Browsing by Subject "Geochemistry"

The Peruvian/Bolivian Altiplano is an important hydrologic system for paleoclimate reconstruction because it is unique in its ability to record climate variability associated with the near-continental scale South American summer monsoon (SASM), which is responsible for much of the precipitation over the Amazon basin and the southern subtropics. Over long timescales moisture on the Altiplano fluctuates in intensity due to changes in precessional insolation forcing as well as teleconnections to decadal-to-millennial scale abrupt temperature shifts in the Northern hemisphere Atlantic. These long-term changes in moisture transport to the Altiplano have been observed in multiple paleoclimate records, including drill core records and paleo-lake level records, as apparent advances and retreats of large lakes in the terminal basin occupied by the Salar de Uyuni and the Salar de Coipasa.

Presented here are the results from three studies that utilize different methods to create a refined reconstruction of paleohydrology, as well as paleoclimate, on the Altiplano. A major goal of this research is a more detailed understanding of millennial scale climate variability as it relates to insolation changes and abrupt warming and cooling in the north Atlantic. The first study discusses the creation of a paleohydrologic profile to reconstruct north-south hydrological history using previously reported lake core sediment records the northern and southern basins of the Altiplano, and a new 14 m core from the Salar de Coipasa representing the last ~45 ka. The second study uses a terrestrial hydrology model to simulate lake level changes through time given changes in precipitation and temperature. The third study uses strontium isotopic measurements of carbonates and halites in a 220-m core from the Salar de Uyuni to determine how source waters to the southern basin have changed through time.

The paleohydrologic profile in the first study is constructed using records from three major basins within the Altiplano: Lake Titicaca in the north, and Salar de Coipasa and Salar de Uyuni in the south. The new continuous sediment core from Salar de Coipasa indicates a lake that has fluctuated between deep and shallow phases for the last 45 ka. Lacking sufficient calcium carbonate, we instead take advantage of the general correlation between d18O and d13C in closed basin lakes to approximate water balance using d13C from organic carbon. This reconstruction is validated with diatom paleoecological records. The isotope measurements and diatom records indicate that from 45-36 ka Coipasa was moderately deep, consistent with paleoshoreline evidence of paleolake Minchin (46-36 ka). From 36-26 ka a shallow lake <10 m deep occupied the Coipasa basin. During the LGM (26-21 ka) the lake varied from moderate to shallow and during the Holocene (< 10 ka) the lake evolved from a shallow lake to a salt flat.

The hydrologic model in the second study was run through many scenarios including increases in precipitation, decreases in temperature, and combinations of the two. During the LGM southern Altiplano lakes fluctuated between 3,660 - 3,700 masl. Model results suggest that during this period basin wide precipitation increased up to 250 mm/yr compared to modern values dependent on a temperature decrease of 5 °C relative to modern values. To create a lake at elevation 3,760 masl consistent with the highest paleolake phase (Tauca, ~16 ka) the model requires an increase of 350 mm/yr compared to modern values dependent on a 5 °C decrease in temperature (relative to modern values). An increase in temperature alone of 2 °C above modern values causes Lake Titicaca water level to decrease ~30 m, creating a closed basin lake. Results indicate that Lake Titicaca outflow is necessary to sustain large lakes in the southern basin, providing ~40-60% of total input via the Rio Desaguadero.

Analysis of a 220 m core from the Salar de Uyuni suggests periods of alternating wet and dry phases (indicated by alternating mud and salt units respectively) at the salar. Evident in the record is a transition at ~60 ka from sediments consistent with dry conditions ("playa lakes") to sediments consistent with deep lakes ("great lakes"). It has been shown that rivers and lakes in the Bolivian and Peruvian Altiplano display a range of Sr isotopic ratios that can be connected to the lithologies of specific drainage basins. Measurements of Sr ratios of the alternating halites and carbonate sediments are used to determine when paleolakes in the Salar were supplied by flow from the northern and central basins of the Altiplano, and when they were more a product of increased precipitation in the Uyuni basin. The results from Sr isotope analysis suggest that prior to ~60 ka the primary source of Sr to the Uyuni was local runoff and direct precipitation. Following the state change from the "play lakes" phase to the "great lakes" phase Sr isotope measurements suggest a significant influence from more radiogenic waters originating in the central and northern Altiplano basins. The reason for this state change is attributed to a combination of a general increase in precipitation following the onset of the MIS-4 (~70 ka) glacial period and downcutting of the Laka Jahuira hydrologic divide, which connects Lago Poopó in the central basin to the Salar de Coipasa.

This approach of reconstructing hydrology using the combination of multiple paleolake records, hydrological modeling, and isotopic tracers allows for a better understanding of how precipitation and temperature changes affect the advance and retreat of large lakes on the Altiplano, and ultimately a more accurate understanding of how decadal-to-millennial forcings influence the climate of the subtropical Andes.

Arsenic (As) exposure via groundwater consumption is a global health problem affecting millions. Monitoring exposure is a key step in understanding and predicating future health outcomes. This thesis explores the relationships between arsenic concentrations in toenails and arsenic in water. Three case studies were investigated, with residents from: North Carolina, USA (n=103); the Rift Valley, Ethiopia (n=60); and the Mekong Delta, Vietnam (n=65). Arsenic concentrations above the WHO's recommended 10ppb limit were found in groundwater from the three research sites.

