No description available.

Numerous anthropogenic disturbances have occurred in large lakes over recent decades. These may alter concentrations of the biomagnifying contaminant mercury (Hg) in fish, but long-term impacts of disturbances on Hg trophodynamics are poorly understood. Elemental analyses of archived museum ichthyology specimens could be used to study historical, pre-disturbance fish food webs, but there is uncertainty about effects of chemical preservatives on the results of such analyses. In this thesis, long-term preservation effects were studied, and archived fish were used to reconstruct historical food webs and Hg trophodynamic patterns in three large North American lakes, Nipigon, Simcoe and Champlain. After 24 months of formalin/ethanol preservation, fish muscle delta-15N and delta-13C had average changes of +0.4 ‰ and -0.9 ‰, respectively. Shifts in mean Hg concentration was +5 % after 12 months. A suite of 26 other elements analyzed over 24 months showed consistent responses to preservation, usually involving an increase in concentration immediately following preservation. In the second phase of the thesis, stable isotope and Hg analyses were performed on archived and modern fish from the study lakes, dating to the 1920s-60s and 2006-7, respectively. Trophic relationships were often relatively stable over time, but stable isotope metrics revealed a decrease in Lake Nipigon delta-15N range and less pelagic feeding among Lake Simcoe pumpkinseed and yellow perch. In Lake Champlain, the re-introduction of lake trout in recent decades did not have a major effect on overall food web dimensions. Significant Hg biomagnification factors were found in 1920s and 2006-7 Lake Nipigon (which were not statistically distinguishable from each other) and 2006 Lake Champlain. These biomagnification factors ranged from 0.09 to 0.17, which is within the range found in other studies globally. Archived fish and government monitoring records indicated that fish Hg concentrations decreased in Lakes Simcoe and Champlain since historical periods, but remained similar or increased in Lake Nipigon. This thesis confirms the utility of archived fish for elemental analyses. It highlights the risks of Hg contamination and food web change that may be faced by remote lakes, and it provides evidence for relatively stable Hg biomagnification rates in large lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2013-01-30 15:43:33.438

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, May 23, 2014. / A systematic experimental investigation was performed of the phenomenon of fine structure, with emphasis on the region of the Isoscalar Giant Quadrupole Resonance (ISGQR), in nuclei across stable even-even neodymium isotopes. The 200 MeV proton beams were delivered by the Separated Sector Cyclotron (SSC) facility of iThemba Laboratory for Accelerator Based Sciences (iThemba LABS). Measurements were made using the state-of-the-art K = 600 magnetic spectrometer, where unique high energy-resolution ( E ≈ 42 − 48 keV FWHM) proton inelastic scattering results were obtained on 142Nd, 144Nd, 146Nd, 148Nd and 150Nd targets. All measurements were taken at θLab = 8◦, where the cross-section of the ISGQR is at a maximum. An additional measurement was also made for the 142Nd at θLab = 7◦. Nuclei with mass number A ≈ 150 and neutron number N ≈ 90 are of special interest since they occupy that region of the nuclide chart wherein the onset of permanent prolate deformation occurs. The stable neodymium (Z = 60) isotopes have been chosen in the present study in order to investigate the effects accompanying the onset of deformation on the excitation energy spectra in the ISGQR region (9 ≤ Ex ≤ 15 MeV). The neodymium isotopes extend from the semi-magic N = 82 nucleus (142Nd) to the permanently deformed N = 90 (150Nd) nucleus. In order to emphasize the ISGQR in the measured excitation energy spectra, a Discrete Wavelet Transform (DWT) background subtraction was carried out. This model independent method for background determination decomposes the spectrum into various approximations and details through the application of high pass and low pass filters. A comparison of the resonance widths extracted shows a systematic broadening of the ISGQR (􀀀 = 3.220 MeV to 5.100 MeV), moving from spherical 142Nd to highly deformed 150Nd nuclei as has already been observed for the Isovector Giant Dipole Resonance (IVGDR) excited by γ-capture. Even though it is known that the IVGDR spectacularly splits and shows a double bump for the deformed 150Nd, no obvious splitting of the ISGQR was observed. In order to investigate the fine structure of the ISGQR, a theoretical microscopic calculation termed the Quasiparticle-Phonon Model (QPM) was applied to predict excitation energy spectra for 142−146Nd targets. These calculations were based on the one- plus two-phonon configuration. Characteristic energy scales were extracted for the resonance region using the Continuous Wavelet Transform (CWT) technique, on both experimental data and theoretical predictions. Comparison of the resulting characteristic energy scales suggests the coupling to low-lying collective vibrations as the dominant contributor to the ISGQR decay width. Level densities of 2+ states were extracted through the application of a fluctuation analysis technique, for full spectra from the ground state upwards in all five Nd targets. Comparisons are made with theoretical predictions from the Back Shifted Fermi Gas, Hartree-Fock-BCS and Hartree-Fock-Bogoluibov models. While there is generally an excellent agreement between experimental level densities and theoretical predictions from the ground state up to less than 10 MeV excitation, there is a marked disagreement beyond 10 MeV in all target nuclei. Comparison of the experimental results for the Nd isotope chain shows a clear systematic trend in which the onset of this disagreement occurs at lower and lower excitation energies, moving from low to high mass. For the spherical 142Nd nucleus the deviation occurs at about 9 MeV while in the case of the deformed 150Nd this occurs much earlier at about 4 MeV, all limited to a maximum of 103 MeV−1 by the energy resolution of the present experiment. Additionally, measurements of elastic scattering and inelastic excitation of lowlying collective states in 144−150Nd has also been possible. Excitation energy spectra in all targets predominantly exhibited various 2+ states, owing to the “spin-filter” effects. A single strong 3− 1 state, together with a weak 4+ 1 state were observed in each target nucleus. Angular distributions were obtained for the various ground and excited states by applying the optical model of elastic scattering and Distorted Wave Born Approximation (DWBA) of inelastic scattering. Deformation lengths δL were obtained for most of the states and these were in good agreement with previously obtained results from the literature.

