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1
Olli, Gull. "Waterborne sediment and pollutant transport into lakes and accumulation in lake sediments /". Stockholm : Department of Physical Geography and Quaternary Geology, Stockholm University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8302.
Testo completo
2
Travers, Sarah. "Toxicity of Lake Sediments". Thesis, Ulster University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487669.
Testo completoAbstract (sommario):
The profundal sediment of many lakes is contaminated by heavy metals and persistent organic pollutants (POPs) deposited from the atmosphere, yet there has been little assessment of the biological effects of these toxicants. A Tier I sediment ecological risk assessment of profundal lake sediment that covers the range of contamination in the UK and Ireland was completed. Three laboratory sediment bioassays were used, Daphnia magna 7-day survival and reproduction, Gammarus pulex 14-day survival and growth and Chironomus riparius 10-day survival and growth/reproduction, and the concentrations of seven heavy metals and four groups of POPs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, organochlorine pesticides and polybrominated diphenyl ethers) were determined.
3
Olago, Daniel Ochieng. "Late Quaternary lake sediments of Mount Kenya, Kenya". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296036.
Testo completo
4
Frappier, Monique G. "Late-glacial, fine-resolution pollen and sediment analyses of Little Dyke Lake sediments, Central Nova Scotia". Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10247.
Testo completoAbstract (sommario):
A detailed analyses of Little Dyke Lake basal sediments revealed two environmental disturbances occurred during the late-glacial. These disturbances were correlated to the previously reported Killarney and Younger Dryas climatic oscillations of the Maritimes. Organic accumulation commenced at about 11 500 yrs BP. Macrofossil and pollen evidence indicate that a forest-tundra including abundant juniper and spruce krummholz had developed 300-600 years after deglaciation. Changes in the vegetation composition were followed by an increased inwash of coarser, siltier sediment. With climate amelioration, a spruce woodland grew during the time when paleo-Indians occupied the nearby Debert site. The deposition of clayey and organic rich sediments are associated with the spruce woodland. Plants found in the understory, especially herbs and grasses, and those most apt to grow under cooler, drier and disturbed conditions then became more important in the landscape. This shift in the vegetation cover is accompanied with the sudden replacement of dark clayey sediment by a reddish coarse silt. The termination of the Killarney cooling is reflected by an increase abundance of coarse mineral sediment. However, high Juniperus pollen percentages accompany a shrub Betula maxima when maximum erosion of sands arrives to the lake basin. Changes in the character of the sediment appear to coincide with pollen changes resulting from climatic cooling. (Abstract shortened by UMI.)
5
Gälman, Veronika. "Varved lake sediments and diagenetic processes". Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-5724.
Testo completoAbstract (sommario):
Varved (annually laminated) sediments are of great interest for inference of past environmental conditions, as they provide dated records with high time resolution. After deposition, the sediment varves are affected by diagenesis; i.e., chemical, physical and biological changes that occur within the sediment. An important premise when reconstructing past environmental conditions using lake sediments is that the signal of interest is preserved in the sediment. In this thesis I have used a unique collection of ten stored freeze cores of varved lake sediment from Nylandssjön in northern Sweden, collected from 1979 to 2007. The suite of cores made it possible to follow long-term (up to 27 years) changes in iron (Fe), sulfur (S), carbon (C), nitrogen (N), δ13C and δ15N in the sediment caused by processes that occur in the lake bottom as the sediment ages. The sediment geochemistry and resulting changes were followed in years for which there are surface varves in the core series. Fe and S concentrations analyzed by X-ray fluorescence spectroscopy showed no diagenetic front in the sediment and the data do not suggest a substantial vertical transport of Fe and S in the sediment. A model based on thermodynamic, limnological, and sediment data from the lake, showed that there are pe (redox) ranges within which either FeS (reduced specie) or Fe(OH)3/FeOOH oxidized species) is the only solid phase present and there are pe ranges within which the two solid phases co-exist. This supports the hypothesis that blackish and grey-brownish Fe-layers that occur in the varves were formed at the time of deposition. C and N analyzed with an elemental analyzer showed that within the first five years after deposition the C concentration of the sediment decreased by 20% and N by 30%, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. The C:N ratio increased with increasing age of the sediment; from ~ 10 in the surface varves to ~12 after 27 years of aging. δ13C and δ15N analyzed on a mass spectrometer showed that δ13C increased by 0.4-1.5‰ units during the first five years, after that only minor fluctuations in δ13C were recorded. Another pattern was seen for δ15N, with a gradual decrease of 0.3-0.7‰ units over the entire 27-year-period. The diagenetic changes in the stable isotope values that occur in Nylandssjön are minor, but they are of about the same magnitude as the variation in the isotopic signal in the varves deposited between 1950-2006. My results show that diagenesis does not change the visual appearance of the varves, except for varve thickness; the varves get thinner as the sediment ages. As the color of Fe in the varves likely reflects the environmental conditions at the time of deposition this creates possibilities for deciphering high-temporal-resolution information of past hypolimnetic oxygen conditions from varves. My findings on C, N, δ13C and δ15N will have implications for interpretations of paleolimnological data. The diagenetic effects should be carefully taken into consideration when C, N, δ13C and δ15N in sediment cores are used to study organic matter sources or paleoproductivity, in particular when dealing with relatively small and recent changes. In addition to the significance of diagenetic effects on sediment parameters, a comparison of the varves in Nylandssjön and the adjacent lake Koltjärnen, and the two deep basins of Nylandssjön show that subtle features in the lakes and their catchments affect the appearance of the varves, which make interpretation of varves complicated.
6
Schmitt, Harold Rolf. "Mobilization of gold into lake sediments". Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6767.
Testo completoAbstract (sommario):
Geochemical exploration methods are able to contribute significantly to the detection of concealed Au mineralization in glaciated terrains. Gold analyses of lake sediments from the glaciated Canadian Shield have been used since the mid-1980s to explore for Au mineralization. For lake sediments to be an effective indicator of Au mineralization, the element must migrate in solution or adsorbed on suspensates in the boreal forest zone where low relief and disorganized drainage restricts dispersal and concentration in clastic form. Organic-rich profundal lake sediments often contain anomalous Au contents near Au mineralization, suggesting that Au is entering the lake environment in mobile form. Confirmation of the processes by which Au is mobilized into lake sediments could thus contribute to improved exploration methodologies. This study investigated the nature of Au mobility and dispersion into lake sediments under alkaline and acid hydrological conditions in the southern Canadian Shield. The study makes recommendations for exploration strategies to be employed under these conditions. Three field areas were selected for detailed study: Napier Lake, Ontario; PAP Lake, Saskatchewan; and Foster Lake, Manitoba. (Abstract shortened by UMI.)
7
Den, Heyer Cornelia E. "Organic matter mineralization in lake sediments : a within and among lake study". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23996.
Testo completoAbstract (sommario):
Organic matter mineralization by sediment bacteria was measured by the accumulation of DIC + CH$ sb4$ in the water overlying intact cores taken from littoral and profundal sediments of 9 lakes. The variability in areal carbon mineralization was much greater within lakes than among lakes, with the rate of organic matter mineralization in littoral sediments, on average, 3-fold higher than in the deeper sediments.Sixty percent of the variation in summer carbon mineralization rates is explained by site depth, a surrogate variable which incorporates the effect of temperature and may also be reflecting organic matter quality and/or supply. Lake-specific variables become useful predictors of carbon mineralization only after the site depth is considered.