Arsenic in toenails was analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

In the Rift Valley of Ethiopia, 53% of the tested drinking wells (n=34) had As above the WHO's limit. Arsenic concentrations in toenails (n=60) were significantly correlated to As concentrations in groundwater (r=0.72; p<0.001), reflecting the direct exposure of rural communities to As in well water, which is their principle water source. Male minors (<18 years old) were found to have greater nail-As concentrations compared with adults consuming equal amounts of As (p<0.05). Estimated As dose specifically from drinking water sources was also associated with nail concentrations (p<0.01).

In the Mekong Delta of Vietnam (Dong Thap Province), 36 out of the 68 tested wells had As content above the WHO's recommended limit of 10ppb, with levels as high as 981 ppb. Arsenic contents in nails collected from local residents (n=62) were significantly correlated to As in drinking water (r=0.49, p<0.001). Demographic and survey data show that the ratio of As in nail to As in water varies among residents that reflects differential As accumulation in the exposed population. The data show that water filtration and diet, particularly increased consumption of animal protein and dairy and reduced consumption of seafood, were associated with lower ratios of As in nail to As in water and thus could play important roles in mitigating As exposure.

Sixty-one wells were tested from Union County, North Carolina, with 15 out of 61 wells exceeded the WHO's 10 ppb limit. Arsenic values ranged from below the limit of detection (0.07) to 130ppb, with a mean of 11ppb (median=1.5ppb). Nails were collected from county residents (n=103) and were statistically correlated with As-water concentrations (r=0.48, p<0.001).

Integration of the data from the three cases studies across different populations and ethnicities show high correlation between As concentrations in groundwater and As in nails in all the three locations (r(Union County)= 0.48, p<0.001; r(Ethiopia)=0.72 p<0.001; r(Vietnam)=0.49, p<0.001). For As-nail to As-water pairs in which As in water was above 1ppb, these three locations are statistically indistinguishable from one another (r=0.62, p<0.001, n=176). These results support the hypothesis that nails can be used as a biomarker of exposure regardless of geographic or ethnic differences in populations considered. Nutrition (meat, seafood, and milk consumption) rather than gender, ethnicity, or dose is suggested to be the major confounding issue affecting the magnitude of As exposure in the human body.

The geochemical evolution of basaltic magmas, in a variety of settings, has been the subject of countless studies. In some instances, basaltic magmas evolve to form economic transition and precious metal ore bodies. The metals extracted from these ore bodies are of critical importance to a wide variety of industries, such as automotive manufacturing. On a larger scale, basaltic magmas evolve to form the oceanic crust, the interface between the Earth’s mantle and the oceans. These are just two examples of how basaltic magmas are entwined with life on Earth and together represent the focus of this dissertation.

The second chapter of this dissertation uses detailed petrography to characterize the late-stage evolution of the Eocene Skaergaard Intrusion, Greenland. Significantly, this study identifies textural and chemical evidence that suggests that late hydrothermal fluids modified the Skaergaard transition (copper) and precious metal (silver, gold, platinum) budget.

The third chapter examines the major and trace element concentrations, as well as the 87Sr/86Sr ratios, for a suite of basaltic lavas dredged from the Cocos-Nazca Spreading Center, the Dietz Volcanic Ridge, and the East Pacific Rise. Prior to this study, this region of the Pacific basin was sparsely sampled. Notably, this study determines that lavas from the Cocos-Nazca Spreading Center are chemically depleted and are likely sourced from mantle that differs from that characteristic of normal mid-ocean ridge basalt.

Finally, the fourth chapter examines the size distribution, morphology, and chemical composition of plagioclase in plagioclase phyric lavas from the Cocos-Nazca Spreading Center. A variety of plagioclase morphologies, textures, and chemical compositions are reported. Importantly, this study demonstrates that combining size distribution analysis with textural and compositional information can provide nuanced information about the processes occurring beneath mid-ocean ridges.

Coal fired power plants are ubiquitous in the United States and most developed countries around the world, providing affordable electricity to consumers. In the US, approximately six hundred power plants generate 136 million tons of Coal Combustion Residuals (CCRs) annually, encompassing fly ash, bottom ash, and flue gas desulfurization materials. The range and blends of CCRs varies substantially across coal-fired plants and depends on a unique set of circumstances for each plant and coal source. Current U.S. regulations mandate the installation of advanced capture technologies to reduce atmospheric pollution, but do not address the transfer and storage, or the potential impacts to water resources. Thus improved air quality is traded for significant enrichments of contaminants in the solid waste and effluent discharged from power plants.

This work examines the geochemical and isotopic characteristics of CCRs, as well as potential environmental impacts from CCRs. This investigation looks at several different aspects of CCR and environmental interactions from 1) the immediate impacts of the 2008 TVA coal ash spill in Kingston, TN, 2) the long-term (18-month) exposure of the spilled ash in the Emory and Clinch rivers, 3) impacts on waterways in North Carolina that receive CCR effluent from coal fired power plants, and 4) examination of boron and strontium isotopes of CCRs from leaching experiments and their application as tracers in the environment of the TVA spill and NC waterways. These investigations have illuminated several conclusions, including contact of surface water with CCRs leach high concentrations of leachable CCR contaminants, such as As, Se, B, Sr, Mo, and V in the surface waters; the dilution effect is critical in determining the concentration of contaminants from the CCRs in surface water (both at the spill and in waterways receiving CCR effluent); recycling of trace elements (such as As) through adsorption/desorption can impact water quality; and elevated boron and strontium concentrations, in addition to their isotopes, can trace CCR effluent in the environment. Combining the geochemical behavior and isotopic characteristics provides a novel tool for the identification CCR effluents in the environment.