Doctor of Philosophy / Division of Biology / Jesse B. Nippert / Water availability is a key driver of many plant and ecosystem processes in tallgrass prairies, yet we have a limited understanding of how grassland plants utilize water through space and time. Considering that tallgrass prairies experience tremendous heterogeneity in soil resources, identifying spatiotemporal variation in plant ecohydrology is critical for understanding current drivers of plant responses to water and for predicting ecosystem responses to future changes in climate. Here, I investigated the patterns, drivers, and ecological consequences of plant water use (e.g., water uptake, water redistribution, and water loss) in a native tallgrass prairie located in northeastern Kansas, USA. Using a combination of leaf gas exchange, sap flow, and isotopic techniques, I addressed four main questions: 1) How does fire and grazing by bison impact use of water from different sources and niche overlap for common grasses, forbs, and shrubs? 2) Does hydraulic lift occur in grazed and ungrazed tallgrass prairie, and does this impact facilitation for water within grassland communities? 3) What are the patterns and drivers of nocturnal transpiration in common grassland species? 4) How does diel stem sap flow and canopy transpiration vary among common grassland species? I found that bison grazing increased the depth of water uptake by Andropogon gerardii and Rhus glabra, reducing niche overlap with co-occurring species. Conversely, grazing did not affect hydraulic lift, which was generally uncommon and likely limited by nocturnal transpiration. Further, leaf gas exchange measurements indicated that nocturnal transpiration occurred commonly in tallgrass prairie plants and was greatest among grasses and early in the growing season. Nocturnal transpiration was not driven by vapor pressure deficit or soil moisture, as commonly observed in other systems, but was regulated by nocturnal stomatal conductance in most species. Finally, I found that daytime sap flow rates were variable among species and functional types, with larger flux rates among woody species. Nocturnal sap flow rates were more consistent across species, which caused nighttime sap flow and transpiration to account for a larger proportion of daily flux rates in grasses than in forbs or shrubs. These results show that water uptake, water redistribution, and water loss are all influenced by different biotic and abiotic drivers and have varying ecological impacts across a heterogeneous landscape. Additionally, extensive differences in water flux exist among co-occurring species and plant functional groups, which likely reflect varying strategies to tolerate water limitation. These results suggest that shifts in the abundance of these species with future climate changes, or with ecosystem state changes, will likely impact ecosystem-level water balance.