A comparison of the mineralization in sediments overlain by epilimnetic water to the whole lake sediment mineralization demonstrates the overwhelming importance of the littoral sediments in organic matter mineralization, with more than half (54-100%) of the mineralization in the sediments occurring in the littoral zone. However, the littoral sediments account for less than 20% of the gross respiration in the epilimnion. (Abstract shortened by UMI.)
8
Rowan, David J. "The distribution, texture and trace element concentrations of lake sediments /". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70361.
Testo completoAbstract (sommario):
Hypotheses regarding the distribution, texture and trace element concentrations of lake sediments were tested by empirical analyses of multi-lake data sets (52 to 83 lakes). Sediment distribution was best characterized by the deposition boundary depth (DBD), the abrupt transition from coarse- to fine-grained sediments. The DBD can now be predicted from either empirical models or empirical-theoretical simplifications of wave of sediment threshold theory, both in terms of exposure (or fetch) and bottom slope. The texture (organic content, water content and bulk density) of profundal sediments was related to the inorganic sedimentation rate and exposure, but not to the lake trophic status or the net organic matter sedimentation rate. The relationships between sediment texture and intra- and inter-site variability, together with the models that predict the DBD and sediment texture, were used to develop an algorithm that should greatly reduce sampling effort in lake sediment surveys. Finally, sediment trace element concentrations were predicted from sediment texture, site depth and simple geologic classifications. The models developed here, provide a framework in which to sample lake sediments and interpret their properties.
9
Zastepa, Arthur. "Fate and Persistence of Microcystin Congeners in Lakes and Lake Sediments". Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30453.
Testo completoAbstract (sommario):
Cyanobacterial blooms and their toxins are a major water quality and potential health risk around the world. This thesis developed an analytical method for microcystin congeners in sediments in order to examine their fate in lakes and establish the history of toxin-producing cyanobacteria in relation to environmental change using lake sediments. A novel method for both intra- and extracellular microcystins in lake sediments was developed, consisting of accelerated solvent extraction, hydrophilic-lipophilic balance solid phase extraction and multiple reaction monitoring-based HPLC-MS/MS quantitation. The method achieved comparable recoveries of intra- and extracellular cyanotoxins based on nine microcystins and nodularin (marine analogue). The analytical method was validated using surficial and deeper sediments from seven lakes of diverse geography and trophic state. To study the fate of microcystins, a multi-year, whole lake study of Microcystis blooms was conducted to obtain both in situ and in vitro half-life estimates of microcystin-LA (MC-LA), an understudied, but increasingly reported microcystin. MC-LA appeared to undergo slower rates of decomposition and persist longer than the more frequently studied MC-LR. Experimentally, high light intensity increased in vitro decomposition of dissolved MC-LA while high temperature enhanced decomposition in the particulate phase. Sediment deposition measurements and estimates of sediment-pore water distribution coefficients, sediment accumulation rates, and diffusive fluxes indicated that microcystin congeners differ in their fate. Notably, MC-LA preferentially distributed into pore water and remobilized (by diffusion) from sediments and into overlying water while MC-RR adsorbed more strongly to sediment particles. Finally, the sediment record of an eutrophic lake of major recreational importance was examined to identify possible drivers of toxigenic cyanobacteria and determine if the perceived increase in toxigenic cyanobacteria could be corroborated. Microcystins were detected to the bottom of the core (early 1800s), indicating that toxigenic cyanobacteria were present prior to the first permanent settlements. Microcystins were significantly correlated with changes in diatom-inferred nutrients (DI-TP and DI-TKN) within the sediment core as well as with specific algal pigments. Sediment microcystins in the upper layers also significantly correlated with a 20-year monitoring record for water column microcystins suggesting that sediment microcystins can be used as a proxy for past surface water conditions.
10
Gudasz, Cristian. "Boreal Lake Sediments as Sources and Sinks of Carbon". Doctoral thesis, Uppsala universitet, Limnologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-150709.
Testo completoAbstract (sommario):
Inland waters process large amounts of organic carbon, contributing to CO2 and CH4 emissions, as well as storing organic carbon (OC) over geological timescales. Recently, it has been shown that the magnitude of these processes is of global significance. It is therefore important to understand what regulates OC cycling in inland waters and how is that affected by climate change. This thesis investigates the constraints on microbial processing of sediment OC, as a key factor of the carbon cycling in boreal lakes. Sediment bacterial metabolism was primarily controlled by temperature but also regulated by OC quality/origin. Temperature sensitivity of sediment OC mineralization was similar in contrasting lakes and over long-term. Allochthonous OC had a strong constraining effect on sediment bacterial metabolism and biomass, with increasingly allochthonous sediments supporting decreasing bacterial metabolism and biomass. The bacterial biomass followed the same pattern as bacterial activity and was largely regulated by similar factors. The rapid turnover of bacterial biomass as well as the positive correlation between sediment mineralization and bacterial biomass suggest a limited effect of bacterial grazing. Regardless of the OC source, the sediment microbial community was more similar within season than within lakes. A comparison of data from numerous soils as well as sediments on the temperature response of OC mineralization showed higher temperature sensitivity of the sediment mineralization. Furthermore, the low rates of areal OC mineralization in sediments compared to soils suggest that lakes sediments are hotspots of OC sequestration. Increased sediment mineralization due to increase in temperature in epilimnetic sediments can significantly reduce OC burial in boreal lakes. An increase of temperature, as predicted for Northern latitudes, under different climate warming scenarios by the end of the twenty-first century, resulted in 4–27% decrease in lake sediment OC burial for the entire boreal zone.
11
Tennant, Richard Kenneth. "Genomic analysis of microfossils in lake sediments". Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/20649.
Testo completoAbstract (sommario):
Botryococcus braunii is a microscopic, colonial green alga that may be found in fresh and brackish waters throughout the globe. B. braunii is unique in that it constitutively synthesises and secretes copious amounts of various long-chain (C23-C40) hydrocarbons, generically termed “botryococcenes”. Botryococcanes, the hydrogenated forms of botryococcenes, comprise 1% of the fossil hydrocarbons found in petroleum deposits and in oil-shales. Microfossils identified as Botryococcus by optical and scanning electron microscopy are also abundant in these strata, but the actual identity and precise relationship between these microfossils and extant Botryococcus species is not known. In this investigation, the relationship between living Botryococcus algae and microfossils identified as Botryococcus using traditional palaeontological analysis and light-microscopy was investigated by analysis of ancient DNA (aDNA). The material used was identified in sediments from Boswell Lake (British Columbia, Canada), a Holocene lake that had remained undisturbed since the glacial retreat. New flow-cytometry methods were developed to rapidly purify enough of the relevant microfossils, from which aDNA was extracted and sequenced. Pollen grains were purified using the same flow-cytometry method and from the same horizons as the Botryococcus microfossils and used to age the sedimentary horizons by 14C radiocarbon dating. Samples of the purified microfossils were imaged by scanning electron microscopy for comparison with published images of fossils identified as Botryococcus from kerogens. In addition, metaDNA from the relevant horizons was extracted and sequenced by NGS, and a chemical analysis for botryococcene derivatives performed using two-dimensional gas chromatography (2D-GC). The genomic analyses show that the sub-fossils identified in Boswell Lake are likely to be representatives of B. braunii, race B. The geochemical analysis identified hydrocarbons that migrate as botryococcenes on 2D-GC in the strata whence the sub-fossils were purified. The SEM images indicate that the microfossils purified from Boswell Lake have similar morphologies to those found in kerogens. Taken together, these data strongly support the proposition that petroleum and kerogen deposits are unusually rich in B. braunii and that these algae have a lineage potentially dating 500 million years. The metagenomic analysis enabled similar conclusions to be reached regarding the presence of B. braunii within the sediment, without the need for targeted microfossil purification. While this analysis was less precise due to the under-representation of algal genomes in the public sequence databases, the metagenomics approach employed was particularly well suited to the temporal analysis of prokaryotic microcosms within Lake Boswell, the succession of which could be associated with periods of climatic variation. The analytical methods described herein are generally applicable to understanding microbial systems over geological periods, and may be used to generate important insights into the cause and effect relationships between microbial populations and environmental perturbation.