Fossil fuels continue to be a major component of the energy economies in North America, accounting for 60% of electricity generation in the U.S. Recent incidences (i.e. spills) and limited regulation of the fossil fuel industry has generated public concern about the risks fossil fuel development pose to water resources. Previous studies have identified negative impacts on water quality associated with the storage and disposal of coal combustion residuals, oil sands process-affected water, and oil and gas wastewater, as well as leaking of methane to groundwater in areas of hydraulic fracturing. In addition, contamination of water resources from natural (geogenic) sources has also been observed in many of the areas associated with fossil fuel development. Since naturally occurring saline water is common in some regions associated with fossil fuel explorations, delineating the effects of anthropogenic contamination sources is a major challenge for evaluating the impact of fossil fuel development on water quality.

This thesis investigates the geochemical and isotopic characteristics of wastewater from coal combustion residual storage ponds, unconventional oil and gas exploration, and oil sands mining, in an attempt to evaluate the use of geochemical and isotopic tracers to identify fossil fuel-associated wastewaters in the environment. This includes the investigation of (1) halogen (Br, I) and ammonium contents of oil and gas wastewater (OGW);(2) the lithium isotope ratios in OGW and coal combustion residuals; and (3) the inorganic geochemistry and boron, strontium and lithium isotope ratios of oil sands processed-affected water (OSPW). In three case studies, these geochemical and isotopic tools were integrated into comprehensive geochemical frameworks that investigated the (1) leaking of coal ash ponds to surface and groundwater in the southeastern United Sates; (2) geochemistry of groundwater in an area of shale gas development in West Virginia through time and space; and (3) evaluation of the sources of molybdenum in contaminated groundwater in southeastern

Wisconsin and possible links to coal ash surface disposal. These investigations illustrate a range of situations in which isotopic fingerprinting provided a unique geochemical tool that can successfully identify fossil fuel-related wastewater in the environment. These studies have also demonstrated the environmental impact upon releasing of fossil fuels wastewater to the environment. The case studies support the use of geochemical and isotope tools as robust methods to not only identify contamination of water resources by fossil fuel-related activities, but also to distinguish wastewater contamination from naturally occurring contamination in areas of fossil fuel development. These studies highlight the benefit of using a suite of geochemical tools when investigating water quality impacts.

The tropics are a significant source of heat and moisture export, which drive global circulation patterns, thus it is vital to systematically understand the land, ocean and sedimentological interactions within the tropics. The Brazilian continental margin is an ideal region to characterize the tropics due to its unique local oceanography and proximity to the atmospheric engine that is the Amazon Basin. A combination of: 1) terrestrial organics and hydrology; 2) oceanographic temperature, isotopic composition, and salinity and 3) early diagenesis and geochemistry of sedimentary interstitial water and methane hydrate, provide a detailed understanding of the primary constituents that influence the South American tropics.

Sedimentological, organic and paleoceanographic reconstructions of the Amazon Basin, Brazilian Nordeste, and western equatorial Atlantic have been undertaken on two sediment cores located on the Brazilian continental slope representing 30 and 110 ka, respectively. High-resolution XRF analyses of Fe, Ti, K and Ca are used to define the sedimentological history of the Amazon Basin and northern Nordeste. Here we present elemental ratios of Ti/Ca and Fe/K, in addition to magnetic susceptibility, to determine variability in Amazon Basin and Nordeste hydrology. Bulk organic proxies d13C and d15N of sedimentary organic carbon are used to define the organic history of the Amazon Basin. Peaks in Ti/Ca and Fe/K ratios largely correlate in both the Amazon Basin and in the Nordeste Record. These excursions correlate with commonly modeled global slowdown of the Atlantic meridional overturning circulation (AMOC) during increased northern hemisphere glaciation. Differences in the Fe/K and Ti/Ca records suggest periods of increased chemical weathering independent of precipitation driven sediment discharge in the Brazilian Nordeste. Bulk organic geochemistry indicates the vegetative history of the Amazon Basin has been relatively stable during the late Quaternary.

High-­resolution stable oxygen isotopic analysis and Mg/Ca paleothermometry undertaken on the near-­surface-dwelling planktic foraminiferal species Globierinoides ruber provide a picture of paleoceanographic forcings in the western equatorial Atlantic. The Nordeste core exhibits a rapid warming of ~3.5ºC between the last glacial maximum and the early Holocene. Furthermore, in almost all cases during the last glacial stage, there was a 0.5 to 2ºC warming of the western equatorial Atlantic during the periods of high Ti/Ca ratios that correlate with slowdown of AMOC. Thus, as observed in some previous studies, the western equatorial Atlantic was warm and the adjacent southern tropical continent was wet coincident with increased glaciation in the high latitude northern hemisphere.

Interstitial pore waters were analyzed from the Amazon Fan and Brazilian continental slope to determine early diagenesis, methane hydrate potential and its geographic variability. Interstitial waters were measured for total Mg, Ca, SO4, alkalinity, Cl, and d18O, combined with seismic bottom simulating reflectors (BSRs) to investigate early diagenesis. Interpolated maps of sulfate reduction, sedimentation rate and maximum alkalinity were produced to examine geographic variability in early diagenesis and methane hydrates. Inorganic precipitation of calcium and magnesium, likely via dolomite and siderite, correlates with a decrease in alkalinity through inorganic carbonate precipitation and methanogenesis, but alternatively increases through redox pathways, specifically sulfate reduction.