Understanding the movement and feeding habits of marine animals is crucial when managing their populations. The molecular, and stable carbon isotope composition of fatty acids from an organism provides time-integrated information on its dietary intake. Hence, when spatial differences in the quality of seston exist it should be able to trace these differences up into higher trophic level organisms. The presented study evaluates the applicability of 13C/12C ratios of individual fatty acids, as natural tags and dietary markers in marine pelagic organisms. In addition, the use of 13C/12C ratios of bulk sample, as well as fatty acid composition data in examining the movement, and diet of animals are further explored. Samples of particulate organic matter, zooplankton, larval fish and juvenile salmon collected during three cruises off the west coast of Vancouver Island were analyzed. The fatty acid composition, stable carbon isotope ratio of either bulk sample, or individual fatty acids could typically distinguish samples collected in continental shelf waters from off-shelf samples. The differences in fatty acid composition between the adjoining food webs seem to be mainly caused by the different contribution of diatom-derived material to the base of the food web. The higher 13C/12C ratios found in the diatom-richer seston in shelf waters were not simply caused by the higher contribution of diatoms. Instead, stable carbon isotope data on individual fatty acids indicate that growth conditions favouring diatom growth caused 13C-enrichment in algae other than diatoms as well. The relative abundance of polyunsaturated fatty acids, such as docosahexaenoic acid (22:6n-3), were found to increase with trophic level. Whereas the abundance of saturated, and monounsaturated fatty acids was higher in organisms from lower trophic levels. This suggests that the fatty acid composition may be a useful trophic level indicator. However, literature data indicate that these trends observed in seston. zooplankton, larval fish and juvenile salmon, do not hold for larger organisms and adult life stages. / Graduate

The problem of interest in this investigation was to determine the cross sections of five nuclear reactions which occur when irradiating natural palladium with neutrons which have energy values of 15.1, 15.9, and 16.3 MeV. The cross sections were measured relative to a copper monitor which was "sandwitched" in with the palladium target.

Recent advances in the analysis of intrinsic markers, particularly stable isotopes, have allowed great insight into interactions between different stages of the annual cycle of migratory birds. Hydrogen isotope ratios, because of strong latitudinal trends in their distribution, have been widely used to address long-distance movements of migratory birds. Likewise, carbon isotope ratios have been useful in examinations of habitat quality because of their responsiveness to changes in plant community composition. However, basic assumptions underlying the use of certain isotopes have yet to be adequately examined. Additionally, much of the research regarding seasonal interactions in migratory songbirds comes from study of a single species, and it is unclear whether these findings are applicable to a wider range of migrant songbirds. In this study, I collected tissue samples from black-throated blue warblers (Dendroica caerulescens) at a breeding site in New Hampshire to address two important questions regarding stable isotopes and the investigation of seasonal interactions. First, using feather samples from both adult and juvenile birds, I investigated the influence of age, molt timing, and reproductive effort in determining the stable hydrogen isotope ratios that are incorporated into tissue samples. Secondly, I took claw samples from adult birds to examine the importance of winter habitat quality, as inferred through carbon isotope ratios, in determining subsequent reproductive success. I found that hydrogen isotope ratios in feather samples were significantly influenced by both age and molt timing, though not by reproductive effort. The mechanism underlying age-related isotopic variation is unclear, but may be widespread among passerines. In addition, this study is the first to note a significant seasonal trend in feathers grown throughout a breeding season, although the mechanism for this pattern is also unclear. Taken together, these findings have important implications for the use of hydrogen isotope ratios for purposes of geographic assignment. Further research is needed to determine the prevalence and magnitude of age-related and seasonal trends in hydrogen isotope ratios. I recommend that future studies note the age class of birds when sampling for hydrogen isotopes, and researchers should attempt to collect feathers grown early in the molt cycle. Analysis of carbon isotope ratios from claw samples indicated that winter habitat quality did not directly influence subsequent reproductive success. However, winter habitat quality may have an indirect influence on reproductive output. Females from higher quality wintering sites were in significantly better body condition on the breeding grounds, and settled on more insect-rich breeding territories. Both body condition on the breeding grounds and breeding territory quality have previously been shown to influence subsequent reproductive success, in this and other songbird species. These results indicate that winter habitat quality may be important in determining future reproductive success for black-throated blue warblers, and interactions between events during the wintering and breeding periods may need to be incorporated into future population models for this species.