12
Hoverson, Darrin. "Phosphorus release from sediments in Shawano Lake, Wisconsin /". Link to full-text, 2008. http://epapers.uwsp.edu/thesis/2008/Hoverson.pdf.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Wisconsin--Stevens Point, 2008.Submitted in partial fulfillment of the requirements of the degree Master of Science in Natural Resources (Water Resources), College of Natural Resources. Includes bibliographical references (leaves 46-53).
13
Mellicant, Emily. "Geochemical signatures of parent materials and lake sediments in northern Minnesota". Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/35446.
Testo completoAbstract (sommario):
Master of ArtsDepartment of Geography
Kendra K. McLauchlan
The importance of local parent material has been recognized as a fundamental control on the geochemistry of lake sediments, but there have been relatively few broad-scale surveys of catchment sources of terrigenous lake sediments. In this paper, I present a geochemical study of catchment parent materials and lake sediments from four lakes in Northern Minnesota. Similar climate and vegetation conditions are present at all four lakes, which vary mainly in catchment parent material and lake morphometry. Geochemical data including major, trace and rare earth elements (REEs) from catchment parent material samples was compared with lake sediment geochemical data using PCA, linear regression, geological indices and elemental ratios. In homogenous till-dominated catchments, patterns of elemental variation in the catchment till could be extended to predict elemental concentrations in the lake sediments. Simple ratios, which are commonly used to analyze lake sediment geochemical data, were not good predictors of lake sediment composition, however. Catchments with mixed bedrock and till were compositionally heterogeneous, and comparison with lake sediments was difficult. Lack of grain size control and biogenic silica measurements further confounded analysis. However, ΣREE/Y ratio was found to be diagnostic of the catchment parent materials and present within the lake sediments. This study makes a contribution to an improved understanding of lacustrine sedimentary archives by analyzing the spatial linkages among catchment, water and sedimentary geochemistry.
14
Owenson, Gerald G. "Obligately anaerobic alkaliphiles from Kenya soda lake sediments". Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/29758.
Testo completoAbstract (sommario):
During the month of December 1992, an expedition was undertaken to collect anaerobic sediment samples from alkaline lakes of the East African Rift Valley to Kenya. During this expedition, eleven samples were collected from the four non-saline, northern lakes (Lake Bogoria, Lake Nakuru, Lake Elmenteita and Lake Sonachi). A further five samples were obtained from the hypersaline Lake Magadi. Utilising an array of media, the isolation of alkaliphilic, obligate anaerobes, representing one of the major undescribed constituents of the trophic network, was attempted. Extensive investigations into the sulphate-reducing bacteria (SRB) community of the sediment samples failed to provide pure culture isolates. However, successful enrichments utilising a range of substrates were obtained. Ethanol as a substrate resulted in the greatest number of positive enrichments, with representatives from each of the northern lakes visited. These are the first indications that ethanol may be used to enrich for alkaliphilic SRB. Lactate also performed well as a growth substrate, whilst acetate, butyrate, formate and fumarate also resulted in one or more positive enrichments. Contrary to previous findings, these data reveal the presence of alkaliphilic SRB capable of utilising a range of substrates. Although positive enrichments under hypersaline conditions were initially obtained using lactate, these cultures could not be maintained. Using the substrates betaine, trehalose, starch, carboxymethyl cellulose, xylan and guar gum (galactomannan), a number of other organisms were isolated. Despite being enriched under anaerobic conditions, all the isolates were found to be facultatively anaerobic although exo-enzyme production appeared to take place only under anaerobic conditions. Six alkaliphilic, obligate anaerobes were isolated from samples taken from two of the northern lakes (Lake Elmenteita and Lake Bogoria) using a complex medium with glucose. Phenotypic and taxonomic data indicated the presence of five species belonging to the Clostridium spectrum, although they were found to be phylogenetically distinct from previously described isolates. Each organism showed optimal growth at alkaline pH, and tolerated only low concentrations of NaCl (ca. 8% w/v). Enrichment of three Lake Magadi samples resulted in the isolation of three haloalkaliphilic obligate anaerobes. These organisms had an obligate requirement for high NaCl concentrations (> 16% w/v), and showed a limited pH range for growth in the alkaline region (> pH 9.5). Phylogenetic analysis of 6S rDNA revealed these isolates also clustered within the Clostridium region of the low G+C Gram-positive bacteria, although they were also unrelated to any of the previously described species. Taxonomic proposals for a new genus and several new species are presented.
15
Richmond, Kelly-Anne. "Paleolimnological analysis of sediments from Killarney Lake, Manitoba". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23475.pdf.
Testo completo
16
Hales, Philip. "Inorganic geochemistry of tropical lake and swamp sediments". Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357524.
Testo completo
17
Scandella, Benjamin P. (Benjamin Paul). "Spatiotemporal variability of methane ebullition from lake sediments". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104157.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 130-140).
Methane is a potent greenhouse gas, and natural sources to the atmosphere include inland waterways and shallow oceans. However, the magnitude of these emissions and their potential for feedbacks with climate change remain poorly constrained. In many settings the majority of atmospheric methane emissions is delivered by bubbles, and the spatiotemporal heterogeneity of ebullition makes measurement challenging and impacts bubble dissolution and atmospheric emissions. In this thesis, we present an analysis of both the episodicity and spatial structure of methane venting from soft sediments in a eutrophic lake over a range of spatial scales, from 1 cm to 20 m, and using a combination of field observations and laboratory experiments. Field-scale measurements of ebullition were acquired at the bottom of Upper Mystic Lake, MA, USA, using a high-resolution multibeam sonar during multiple deployments over a 9-month period. The sonar was calibrated to estimate the gas flow rates throughout a 330 m2 lateral observation area with resolution of 0.5 m. The results confirm that ebullition is strongly episodic, with distinct regimes of high- and low-flux largely controlled by changes in hydrostatic pressure. Statistical analysis shows that the spatial pattern of ebullition becomes homogeneous at the sonar's resolution over timescales of hours (for high-flux periods) or days (for low-flux periods), demonstrating that meter-scale methane vents are ephemeral rather than persistent. Laboratory-scale measurements were made in a controlled incubation of reconstituted sediments from the same field site. Image analysis of the 0.14 m2 observation area allowed identification of individual bubble outlets and resolved their location to ~ 1 cm. While ebullition events were typically concentrated in bursts lasting ~ 2 min, some major outlets showed persistent activity over the scale of days and even months. This persistence was surprising given the ephemerality of spatial structure at the field-scale. It suggests that, at the centimeter scale, conduits are re-used as a result of a drop in tensile strength due to deformation of sediments by the rising bubbles. By combining novel measurement techniques at different scales, we elucidate the mechanisms governing bubble growth and mobility, thereby supporting estimates of global methane fluxes from lakes and how their magnitude may vary with climate change.
by Benjamin Paul Scandella.
Ph. D.
18
Braisby, John David James. "Magnetic properties of Mexican soils and lake sediments". Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/12647.