Through multiple lines of evidence it is likely that there is extensive methane hydrate occurrence on the Amazon continental shelf. A combination of: 1) A rapid linear decline in sulfate at an unusually shallow depth; 2) Uncommonly high sedimentation rates and terrestrial organic carbon input; 3) Significant variability in what should be conservative chloride concentrations; 4) Large variability in interstitial oxygen isotopes; 5) Widespread occurrence of BSRs provide substantial support for the presence of methane hydrates. Sulfate reduction rates are lowest along the main Amazon channel, with highest values distal of the main channel. Sedimentation rates are relatively low on the continental shelf and surrounding the main channel and highest toward the distal end of the main channel. Sulfate reduction rates provide key insights to the potential geographic variability of methanogenesis and methane hydrate formation. Given the tremendous influx of sediment from the Amazon River, this region is prone to massive sediment failures, subsequent release of methane hydrates, as well as significant potential for natural gas hydrates.

Extraction of energy resources and energy production can redistribute and concentrate naturally occurring radioactive materials (NORM), particularly from the uranium (238U t1/2=4.5 x 109 yr) and thorium (232Th t1/2=1.4 x 1010 yr) decay series, posing potential human and environmental health risks if not managed properly. In particular, elevated activities of NORM have been measured in coal combustion residuals (CCRs) generated from coal combustion and oil and gas wastewater (OGW) drawn from both conventional and unconventional oil and gas producing wells. This dissertation characterizes the radioactivity associated with CCRs and OGW and further investigates the use of this radioactivity as a tracer and timer of contamination, particularly from OGW following its accidental or intentional release to the environment.

232Th and its decay product 228Ra and 238U and its decay products 226Ra and 210Pb were measured in coals and CCRs from the majors coal producing basins in the United States as well as in coals and CCRs from high-U coal producing basins in China. 228Ra and 226Ra were measured in OGW from the Appalachian Basin in the United States. Finally, 228Ra, 228Th, 226Ra, and 210Pb were measured in soils and sediments impacted by spills of OGW and the permitted release of treated OGW to surface water.

Characteristic 228Ra and 226Ra activities 228Ra/226Ra activity ratios were found in CCRs and OGW derived from distinct formations, suggesting that the radioactivity can serve as a potential fingerprint of for contamination when CCRs and OGW are accidentally or intentionally released to the environment. Additionally, the decay of 226Ra and 228Ra into their respective decay products 210Pb and 228Th offers the ability to source and age date contamination from OGW. The 228Th/228Ra activity ratio in particular is useful for age dating contamination in impacted sediments up to about 10 years old, which is ideal for age dating recent contamination. The 228Ra/226Ra and 228Th/228Ra activity ratios were successfully used to constrain the age and source of contamination from two scenarios including OGW spills and treated OGW disposal to surface water.

Prior studies of groundwater systems have associated increasing salinity and anoxic conditions with increasing radium (Ra) activities in water due to the decreasing effectiveness of Ra removal processes. However, the components of salinity (e.g. Ca vs. Na and SO₄^2- vs. Cl^--dominated waters), and the relative importance of salinity-sensitive vs. redox-sensitive processes for Ra mobilization, are less well understood. In this research, the response of Ra to hydrochemical change was examined using a multiple tracer approach to obtain detailed information on divalent cation and Ra mobility. A range of salinity and redox conditions was examined in five field-based studies in the United States and Morocco: (1) fresh waters in fractured crystalline rocks in the Piedmont region of North Carolina; (2) the Willcox Basin, an oxic alluvial basin-fill aquifer in southeastern Arizona; (3) the Jordan sandstone aquifer, a carbonate-cemented quartz sandstone in southeastern Minnesota; (4) an unconfined coastal aquifer undergoing salinization in the city of Agadir, Morocco; and (5) the confined, fresh to saline Cretaceous and Pliocene aquifers of the Atlantic Coastal Plain in North Carolina.

In addition to analysis of major element concentrations, trace metal concentrations, and ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra activities, complementary isotope systems were applied to gain insights on the relative stability of chemical processes that remove radium and other alkaline earth metals: (1) strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) trace divalent cation release from sources such as clay and carbonate minerals in the aquifer solids and also indicate conditions in which divalent cation release (rather than uptake) is dominant; (2) boron concentrations and isotopes (δ¹¹B) coincide with the opposite condition in freshening conditions of the Atlantic Coastal Plain, in which divalent cations are removed in exchange for Na; and (3) sulfur and oxygen isotopes (δ³⁴S, δ¹⁸O) of sulfate trace sulfate sources and provide information on sulfate-reducing conditions, which can inhibit barite (BaSO₄) from removing Ra by coprecipitation. In addition, other isotopic and ion measurements trace salinity sources and groundwater residence time, including δ²H, δ¹⁸O, ³H, Br^-/Cl^-, Na/Cl^-, and Ca/Na.

