into electrospun polymers. Implications of ENP release were investigated using phase distribution functional assays of nanoscale silver and silver sulfide, as well as photolysis experiments of nanoscale titanium dioxide to quantify hydroxyl radical production. Functional assays are a means of screening the relevant importance of multiple processes in the environmental fate and transport of ENPs. Four functional assays – water-soil, water-octanol, water-wastewater sludge and water-surfactant – were used to compare concentrations of silver sulfide ENPs (Ag2S-NP) and silver ENPs (AgNP) capped by four different coatings. The functional assays resulted in reproducible experiments which clearly showed variations between nanoparticle phase distributions; the findings may be a product of the effects of the different coatings of the ENPs used. In addition to phase distribution experiments, the production of hydroxyl radical (HO•) by nanoscale titanium dioxide (TiO2) under simulated solar irradiation was investigated. Hydroxyl radical are a short-lived, highly reactive species produced by solar radiation in aquatic environments that affect ecosystem function and degrades pollutants. HO• is produced by photolysis of TiO2 and nitrate (NO3-); these two species were used in photolysis experiments to compare the relative loads of hydroxyl radical which nanoscale TiO2 may add upon release to natural waters. Para-chlorobenzoic acid (pCBA) was used as a probe. Measured rates of pCBA oxidation in the presence of various concentrations of TiO2 nanoparticles and NO3- were utilized to calculate pseudo first order rate constants. Results indicate that, on a mass concentration basis in water, TiO2 produces hydroxyl radical steady state concentrations at 1.3 times more than the equivalent amount of NO3-; however, TiO2 concentrations are generally less than one order of magnitude lower than concentrations of NO3-. This has implications for natural waterways as the amount of nanoscale TiO2 released from consumer products into natural waterways increases in proportion to its use. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2015

Reducing agricultural nutrient loading in Iowa is critical to achieving Gulf of Mexico hypoxia water quality goals. Iowa comprises 4.4% of the Mississippi-Atchafalaya River Basin but contributes an average of 29% of the annual nitrate (NO3-N) load to the Gulf of Mexico (Jones et al., 2018). The main goal of this research was to study nitrogen fate and transport in agricultural areas of Iowa at different spatial scales using a unique combination of water monitoring and numerical modeling. High-frequency, continuous water quality monitoring provided valuable insights into stream and wetland NO3-N dynamics. A biogeochemical model was written and coupled to a spatially distributed, surface-subsurface hydrologic model to perform continuous (multi-year) nitrogen fate and transport simulations at the field, wetland, and watershed scales. Field scale simulations of a tile-drained, corn-soybean rotation under conventional agricultural management over a 5-yr period illustrated strengths and weaknesses of the soil nitrogen model. Using a simplified approach to describe soil organic matter dynamics, the simulated annual nitrogen balance and NO3-N loss in tile drainage were comparable to observations and literature estimates. However, the model was not able to predict the correct response of NO3-N loss in tile drainage to fertilizer rate, which was attributed in part to limitations with the current plant uptake function which did not capture the nonlinear relationship expected between fertilizer rate and crop nitrogen uptake. NO3-N removal was quantified at one of Iowa’s largest constructed wetlands using high-frequency (15-min), continuous water quality monitoring and hydrologic modeling. The wetland reduced incoming NO3-N concentrations 49% and loads by an estimated 61 kg day-1 from May-Nov over a 3-yr period. Wetland removal was influenced by both hydrologic and biological conditions; mass removal was greatest in Jun when discharge and NO3-N loading were highest, while percent removal was greatest in Aug when discharge was low, water residence times in the wetland were high, and warm water temperatures enhanced processing. The high-frequency monitoring captured NO3-N dynamics not possible with traditional lower frequency grab sampling, including concentration dynamics connected to storm events telling of sources and pathways of NO3-N delivery, diurnal variations in concentration indicative of biological processes, and the marked variability in wetland removal performance during low and high flow conditions. Over 5600 wetlands of similar removal performance treating over 60% of Iowa’s area and costing $1.5 billion would be required to reduce the state’s baseline NO3-N load by 45%. The high-frequency monitoring guided and informed numerical simulations of nitrogen fate and transport at the wetland and watershed scales. Wetland simulations using imposed discharge and water quality conditions upstream of the wetland (inlet) and first order, temperature dependent kinetics produced satisfactory daily and monthly predictions of NO3-N concentration and water temperature downstream of the wetland (outlet) from May-Nov in 3/4 and 4/4 study years, respectively. NO3-N predictions were most sensitive to the denitrification first order rate constant and temperature during low discharge periods and least sensitive to both during storm events. Temperature dependent kinetics were necessary to accurately predict wetland NO3-N removal in late summer. The continuous watershed simulations produced satisfactory monthly predictions of inlet and outlet NO3-N concentration and outlet water temperature. Consistent with findings from other modeling studies, annual nitrogen components and NO3-N dynamics were simulated reasonably well under average hydrologic conditions, while simulated NO3-N dynamics weakened under extreme (wet) hydrologic conditions. Temperature was important for predicting the seasonality of wetland NO3-N removal during the growing season, while other factors such as organic carbon and dissolved oxygen may be more influential outside the growing season when removal can still occur despite cold conditions. A preliminary evaluation of six recently constructed wetlands that detain and process agricultural runoff from 12% of a 45 km2 watershed in north central Iowa estimated sizable flood and NO3-N reductions locally which diminished moving downstream. Continuous watershed simulations over a 13 month period following wetland implementation estimated peak flow reductions of 3-43% at the wetlands that dissipated with drainage area; similarly, the wetlands reduced NO3-N loads by an estimated 7-25% locally and 2% at the watershed outlet. Further refinements to the biogeochemical-hydrologic model are needed to improve simulated NO3-N dynamics in order to more reliably assess downstream flow and NO3-N reduction benefits. This work identified limitations with the current modeling approach, areas of future work, and offers recommendations to guide future conservation design. Sensible hydrologic predictions are imperative to the success and dependability of the water quality simulations, which may seem obvious but can be difficult to ascertain in ungauged catchments. Future work aspires to couple a complete agricultural systems model with a physically-based hydrologic model to simulate the nitrogen cycle in a more comprehensive manner to assess which field scale nitrogen processes are most important to accurately predict stream nutrient loading at the watershed scale. Constructed wetlands could provide greater flood and nutrient reduction benefits if the normal pool hydraulics were designed with smaller hydraulic structures that more effectively throttle down incoming flows and provide the opportunity for active rather than passive pool management. As the ultimate goal of this research and other like work is to quantify progress of water quality goals set forth by the Gulf Hypoxia Task Force and help guide future conservation practice implementation, continued investment in science-based water research, water monitoring, and water modeling is necessary.

