• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 65
  • 28
  • 10
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 119
  • 46
  • 42
  • 19
  • 19
  • 17
  • 16
  • 16
  • 14
  • 13
  • 12
  • 12
  • 12
  • 11
  • 11
  • 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.
111

The impact of dryland salinity on Ross River virus in south-western Australia : an ecosystem health perspective

Jardine, Andrew January 2007 (has links)
[Truncated abstract] A functional ecosystem is increasingly being recognised as a requirement for health and well being of resident human populations. Clearing of native vegetation for agriculture has left 1.047 million hectares of south-west Western Australia affected by a severe form of environmental degradation, dryland salinity, characterised by secondary soil salinisation and waterlogging. This area may expand by a further 1.7-3.4 million hectares if current trends continue. Ecosystems in saline affected regions display many of the classic characteristics of Ecosystem Distress Syndrome (EDS). One outcome of EDS that has not yet been investigated in relation to dryland salinity is adverse human health implications. This thesis focuses on one such potential adverse health outcome: increased incidence of Ross River virus (RRV), the most common mosquito-borne disease in Australia. Spatial analysis of RRV notifications did not reveal a significant association with dryland salinity. To overcome inherent limitations with notification data, serological RRV antibody prevalence was also investigated, and again no significant association with dryland salinity was detected. However, the spatial scale imposed limited the sensitivity of both studies. ... This thesis represents the first attempt to prospectively investigate the influence of secondary soil salinity on mosquito-borne disease by combining entomological, environmental and epidemiological data. The evidence collected indicates that RRV disease incidence is not currently a significant population health priority in areas affected by dryland salinity despite the dominant presence of Ae. camptorhynchus. Potential limiting factors include; local climatic impact on the seasonal mosquito population dynamics; vertebrate host distribution and feeding behaviour of Ae. camptorhynchus; and the scarce and uneven human population distribution across the region. However, the potential for increased disease risk in dryland salinity affected areas to become apparent in the future cannot be discounted, particularly in light of the increasing extent predicted to develop over coming decades before any benefits of amelioration strategies are observed. Finally, it is important to note that both dryland salinity and salinity induced by irrigation are important forms of environmental degradation in arid and semi-arid worldwide, with a total population of over 400 million people. Potential health risks will of course vary widely across different regions depending on a range of factors specific to the local region and the complex interactions between them. It is therefore not possible to make broad generalisations. The need is highlighted for similar research in other regions and it is contended that an ecosystem health framework provides the necessary basis for such investigations.
112

Mapping potential soil salinization using rule based object-oriented image analysis

Stals, Jacobus Petrus 12 1900 (has links)
Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2007. / Soil salinization is a world wide environmental problem affecting plant growth and agricultural yields. Remote sensing has been used as a tool to detect and/or manage soil salinity. Object-oriented image analysis is a relatively new image analysis technique which allows analysis at different hierarchical scales, the use of relationships between objects and contextual information in the classification process, and the ability to create a rule based classification procedure. The Lower Orange River in South Africa is a region of successful irrigation farming along the river floodplain but also with the potential risk of soil salinization. This research attempted to detect and map areas of potential high soil salinity using digital aerial photography and digital elevation models. Image orthorectification was conducted on the digital aerial photographs. The radiometric variances between photographs made radiometric calibration of the photographs necessary. Radiometric calibration on the photographs was conducted using Landsat 7 satellite images as radiometric correction values, and image segmentation as the correction units for the photographs. After radiometric calibration, object-oriented analysis could be conducted on one analysis region and the developed rule bases applied to the other regions without the need for adjusting parameters. A rule based hierarchical classification was developed to detect vegetation stress from the photographs as well as salinity potential terrain features from the digital elevation models. These rule bases were applied to all analysis blocks. The detected potential high salinity indicators were analyzed spatially with field collected soil data in order to assess the capability of the classifications to detect actual salinization, as well as to assess which indicators were the best indicators of salinity potential. Vegetation stress was not a good indicator of salinity as many other indicators could also cause vegetation stress. Terrain indicators such as depressions in the landscape at a micro scale were the best indicators of potential soil salinization.
113

Comunidades zooplanct?nicas como bioindicadoras da qualidade da ?gua de quatro reservat?rios da regi?o semi-?rida do Rio Grande do Norte