This dissertation documents correlations between salinity and radium in the brackish to saline North Carolina coastal plain aquifer with total dissolved solids (TDS) up to ~18,000 mg L^-1 and to some degree in the Moroccan coastal aquifer, but even the lower-salinity waters (TDS <3000 mg L^-1) exhibit a range of Ra activities spanning approximately 3 orders of magnitude. Among these low-TDS waters, the highest Ra activities were observed in the anoxic Jordan sandstone aquifer and the lowest were observed in the oxic Willcox Basin aquifer. Although the main control on radium activities in fresh groundwater is the U- and Th-series radionuclide content of the aquifer solids, important secondary controls include the stability of redox-sensitive radium adsorption sites (Mn and Fe oxides), the relative dominance of divalent vs. monovalent cations (e.g. the Ca/Na ratio), formation of the uncharged RaSO₄⁰ complex, and/or the saturation state with respect to barite. These processes interact in varied ways in the field-based studies. Increasing radium activities and decreasing ²²²Rn/²²⁶Ra ratios in the North Carolina fractured crystalline rock groundwater system are correlated with increasing Ba, Mn, and Fe concentrations and decreasing dissolved oxygen concentrations, related to weathering and/or organic carbon oxidation. Radium activities in the oxic, neutral to slightly basic Willcox Basin are very low (median ²²⁶Ra activity 2 mBq L^-1), probably due to a combination of effective Ra removal processes including adsorption to Mn and/or Fe oxides and the overall removal of divalent cations during groundwater evolution in this system. These are the same surface charge conditions that release arsenic, of regional water concern, in this pH range. Radium in Jordan aquifer groundwater is dependent on local variations in solid-phase radionuclide levels, probably hosted in the carbonate cement phase. Also, Ra is inefficiently adsorbed to the aquifer solids in the aquifer's anoxic conditions, resulting in the highest radium levels reported in this dissertation (²²⁶Ra up to 420 mBq L^-1) despite apparent barite precipitation that partially removes Ra. Radium-224 activity in the Moroccan coastal aquifer is associated with salinity, but Ra overall is apparently controlled by barite, indicated by conditions near BaSO₄ saturation. Radium activity in the saline waters of the Atlantic Coastal Plain aquifers is associated with TDS concentrations, but the cation exchange properties of the aquifer may provide a major mechanism of Ra removal in the Na-HCO₃^- and Na-Cl^- waters. Overall, the complex interaction between groundwater chemistry and Ra-removing processes implies that in waters with TDS below approximately 3,000 mg L^-1, dissolved solids concentration alone does not fully describe radium's response to hydrochemical conditions, but rather that aquifer-specific examination of Ra removal mechanisms is needed.

Groundwater has an important role in forging the composition of surface water, supplying nutrients crucial for the development of balanced ecosystems and potentially introducing contaminants into otherwise pristine surface water. Due to water-rock interactions radium (Ra) in groundwater is typically much more abundant than in surface water. In saline environments Ra is soluble and is considered a conservative tracer (apart for radioactive decay) for Ra-rich groundwater seepage. Hence in coastal environments, where mostly fresh groundwater seep into saline surface water, Ra has been the prominent tracer for tracking and modeling groundwater seepage over more than three decades. However, due to its reactivity and non-conservative behavior, Ra is rarely used for tracing groundwater seepage into fresh or hypersaline surface water; in freshwater, Ra is lost mostly through adsorption onto sediments and suspended particles; in hypersaline environments Ra can be removed through co-precipitation, most notably with sulfate salts.

This work examines the use of Ra as a tracer for groundwater seepage into freshwater lakes and rivers and into hypersaline lakes. The study examines groundwater-surface water interactions in four different environments and salinity ranges that include (1) saline groundwater discharge into a fresh water lake (the Sea of Galilee, Israel); (2) modification of pore water transitioning from saline to freshwater along their flow through sediments (pore water in sediments underlying the Sea of Galilee, Israel); (3) fresh groundwater discharge into hypersaline lakes (Sand Hills, Nebraska); and (4) fresh groundwater discharge into a fresh water river (Neuse River, North Carolina). In addition to measurement of the four Ra isotopes (226Ra, 228Ra, 223Ra, 224Ra), this study integrates geochemical (major and trace elements) with additional isotopic tools (strontium and boron isotopes) to better understand the geochemistry associated with the seepage process. To better understand the critical role of salinity on Ra adsorption, this study includes a series of adsorption experiments. The results of these experiments show that Ra loss through adsorption decreases with increasing salinity, and diminishes in salinity as low as ~5% of the salinity of seawater.

Integration of the geochemical data with mass-balance models corrected for adsorption allows estimating groundwater seepage into the Sea of Galilee (Israel) and the Neuse River (North Carolina). A study of the pore water underlying the Sea of Galilee shows significant modifications to the geochemistry and Ra activity of the saline pore water percolating through the sediments underlying the lake. In high salinity environments such as the saline lakes of the Nebraska Sand Hills, Ra is shown to be removed through co-precipitation with sulfate minerals, its integration into barite (BaSO₄) is shown to be limited by the ratio of Ra:Ba in the precipitating barite.

Overall, this work demonstrates that Ra is a sensitive tracer for quantifying groundwater discharge even in low-saline environments. Yet the high reactivity of Ra (adsorption, co-precipitation, production of the short-lived isotopes) requires a deep understanding of the geochemical processes that shape and control Ra abundances in water resources.

This research explores the beneficial reuse of coal combustion fly ash as a source of rare earth elements (REE). We characterized fly ashes of varied geological origin, tested several extraction methods and parameters, and investigated REE location and speciation in fly ash. Total REE content in a broad sample of U.S. fly ashes were quantified using HF/HNO3 digestion, Na2O2 sintering, and HNO3 digestion. If was found that Appalachian Basin coal ashes had significantly higher total REE content than Illinois Basin or Powder River Basin ashes. However, Powder River Basin ashes had higher HNO3-extractable REE content. Sinter-based extraction methods were tested for REE recovery from fly ash. Optimal sintering conditions were found to be a 1:1 NaOH-ash ratio and 1-2 M HNO3 leaching solution. Bulk and microscale Y speciation in fly ash were compared using sequential selective extractions and x-ray absorption spectroscopy. Bulk speciation suggested Y entrained in the aluminosilicate glass phase while microscale speciation resembled trace yttrium minerals.

