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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Concentrations and sources of polycyclic aromatic hydrocarbons in sediment cores of southern continental shelf of Kaoping submarine canyon

Li, Kun-je 30 July 2007 (has links)
This study investigated distributions and the concentrations of polycyclic aromatic hydrocarbons (PAHs) in the sediment cores in southern continental shelf of Kao-Ping submarine canyon. The sediment cores collected were analyzed for PAHs to reconstruct historical record of PAH contamination and to find out the possible sources, trends and fluxes. The findings demonstrated the average concentrations of PAHs in the northern continental shelf of Kao-Ping submarine canyon were higher than in the southern continental shelf. The average concentrations of £U51 PAHs and £U16 PAHs ranged from 578 to 697 and from 132 to 173 ng/g , respectively. Because particle sedimentation rates and PAH sources were different along cores, vertical distributions of PAH concentrations among cores were not the same. Identification by diagnostic ratios and result of hierarchical cluster analysis (HCA) suggesting PAHs in the core of northern continental shelf were from pyrogenic and petrogenic sources, while those in the cores of southern continental shelf were from petrogenic source. Compared with sediment quality guidelines (SQGs), most of the sample sediment cores are below the outlined criteria. Only the PAH concentrations of the sediments between 2-16 cm in the core L27 were higher than the Threshold Effect Level (TEL) value. Total PAH concentrations in this study were lower than those from other coastal areas in literature. According to the PAH concentrations along cores in the southern continental shelf, significant increase of total PAH concentrations was evident in the early 1900s. Our results also demonstrate that PAH concentrations and sources in the southern continental shelf area related to the increasing industrial activities in Kao-Ping coastal area.
2

USING PRE-EXISTING CHANNEL SUBSTRATES TO DETERMINE THE EFFECTIVENESS OF BEST MANAGEMENT PRACTICES

Murphy, Ryan P. 18 May 2006 (has links)
No description available.
3

A Re-Evaluation of Mountain Lake, Giles County, Virginia: Lake Origins, History and Environmental Systems

Cawley, Jon C. 17 December 1999 (has links)
This project included the following goals: 1. To review and assess the geomorphology and lake morphometry of Mountain Lake, Giles County, Virginia with regard to its age and origin. This included production of an updated bathymetric map of Mountain Lake using Sonar imaging of the lake bottom. 2. To evaluate present trophic conditions in the lake waters. This analysis included the first-reported nutrient conditions for input streams to the lake and rainwater. 3. To collect representative "modern" bottom sediment samples and to analyze these sediment samples for sedimentological characteristics, diatoms , and terrestrial pollen. This analysis focussed on present environmental conditions in the lake, and the determination of modern diatom thanatocommunities. 4. To collect complete bottom sediment cores from the lake. Coring was done using a diver-assisted manual coring device designed specifically for this project. 5. To analyze Mountain Lake sediment cores for sedimentology, age determination, and temporal differences in sediment characteristics, diatoms and pollen. This analysis focussed on interpretation and documentation of environmental changes through the lake's history. Primary discharge from the lake presently occurs through a leaky subterranean pathway associated with the deepest, crevice-like portion of the lake. This discharge results in the crevice drain not filling shut with sediment despite its location within the lowest portion of the lake. The lake structure, crevice, and subterranean drain are associated with a regional lineation feature represented in part by the path of Salt Pond Drain and a small input stream ("I-4") to the lake. Initial damming was caused by downdrop of overlying rock. The damming is not complete, and the rate of discharge through time is controlled, in part, by regional tectonic events and by a balance of hydrologic conditions and sedimentation factors. The present lake is generally oligotrophic in nature, with phosphorus representing the major limiting nutrient. Rainfall presently represents the largest source of nutrient to the lake. Present diatom flora in Mountain Lake includes 66 individual taxa, representing 25 genera. Of these, 12 forms or species have not been reported in Virginia inland waters prior to this project. The diatoms reflect the oligotrophic and circumneutral nature of the lake. At least seven diatom thanatocommunities can be defined in the lake, based on taxa, delineated by depth and nutrient conditions. The ratio metric of planktonic to littoral diatoms can be used to estimate past water depths in the lake from bottom sediment. An orange clay layer at 5 cm from the modern sediment/water interface represents human intervention in lake history, namely the hotel and road building in the early 20th Century. The age of the lake is greater than 6000 years. Specific 14C from sediment produced dates of 1860 +100, 4220 +50 and 6160 +70 bp. Within this interval, at least 6 extended periods of low or empty lake level occurred (at approximately 100, 400, 900, 1200, 1800, and 4200 yrs bp). Several of these low intervals are likely to correspond with cool dry conditions co-incident with solar minima events. When the lake has been low or empty, it has tended to develop Sphagnum bog conditions with the low lake surrounded by open or wooded meadows. Terrestrial flora surrounding the lake appears to have remained relatively similar through 6100 years, although red spruce originally accompanied hemlock. / Ph. D.
4