Sousa, Wanessa de 12 February 2007 (has links)
Made available in DSpace on 2014-12-17T14:02:04Z (GMT). No. of bitstreams: 1 WanessaS.pdf: 455733 bytes, checksum: f1698247e4a0491cd094aa4ffa270c21 (MD5) Previous issue date: 2007-02-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The response of zooplankton assemblages to variations in the water quality of four man-made lakes, caused by eutrophication and siltation, was investigated by means of canonical correspondence analysis. Monte Carlo simulations using the CCA eingenvalues as test statistics revealed that changes in zooplankton species composition along the environmental gradients of trophic state and abiogenic turbidity were highly significant. The species Brachionus calyciflorus, Thermocyclops sp. and Argyrodiaptomus sp. were good indicators of eutrophic conditions while the species Brachionus dolabratus, Keratella tropica and Hexarthra sp. were good indicators of high turbidity due to suspended sediments. The rotifer genus Brachionus was the most species-rich taxon, comprising five species which were associated with different environmental conditions. Therefore, we tested whether this genus alone could potentially be a better biological indicator of these environmental gradients than the entire zooplankton assemblages or any other random set of five species. The ordination results show that the five Brachionus species alone did not explain better the observed pattern of environmental variation than most random sets of five species. Therefore, this genus could not be selected as a target taxon for more intensive environmental monitoring as has been previously suggested by Attayde and Bozelli (1998). Overall, our results show that changes in the water quality of man-made lakes in a tropical semi-arid region have significant effects on the structure of zooplankton assemblages that can potentially affect the functioning of these ecosystems / As respostas das assembl?ias zooplanct?nicas ?s varia??es na qualidade da ?gua de quatro reservat?rios, causadas por eutrofiza??o e assoreamento, foram investigadas por meio de uma an?lise de correspond?ncia can?nica. Simula??es de Monte Carlo utilizando os autovalores da CCA como estat?sticas teste revelaram que as mudan?as na composi??o de esp?cies zooplanct?nicas ao longo dos gradientes ambientais de estado tr?fico e turbidez abiog?nica foram altamente significativas. As esp?cies Brachionus calyciflorus, Thermocyclops sp. e Argyrodiaptomus sp. foram boas indicadoras de condi??es eutr?ficas enquanto que as esp?cies Brachionus dolabratus, Keratella tropica e Hexarthra sp. foram boas indicadoras de elevada turbidez por sedimentos em suspens?o. O g?nero de rot?feros Brachionus foi o mais rico em esp?cies, compreendendo cinco esp?cies que estiveram associadas a diferentes condi??es ambientais. Portanto, n?s testamos se esse g?nero sozinho poderia ser potencialmente um melhor indicador biol?gico desses gradientes ambientais do que toda a assembl?ia zooplanct?nica ou qualquer outro conjunto aleat?rio de cinco esp?cies. Os resultados da ordena??o demonstram que as cinco esp?cies de Brachionus quando sozinhas n?o explicaram melhor os padr?es observados de varia??o ambiental que a maioria dos conjuntos aleat?rios de cinco esp?cies. Portanto, este g?nero n?o pode ser selecionado como um t?xon alvo para um monitoramento ambiental mais intensivo conforme previamente sugerido por Attayde e Bozelli (1998). De um modo geral, nossos resultados mostram que mudan?as na qualidade da ?gua de reservat?rios em uma regi?o semi-?rida tropical t?m efeitos significativos sobre a estrutura das assembl?ias zooplanct?nicas, os quais podem afetar potencialmente o funcionamento desses ecossistemas
114

Road Salt Runoff into Freshwater Wetlands: Trends in SpecificConductance and Ion Concentration

Weatherholt, Riley Madison 29 May 2019 (has links)
No description available.
115

Water-borne geophysics for Murray River salt-load detection

Barrett, Brian Edward. January 2003 (has links) (PDF)
Includes bibliographical references (leaves 112-115) Towed DC Resistivity and Transient Electromagnetic arrays have been trialled for suitability in monitoring salt-loads on the Murray River at Waikerie, South Australia.
116

Growing mallee eucalypts as short-rotation tree crops in the semi-arid wheatbelt of Western Australia