Layered igneous intrusions such as the Stillwater Complex in Montana contain the most economic concentrations of platinum-group elements (PGE) in the world, yet the processes involved in the enrichment of these PGE remain unclear. Some researchers propose that the PGE were enriched into sulfide phases through purely magmatic processes, while others postulate that late-stage, high-temperature fluids caused remobilization of the more soluble elements upwards from the base of the crystal pile. Although much work has been carried out on the economic PGE-enriched ore zone (J-M reef), the silicate mineralogy and the bulk geochemistry of the Complex, the detailed petrographic trends have not been investigated. This dissertation comprises a detailed petrographic study into the assemblages associated with sulfide and other trace minerals throughout the stratigraphy.

Sampling was carried out from both surface outcrops and drill cores over four consecutive field seasons. Polished thin sections were produced which were then examined by petrographic microscope and electron microprobe. In addition, bulk rock analysis was carried out by x-ray fluorescence spectrometry (XRF).

In brief, the sulfide and trace mineral assemblage studies described below reveal a number of interesting observations. An upwards trend from pentlandite-rich to pyrrhotite-rich to chalcopyrite + pyrite-rich assemblages is observed below the reef, and the same trend occurs above the reef with the transition occurring just below the reef, in upper GN-I. Trace element analysis shows that Cu levels are higher above the reef than below it, and that although Zn and Cu contents are correlated below the reef, a restricted range of Zn contents occurs above the reef, while Cu is highly variable. As all `low-temperature' assemblages (those associated with extensive silicate alteration or the presence of greenschist facies minerals such as chlorite, clinozoisite and epidote) were discounted, the majority of sulfide assemblages present were either pristine(multiphase, often globular in shape, with no associated silicate alteration) or high-temperature (multiphase, with high-temperature minerals such as biotite, hornblende, carbonates, etc, and with little associated silicate alteration) in occurrence. Some differences were observed between the hanging-wall and footwall rocks, including the presence of native copper, sphalerite in a calcite-hornblende vein, and high-temperature carbonates in footwall and not hanging-wall rocks. The high-temperature carbonates observed comprise dolomite with exsolved patches of calcite. The textural relationships and Fe-Mn compositions of the Stillwater carbonates are similar to those of mantle carbonates. High-temperature desulfidation is also observed both above and below the reef, in the form of pyrite being converted to magnetite, and chalcopyrite to a Cu-Fe-oxide (delafossite). Both sets of assemblages are associated with little to no silicate alteration. When taken together, the upwards increase in Cu and S, the variable Cu contents above the reef, the native copper, high-temperature carbonates and high-temperature sphalerite-bearing veins below the reef, and the evidence for desulfidation are all most readily explained by the remobilization of selected phases by a high-temperature fluid. This dissertation provides evidence that the fluid present in the latter stages of Stillwater formation had a carbonic as well as a Cl-rich component, and would therefore have been efficient in PGE remobilization.

The Skaergaard Intrusion of East Greenland is unusual in that the trace sulfide assemblage is characterized by unusually high Cu/S ratios, containing abundant chalcopyrite and bornite (Cu5FeS4), the latter otherwise rare in most layered intrusions. Explanations for the high Cu/S ratio range from the parent magma inheriting low S concentration from the mantle source to

suggestions that S was lost to hydrothermal fluids as the intrusion cooled. The sulfide assemblage beneath the Au- and PGE-rich Platinova Reef show the common replacement of the sulfide assemblage with a Ti-poor magnetite. A non-equilibrium thermodynamic analysis of modal variations is consistent with the general reaction of chalcopyrite --> bornite + magnetite + S (lost) and that the original Cu:S mass ratio of the magma that crystallize the Lower Zone was

~1:1. In addition, a comparison with other hot spot and flood basalt provinces suggest that these magmas begin to degas while still at mantle depths and can lose significant S to shallow level degassing. It is concluded that degassing of the parent Skaergaard magma prior to solidification

and continuous S loss during crystallization both contributed to the overall high Cu/S ratio of the Skaergaard system. More generally, variations in the Cu/S ratio of sulfides in basaltic systems may be a useful indicator of the extent of magma degassing.

The water energy nexus represents the intersection of water use, energy production, electricity generation, and waste generation and disposal. The rapid rise of unconventional natural gas and oil production through the combined processes of horizontal drilling and hydraulic fracturing have shifted the energy dynamic in the United States. Concurrently, the rising utilization of unconventional gas and oil production has intensified the water use for hydraulic fracturing and generation of flowback and produced water associated with shale gas and tight oil production. Among the major environmental risks associated with the rise of unconventional oil and gas exploration water availability, water contamination from leaking or disposal of wastewater, and adequate disposal of the wastewater are the key issues associated with the water-energy nexus. This dissertation aims to quantify the water use for hydraulic fracturing across the U.S., evaluate the water use for electricity production from natural gas in comparison to coal combustion, estimate the flowback and produced water production, and assess possible recycling of oilfield water through irrigation in California.

This dissertation describes the water footprint of hydraulic fracturing by examining total water use, water use per well, water use per length of horizontal well, and the changes in water use through time. The data show that hydraulic fracturing water use per well has been increasing between early stages (2008-2012) to later stages (2012-2016) of operation. In addition to water use, this dissertation estimated waste water generated from unconventional oil and gas wells and find a concurrent increase in flowback and produced water (FP water) per well through time. Using salinity as a marker to distinguish FP water from water injected for hydraulic fracturing, this dissertation observes the sequestration of the injected freshwater, while the return flow composed primarily of more saline formation brines entrapped within the shale formations.

In addition, this this dissertation explored two downstream impacts of the increasing water use and FP water generation. First, as abundant natural gas resources from the expansion of hydraulic fracturing have shifted the electricity sector from primarily coal- to primarily natural gas-fired, this study examined the impact increasing water use associated with hydraulic fracturing has had on power plant lifecycle water consumption and withdrawal. The study found that despite increasing water use for hydraulic fracturing, natural gas-fired generation on average used less water for cooling relative to coal-fired generation. Finally, this this dissertation examined the risks from recycling of oilfield produced water (OPW) as an agricultural makeup water source. The data from field studies in California show that by using low salinity OPW, farmers are able to successfully recycle OPW without risking metals accumulation in soil and consequently in crop and human health.