Testo completoAbstract (sommario):
This study addresses two topics in environmental magnetism, i) the magnetic unmixing of lake sediments in terms of catchment samples and, ii) a connection between soil magnetic properties and annual rainfall. Soil and lake sediment cores from Mexico provided the material used. Palaeolimnology facilities the understanding of past environments by the analysis of lake sediments. Many palaeolimnological techniques are both time consuming and destructive. Analysis of pollen and diatoms require an expert to identify and count hundreds of pollen grains or diatoms, for each core horizon to be characterised. In contrast, magnetic remanence and susceptibility measurements can be obtained rapidly and without changing the physical properties of the sample that is being measured. The problem with magnetic measurements on lake sediment is the interpretation of the results. Previous workers have analysed trends in the magnetic properties of sediments. Linking high susceptibility to soil erosion, and low susceptibility to reduced sedimentation through, for example, the accumulation of organic material, low in magnetic content. In order to analyse environmental magnetic results I have developed a new magnetic unmixing technique. It uses non-negative least squares to unmix the magnetic properties of a target sample in terms of the magnetic properties of potential end-member samples. A stepwise technique is used to select appropriate end-members and estimate the errors involved. The newly developed magnetic unmixing procedure has been applied to the sediments of two lakes in Mexico, Lake Pátzcuaro, in the central Mexican highlands, and Lake Babicora in the northern Mexican highlands. The results for Lake Pátzcuaro indicate changes in the lake sediments’ magnetic properties that can be ascribed to climate changes and farming. The main climatic change is a reduction in lake level at approximately 11,0001 4C yr B.P. Human arrival, at approximately 3,5001 4C yr B.P. coincides with a dramatic increase in topsoil erosion. At Lake Babicora the results indicate that a reduction in rainfall led to a dramatic reduction in catchment material delivered to the core site. This change in the depositional regime occurred at approximately 17,000 1 4C yr B.P.
19
Peinerud, Elsa. "Diatom silica in lake sediments and suspended matter". Licentiate thesis, Luleå tekniska universitet, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25653.
Testo completo
20
Scandella, Benjamin P. (Benjamin Paul). "Numerical modeling of methane venting from lake sediments". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62088.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 91-96).
The dynamics of methane transport in lake sediments control the release of methane into the water column above, and the portion that reaches the atmosphere may contribute significantly to the greenhouse effect. The observed dynamics are poorly understood. In particular, variations in the hydrostatic load on the sediments, from both water level and barometric pressure, appear to trigger free gas bubbling (ebullition). We develop a model of methane bubble ow through the sediments, forced by changes in hydrostatic load. The mechanistic, numerical model is tuned to and compared against ebullition data from Upper Mystic Lake, MA, and the predictions match the daily temporal character of the observed gas releases. We conclude that the combination of plastic gas cavity deformation and ow through "breathing" gas conduits explains methane venting from lake sediments. This research lays the groundwork for integrated modeling of methane transport in the sediment and water column to constrain the atmospheric flux from methane-generating lakes.
by Benjamin P. Scandella.
S.M.
21
Boygle, Jane E. "Tephra in lake sediments : an unambiguous geochronological marker?" Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/20193.
Testo completoAbstract (sommario):
This thesis has three aims: (1) to construct tephrochronologies on large and small scales at sites in Sweden and Iceland; (2) to assess the effects of erosional and depositional processes on the nature and distribution of tephra in the sedimentological record; (3) to use these case studies to propose a model of the deposition of tephra in lakes. The Swedish Timescale based on the annually laminated sediments (varves) has recently been linked to the present. To test the chronology, traces of volcanic glass (tephra) from five historical eruptions of Icelandic volcanoes were sought within relevant sections of the varve deposits. Difficulties in isolating and identifying tephra to define isochrones in distal deposits led to the adoption of an integrated catchment and lake basin sampling strategy to assess the processes which affect the temporal and spatial distribution of tephra in lakes. A detailed tephrochronology of Svínavatn, a lake in northern Iceland, was constructed by identifying and correlating 95 tephra deposits from five lake cores and twelve profiles situated in the lowland peats, hillslopes and delta areas of the catchment. The tephra record from each site was highly variable due to both uneven fallout of the tephra following the eruption, and later reworking of the deposits in the lake and the catchment. The environmental changes of Svínavatn and its catchment were reconstructed using tephra as a geomorphological tracer. The peats and soils of the catchment were stable throughout most of the Holocene until the deposition of Hekla 3 (2800 yBP). Repeating layers of reworked Hekla and Katla tephra after this period at several terrestrial and lacustrine sites reflect increasing episodic instability of the catchment and the effects of this disturbance on the lake record. Until the arrival of Norse settlers in the 9th century, much of this disturbance was linked to climate and vegetation changes around the catchment. Significant, but temporally discrete, secondary inputs of H3 and H4 (3800 yBP) into the lake occur several thousand years after the original airfall.
22
McLean, Donald C. H. "Magnetic and sedimentological analyses of quaternary lake sediments from the English Lake District". Thesis, University of Bedfordshire, 1991. http://hdl.handle.net/10547/600845.
Testo completoAbstract (sommario):
Results of mineral magnetic, mobile clement, and granulometric analyses of Holocene sediments from Buttermere and Crummock Water (two closely-linked lakes in the north-west of the English Lake District) are presented. These are used to: (1) identify effects of internal (lacustrine) and external (catchment) controls on sedimentation; (2) establish catchment source-lake sediment linkages and assess the value of mineral magnetic techniques in palaeolimnological studies; (3) identify major catchment environmental changes. Analyses of lake sediment fabrics (using sediment thin sections, SEM clay flake analysis, standard granulometric analysis, and mineral magnetic indicators of grain size change) indicate that river plume sedimentation is the normal sediment dispersal mechanism in these lakes. Thin (< = 3.0 mm) chlorite-rich laminae, found at intervals in the otherwise homogeneous Holocene sediment sequence, are probably formed by trapping and concentration of fine, platy particles within lake waters. They are subsequently deposited during lake overturn. This represents an "internal" control on sedimentation. A model of sedimentation processes operating in these lakes is developed, incorporating river plume sedimentation, episodic density surges, and lake thermal structure. Mineral magnetic measurements allow the objective subdivision of the lacustrine lithostratigraphy, identifying broad changes in lake sediment characteristics. Samples from both lake catchments are clustered into six magnetically distinct groups - despite the lithological complexity of the catchment. Comparison of these with the lake sediments has enabled identification of major sources during the Holocene. Following deposition of relatively unaltered bedrock-derived material during the Late-glacial ("primary" sources), secondary sources (which may include glacial diamicts, soils and stream sediments) dominate the lake sediments. Direct input of topsoil-derived sediment from circa 1000 A.D. onwards (during and following the main period of Norse settlement of the Lake District) is identified by its distinctive mineral magnetic characteristics, (high Xfd% values, >-4%). Industrially-derived magnetic spherules contribute significantly to the mineral magnetic characteristics of the more recent sediments, (mainly those post-dating circa 1900 A.D.). These are used to construct a proxy chronology for recent sediments. Catchment environmental changes arc mainly related to stabilisation of vegetation following deglaciation and, from circa 2,000 B.P., anthropogenic effects of deforestation and land disturbance, thus increasing lake sediment accumulation rates. These findings are broadly consistent with the interpretation of the Lake District Post-glacial sediment sequence presented in studies by Mackereth, (1966a), and Pennington, (1981), demonstrating a uniformity of lake and catchment development within the Lake District. A prominent minerogenic layer present in the Buttermere and Crummock Water sediment sequence however broadly correlates with similar horizons deposited in other Lake District lakes from circa 7,400 - 5,000 B.P. These have been previously interpreted as composed of topsoil-derived material derived from human actions, (Pennington 1973, 1981). In the Buttermere and Crummock Water sediments, this layer is best interpreted as derived from glaciogenic sediment') reworked from within the lake basins, probably following lowered lake water levels during the period circa 7,300 - 5,300 B.P. Thus it is suggested that a reinterpretation of similar Lake District lacustrine sediments using the methods employed in this study would be appropriate.
