This study investigated the role of an invasive tall cane, Arundo donax L. (Arundo), in the riparian water cycle. Four 100 meter transects were arrayed perpendicular to the lower Rio Grande in southwest Texas. The first objective was to determine the primary water source for Arundo by using naturally occurring stable isotopes. Surface soil, river water, groundwater, precipitation and rhizome samples were collected every month during 2010 and 2011 growing seasons, which coincided with a major flood that saturated soils in the first year followed by extreme drought in the second year. The second objective was to characterize how Arundo water use varied with water availability gradients in the riparian zone. Leaf gas exchange and leaf delta13C were measured along potential moisture gradients. The third objective was to understand the interaction between groundwater and surface water, and whether Arundo water use affected daily groundwater fluctuations. The isotope ratio of rhizome water was consistent with shallow soil moisture uptake and with previous observations of a relatively shallow, fibrous root system. Floodwater from July 2010 persisted in the soil for at least a year despite a severe drought, and became the dominant water source for Arundo during much of the study period. Although the alluvial water table in this floodplain was shallow (< 6 m) and subject to changes in river level, groundwater seemed not to be an important source for Arundo, so long as the soil moisture was sufficient. In this study, Arundo was not found to experience soil moisture limitation, and the spatial variability of Arundo transpiration was not associated with any soil moisture availability gradients. Arundo was found to close its stomata in response to increasing vapor pressure deficit (VPD), causing declining transpiration rate and increasing leaf delta13C composition. Significant exchange between the river and the alluvial groundwater was reflected in the similarity of isotopic compositions and the high correlation between river and groundwater elevations. Cross correlation analysis showed that over 50% of the diurnal groundwater fluctuations were caused by river stage changes. Consistent with the above ecophysiological and stable isotope results, Arundo water use was not found to influence daily groundwater fluctuations.

The technique of ESR-dosimetry and strategies for investigation of new materials as in regard to their applicability as ESR-dosimeters for radiotherapy has been reviewed. As an example six salts of formic and lactic acid has been evaluated. The applicability of the dosimeter has been judged by evaluating the tissue equivalence, radical yield, radical stability, spectral suitability, optimal readout parameters, dose response and sensitivity of the dosimetric system. Dependence of material characteristics and influence parameters has been analysed. The reviewed methods have been successfully used for evaluation of the new materials. Lithium formate has been shown to be a good candidate relative to the state of the art dosimeter of alanine. Using optimal readout parameters lithium formate has been shown to be nine times as sensitive but even at moderate settings lithium formate is more sensitive. The results for lithium formate are in accordance to those of previous studies. The signal intensity of sodium formate has also proved to be high but unfortunately the signal fades rapidly. Two new methods have been proposed as synthesis of the reviewed methods. The first allows flexible, effective and objective baseline correction of the ESR-spectrum. The second deals with dose response measurement by linear regression of the entire spectrum and was found to be successful in separating the spectral peaks of the induced radicals from the background signal.

<p>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.</p><p> </p><p>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 (&delta;¹¹B) 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 (&delta;³⁴S, &delta;¹⁸O) 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 &delta;²H, &delta;¹⁸O, ³H, Br^-/Cl^-, Na/Cl^-, and Ca/Na.</p><p>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.</p> / Dissertation