We use cosmogenic 10Be analysis of fluvial sediments and bedrock to estimate erosion rates (103 – 106 year timescale) and to infer the distribution of post-orogenic geomorphic processes in the Blue Ridge Province in and around Shenandoah National Park, VA. Our sampling plan was designed to investigate relationships between erosion rate, lithology, slope, and basin area. Fifty-nine samples were collected from a variety of basin sizes (<1 – 3351 km2) and average basin slopes (7 - 26°) in each of four different lithologies that crop out in the Park: granite, metabasalt, quartzite, and siliciclastic rocks. The samples include bedrock (n = 5), fluvial sediment from single-lithology basins (n = 43), and fluvial sediment from multilithology basins (n = 11): two of these samples are from rivers draining streams exiting the eastern and western slopes of the Park (Rappahannock and Shenandoah Rivers). Inferred erosion rates for all lithologies for fluvial samples range from 3.8 to 24 m/My. The mean erosion rate for single-lithology basins in the Park is 11.6 ± 4.8 m/My. Singlelithology erosion rates ranges for fluvial samples are: granite (basin size = ~0.4-40 km2 and slope = 11-23°), 7.9–22 m/My; metabasalt (basin size = ~1-25 km2 and slope = 11-19°), 4.8–24 m/My; quartzite (basin size = ~0.1-9 km2 and slope = 12-23°), 4.7–17 m/My; and siliciclastic rocks (basin size = ~0.3-13 km2 and slope = 18-26°), 6.2–17 m/My. The mean erosion rate for multilithology basins (basin size = ~1-3351 km2 and slope = 7-22°) is 10.2 m/My, and individually for the Shenandoah River 7.3 m/My and the Rappahannock River 13.8 m/My. Bedrock erosion rates range from 2.4-13 m/My across all lithologies, with a mean erosion rate of 7.9 ± 5.0 m/My. Grain-size specific 10Be analysis of four samples showed no consistent trend of concentration with grain size. These data support Hack’s dynamic equilibrium model. Slope and erosion rate are not well correlated, and mean erosion rates are similar for different lithologies. Cosmogenicallydetermined erosion rates in Shenandoah Park are similar to or lower than those reported elsewhere in the Appalachians including those of Matmon and others (2003), 25 to 30 m/My for metaclastic rocks in the steep Great Smoky Mountains, Reuter and others (2004), 4 – 54 m/My in Susquehanna River basin for shale, sandstone, and schist, and Sullivan and others (2006), 6-38 m/My in the micaceous schist and gneiss of the Blue Ridge Escarpment. Cosmogenic erosion rates (integration over 104 yrs) in the Blue Ridge province of Shenandoah National Park are consistent with long-term unroofing rates (integration over 107 yrs) estimated from U-Th/He measurements (11-18 m/My) in samples collected near the Blue Ridge Escarpment by Spotila and others (2004), and fission tracks (20 m/My) in the Appalachians by Naeser and others (2005). The consistency of denudation rates integrated over very different periods of time suggests steady erosion most likely in balance with, and driving isostatic uplift of rock.

Through isotopic analysis of Viviparus lentus (V. lentus) a high resolution record of stepwise changes in δ18O and δ13C across the Eocene / Oligocene transition and Oi-1 glacial maximum has been produced for the continental Solent Group strata, Isle of Wight (UK). Comparison of this V. lentus δ18Ocarb. record with high resolution marine δ18Ocarb. records shows that similar isotopic shifts exist in the near coastal continental and marine realms. In order to calculate palaeotemperatures from this new continental record an investigation into the biology of modern Viviparus and its effect on the isotopic composition of its shell carbonate was undertaken. Experimental measurements of the 18O/16O isotope fractionation between the biogenic aragonite of Viviparus and its host freshwater were undertaken on samples derived from the Somerset Levels in order to generate a genus specific thermometry equation. The results from using this new Viviparus equation on fossil V. lentus shell fragments suggests that aquatic and terrestrial biota were being affected by climate change associated with the Late Eocene Event. This conicides with a decrease in mammal species richness in the Osborne Member, reaching its climax at the end of the Osborne / Seagrove Bay Members. This event is followed by a brief warming in the Bembridge Limestone which was marked by a within-Europe mammal turnover involving dispersal from the south and an increase in species richness, concurrent with this is an increase in size of Harrisichara gyrogonites. An additional investigation into seasonal isotopic variability using whole well preserved V. lentus specimens has also revealed a shift from tropical /subtropical to temperate climatic zones occurring before the Eocene /Oligocene boundary and Oi-1 glacial maximum. Overall the evidence provided by these investigations would suggest that climatic change was already in progress prior to the build up of glacial ice on Antarctica.

