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WINTER LIMNOLOGY IN FLOODPLAIN LAKES OF THE SASKATCHEWAN RIVER DELTA, SK2016 February 1900 (has links)
Floodplains are among the most productive and biologically diverse freshwater ecosystems on earth. The exchange of nutrients and biota that occurs within these systems during seasonal inundation is essential in maintaining floodplain and river health. Anthropogenic structures, such as weirs, channels, and dams, have altered the natural flood hydrology of floodplain systems minimizing the frequency, strength and duration of flood events. This reduction ultimately leads to the isolation of important floodplain habitat, such as off-channel lakes, from the main channel, decreasing connectivity. Although some studies have examined the productivity of off-channel floodplain lakes in relation to connectivity, most are limited to tropical or highly degraded systems. Northern floodplains are not as well understood, with most of the research limited to the spring, summer, and fall seasons, when waterbodies are free of ice. With research limited to ice free seasons, there is not a full understanding of the year-round processes that occur within these off-channel lake habitats. This knowledge is crucial as the winter season is often when conditions within these habitats are at their most extreme. Such conditions prevent many fish species from permanent settlement; however, no research has been attempted to understand fish presence within these habitats during the winter season. In tropical systems, hypoxia-tolerant species and juveniles utilize these habitats as refuge from intolerant predators, so such habitat may be used similarly in more northern systems.
The purpose of this research was to understand the connectivity, limnology and suitability as fish habitat of off-channel floodplain lakes in the Saskatchewan River Delta (SRD), SK, during winter months. I determined the degree of connectivity to the main channel for 26 individual lakes within the SRD by two modern methods: remote sensing imagery, and stable isotopes (δ18O, δ2H). Both of these techniques proved effective at determining connectivity of individual lakes and showed good agreement, with lakes arranged into five connectivity categories using remote sensing imagery. Winter limnological conditions within these lakes were significantly influenced by their degree of connectivity, with lakes that were more connected having characteristics similar to that of the river, with higher levels of dissolved oxygen (DO), nitrates (NO3-NO2), pH, and lower levels of nutrients (TN,TP). Lakes that were less connected were characterized by low levels of DO and nutrients, and high levels of ammonia/ammonium (NH3-NH4), conditions that are not favourable for the survival of many fish species. Some of the more hypoxia-tolerant species found within the SRD appear, however, to use these habitats in the winter. This was supported by detection of fish presence using environmental DNA; five fish species were detected in many of the 26 lakes sampled, but only in lakes with NH3-NH4 levels below 1.77 mg/L and volumes greater than 178000 m3.
Together, these analyses suggest the influence of a spring/summer flood pulse on limnology is not limited to the months following a flood event, but rather extends well into the ice-cover season. This knowledge is critical as it points to controls on key processes (e.g. nutrient cycling, provision of fish habitat) during the period when lake conditions are most severe. As a result of human induced climate change, and from increased water demands for agriculture and hydropower, the natural flood pulse is expected to further decrease in size and frequency in large river-wetlands such as the SRD. This will reduce the connection between the floodplain and the main channel, with profound impacts on the SRD ecosystem as a whole. Lakes that currently experience frequent inundation will likely have conditions characteristic of infrequently flooded lakes, with low DO and nutrients and high NH3-NH4. Lakes which currently experience infrequent inundation will likely dry up completely due to decreased water renewal.
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Synthesis and radiochemical stability evaluation of radiopharmaceutical compounds containing radioiodinated prosthetic groupsRossouw, Daniel Du Toit 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: A study was undertaken to investigate the radiochemical stability of the βiodoethoxyl moiety,
a relatively novel prosthetic group employed in radiopharmaceutical chemistry, in which an
oxygen atom in a β-position relative to the radioiodine atom has a stabilising effect on the
aliphatic carbon-iodine bond. The investigation was started as a pilot study by synthesising
various model compounds containing a β-radioiodoethoxyl moiety, as well as two reference
compounds lacking such a moiety. The purpose was to determine the influence of various
groups in the vicinity of the β-oxygen atom on the stability of the abovementioned moiety.
Radiochemical stability tests were carried out in vitro at 37°C in human blood serum. The
results confirmed the superior stability of such a moiety compared to that of the reference
compounds and also showed that the branching of such an aliphatic unit resulted in a
considerable improvement in its stability, especially over a longer period.