Wildy, Daniel Thomas January 2004 (has links)
[Truncated abstract] Insufficient water use by annual crop and pasture species leading to costly rises in saline watertables has prompted research into potentially profitable deep-rooted perennial species in the Western Australian wheatbelt. Native mallee eucalypts are currently being developed as a short-rotation coppice crop for production of leaf oils, activated carbon and bio-electricity for low rainfall areas (300—450 mm) too dry for many of the traditional timber and forage species. The research in this study was aimed at developing a knowledge base necessary to grow and manage coppiced mallee eucalypts for both high productivity and salinity control. This firstly necessitated identification of suitable species, climatic and site requirements favourable to rapid growth, and understanding of factors likely to affect yield of the desirable leaf oil constituent, 1,8-cineole. This was undertaken using nine mallee taxa at twelve sites with two harvest regimes. E. kochii subsp. plenissima emerged as showing promise in the central and northern wheatbelt, particularly at a deep acid sand site (Gn 2.61; Northcote, 1979), so further studies focussed on physiology of its resprouting, water use and water-use efficiency at a similar site near Kalannie. Young E. kochii trees were well equipped with large numbers of meristematic foci and adequate root starch reserves to endure repeated shoot removal. The cutting season and interval between cuts were then demonstrated to have a strong influence on productivity, since first-year coppice growth was slow and root systems appeared to cease in secondary growth during the first 1.5—2.5 years after cutting. After decapitation, trees altered their physiology to promote rapid replacement of shoots. Compared to uncut trees, leaves of coppices were formed with a low carbon content per unit area, and showed high stomatal conductance accompanied by high leaf photosynthetic rates. Whole-plant water use efficiency of coppiced trees was unusually high due to their fast relative growth rates associated with preferential investments of photosynthates into regenerating canopies rather than roots. Despite relatively small leaf areas on coppice shoots over the two years following decapitation, high leaf transpiration rates resulted in coppices using water at rates far in excess of that falling as rain on the tree belt area. Water budgets showed that 20 % of the study paddock would have been needed as 0—2 year coppices in 5 m wide twin-row belts in order to maintain hydrological balance over the study period. Maximum water use occurred where uncut trees were accessing a fresh perched aquifer, but where this was not present water budgets still showed transpiration of uncut trees occurring at rates equivalent to 3—4 times rainfall incident on the tree belt canopy. In this scenario, only 10 % of the paddock surface would have been required under 5 m wide tree belts to restore hydrological balance, but competition losses in adjacent pasture would have been greater
117

Vulnérabilité des ressources en eau souterraine : origines de la salinité en domaine karstique côtier et de la contamination après-mine en métaux lourds. Approche par multitracage géochimique / Groundwater resources vulnerability : origins of salinity in coastal karst groundwater, contamination by heavy metals in post closure mine : multiple tracers, geochemical approach