Coal combustion residuals (CCRs or coal ash), phosphate rocks and fertilizers, and leaded gasoline and lead-based paint represent major anthropogenic sources of metal and metalloid (i.e., metal(loid)) contaminants released to the environment. This dissertation aims to characterize the compositions of trace elements and radiogenic isotopes (Pb, Sr) of these anthropogenic sources and further explore their individual applicability and/or conjunctive utility with radioactive isotopes (228Ra, 226Ra, 137Cs, and 210Pb) in tracing the origin, timing, and impacts of metal(loid) contamination at various scales and in multiple environmental settings.The trace element compositions and isotopic signatures of Pb and Sr in fly ash originating from coals of different coal basins in the United States were characterized. In addition, an extended database of the Pb isotope fingerprints of coal and coal ash from China and India – the world’s top two coal producers and consumers – was established, combining newly measured values of coal and coal ash samples in this dissertation and data compiled from the literature. The results showed that (1) the Pb isotope signature of coal fly ash is distinctive from the isotope compositions of both the legacy anthropogenic Pb sources (i.e., leaded gasoline and lead-based paint) as well as natural Pb, which can be used for detecting fly ash contamination in the environment; (2) the 87Sr/86Sr ratio of bulk coal fly ash is distinctive from that of water-soluble fraction, which reflects the heterogenous distribution of Sr in fly ash and indicates the different uses of 87Sr/86Sr ratio for tracing its contamination in different environmental settings (i.e., terrestrial versus aquatic); and (3) the integrative use of trace elements, Ra isotopes (228Ra/226Ra), and Pb isotopes can further improve the detection of trace levels of coal fly ash dispersed in the environment. Through the integration of geochemical and isotopic tools (i.e., trace element distribution and 87Sr/86Sr ratio) with morphological and magnetic observations, this dissertation revealed the decades of historical and current unmonitored releases of coal ash and associated metal(loid) contaminants from the inadequate coal ash disposal units to the adjacent freshwater lakes across North Carolina (NC). The temporal distribution and evolution of coal ash contamination in the lake sediments were constructed by 137Cs- and 210Pb-based chronology techniques. The contributions of coal fly ash to the total Pb accumulation in the sediments of these contaminated lakes were quantified using a Bayesian-based Pb isotope mixing model, and the results suggested that regionally Pb contamination from fly ash can significantly outweigh the Pb input of atmospheric deposition (i.e., leaded gasoline) in the environment. Furthermore, the Pb isotope compositions of coal fly ash from China, India, and the U.S. were constrained and the fluxes of Pb associated with coal fly ash disposal in the three countries were estimated, laying the groundwork for future research on the impacts of coal ash on the Pb biogeochemical cycles at larger scales. Additionally, this dissertation reported the first set of data on the Pb isotope compositions along with rare earth elements and yttrium (REY) of phosphate rocks and fertilizers sourced from different regions and origins around the world. The geological imprints reflected in the geochemical and Pb isotopic fingerprints of the phosphate rocks were discussed and their potential utilizations and limitations in tracing phosphate-associated metal(loid) contamination in the environment were evaluated. This lays the groundwork for future local and regional studies on tracing the impacts of metal(loid) contaminants from phosphate rock mining and phosphate fertilizer application. Furthermore, this dissertation showcased a holistic assessment of the legacy anthropogenic contamination of Pb and other metal(loid)s in urban soils from Durham, NC, whereby fallout radionuclides 137Cs and 210Pb were proposed as potential indicators of the extent of soil disturbances that can impact the mobilization and redistribution of metal(loid) contaminants. The imprints of distinctive Pb isotopic fingerprints of leaded gasoline and lead-based paint in the soils reflected the persistent presence of these legacy sources in the urban environment of today, and the potential bioavailability of toxic metal(loid)s in the contaminated soils upon oral ingestion was assessed via in vitro arrays.

Production of oil and gas from unconventional natural gas reservoirs such as impermeable organic-rich shale formations was made possible through the use of horizontal drilling and high volume slick water hydraulic fracturing (HVHF). This combination of technologies has changed the energy landscape in the Unites States and possibly provided a vast new energy source from multiple sedimentary basins in the United States (Kargbo et al., 2010; Kerr, 2010) (Figure 1). HVHF requires large volumes of water (~5 million gallons/well) (Lutz et al., 2013) injected under high pressure to stimulate methane release from the fracture systems in the shale formations. The process is conducted within low-permeability formations, which include organic-rich shale rocks that are often the source rock for overlying conventional oil and gas reservoirs but do not easily transport gas to the well bore without stimulation. Once the permeability of the target formation is increased to a level that oil and gas can be recovered, pressure is released and 20-30% of the fluid that was injected flows back up to the surface through the well (Lutz et al., 2013). The remaining 70% stays underground, either lost to adjacent formations or imbed within the formation itself.

While HVHF operations rapidly expanded in many shale plays (e.g., Marcellus, Fayetteville), the possible negative environmental impacts remained un-quantified but a debated topic (Howarth et al., 2011). This dissertation focuses on quantification and evaluation of several water resources for evidence of contamination from HVHF. My hypotheses are: (1) HVHF have distinctive chemical and isotopic fingerprints that are different from other potential contamination sources; and (2) these fingerprints could be identified in aquifers and surface water systems.