Pulse crops have been long associated with biological dinitrogen fixation and therefore improve the sustainability of cropping systems when included in rotation. However, studies indicate there may be additional benefits of including pulse crops in rotation. To quantify these potential benefits, soil processes and properties related to nitrogen (N) and carbon (C) cycling were examined in five crop rotations with and without field pea (<i>Pisum sativum</i> L.) in Scott, Saskatchewan. Gross mineralization and nitrification rates were determined using the 15N isotope dilution technique in intact soil cores. To estimate the proportion of nitrous oxide (N2O) emissions derived from nitrification related processes rather than denitrification processes tracer techniques using 15N were used. Field incubations were performed in 2008 at seeding (May 13), anthesis (July 8) and just after harvest (October 8). Mean mineralization and nitrification rates were not significantly different among rotations on any date and there was no significant difference in mean N2O emissions among rotations. From labeled 15NO3- cores, it was determined that nitrification-related processes were the major contributors to N2O emissions. There was no difference among the rotations in microbial biomass carbon (MB-C) or microbial biomass N (MB-N) with the exception of MB-C in the continuous field pea (FP) and the canola (<i>Brassica napus</i> L.)-wheat (<i>Triticum aestivum</i> L.)-field pea (CNL-W-FP) rotation at anthesis. There was no effect of rotation on dissolved organic carbon (DOC) and only seasonal differences were observed with DOC levels being lower before seeding than at anthesis and post-harvest. Based on the results obtained from a single growing season, our results show that N benefits of including field pea in rotation, beyond dinitrigen fixation, were not detectable and that the immediate N benefit of including field pea in rotation may be due simply to the direct effects of biological dinitrogen (N2) fixation. However, there have been reports of pulse crop benefits to succeeding crops in rotation. As a result, we investigated both the quantity and quality of crop residues, which can have an impact on soil properties and processes. Plants enriched with isotopic tracers can be used to trace crop residue decomposition to various C pools but only if the tracer is homogeneously distributed throughout the plant. In order to determine if repeat-pulse labeling could be used to trace crop residue decomposition, this method was followed using 13CO2 to enrich plant material of field pea and canola plants in a controlled environment. The distribution of 13C throughout the plant parts (roots, stem, leaves, and pod) and biochemical fractions [acid detergent fiber (ADF) and acid detergent lignin (ADL)] were determined. It was found that 13C was not homogeneously distributed throughout the plant parts or biochemical fractions. The pod fraction in particular was much less enriched in comparison to the other fractions. The ADL fraction was less enriched than the ADF fraction. Because of the heterogeneity of the label throughout the plant, modifications of the method are needed and 13C distribution through out the plant needs to be assessed before the repeat-pulse method can be used to trace C residue through various C pools. Nevertheless, root contributions to below-ground C were successfully determined from the enriched root material and the resulting enriched soil. It was found that canola contributed more above- and below-ground residues than field pea, however canola was also higher in ADF and ADL fractions indicating a more recalcitrant residue. Research should continue to better define the impact of pulse crop residues on C and N cycling and subsequent crops in rotation.

Tree-ring analyses have contributed significantly to investigations of climate change and climate cycles, including the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation (ENSO). Stable isotope climate proxies (?18O, ?D, and ?13C) have enhanced traditional ring-width data, although poor preservation of ancient wood has generally constrained reconstruction of stable isotope proxy records to the Holocene and Late Pleistocene. An opportunity to apply these stable isotope methods to older wood has been presented by recovery of remains of Mixed-Coniferous Boreal Vegetation, in Early Pliocene (4-5 Ma) deposits at Strathcona Fiord, Ellesmere Island, Canada (~79°N). An exceptionally well-preserved tree trunk, identified as Larix (larch) through wood anatomical characteristics, from this high Arctic site provided a 203-year tree-ring record, from which we present the first high-resolution, secular isotope record of Pliocene climate. ?18O, ?D, and ?13C isotope values indicate a variable climate with alternating intervals of cool/wet to warm/dry weather. These fluctuations in climate may be attributable to phase changes in climate cycles observed in the record. A growing season mean temperature of 14.4 °C was calculated from isotopic analysis of gastropod shells. Palaeoclimatic modeling of tree isotope values has revealed growing season temperatures of 11-15 °C, and estimated isotope values of precipitation of 18.3 (?18O) and 228 (?D). Both palaeotemperature estimates and source water calculations are comparable to those found in a modern Boreal Forest. Time-series wavelet analysis was applied to these data revealing prominent short (<10 years), intermediate (16-35 years) and long-term (~45-50 years) cyclicity. These are the highest resolution climate cycles recovered from the pre-Holocene terrestrial record, providing evidence for decadal scale cyclicity similar to the NAO and/or PDO 4-5 million years ago.