No description available.

Pathogen contamination, typically quantified by elevated levels of fecal indicator bacteria (FIB), remains the leading cause of surface water-quality impairments in the United States. Continuous watershed-scale models are typically employed to facilitate Total Maximum Daily Load (TMDL) restoration efforts. Due to limited understanding of microbial fate and transport, predictions of FIB concentrations are associated with considerable uncertainty relative to other water-quality contaminants. By focusing on a data-rich instrumented urban watershed, this study aims to improve understanding of microbial fate and transport processes. Weekly FIB concentrations in both the water column and streambed sediments were monitored for one year, and statistical correlations with hydrometeorological and physicochemical variables were identified. An intensive six storm intra-sampling campaign quantified and contrasted loading trends of both traditional regulatory FIB and emerging Microbial Source Tracking (MST) markers. Together, these intensive monitoring efforts facilitated evaluation of the impacts of bacteria-sediment interactions on the predictions of daily FIB concentrations in Hydrological Simulation Program-Fortran (HSPF) over multiple years. While superior overall model performance was demonstrated as compared to earlier efforts, the inclusion of bacteria-sediment interactions did not improve performance. Large wet-weather microbial loading appears to have dwarfed the effects of FIB release and resuspension from sediment. Although wet-weather loading is generally considered as a primary source of waterbody microbial loads, dry-weather periods are more directly associated with public health concern, which may be a more suitable area for future model-refinement efforts. Site evaluation is critical to determine whether the added model complexity and effort associated with partitioning phases of FIB can be sufficiently offset by gains in predictive capacity. Finally, a stochastic framework to translate simulated daily FIB concentrations into estimates of human illness risks is presented that can be can be readily integrated into existing TMDLs. As even small concentrations of FIB from human sources are associated with great risk, and monitoring efforts indicated moderate/high levels of human-associated MST marker in this watershed, remediation efforts to protect public health would be best directed toward infrastructure improvements. Uncertainty analysis indicates more site-specific knowledge of pathogen presence and densities would best improve the estimation of illness risks. / Ph. D.

Sediment is a major source of water quality impairment in streams, rivers and lakes in the US. However, sediment fate and transport in small streams is poorly understood. Previous attempts to characterize sediment transport often insufficiently represented the physical and chemical sediment properties and lacked spatial and/or temporal resolution. Therefore, there is a need to develop better sediment tracers, for which rare earth element (REE)-labeled sediment is examined as an alternative. The objectives of this study were to: 1) assess the adsorption of REEs to natural soils and ensure their reliability as a tracer in a fluvial environment; and 2) evaluate the efficacy of utilizing REE-labeled sediment to quantify fate and transport in a second-order stream during a series of storm events. Two natural stream bank soils from Stroubles Creek in Virginia were labeled with the REEs lanthanum and ytterbium. The REEs adsorbed equally to both soils and had minimal desorption after several washes with stream water. This suggests that REEs form a dependable natural sediment tracer and sufficiently label natural soils for use in a sediment tracing study. During two storm events, two unique REE tracers were injected into Stroubles Creek. These tracers were detected at varying discharges and sediment loads in bed and suspended sediment samples up to 875 m downstream. REE tracers proved to be an ideal tracer for detecting sediment fate and transport in a small stream during a series of storm events and hold great potential for evaluating best management practices and sediment transport models. / Master of Science