STRATIGRAPHY AND ORGANIC GEOCHEMISTRY REVEAL PATTERNS OF LATE QUATERNARY PALEO-PRODUCTIVITY AT MONO LAKE, CALIFORNIA

Hodelka, Bailee Nicole 01 January 2018 (has links)
Mono Lake (CA) is a hydrologically closed lacustrine basin well-known for its paleo-shorelines, which record fluctuations in water level for the last deglacial and late Holocene. Mono Lake is a sentinel of California’s water supply, situated in the rain shadow of the Sierra Nevada, a mountain range whose snowpack is a vital source of freshwater for urban and agricultural districts to the west and south. Recent droughts, floods, and wildfires show that California is threatened by climate change, but how these changes impact and get recorded by Mono Lake sediments remains poorly known. Here, we use a new radiocarbon-dated deepwater sediment core from Mono Lake to test the hypothesis that organic facies development is controlled by climate and limnological change. An integrated stratigraphic analysis of the core reveals seven lithostratigraphic units that track environmental changes from ~16-4 ka. When compared to available paleo-shoreline and shallow water core data, our results show that high amplitude lakelevel fluctuations of the late Pleistocene produce different patterns of sedimentation and organic enrichment than lower-amplitude water level changes of the early and middle Holocene. The results have implications for understanding patterns of paleo-production and hydroclimate change at Mono Lake.
5

Συμβολή στην Ολοκαινική εξέλιξη της βόρειας ακτής του Αμβρακικού κόλπου με βάση αναλύσεις αβαθών γεωτρήσεων / Contribution to the Holocene evolution of the northern coast of Amvrakikos Gulf, by using sediment core analysis

Αγοργιανίτη, Χριστίνα 19 October 2007 (has links)
Μελετάται η Ολοκαινική εξέλιξη των βόρειων ακτών του Αμβρακικού κόλπου, με τη βοήθεια τεσσάρων γεωτρήσεων οι οποίες εντοπίζονται στον οδικό άξονα Αρτας-Σαλαώρας. / Studying the Holocene evolution of the northern coasts of Amvrakikos Gulf, by using four sediment cores, which are located along the main road that connects Arta to Salaora region.
6

Microfossil Evidence for Recent and Past Changes to Hudson Bay Oceanography

Griffiths, Julie 26 November 2010 (has links)
In 2005, box cores were collected throughout the Hudson Bay and Strait. A detailed micropaleontological data set has been generated from these cores for this study and is combined with geochemical and geochronological data to observe temporal and spatial oceanographic changes throughout the bay and strait. All of the cores show an increase in tintinnid species and agglutinated foraminifera, and coincident decreases in calcareous foraminifera in younger core sections. In general, these microfossil trends are correlated with higher organic matter content of the younger core sections. This results from a more extensive freshwater plume that causes lowered pH in the superficial sediments and conditions less favourable for the preservation of calcareous tests. Furthermore, with a 14C age constraint in one of the cores, the mid-Holocene depositional and paleoceanographic history is represented, and provides evidence of marine invasion by 7100 cal yrs BP.
7

The Response of Utah Lake's Plant and Algal Community Structure to Cultural Eutrophication