The investigation was extended to the synthesis of other compounds containing a few selected
β-iodoethoxyl moieties that showed improved stability in the pilot study work. Reference
compounds containing the classical iodovinyl unit, as well as those lacking a stabilising β-
oxygen atom, were also prepared. The carrier molecules used in this part of the work was a
benzamide containing a phenolic oxygen atom which acted as the β-oxygen atom, as well as
two heterocyclic amines, benzotriazole and 2-methyl-5-nitroimidazole, in which the β-
iodoethoxyl moiety was linked to a secondary nitrogen atom. Various suitable alkylating agents
were prepared, chemically linked to the carrier molecules, the resulting intermediate
compounds converted into tosylate or triflate iodination precursors and labelled with
radioiodine by means of iodide-for-tosylate/triflate exchange. In vitro stability tests of these
compounds showed similar trends to those obtained with the model compounds. Moreover, the
stability of the stabilised β-iodoethoxyl moiety compared favourably with that of the iodovinyl
unit, especially when incorporated into a heterocyclic amine. The results of this study have shown that some of the radioiodinated compounds synthesized in this work, especially the
nitroimidazole derivatives, have the potential to be considered as novel radiopharmaceuticals. / AFRIKAANSE OPSOMMING: 'n Studie is onderneem om die radiochemiese stabiliteit van die β-jodium-etoksi-eenheid te
ondersoek. Dié eenheid is 'n relatief nuwe prostetiese groep wat in radiofarmaseutiese chemie
gebruik word. Die suurstofatoom wat in 'n β-posisie relatief tot die radiojodiumatoom
voorkom, oefen 'n stabiliserende invloed op die alifatiese koolstof-jodiumbinding uit. Die
ondersoek het met 'n loodsstudie begin deur verskillende modelverbindings te sintetiseer wat 'n
β-radiojodium-etoksi-eenheid bevat, asook twee verwysingsverbindings waarin so 'n eenheid
ontbreek. Die doel hiermee was om die invloed van verskillende groepe, wat in die omgewing
van die β-suurstofatoom voorkom, op die stabiliteit van die eenheid te bepaal. Radiochemiese
stabiliteitstoetse is uitgevoer deur middel van inkubering in menslike bloedserum by 37°C. Die
resultate het die groter stabiliteit van so 'n eenheid in vergelyking met dié van die
verwysingsverbindings aangetoon, en het ook uitgewys dat vertakking van so 'n alifatiese
eenheid 'n aansienlike verbetering in die stabiliteit tot gevolg gehad het, veraloor 'n langer
periode.
Die ondersoek is vervolgens uitgebrei deur verdere verbindings te sintetiseer wat beskik oor
bepaalde uitgesoekte β-jodium-etoksi-eenhede, wat verbeterde stabiliteit in die loodsstudie
getoon het. Verwysingsverbindings wat die klassieke jodiumvinieleenheid bevat het, sowel as
dié waarin 'n stabiliserende β-suurstofatoom ontbreek het, is ook berei. Die draermolekules
wat in hierdie deel van die studie gebruik is, was 'n bensamied met 'n fenoliese suurstofatoom
wat as die β-suurstofatoom gedien het, sowel as twee heterosikliese amiene, bensotriasool en 2-
metiel-5-nitroimidasool, waarin die β-jodium-etoksi-eenheid aan 'n sekondêre stikstofatoom
geheg is. Verskillende geskikte alkileermiddels is berei, aan die draermolekules geheg, die
tussenprodukte omskep in tosilate of triflate en met radiojodium gemerk deur middel van
jodium-vir-tosilaatltriflaat-uitruiling. Stabiliteitstoetse van hierdie verbindings in bloedserum
het soortgelyke tendense as dié van die aanvanklike modelverbindings getoon. Daarbenewens
het die stabiliteit van die gestabiliseerde β-jodium-etoksi-eenheid gunstig vergelyk met dié van die jodiumviniel-eenheid, veral wanneer dit deel gevorm het van 'n heterosikliese amien. Die
resultate van die studie het getoon dat sommige van die radiogejodeerde verbindings wat berei
is, veral die nitroimidasoolderivate, die potensiaal het om as nuwe radiofarmaseutiese
verbindings gebruik te kan word.
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APPLICATION OF BORON ISOTOPE RATIOS FOR IDENTIFYING NITRATE CONTAMINATION SOURCES IN THE GROUNDWATER OF AVRA VALLEY, ARIZONALeenhouts, James Merrell, Basset, R. L., Maddock, Thomas, III 06 1900 (has links)
The stable isotopes of the conservative element boron, 11B and 1°B, have been
employed as co- migrating isotopic tracers to determine the origin of nitrate observed in
groundwater from a large capacity (2500 gpm) irrigation well in the Avra Valley of
southeastern Arizona. The isotopic ratios of the conservative element, boron, provided an
identifying signature for various nitrate rich source waters. Additional chemical
parameters were also examined to corroborate the isotopic indications.
Findings of this investigation indicate that most of the nitrate observed in
groundwater from well CMID 18 at the beginning of the 1993 irrigation season was due
to municipal wastewater contamination. As the irrigation season progressed, an increasing
proportion of nitrate was contributed by irrigation return flow from neighboring
agricultural fields.
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The determination of molybdenum in botanical samplesSu, Lee-ping, 許禮聘 January 1974 (has links)
published_or_final_version / Radioisotope / Master / Master of Science
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Ballistic excitation scattering processes in superfluid '3He-B and spin-lattice relaxation in copper down to 7#mu#KEnrico, Michael Paul January 1995 (has links)
No description available.