The Platreef has been the site of platinum mining since the 1920’s. The reef itself comprises a series of pyroxenites, gabbronorites and norites that contain xenoliths/rafts of footwall rocks. The Platreef is irregularly mineralised with PGE, Cu and Ni, and has a greater abundance of sulphides than the Merensky Reef. The main base metal sulphides within the Platreef are pyrrhotite, pyrite, pentlandite, and chalcopyrite. Extremely varied platinum group minerals occur as tellurides, bismuthotellurides, antimonides and arsenides. This study aimed to gain a clearer understanding of the formation of sulphides within the Platreef. In order to do this, cores from both the northern and southern sectors of the Platreef were sampled. A detailed study of the sulphides within these cores was conducted to identify different styles of mineralisation and their occurrences. Four different styles of mineralisation were identified: massive, net-textured, blebby and interstitial. In general, sulphides in the southern sector of the Platreef are concentrated in the lower portion of the package, whereas in the northern sector they are concentrated in the upper part although in both sectors the sulphide occurrences are associated with metasedimentary xenoliths. Conventional and multiple sulphur isotope analyses were undertaken on sulphides from cores from both the southern and the northern sectors. This was done in order to determine the source of the sulphur. These analyses were also conducted to examine sulphur isotope variations with changing footwall. Previous sulphur isotope data predominantly obtained from the central sector of the Platreef indicated a crustal contribution to the sulphur budget but did not provide much data on footwall sulphides so the nature of the crustal component was only implied. In this thesis sulphur from an external source was identified as having contributed to the formation of sulphides in both the southern and the northern sectors of the Platreef, especially for sulphides in proximity to metasedimentary xenoliths. In the southern sector of the Platreef this source was identified as most likely being pyritic shales of the Lower Duitschland Formation. In the northern sector, Malmani dolomites, which are suggested to have collapsed from the roof of the Platreef, are the most likely source of sulphur. Importantly, in the northern sector no sulphur is thought to have come from the Archaean granite footwall. Oxygen isotope analyses were conducted on samples from the southern sector of the Platreef to verify the presence of crustal contamination. Data collected indicated that there had been a crustal oxygen component involved in the formation of silicates that led to their partial recrystallisation. When compared to oxygen isotope data from the central sector of the Platreef it appears that there are variations along strike that most likely result due to the changing footwall. This data indicates a major contribution of oxygen-, sulphur- and other volatile-rich fluids to the Platreef. This led to the partial re-crystallisation of silicates, and in areas in close proximity to sulphur-bearing metasedimentary xenoliths aided in the formation of sulphides. These volatile-rich fluids most likely originated from metasedimentary xenoliths during metamorphism that then migrated through the Platreef package. When the observations from both the southern and northern sectors of the Platreef are compared and combined with pre-existing data for the central sector, several general observations can be made. 1. The entire length of the Platreef has been affected by contamination from crustal sulphur sources to some degree. This contamination is suggested to be from volatile-rich fluids which were released from metasedimentary crustal xenoliths and footwall during metamorphism. 2. The proximity between sulphide enrichment and sulphur-bearing sediments (as footwall or xenoliths) is important and indicates the source of the sulphur which led to sulphide formation. 3. Contamination occurred on a localised scale, depending on the composition of the sedimentary lithologies and the proximity of the contaminant to the magma. In the southern sector of the Platreef the source of the sulphur is almost certainly pyritic shales of the Lower Duitschland Formation. In the central sector, sulphur has most likely come from sulphur-rich dolomites and evaporites from the Malmani dolomites. In the northern sector, sulphur-rich fluids were released from Malmani dolomite rafts that collapsed from the roof into the magma during the emplacement of the Platreef. The Archaean footwall in this area has had little or no control on the formation of the sulphides within the Platreef.