King, Leighton R. 01 December 2019 (has links)
Human activities have long had a negative impact on the water quality of freshwater lakes around the world. Utah Lake, located in north-central Utah, has been a subject of such impacts, as the lake experiences recurrent harmful algal blooms during the summer months. Lake warnings and closures have made the public increasingly aware of the ecological and economic impact of these blooms. The objectives of this study were to: 1) compare historical and present-day water quality and ecosystem conditions using environmental data contained in sediment cores, 2) identify whether, and when, Utah Lake transitioned from clearwater to turbid conditions, and 3) incorporate historically-validated lake plant community structure models into establishing forward-thinking lake management targets. The first two objectives will guide lake remediation efforts by providing insight into where lake managers should set our water quality goals and help identify the main driver(s) of eutrophication in Utah Lake. Environmental data from sediment cores indicate a transition in the lake’s recent history, marking a shift to greater phytoplankton dominance, which I attribute to the introduction of invasive common carp around 1881. The third objective provides management and restoration efforts with the water clarity requirements for returning the lake to its historical ecological state.
8

The geochemical status of the surface water and the sediments in the estuary of the Sangis River, Kalix, Sweden

Sandberg, Anton January 2023 (has links)
It has been common in forestry and agriculture to drain waterlogged areas through ditching in order to cultivate them. The ditches that drain water are usually connected to some watercourse, such as a river. When the water flow of the river decreases and becomes more still, particles will settle and fall to the bottom of the water body and form sediment. If there is an increasing amount of nutrients and metals transported with the water, it could affect the water quality negatively, since an increased amount of nutrients could result in eutrophication and many metals are toxic in high amounts. In the Sangis River there is an increased amount of sediment deposited at the mouth of the river and inside the estuary, which has resulted in the river and the estuary becoming shallower. The origin of the deposited sediments is believed to partly be from ditching. The residents of the village of Sangis have said that it is difficult to cross the estuary by boat because of the deposited sediments, therefore, their wish is for a channel dredged in the Sangis River and its estuary that they can use. The main aim of this master's thesis was to analyse the geochemical status of the surface water and the sediment in the estuary of the Sangis River and to give recommendations for future actions preventing sedimentation of the river channel. The analyse of the geochemical status of the sediment was achieved by sampling six sediment- cores in the estuary and analysing for different parameters. The analyse of the geochemical status of the surface water was achieved by comparing the water quality regarding metal concentrations in the estuary with other nearby rivers and classifying the concentration of phosphorous in the estuary, to determinate if there was an ongoing eutrophication. The following analyses were conducted for the sediment-cores: Element distribution were analysed with P-XRF, pH and electrical conductivity were measured and loss on ignition was also calculated trough combustion of the sub-samples. The results showed for the P-XRF that the dominating main elements were iron, sulfur, calcium and potassium. Iron and sulfur were correlated to each other in all profiles and had a peak between 20-35 cm in the sediment. This indicated that there could be formation of iron sulfides at that depth. Therefore, sub-sample 4.D was analysed with SEM-EDS instrument and framboidal pyrite (FeS2) was detected in the sample. The results from the pH and conductivity showed that the pH-value varies greatly both with depth and between the sediment cores. However, for the conductivity it could be seen how it peaked at around 20-35 cm in all profiles, with the highest EC-value in profile 4. It could be concluded that the surface water in the estuary contains elevated concentrations of copper and that there is an ongoing eutrophication as well. Due to the eutrophication, it has most likely resulted in an increased amount of aquatic plants during the summer. The increased amount of organic material has probably resulted in oxygen-free bottoms, since all the oxygen has been consumed when the organic material has been decomposed. The formation of framboidal pyrite shows that the redox ladder has reached the two last steps, since framboidal pyrite (FeS2) consists of reduced sulfur and dissolved iron and is formed during anoxic conditions. Reduced sulfur forms when sulfate is reduced in order to oxidize organic matter and dissolved iron forms when iron-oxide hydroxides are reduced in order to oxidize organic matter. If dredging is carried out in the Sangis river and its estuary, oxidation of framboidal pyrite will occur, this could result in formation of acid and leachate of metals that were previously bound to framboidal pyrite. The consequences if it leaches into the river and the estuary is that it creates an acidic environment with elevated metal concentrations, where marine life would find it hard to live. The extent and impact of leached acidity and metals needs to be studied further.
9

Plio-Pleistocene Environments In The Western Arctic Ocean Based On Sediment Records From The Northwind Ridge

Dipre, Geoffrey R. January 2019 (has links)
No description available.
10

DETERMINATION OF BAFFIN BAY SEDIMENT COMPOSITION VARIABILITY AND PROVENANCE

Brenner, Alan R. 01 August 2014 (has links)
No description available.

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