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DECIPHERING ARCTIC CLIMATE IN A PAST GREENHOUSE WORLD: MULTI-PROXY RECONSTRUCTIONS OF PLIOCENE CLIMATECsank, Adam January 2011 (has links)
The high sensitivity of high latitudes to global climate changes is the stimulus for the study of ancient Arctic ecosystems under greenhouse conditions. With an increasing number of studies, including the most recent Intergovernmental Panel on Climate Change (IPCC) report highlighting Pliocene climate as key example for the study of Earth system sensitivity to higher levels of atmospheric CO₂, the need for accurate proxy records for this period is crucial. In order to investigate Pliocene climate, I used stable isotopic studies of fossil molluscs, moss and wood from two fossil forest deposits in the Canadian High Arctic. Temperatures were determined for an Early Pliocene (4-5 Ma) fossil forest site located on Ellesmere Island using 'clumped' and stable isotopic analysis of mollusc shells and stable isotope values of fossil wood. Mollusc inferred growing season (May-Sept) temperatures derived using two independent techniques were estimated to be 11-16° C warmer than present (1950-1990) Ellesmere Island temperatures. Tree ring inferred growing season (June-July) temperatures (JJ) were 10-16° C and mean annual temperatures (MAT) were 18-20° C warmer than present (1950-1990). Mean annual and growing season (JJ) temperatures were also determined using fossil wood from a younger (2.4-2.8 Ma) late Pliocene-early Pleistocene site on Bylot Island. This deposit represents the remains of a flora that grew during an interglacial warm period during the transition to large-scale Northern Hemisphere glaciation that occurred between 2.5 to 3 million years ago. Mean annual temperatures were ~12° C and growing season temperatures were ~13° C warmer than present (1923-2010). The interglacial setting of the Bylot Island site and the warm temperatures suggests that prior to using such sites as true analogues of future conditions we may need to consider how close the feedbacks operating then were to the feedbacks we might expect in the future. However, that temperatures so much warmer than present existed in the high Arctic during a period when levels of atmospheric CO₂ were at nearpresent levels indicates that we may be moving beyond our ability to use the Pliocene as an example of the future.
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The carbon-13 content of atmospheric formaldehyde.Johnson, Brian James. January 1988 (has links)
A measurement of the stable carbon isotopic composition of atmospheric formaldehyde was undertaken as a means of testing current photochemical theories. Sulfito surfaces were shown to meet the stringent analytical requirements of the project; an extensive characterization of these surfaces was performed for the first time. Models were developed to describe the chemical evolution of the surfaces during sampling. It was established that potassium salts have more favorable properties for an atmospheric collection system than do sodium salts. Considerable selectivity in collection was also demonstrated. A highly selective multistep procedure for the isolation and chemical oxidation of collected formaldehyde was developed expressly for this project. A previously unreported combination of reagents, HgCl₂ and AgClO₄, was used in the final reaction step of the procedure. Through the use of synthetic samples, the method was shown to be isotopically reproducible and highly chemically selective. The first data for the carbon-13 content of atmospheric formaldehyde have been obtained, with an observed mean value of δ¹³C = -17‰. This value is enriched in carbon-13 over the known atmospheric sources of formaldehyde; isotopic fractionation in the atmosphere is therefore indicated. It is believed that fractionation due to photolysis can account for the observed effect.
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COINCIDENCE DETECTION OF PROTONS AND METASTABLE HYDROGEN ATOMS FROM DISSOCIATIVE IONIZATION OF MOLECULAR HYDROGEN BY ELECTRON IMPACT (TIME-OF-FLIGHT).CHO, HYUCK. January 1985 (has links)
A coincidence has been observed between H(2S) and H⁺ fragments resulting from the bombardment of H₂ with 100 eV electrons. A significant source of this coincidence is believed to be the 2sσ(g) state of H₂⁺. The time-of-flight (TOF) distribution of H(2S) fragments from the 2sσ(g) state was measured and converted to the kinetic energy distribution from which the potential energy of the 2sσ(g) state in the Franck-Condon region was constructed. The result is in good agreement with a published calculation.
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Solute Inputs to Soil and Stream Waters in a Seasonally Snow-Covered Mountain Catchment Determined Using Ge/Si, ⁸⁷SR/⁸⁶SR and Major Ion Chemistry: Valles Caldera, New MexicoPorter, Courtney January 2012 (has links)
Weathering releases lithogenic elements to soil and stream waters that support life in catchment ecosystems. Seasonal and inter-annual variations in hydrologic conditions change subsurface flowpaths, modifying the influence of weathering on stream waters. This study, over two climatically variable years, determined seasonal and inter-annual changes in solute sources to streams using a multi-tracer approach including major cations, strontium isotopes, germanium (Ge)/silica ratios, carbon species, and trace metals. Stream water cations display constant concentrations although discharge response was highly variable, suggesting that there is a consistent subsurface water supply. However, Sr isotope ratios, and concentrations of Ge, Fe, Al, and dissolved organic carbon, which originate from shallow soil waters, increase with the hydrograph during a wet winter snowmelt. This indicates that during a year with a thick snowpack, stream waters contain components of both shallow soilwater and groundwater during snowmelt, whereas during all other times groundwater contributes predominantly to the stream.
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Diagenetic and geochemical history of the Rotliegend of the southern North Sea (UK sector) : a comparative studyZiegler, Karen January 1993 (has links)
No description available.
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