I tested these hypotheses in two shallow drinking water aquifers overlying current unconventional gas development, northeastern Pennsylvania and north-central Arkansas, and one area of surface water disposal in western Pennsylvania. I used specific geochemical (Br, Cl, SO4, Na, Ca, Mg, Ba, Sr, B, and Li) and isotopic (87Sr/86Sr, 2H/H, 18O/16O, δ11B, and 228Ra/ 226Ra) tracers to characterize the target-formation brines and delineate possible contamination. The combined geochemical fingerprint distinguished hydraulic fracturing fluids and brines from other types of contamination that could influence water quality (e.g., road salt, sewage, acid mine drainage).

In Pennsylvania (Chapter 1), geochemical and isotopic data shows no direct evidence of contamination in shallow drinking-water aquifers associated with natural gas extraction of the Marcellus Formation. The data instead demonstrated that brine with the same geochemical (Br/Cl, Sr/Cl, and Ba/Cl) and isotopic fingerprint (87Sr/86Sr) of the Marcellus brine was likely naturally present in the shallow formations prior to the most recent oil and gas development. The data indicates that there may be areas in northeastern Pennsylvania that may be at increased risk of contamination from HVHF because of the presence of natural pathways that connect the shallow drinking water aquifers with deeper formations. This Chapter was published in Proceedings of the National Academy of Sciences in July 2012.

A very different result was observed in Arkansas (Chapter 2). While the shallow groundwater data indicated that there was no direct evidence of contamination, there was also no indication of hydrodynamic connections between the deeper formation brine and the shallow aquifers. Indeed 87Sr/86Sr, δ11B, 18O, and 2H values exclude Fayetteville Formation water as a source of salinity in shallow aquifers in the study area. The combined studies indicate that site and basin-specific studies of groundwater quality are necessary in order to evaluate the potential for contamination from HVHF. The Chapter was published in Applied Geochemistry in May 2013.

Surface water disposal of hydraulic fracturing fluids and brines (Chapter 3) clearly impacted western Pennsylvania sediment and water quality. Sediments in the stream at the point of effluent discharge from a treatment facility indicate radium activities 200 times higher than any background values. The 228Ra/226Ra ratios in the sediments also indicate that the source of contamination is likely the recent treatment and disposal of Marcellus brine. Impacts were also observed farther downstream. The concentrations of bromide and chloride in the effluent were so high that an increase in the concentrations measured in the stream was elevated almost two kilometers downstream. Chapter 3 was submitted to Environmental Science and Technology in May 2013.

Overall, this thesis aims to establish inorganic geochemical and isotopic tools for identification of hydraulic fracturing fluids in the environment and assess their possible impact on both surface and groundwater resources.

The genesis of layered intrusions has been the focus of countless studies. Layered intrusions have historically been viewed as natural laboratories to understand the evolution of a single large magma chamber. Many contain platinum- and palladium-rich reef-type deposits, making layered intrusions particularly important economically. Further, layered intrusions may be a useful analogue for understanding subduction zone hydrothermal systems.This dissertation investigates layered intrusion genesis, specifically in relation to the suggested hydrothermal model of layered intrusion formation, which suggests migrating fluids may have remobilized economically important elements, creating the deposits observed in these intrusions today. The work is divided into eight chapters that explore three layered intrusions: the Bushveld Complex, South Africa, the Stillwater Complex, Montana, and the Skaergaard Intrusion, Greenland. New samples collected from the Stillwater Complex were analyzed for major and trace element compositions and radiogenic and stable isotopes. Investigations into the Bushveld Complex and Skaergaard Intrusion were based on previously published data. The second chapter examines evidence for fluid circulation in the Bushveld Complex, South Africa, as responsible for some of the geochemical and isotopic signatures present in the complex. Previous isotopic studies of Bushveld are combined with numerical modeling of footwall dehydration to suggest that diapir-like structures injected fluids into the Main Zone of the intrusion. This chapter further details the similarities between diapiric structures in the Bushveld Complex and those that have been modeled in subduction zone hydrothermal systems. The third chapter expands upon the Bushveld model, specifically in relation to the formation of iron-rich ultramafic pegmatoids and dunite pipes, which the work presented here suggests to be fluid-related. In the fourth chapter, strontium, neodymium, and lead isotopes are analyzed for rocks from the Stillwater Complex, Montana, to compare with the isotopic mixing model results of the Bushveld Complex. Initial isotopic ratios are used to explore various proposed models of complex formation. Results suggest isotopic heterogeneity during complex formation, whether due to heterogeneous source regions or crustal/fluid contamination. In the fifth chapter, stable isotope analyses (oxygen, hydrogen, and lithium) are used to better understand the formation of the pegmatoidal bodies thought to be related to fluids at Stillwater. Some evidence of fluid circulation may be observed in hydrogen and lithium isotopes. Geothermometry using oxygen isotopes is suggestive of lower cooling temperatures in the pegmatoids, and may provide evidence of mineral-scale disequilibrium attributable to fluid circulation. The sixth and seventh chapters utilize the thermodynamic modeling program MELTS to explore problems of layered intrusion evolution. Understanding the evolution of the liquids that formed various layered intrusions, and identifying magmas parental to layered intrusions, can pose a challenge. Using MELTS, bulk rocks can be synthetically remelted, and the evolution of the complex can be examined through analysis of estimated trapped liquid contents. The sixth chapter applies this method to the Stillwater Complex, while the seventh chapter extends this work to the Skaergaard intrusion in East Greenland. These investigations allow for examination of the magmatic processes operating alongside hydromagmatic processes in layered intrusions.