23
Demory, François. "Paleomagnetic dating of climatic events in Late Quaternary sediments of Lake Baikal (Siberia)". Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/181/.
Testo completoAbstract (sommario):
Der Baikalsee ist ein ideales Klimaarchiv für die Mitte Eurasiens. In dieser Arbeit wurde gesteinsmagnetische und paleomagnetische Analysen an hemipelagischen Sequenzen von vier Lokationen analysiert. Die Kerne erreichen ein Alter von maximal 300 ky.
In Kombination mit TEM, XRD, XRF und geochemischen Analysen zeigt die gesteinsmagnetische Studie, dass detritischer Magnetit das magnetische Signal der glazialen Sedimente dominiert. Die magnetischen Signale der interglazialen Sedimente wurden durch diagenetische Prozesse verändert. Mittels HIRM können Hämatit und Goethit quantifiziert werden. Diese Methode eignet sich, den detritischen Eintrag in den Baikalsee abzuschätzen.
Relative Paleointensitäten des Erdmagnetfeldes ergaben reproduizerbare Muster, welche in Korrelation mit gutdatierten Referenzproben die Ableitung eines alternativen Altersmodells für die Datierung der Baikalsedimente ermöglichten. Bei Anwendung des paleomagnetischen Altersmodells beobachtet man, dass die Abkühlung im Baikalgebiet und im Oberflächenwasser des Nordatlantiks wie sie aus den δ18 O-Werten planktonischer Foraminiferen abgeleitet werden kann, zeitgleich ist. Wird das aus benthischen δ18 O-Werten abgeleitete Altermdodell auf den Baikalsee angewandt, ergibt sich eine deutliche Zeitverschiebung. Das benthische Altersmodell repräsentiert die globale Veränderung des Eisvolumens, welche später als die Vänderung der Oberflächenwassertemperatur auftritt.
Die Kompilation paleomagnetischer Kurven ergab eine neue relative Paleointensitätskurve “Baikal 200”.
Mittels Korngrössenanalyse des Detritus konnten drei Faziestypen mit unterschiedlicher Sedimentationsdynamik unterschieden werden:
1) Glaziale Peroiden werden durch hohe Tongehalte infolge von Windeintrag und durch grobe Sandfraktion mittels Transport durch lokale Winde über das Eis charakterisiert. Dieser Faziestyp deutet auf arides Klima.
2) Während der Glazial/Interglazial-Übergänge steigt die Siltfraktion an. Dies deutet auf erhöhte Feuchtigkeit und damit verbunden erhöhte Sedimentdynamik. Windtransport und in den Schnee der Eisdecke eingetragener Staub sind die vorherrschenden Prozesse, welche den Silt in hemipelagischer Position zur Ablagerung bringen.
3) Während des klimatischen Optimum des Eeemian werden Grösse und Quantität des Silts minimal, was auf eine geschlossene Vegetationsdecke im Hinterland deutet.Lake Baikal provides an excellent climatic archive for Central Eurasia as global climatic variations are continuously depicted in its sediments. We performed continuous rock magnetic and paleomagnetic analyses on hemipelagic sequences retrieved from 4 underwater highs reaching back 300 ka. The rock magnetic study combined with TEM, XRD, XRF and geochemical analyses evidenced that a magnetite of detrital origin dominates the magnetic signal in glacial sediments whereas interglacial sediments are affected by early diagenesis. HIRM roughly quantifies the hematite and goethite contributions and remains the best proxy for estimating the detrital input in Lake Baikal. Relative paleointensity records of the earth′s magnetic field show a reproducible pattern, which allows for correlation with well-dated reference curves and thus provides an alternative age model for Lake Baikal sediments. Using the paleomagnetic age model we observed that cooling in the Lake Baikal region and cooling of the sea surface water in the North Atlantic, as recorded in planktonic foraminifera δ18 O, are coeval. On the other hand, benthic δ18 O curves record mainly the global ice volume change, which occurs later than the sea surface temperature change. This proves that a dating bias results from an age model based on the correlation of Lake Baikal sedimentary records with benthic δ18 O curves. The compilation of paleomagnetic curves provides a new relative paleointensity curve, “Baikal 200”. With a laser-assisted grain size analysis of the detrital input, three facies types, reflecting different sedimentary dynamics can be distinguished. (1) Glacial periods are characterised by a high clay content mostly due to wind activity and by occurrence of a coarse fraction (sand) transported over the ice by local winds. This fraction gives evidence for aridity in the hinterland. (2) At glacial/interglacial transitions, the quantity of silt increases as the moisture increases, reflecting increased sedimentary dynamics. Wind transport and snow trapping are the dominant process bringing silt to a hemipelagic site (3) During the climatic optimum of the Eemian, the silt size and quantity are minimal due to blanketing of the detrital sources by the vegetal cover.
24
Demory, François Tribovillard Nicolas Oberhänsli Roland. "Paleomagnetic dating of climatic events in late quaternary sediments of Lake Baikal (Siberia)". Villeneuve d'Ascq : Université des sciences et technologies de Lille, 2007. https://iris.univ-lille1.fr/dspace/handle/1908/338.
Testo completoAbstract (sommario):
Reproduction de : Thèse de doctorat : Dynamique et environnement sédimentaires : Lille 1 : 2004. Reproduction de : Doctoral thesis : Naturwissenschaften : Universität Potsdam : 2004.Thèse en cotutelle. N° d'ordre (Lille 1) : 3513. Résumé en anglais, en allemand et en français. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 91-101.
25
Väisänen, T. (Tero). "Sedimentin kemikalointikäsittely:tutkimus rehevän ja sisäkuormitteisen järven kunnostusmenetelmän mitoituksesta sekä sen tuloksellisuuden mittaamisesta". Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514292989.