Identifying the ecological mechanisms that determine food web structure is critical for understanding the causes and consequences of diversity. The objective of this thesis was to identify the mechanisms structuring aquatic food webs across environmental gradients from a multi-level perspective (individual to ecosystem) using integrative methodology and field experiments to test classic ecological theory. My results demonstrate support for the dynamic constraints hypothesis, which predicts habitats with greater disturbance should have shorter food chains, but are not consistent with the ecosystem size hypothesis that predicts larger ecosystems have longer food chains. Insect and amphibian richness increased with increasing pond size and hydroperiod, indicating that insertion of new consumers into pond communities was driving variation in food-chain length. A multivariate analysis testing the influence of physicochemical variables on food-web characteristics revealed that hydroperiod and pond area had a strong influence on amphibian and invertebrate assemblages, trophic diversity and 15N range. Food-chain length did not respond strongly to any one variable, but instead responded weakly to multiple environmental variables, suggesting interacting influences on food-web structure. Conversely, the trophic niche of amphibian larvae was not influenced by pond hydroperiod, but did exhibit ontogenetic diet shifts. Populations of amphibian larvae with broader niche widths also had increased individual variation, supporting the niche variation hypothesis. In addition, I assessed whether species diversity influenced the magnitude of cross-habitat resource flow between aquatic and terrestrial habitats via emerging aquatic insects, metamorphosing amphibians, and litter deposition. Deposition into ponds far exceeded carbon exported via insect and amphibian emergences. We found a negative relationship between resource flux and the diversity of amphibians and insects, which contradicts the general pattern of positive biodiversity-ecosystem function relationships. My research strongly suggests environmental variation is a key process in shaping food-web structure and function and that multiple methodologies are needed to understand temporal and spatial dynamics of aquatic ecosystems.

Lack of calibrated instruments and written records prior to European contact in North America has forced palaeoclimatic researchers to develop various proxies capable of reconstructing ancient environments. Stable isotope analysis of tooth enamel of large terrestrial herbivores has increasingly become a creditable method of determining the ancient environments which these large mammals occupied during life. Archaeological evidence indicates human inhabitants of the northern Great Plains relied heavily on bison procurement throughout much of the Holocene. Because of this correlation, stable isotope analysis of bison tooth enamel has the capability of informing on palaeoenvironmental conditions which these ancient cultural groups occupied for the last 10,000 years on the northern Great Plains. Decades of research has provided evidence that stable isotope analysis of tooth enamel of large bodied herbivores (e.g. bovids) has the potential to be used as a proxy for reconstructing palaeoclimate, palaeoecology, foraging strategies and herd behaviour. Oxygen (δ 18O) isotope ratios are used as a proxy to track the meteoric hydraulic cycle (i.e. precipitation), which in turn is driven by local surface temperatures. Carbon (δ13C) isotope ratios have the ability to indicate photosynthetic pathways used by plant species, thus indicating local terrestrial plant cover. Dietary intake of water (δ 18O) and food (δ13C) are associated with isotopic signals which are recorded in the tooth enamel of a bison during amelogenesis (tooth enamel formation). Once tooth enamel is formed it never remodels; therefore, isotopic ratios recovered from fossil enamel become an archive of dietary consumption. In general, δ 18O isotope ratios are used to determine surface water and surface temperature conditions, whereas δ13C isotope values are used to indicate the abundance of C3 to C4 grasses consumed during an animal’s life. This study analyzes stable isotope (δ 18O and δ13C) ratios obtained from fossil bison enamel associated with archaeological sites in the northern Great Plains (Saskatchewan) region. The purpose of this study is to create a comparative model used to indicate ancient seasonality and palaeoenvironmental conditions over a 9,000 year period in the Holocene. A total of eight archaeological sites were examined, with each site representing a distinct time period and an affiliated human culture. In addition, isotope (δ 18O and δ13C) ratios recovered from tooth enamel was compared to isotope (δD and δ13C) values previously (Leyden 2004) examined from bone collagen of bison remains from the same archaeological sites. Results of this study demonstrates that original isotopic values from consumed water (δ 18O) and food (δ13C) from archaeological bison tooth enamel reflects seasonal changes for an approximate 18 month period. Further, results from this study also indicate that several climate and plant ecology changes occurred in the Saskatoon, Saskatchewan region over the last 9,000 years. Episodes of climate warming and cooling have been inferred by changes in δ 18O ratios at different time periods of the Holocene. Similarly, significant differences are also detected in δ13C values from different archaeological sites, inferring that bison populations consumed various abundances of C4 grasses at different time periods. In addition, evidence from this study has indicated that stable isotope ratios from enamel (δ 18O) and collagen (δD) from the same archaeological site, for the purpose of inferring climate conditions, demonstrate differing data for several time periods and close correlations for others. On the contrary, δ13C from both tooth enamel and bone collagen from each archaeological site produce comparable data which were used to measure the abundance of C4 grasses consumed by bison population during particular time periods.