Doctor of Philosophy / Department of Chemical Engineering / Larry E. Erickson / Chlorinated solvents are the second most ubiquitous contaminants, next to petroleum hydrocarbons, and many are carcinogens. Tetrachloroethylene or perchloroethene (PCE) has been employed extensively in the dry cleaning industry and carbon tetrachloride (CT) has been used as a fumigant in grain storage facilities. In this work, remediation feasibility studies were conducted by mesocosm experiments; a chamber was divided into six channels and filled with soil, and plants were grown on top. Each channel was fed with contaminated water near the bottom and collected at the outlet, simulating groundwater flow conditions. The contaminants were introduced starting from March 12, 2004. PCE was introduced at a concentration of about 2 mg/L ([similar to]12 [Mu]moles/L) in three channels, two of them with alfalfa plants and the other with grass. CT was introduced at a concentration of about 2 mg/L ([similar to]13 [Mu]moles/L) in the other three channels, two of them with alfalfa plants and the other with grass. After the system had attained steady state, the concentrations of PCE and CT at inlet and outlet were monitored and the amount of PCE and CT disappearing in the saturated zone was studied. Since no degradation products were found at the outlet after about 100 days, one channel-each for PCE and CT (with alfalfa) was made anaerobic by adding one liter of 0.2 % glucose solution. The glucose solution was fed once every month starting from July 1, 2004 and continued until February 2005. From October 1, 2004, one liter of 0.1 % emulsified soy oil methyl esters (SOME) was fed to two other channels (with alfalfa), one exposed to PCE and another exposed to CT. The SOME addition dates were the same as that for glucose. The outlet liquid of the channel fed with PCE and SOME started to contain some of the degradation compounds of PCE; however, the extent of degradation was not as great as that of the glucose fed channel. No degradation compounds were observed in the outlet solution of the channel (grass grown on top) in which no carbon and energy supplements were added. Similar trend was observed in the CT fed channels also. KB-1, a commercially available microbial culture (a consortium of dehalococcoides) that degrades dichloroethene (DCE), was added through the inlet of the PCE fed channels, but this did not lead to sufficient conversion of DCE. Addition of KB-1 at well 3, located approximately in the middle of the channel, had a greater impact in the degradation of DCE, in both glucose and SOME amended channels, compared to addition at the inlet. KB-1 culture added to the channel was active even 155 days later, suggesting that there is sustainable growth of KB-1 when provided with suitable conditions and substrates. A pilot field study was conducted for remediation of a tetrachloroethylene (PCE) contaminated site at Manhattan, KS. The aquifer in the pilot study area has two distinct zones, termed shallow zone and deep zone, with groundwater velocities of about 0.3 m/day and 0.1 m/day. Prior to the pilot study, PCE concentration in groundwater at the pilot study area was about 15 mg/L (ppm) in the deep zone and 1 mg/L in the shallow zone. Nutrient solution comprising soy oil methyl esters (SOME), lactate, yeast extract and glucose was added in the pilot study area for biostimulation, on August 18, 2005. Potassium bromide (KBr) was added to the nutrient solution as a tracer. PCE was converted to DCE under these conditions. To carry out complete degradation of PCE, KB-1, a consortium of Dehalococcoides, and a second dose of nutrient solution were added on October 13, 2005. After addition of KB-1, both PCE and DCE concentrations decreased. Nutrients were again injected on March 3, 2006 (with KBr) and on August 1, 2006. The total chlorinated ethenes (CEs) have decreased by about 80 % in the pilot study area due to bioremediation. Biodegradation of CEs continued for a long time (several months) after the addition of nutrients. The insoluble SOME may be retained at the feeding area and provide a long time source of electron donors. Biostimulation and bioaugmentation of PCE contaminated soil and groundwater was evaluated in the laboratory and this technique was implemented successfully in the pilot field study. Modeling of the tracer study was performed using an advection-dispersion equation (ADE) and traditional residence time distribution (RTD) methods. The dispersion coefficient, groundwater velocity and hydraulic conductivity were estimated from the experimental data. The groundwater velocities vary from 1.5 cm/d to 10 cm/d in the deep zone and 15 cm/d to 40 cm/d in the shallow zone. The velocities estimated from the 2004 tracer study and 2005 tracer study were higher compared to the velocity estimated from the 2006 tracer study, most likely because of microbial growth and product formation that reduced the hydraulic conductivity. Based on data collected from several wells the hydrologic parameter values obtained from tracer studies appear to vary spatially.