Testo completoAbstract (sommario):
Abstract There are many methods for the restorating a eutrophicated lake. This study has concentrated on chemical treatment of the sediment and the restoration measurements. This study is divided into three parts: studies of the chemical restoration of study lakes, the optimization of the sediment chemical restoration method, and the evaluation of the method effectiveness of the lake restoration. According to the results, it is possible to adsorb phosphorus to the sediment and keep it adsorbed, but chemical treatment will not improve the long term phosphorus adsorption capacity of the sediments. Therefore, the internal phosphorus load from sediments is only temporarily decreased. Contrary to the claims of earlier studies, the chemical treatment should be executed with small doses successively over many years. In this case, the phosphorus from the hypolimnion and the interstitial water is engaged and stored in the sediment. The phosphorus will remain stored unless the acidity of the sediment changes so that the phosphorus-aluminum bond is broke. The most important factors in the sediment chemical restoration are the pH-reaction of the chemical and sediment-water mixture. Also, available phosphorus that can be engaged is important. In addition, the natural variety of the pH-value of the lake must be considered. A laboratory test was made that compared the suitability of five different chemicals for the restoration of lakes. The tested chemicals were chemicals that are commonly used in the production of drinking water and in waste water treatment. The most suitable chemical for lake restoration was Kemira’s CFH0818 which had the best ability to engage phosphorus and the best pH-reaction. The successfulness of the lake restoration can be determined from the phosphate in the interstitial water of the sediment as a primary source of internal phosphorus load. This diffusion calculation can be made in every restoration object before and after the restoration measures. Also, oxygen conditions, pH-value and the process environment of the breakdown of the organic material are determined as tools for the restoration measures. The use of the evaluation methods is mostly limited by the dynamic nature of the process environment over different seasons of the year. So for reliable restoration measurement one must know why, when and where the measurements are madeTiivistelmä Rehevän järven kunnostamiseksi on useita menetelmiä: joista tässä tutkimuksessa on keskitytty sedimentin kemikaalikäsittelyyn sekä sen tuloksellisuuden mittaamiseen. Tutkimus jakautuu kolmeen osaan: kemikaalikunnostusten järvikohtaiseen tarkasteluun, sedimentin kemikaalikunnostuksen mitoituksen optimointiin sekä järvikunnostuksen tuloksellisuuden arvioimiseen. Tutkimustulosten mukaan sedimentin kemikaloinnilla voidaan sitoa järvessä kiertävää fosforia sedimenttiin, mutta pysyvää sedimentin fosforinsidontakykyä kertaluontoisella kemikaloinnilla ei saavuteta. Järven sisäinen kuormitus siis hetkellisesti hidastuu, mutta ei lopu sedimentin kemikalointiin. Kemikalointi tulee tehdä pienin kerta-annoksin useana vuonna peräkkäin ja sedimentin pH:n tulisi säilyä välillä 6–8 läpi vuoden. Tällöin kemikaali varastoi sitomansa fosforin sedimenttiin. Kemikaalikunnostuksen tärkeimmät mitoitustekijät ovat kemikaalin pH-vaste vesimassaan ja sedimenttiin sekä sidottavissa oleva fosforimäärä kunnostettavassa järvessä. Tutkimuksen mukaan PAX-18-kemikaali ja vastaavat liuosmaiset alumiini- ja rautakemikaalit eivät ole ensisijaisia järvikunnostuskemikaaleja. Ne on kehitetty juoma- ja jäteveden puhdistamiseen, eli sitomaan nopeasti fosforia ja orgaanista ainetta. Sitä vastoin laboratoriokokeen tulosten perusteella rakeiset adsorptio-kemikaalit, kuten Kemiran CFH0818 sitovat sedimentin fosforia itseensä ilman merkittäviä happamoitumisvaikutuksia. Järvikunnostuksen tuloksellisuutta voidaan arvioida mittaamalla sedimentissä vapaana oleva fosfaattimäärä ja sedimentin hapetustila, happamuus sekä määrittämällä sedimentin fosforinsidontakyky. Mittaukset on tehtävä ennen ja jälkeen kunnostustoimia. Näiden mittausten perusteella voidaan kunnostustoimien tuloksellisuutta arvioida varsin luotettavasti. Tulosten käyttöä rajoittavat lähinnä muuttuvat prosessiolosuhteet eri vuodenaikoina ja toistaiseksi riittävän vertailuaineiston puute. Järvikunnostuksen tuloksellisuuden arvioimiseksi on tiedettävä kohdekohtaisesti miksi, milloin ja mistä mitataan, jotta arvio on luotettava
26
Haring, Peter G. "The nature of heavy metal contamination in organic lake sediments near the Buchans massive sulphide base metal mines, Central Newfoundland /". Internet access available to MUN users only, 2002. http://collections.mun.ca/u?/theses,25133.
Testo completo
27
Zale, Rolf. "Lake sediments around the Antarctic Peninsula : archives of climatic and environmental changes". Doctoral thesis, Umeå universitet, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96890.
Testo completoAbstract (sommario):
Lakes and lake sediments from four areas around the Antarctic Peninsula are described. The concentrations of trace metals in sediment are found to be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment. A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area. The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Boeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size. A radiocarbon dating model developed for the sediment of Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica. Deglaciation dates, as well as data on the climatic and environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given.Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser.
digitalisering@umu
28
Smith, Lydia. "Missisquoi Bay Sediment Phosphorus Cycling: the Role of Organic Phosphorus and Seasonal Redox Fluctuations". ScholarWorks @ UVM, 2009. http://scholarworks.uvm.edu/graddis/217.
Testo completoAbstract (sommario):
Missisquoi Bay, Lake Champlain is a eutrophic, northern shallow freshwater bay that experiences toxic cyanobacteria blooms during the summer months, largely as result of high nutrient (P and N) loading from the agricultural watershed. The sediments, which contain minerals that readily sorb P, can act as a sink or source of water column nutrients. Phosphorus, both inorganic and some organic forms, sorbs to metal oxides at neutral pH in the sediment, thus P release into overlying and pore water can be significantly affected by the reduction and subsequent solubilization of these oxides. This study addresses novel aspects of nutrient cycling in lake sediments as part of a larger study to better understand the link between phosphorus forms, mobility, and cyanobacteria blooms. These aspects include: 1) diel and seasonal sediment redox fluctuations and 2) the role of organic P (Porg) in overall P mobility within sediments as a function of depth and time. Missisquoi Bay sediment porewater redox chemistry was monitored across diel and seasonal cycles over the course of two summers (May-October, 2007 and 2008) by using in-situ voltammetry. Redox chemistry was monitored at the sediment-water interface (SWI) continuously over diel cycles, and the vertical concentration profiles of several key redox species (O2, Mn2+, Fe2+, and FeS(aq)) were obtained from cores collected at different times. The sediments were then analyzed for Total P (TP), Reactive P (RP), Porg, Mn, Fe, Ca, Al, Total Organic C and N. A bloom did not occur in Missisquoi Bay during the summer of 2007, but did in summer of 2008, providing an opportunity to compare the sediment chemistry between non-bloom and bloom conditions. Increasingly anoxic SWI conditions across summer 2008 were observed but the SWI remained oxic for the duration of summer 2007. Significant changes in diel cycle redox chemistry at the SWI were also detected in both summers. Reactive P in the surface sediments decreased across the 2008 season but not in 2007. A strong correlation found between RP and RFe (operationally defined as Fe(III)OOH) suggests that a significant portion of sediment P (30-40%) is closely associated with Fe(III)OOHs, which are susceptible to reduction in anoxic conditions. Phosphorus mobility from the sediment into the water column can be limited by the amount of Fe(III)OOH at the surface, thus P flux from the sediments would be greatest when reducing conditions promote solubilization of these minerals. Completely anoxic surface sediments were only observed during the presence of a bloom, explaining the loss of RP in the surface sediments in 2008 in the late summer. Organic P species represent 18-26% of the P in sediments and the lack of a definite, consistent trend of Porg fractionation across the season suggests that there is variable mobility and degradation of these complex organic compounds on small timescales. The loss of RP from the sediment in 2008 could have contributed to an estimated water column P increase on the order of thousands of μg/L, which in addition to measured increases in NH4+ gradients and subsequent N flux estimates in the upper sediment, could have sustained the bloom for an extended period of time. The relationship between the bloom and reducing sediment conditions suggest that bloom dynamics enhance nutrient release from the sediments, allowing for proliferation and sustainability of the bloom.
29
Egli, Ramon. "Environmental influences on the magnetic properties of lake sediments". Zürich : [s.n.], 2003. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15090.
Testo completo
30
Chan, Yau-Fei. "The sorption of arsenic species to Moira Lake sediments". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0006/MQ46008.pdf.
Testo completo
31
Berry, Patricia A. "Lake Cycles and Sediments: Locality 80, Olduvai Gorge, Tanzania". Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/geosciences_theses/47.