AbstractIn this study a coincidence circuit composed of Ortec modules with Ge(Li)-NaI(Tl) detectors was utilized. An investigation of the different fractional threshold settings of a Constant Fraction of Pulse Height Trigger was made.Two different isotopes were investigated. A sample of 22Na was used as a prompt source. The half-life of the 0.081 Mev energy levelof 133Cs was studied. This half-life has been reported as being 6.3 nsec. Results were compared with results of a previous study at Ball State University which had used a conventional single channel analyzer and had used the zero crossover point for timing purposes.The best value received for the 133Cs energy state using a slope measurement was 8.12 t 0.25 nsec. Using a centroid shift measurement the best value of the 133Cs energy state was 5.66 nsec.Ball State UniversityMuncie, IN 47306

The Saint-Urbain and Big Island rutile-bearing ilmenite Fe-Ti oxide deposits are located in the composite 450 km² Saint-Urbain anorthosite (1055-1046 Ma, U-Pb zircon) and in the Lac Allard intrusion (1057-1062 Ma, U-Pb zircon) of the 11,000 km² Havre-Saint Pierre anorthosite suite, respectively, in the Grenville Province of Eastern Canada. Slow cooling rates of 3-4°C/m.y. are estimated for both anorthosites, based on combined U-Pb zircon/rutile/apatite and ⁴⁰Ar/³⁹ Ar biotite/plagioclase geochronology, and resulted from emplacement during the active Ottawan Orogeny. Slow cooling facilitated (1) diffusion of Zr from ilmenite and rutile, producing thin (10-100 microns) zircon rims on these minerals, and (2) formation of sapphirine via sub-so lidus reactions of the type: spinel + orthopyroxene + rutile ± corundum → sapphirine + ilmenite. New chemical and analytical methods were developed to determine the trace element concentrations and Hf isotopic compositions of Ti-based oxides. Rutile is a magmatic phase in the deposits with minimum crystallization temperatures of 781°C to 1016°C, calculated by Zr-in rutile thermometry. Ilmenite present in rutile-free samples has higher Xhem (hematite proportion in ilmenite), higher high field strength element concentrations (Xhem = 30-17; Nb = 16.1-30.5 ppm; Ta 1.28-1.70 ppm), and crystallized at higher temperatures than ilmenite with more fractionated compositions (Xhem = 21-11; Nb = 1.36-3.11 ppm; Ta = <0.18 ppm) from rutile-bearing rocks. The oxide deposits formed by density segregation and accumulation at the bottom of magma reservoirs, in conditions closed to oxygen, from magmas enriched in Fe and Ti. The initial ¹⁷⁶Hf/¹⁷⁷ Hf of rutile and ilmenite (Saint Urbain [SU] = 0.28219-0.28227, Big Island [BI] = 0.28218-0.28222), and the initial Pb isotopic ratios (e.g.²⁰⁶Pb/²⁰⁴ Pb: SU = 17.134-17.164, BI = 17.012-17.036) and ⁸⁷Sr/⁸⁶ Sr (SU = 0.70399-0.70532, BI = 0.70412-0.70427) of plagioclase from the deposits overlap with the initial isotopic ratios of ilmenite and plagioclase from each host anorthosite, which indicates that they have common parent magmas and sources. The parent magmas were derived from a relatively depleted mantle reservoir that appears to be the primary source of all Grenvillian anorthosite massifs and existed for --600 m.y. along the margin of Laurentia during the Proterozoic.