Testo completoAbstract (sommario):
Studies have shown that Bed I and Lower Bed II (1.92Ma- 1.76Ma) of Paleolake Olduvai at Locality 80 are primarily composed of the authigenic lacustrine clay minerals illite, smectite, and interlayered illite-smectite. X-ray fluorescence analysis and the sedimentation rates of Hay and Kyser (2001) were used to identify four apparent lake cycles beginning and ending with saline alkaline phases. Peaks in Al2O3/MgO ratios, and TiO2 and P2O5 abundances occur at approximately the same elevations within the stratigraphic section. Low values in these three parameters indicate saline alkaline conditions whereas high values represent fresh water conditions. Lake Cycles (LC) 1 and 4 completed in approximately 44,000 years and 42,000 years respectively, which is similar to the 41k.y. year cycle associated with Earth’s obliquity. Lake Cycles 2 and 3 span approximately 24,000 years and are similar to the 21k.y. precession cycle.
32
Looft, Torey P. "MOLECULAR CHARACTERIZATION OF MICROBIAL COMMUNITIES IN LAKE ERIE SEDIMENTS". Bowling Green State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1131392301.
Testo completo
33
Rahalkar, Monali. "Aerobic methanotrophic bacterial communities in sediments of Lake Constance". [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-23787.
Testo completo
34
Freitas, Nancy Louise. "Methane and Carbon Dioxide Dynamics in Arctic Lake Sediments". Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/579063.
Testo completoAbstract (sommario):
Rising global temperatures are expected to increase concentrations of greenhouse gases emitted by northern latitudes within the current century. The impact of global warming on Arctic lacustrine systems is generally unknown, although recent studies have examined fluxes of carbon dioxide (CO₂) and methane (CH₄) produced in ebullition events. Few studies have investigated the added impact of atmospheric warming on lake sediments, which produce CO₂ and CH₄ through microbial decomposition and diffusive loss in the water column. To better understand carbon emission scenarios at elevated temperatures, sediment samples from Abisko, Sweden were analyzed for CO₂ and CH₄ production rates through incubation studies, and for concentrations of dissolved inorganic carbon (DIC) and dissolved CH₄ in sediment and porewater. Results showed that room temperature incubations emitted concentrations of CO₂ and CH₄ up to five times greater than those emitted by +5°C incubations. Furthermore, documented peat emissions were one to two orders of magnitude lower than the lake sediment incubation emissions reported in this paper. This study provides some of the first point source microbial emissions by lake sediment depth, and highlights that northern latitude sediments could have unprecedented effects on current spatial and temporal projections of Arctic warming.
35
Amalfi, Frederick A., e Milton R. Sommerfeld. "Organic Contaminants in Urban Lake Sediments: A Preliminary Assessment". Arizona-Nevada Academy of Science, 1989. http://hdl.handle.net/10150/296424.
Testo completoAbstract (sommario):
From the Proceedings of the 1989 Meetings of the Arizona Section - American Water Resources Association and the Hydrology Section - Arizona-Nevada Academy of Science - April 15, 1989, University of Nevada, Las Vegas, NevadaBottom sediments from several urban lakes located in the Phoenix metropolitan area were collected and analyzed for organic priority pollutants. The lakes selected for analysis were broadly representative of the diversity of lake characteristics found in the Phoenix area. That is, lakes were sampled that had different types of primary water sources and that were located in watersheds of differing degrees of urbanization. Preliminary results indicate that only nine of the 114 listed organic priority pollutants were found in measurable quantities in the sediments of the lakes surveyed. The pollutants detected were either phthalate esters or volatile or semi-volatile halogenated compounds. None of the pollutants were common to all the lakes sampled. Dibutyl phthalate was detected in three of the six lakes. A larger database is being developed and will be necessary to determine whether a statistical correlation exists between watershed characteristics and feedwater, and organic composition of lake sediments.
36
Ridenoure, Brian D. "Evaluation and enhancement of the effectiveness of sediment trapping and retention devices installed on the Nevada side of Lake Tahoe /". abstract and full text PDF (UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1451078.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Nevada, Reno, 20007."December 2007." Includes bibliographical references (leaves 122-124). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2008]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.
37
Hartley, Kelley A. "Stratigraphic anaylsis [sic] of areal discontinuities of late Wisconsinan till sheets near Conneaut Lake, northwestern Pennsylvania". Akron, OH : University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1248371875.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Akron, Dept. of Geology, 2009."August, 2009." Title from electronic thesis title page (viewed 10/21/2009) Advisor, John P. Szabo; Faculty readers, Linda Barrett, LaVerne Friberg; Department Chair, John P. Szabo; Dean of the College, Chand Midha; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
38
Le, Tran Thai. "Mineralogy of Lake Hotagen Sediments: Variations with Grain Size throughout Vertical Profile of a Sediment Core". Thesis, Umeå universitet, Kemiska institutionen, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-160376.
Testo completo
39
Basapuram, Laxmi Gayatri Devi. "Lake Victoria - Carbon, Nitrogen, Phosphorus and Stable Isotope (δ13C) comparison between lake and catchment sediments". Thesis, Linköpings universitet, Tema Miljöförändring, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-149283.
Testo completoAbstract (sommario):
Lake Victoria situated in East Africa faces an acute problem with eutrophication. Many reasons like agricultural production, industrialization, anthropogenic processes, the introduction of species, and economic activities have caused a stress to the overall well-being of the lake. Excess carbon, nitrogen, and phosphorus drive an increase in productivity which affects eutrophication. Previous studies on sediments and nutrient concentrations in the lake have concluded that nutrient concentrations increase due to release from the catchment. This study focuses on catchment sediments collected from four different sites and compares the results with sediments from two additional sites in the lake. The sediment core from Siaya indicates the highest concentrations of TOC (180 g/kg), TN (13 g/kg) and TP (17000μg/L). It is a rural site and poor agricultural practices such as the burn and slash, use of too many fertilizers, clearance of land, atmospheric deposition and precipitation increase elemental concentrations in the sediments compared to the more urban sites. In the lake sediments, the BILL core had higher concentrations of TP (430g/kg) and TN (16 g/kg) compared to the other site (LV-95) which is located far away from the margins of the lake. This core, however, had high TOC levels (180g/kg). The increase of nutrient levels in lake sediments is thought to be due to non-point sources from the catchment. Analyses of stable carbon isotope were used to infer the different organic matter source in the sediments. Based on the range of values for δ13C vs. C/N it is inferred that aquatic algal production and C4 vascular plants are the dominant sources for the organic matter input. The chemical characterization of catchment and lake sediments provides a qualitative link to nutrient influx and eutrophication in the lake.
40
Moberly, James Gill. "Biogeochemical cycling of toxic metals in Lake Coeur d'Alene sediments". Online access for everyone, 2006. http://www.dissertations.wsu.edu/Thesis/summer2006/J%5FMoberly%5F063006.PDF.
Testo completo
41
Schallenberg, Marc. "The ecology of sediment bacteria and hypolimnetic catabolism in lakes : the relative importance of autochthonous and allochthonous organic matter". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39519.