Reservoirs impound and store large volumes of water and flood land. The water is used for electricity generation, irrigation, industrial and municipal consumption, flood control and to improve navigation. The decomposition of flooded soil and vegetation creates greenhouse gases and thus reservoirs are a source of greenhouse gases. Reservoirs are not well studied for greenhouse gas flux from the water to the atmosphere. The FLooded Upland Dynamics EXperiment (FLUDEX) involves the creation of three experimental reservoirs in the upland boreal forest to study greenhouse gas and mercury dynamics. The balance of biological processes, decomposition, primary production, CH₄ oxidation and the nitrogen cycle in the reservoirs controls the greenhouse gas flux from the reservoir to the atmosphere. Understanding the importance and controlling factors of these processes is vital to understanding the sources and sinks of greenhouse gases within reservoirs. The carbon and oxygen dynamics near the sediment-water interface are very important to the entire reservoir because many processes occur in this area. Light and dark benthic chambers were deployed, side-by-side, to determine the benthic flux of DIC and CH₄ across the sediment-water interface and to determine the role of benthic photoautotrophs in benthic DIC, CH₄ and O₂ cycling. Benthic chambers have shown photoautotrophs use the decomposing soil, rocks and exposed bedrock as a physical substrate to colonize and the CO₂ produced by the decomposing soil as a carbon source since the delta¹³C-DIC value of the DIC added to light chambers is enriched relative to dark chambers and net photosynthesis rates are linked to community respiration. Benthic photoautotrophs consume 15-33% of the potential DIC flux into the water column. CH₄ produced by the decomposition of soils is partially oxidized by methanotrophs that use the photosynthetically produced oxygen. The delta¹³C-CH₄ values of the CH₄ added to light chambers is enriched relative to dark chambers and 15-88% of the potential CH₄ flux into the water column is oxidized. An isotope-mass budget for DIC and CH₄ is presented for each reservoir to identify the importance of processes on areservoir scale. Input of DIC to the reservoirs from overland flow can be important because concentration is greater and delta¹³C-DIC values are depleted relative to inflow from Roddy Lake. Estimates of total reservoir primary production indicate that 3-19% of the total DIC production from decomposition is removed by photoautotrophs. The carbon cycling in biofilm and the importance of periphytic primary production needs to be better understood. Dissolved delta¹³C-CH₄ values of CH₄ in reservoir outflow enriched 45-60permil, indicating that CH₄ oxidation was an important CH₄ sink within the reservoirs. Stable carbon isotope data indicates that the CH₄ in the bubbles is partially oxidized so the site of bubble formation is the upper portion of the flooded soil. The fraction of CH₄ converted to CO₂ in the FLUDEX reservoirs is similar to that of the wetland flooded for the Experimental Lakes Area Reservoir Project (ELARP). Approximately half of the dissolved CH₄ in the FLUDEX reservoirs was removedby CH₄ oxidation. The ebullitive flux of CH₄ from FLUDEX reservoirs is reduced 25-75% by CH₄ oxidation. The CH₄ flux to the atmosphere from peat surface of the ELARP reservoir became less oxidized after flooding: 91% to 85% oxidized. The floating peat islands of the ELARP reservoir were less oxidized than the peat surface. Similar to the CH₄ in the FLUDEX reservoirs, CH₄ in the ELARP peat islands was oxidized 56%. CH₄ oxidation is an important process because it reduces the global warming potential of the greenhouse gas flux since CO₂ is less radiatively active than CH₄.