Testo completoAbstract (sommario):
Microbial metabolic activity in the hypolimnia and sediments of lakes drives the recycling of organic matter both through mineralization and the production of microbial biomass, which may be utilized by grazers. A correction factor was developed based on the water content of sediment samples that corrects sediment bacteria microscopic counts for masking due to sediment particles. Using this correction factor, it was found that sediment bacterial biomass in 22 lakes was positively related to an indicator of the rate of allochthonous organic matter input to lakes. However, the total hypolimnetic carbon mineralization rate of lakes, which integrates both sediment and hypolimnetic water column mineralization, was found to be driven mainly by phytoplankton carbon and to occur mainly in the hypolimnetic water column. Indeed, various hypolimnetic and sediment catabolic processes were found to show a strong positive relationship with indicators of autochthonous organic matter standing stocks and production. In no cases were the processes significantly positively correlated with allochthonous organic matter standing stocks. Results of this research show that autochthonous primary production drives carbon recycling in the hypolimnetic water column, with the ultimate fate of this production being determined principally by the hypolimnetic thickness. The main fate of allochthonous organic matter in lakes is to become a major component of sediment organic matter where it likely drives a much slower catabolism due to its recalcitrance.
42
Korsman, Tom. "Acidification trends in Swedish lakes : an assessment of past water chemistry conditions using lake sediments". Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-140821.
Testo completoAbstract (sommario):
This thesis presents temporal perspectives of lake acidification in Sweden. Sediment records have been used to study timing, trends and causes of acidification, and two different techniques for assessing past lake-water acidity are presented. A new technique for pH prediction, based on near-infrared (NIR) spectroscopy of surface sediments, is developed. This study shows that there is a pH related fraction of lake sediments that can be recorded by NIR analysis. Relationships between NIR spectra of surface sediment samples and measured lake-water pH values, and between NIR spectra of sediment cores and historical pH values inferred by diatom analysis, are modelled by partial least squares regression. The prediction errors of the models are comparable to those obtained by modelling of diatom and lake-water pH data. By further development NIR spectroscopy can become useful for inferring past pH, as well as several other lake-water parameters, from sediment cores. Diatom-based predictive models, using multivariate calibration methods, are developed for inferences of lake-water pH, alkalinity and colour. These models are used to provide a regional assessment of recent lake acidification in the provinces of Västerbotten and Norrbotten, northern Sweden. The study shows that a pH decline has occurred in some southeastern lakes, but that most of the lakes have not faced significant changes in lake-water pH, alkalinity and colour. The inferred water chemistiy changes are discussed in relation to atmospheric deposition and land-use. In a study of eight acid-sensitive Swedish boreal-forest lakes a past-analogue approach is used to test whether contemporary expansion of conifers could cause lake acidification. Water chemistry changes associated with the natural pre-historic colonization and expansion of spruce in Sweden (≈3000 years B.P.), at times of background atmospheric acidity, are inferred to evaluate the acidification ability of spruce per se on surface waters. This study shows that under natural, unpolluted conditions spruce colonization and expansion did not cause lake acidification. In a synthesis of palaeolimnological acidification research in Sweden a general model for pH- development for acid clear-water lakes in southern Sweden is presented. The pH-development from the last deglaciation to present time can be divided into four different periods; (i) a natural long-term acidification period (12000 B.P. - 2300 B.P., or later), with a gradual decrease in pH resulting from declining fluxes of base cations from catchment soils; (ii) a human induced alkalization period (2300 B.P. - 1900 A.D.), with a pH increase due to human activities in the catchments; (iii) the recent acidification period (about 1900 A.D. - present), when pH decreased towards 4.5 due to acid deposition and possibly ceased land-use; and (iv) the liming period (1970s - present), when pH often increases to values above 7 following lime treatment to counteract acidification. The implications of these past pH changes for the concept of contemporary lake acidification and for liming policy are outlined.digitalisering@umu
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Smirnov, Anna. "Polycyclic aromatic hydrocarbons in sediments of Lake Erie, Great Lakes : spatial distribution, sources and pathways /". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23174.pdf.
Testo completo
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Wällstedt, Teresia. "Influence of acidification and liming on metals in lake sediments". Doctoral thesis, Stockholm University, Department of Applied Environmental Science (ITM), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-471.
Testo completoAbstract (sommario):
Emission and precipitation of acidifying substances and metals has caused severe acidification and increased metal concentrations in lakes and streams in Sweden as well as many other countries during the last decades. To counteract the negative effects of acidification, liming has been used extensively in Sweden since the 1970’s, a treatment that has been called one of the largest man-maid manipulations of aquatic ecosystems ever.
The aim of this thesis is to investigate the influence of acidification and liming on deposition of metals to lake sediments, and to look at the fate of metals in sediments during a possible reacidification process because of terminated liming.
Studies of both surface sediments and dated sediment profiles sampled from limed lakes and non-limed reference lakes indicated that liming causes increased sedimentation of many metals. Increased deposition to the sediments was found for Al, Cd, Co, Ni, Fe, Mn and Zn, probably as a direct result of the increased pH. Liming was also found to increase the deposition of As and Cr, but that was probably due to the secondary effect of association to Fe and Mn complexes. No influence of lime treatment on the deposition of Hg, Pb and V to lake sediments could be demonstrated. The studies also indicated that acidification can decrease the deposition of Cd, Fe, Mn and possibly also Co and Zn to the sediments.
The contribution from the used lime products to the metal load in sediments of lakes limed directly on the lake surface was also evaluated. The lime products were found to be an important source for Al, Cu and Ni and a relatively important source for Co, Cr, Hg and V, but did not seem to contribute much to the content of As, Cd, Pb or Zn in lake sediments.
An experimental study of reacidification showed that (re)mobilisation of metals, e.g Al, Cd, Mn and Zn, from sediments may occur and that reacidification of formerly lime treated lakes may contribute to increased concentrations of these metals in the lake water. Cu, Fe and Pb are less affected by pH changes and the concentrations of these metals will probably not increase in lake water during reacidification.
Altogether, the thesis shows that lime treatment causes increased deposition of many metals to the lake sediments, whereas reacidification may lead to remobilisation of some metals from the sediments with increased concentrations in the water phase as a result.
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Carroll, Bryan P. "Paleolimnological investigation of recent sediments from Lake Monroe, Florida, USA". FIU Digital Commons, 2005. http://digitalcommons.fiu.edu/etd/2059.
Testo completoAbstract (sommario):
Sediments recovered in October 2003 from Lake Monroe, a hypereutrophic lake in central Florida, have been sub-sampled and analyzed for δ13C, δ15N, TC, TIC, TOC, and TN. A chronology of bulk sediment and nutrient accumulation was established by radiometric analyses (210Pb, 137Cs, and 14C), to aid in evaluating spatial and temporal patterns within the lake since development in the watershed began. A continuous 100- year sediment record from Lake Monroe shows significant changes in production, sedimentation, and nutrient abundance following land settlement in the mid 1800's. Sediment nutrient and isotopic analyses demonstrate an increasing trend in nutrients, δ-values, and sediment accumulation relative to pre-disturbance deposits. The sediment geochemical record suggests increased production, possible nutrient limitation, and shifts in primary producer communities through time. The data demonstrates that these historic increases are a direct result of watershed development, land use alterations, and increased nutrient loading within the basin.
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Toms, Andrew David. "Mercury and methylmercury in the sediments of Lake St. Clair". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0018/MQ52669.pdf.
Testo completo
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Edirveerasingam, Veronica. "Implications of vehicle emissions in Lake Tahoe soils and sediments". abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239872.
Testo completo
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Wällstedt, Teresia. "Influence of acidification and liming on metals in lake sediments /". Stockholm : Dept. of Applied Environmental Science, Univ, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-471.
Testo completo
49
Lawlor, Kirsten. "Distribution of bacteria and bacterial plasmids in lake water sediments". Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240596.
Testo completo
50
Teague, Eleanor. "Evaluating methods for detrital grain-size analysis of lake sediments". Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516796.
Testo completo