Khaska, Mahmoud 03 December 2013 (has links)
La premier thématique a pour objectifs :1) de tracer l’origine de la salinité des eaux des aquifères karstiques en milieu côtier méditerranéen,2) de quantifier les proportions de mélange entre les eaux salées et les eaux karstiques,3) de discriminer les traceurs géochimiques pour identifier et modéliser les processus de salinisation d’aquifères karstiques côtiers. La seconde thématique a pour objectifs:1) d’établir les [As] d’origine naturelle des eaux de surface et des eaux souterraines, 2) de quantifier le niveau de contamination en arsenic de ces eaux et sa variabilité spatio-temporelle 3) de tracer l’origine naturelle ou anthropique de la pollution en As à l’aide d’outils isotopiques adaptés. les origines de la salinité identifié inclue i) des venues d’eaux profondes salées ii) des venues profondes d’eau salées remontant vers la surface par une faille majeure normale. Le 36Cl/Cl a permis d’identifier l’origine profonde des eaux salées et une recharge d’eau météorique infiltrée lors de la période des essais thermonucléaires. La modélisation PHREEQC permet de différentier le mélange avec une eau profonde salée de celui avec une eau de mer actuelle. Le 87Sr/86Sr montre un comportement conservatif pour tracer l’origine des eaux salées dans les aquifères karstiques. Les traceurs Cs, Rb, Li et B permettent de différentier les trois origines identifiées de la salinité. Les données acquises sur la contamination en As soulignent une augmentation nette et pérenne des [As] à partir des anciens sites de traitement minier réhabilités. Les rapports 87Sr/86Sr et δ18O et δ2H se révèlent dans ce cas un traceur très discriminant de l’origine naturelle ou anthropique de l’arsenic. / The first theme has for objectives: 1) to trace the origin of the salinity of the waters of the karst aquifers in coastal environment mediterraneen,2) to quantify the mixing proportions between salt waters and the waters karstiques,3) to discriminate the geochemical tracers to identify and model the process of salinization of aquifers coastal karst. The second theme has for objectives:1) to establish the [hast] of natural origin of surface waters and groundwater, 2) to quantify the level of contamination by arsenic in these waters and its spatial and temporal variability 3) to trace the natural or anthropogenic origin of pollution in hast to the aid of isotopic tools adapted. the origins of the salinity identified include i) of came from deep waters salted ii) of come deep water salted dating back toward the surface by a major flaw normal. The 36Cl/Cl has allowed us to identify the origin of deep saline waters and a recharge of meteoric water infiltrated during the period of thermonuclear tests. The PHREEQC modeling used to differentiate between the mixture with a deep water of salt that one with a sea water current. The 87SR/ 86Sr shows a conservative behavior for tracing the origin of saline waters in karst aquifers. The plotters Cs, Rb, Li and B allows to differentiate the three origins identified of salinity. The data acquired on the contamination in hast underline a net increase and perennial of [hast] from the ancient sites of mining processing rehabilitated. The reports 87SR/ 86Sr and δ18O and δ2H will reveal in this case a chartplotter very discriminant of natural or anthropogenic origin of arsenic.
118

Effekte von abwasserinduzierten Ionenimbalanzen auf die Reproduktion von Fischen am Beispiel von Danio rerio

Wagler, Marit 04 August 2020 (has links)
Die salzhaltigen Abwässer des Kalibergbaues führen in natürlichen Süßwassersystemen zu Ionenimbalanzen und einer sekundären Versalzung der Werra in Deutschland. Die Auswirkungen dieser Ionenungleichgewichte auf die Reproduktion von Süßwasserfischen wurden unter Verwendung der Modellfischart Danio rerio untersucht. Angepasst an die aktuellen Grenzwerte für die Einleitung der Abwässer aus dem Kalibergbau wurden fünf verschiedene Kombinationen erhöhter Ionenkonzentrationen getestet. Während eines partiellen Lebenszyklustests wurden adulte Fische 35 Tage lang in den Salzkombinationen exponiert. Anschließend wurden die Nachkommen dieser Fische bis zum 8. Tag nach der Befruchtung den gleichen Salzkonzentrationen ausgesetzt. Zusätzlich wurden Early-Life-Stage-Tests (ELST) mit den Nachkommen von nicht exponierten Eltern durchgeführt. Im Vergleich zu natürlich vorkommenden Ionenkonzentrationen und -verhältnissen in Süßwassersystemen war die Befruchtungsrate der Eier für alle Ionenkombinationen signifikant niedriger, die Koagulations- und Deformationsrate jedoch signifikant höher. Die ELST ergaben bei den Embryonen und Larven u.a. vorzeitige und verlängerte Schlupfzeiten, verringerte Überlebensraten, erhöhte Deformationsraten und Herzschlagfrequenzen sowie Unregelmäßigkeiten des Ganzkörpergehalts von K, Mg, Na und Ca und des Ganzkörper-Ionenverhältnisses von Ca:Mg bei erhöhten Ionenkonzentrationen und Ionenimbalanzen. Im Vergleich zu den Effekten auf die Fortpflanzung und Entwicklung der Nachkommen waren die Effekte auf die adulten Tiere moderat. Die Ergebnisse dieser Dissertation zeigen, dass Teillebenszyklus-Tests besser als Fischeitests oder ELST geeignet sind, die Effekte von durch Abwasser verursachten Ionenimbalanzen, auf die Fortpflanzung und frühe Entwicklung von Süßwasserfischen, zu untersuchen. Weder die momentan gültigen noch die zukünftig herabgesetzten Grenzwerte bis 2027 sind danach als unschädlich, für die Reproduktion von Süßwasserfischen, zu betrachten. / The potash mining industry discharges saline effluents which generate ion imbalances in natural freshwater systems and cause severe secondary salinization in the river Werra in Germany. The effects of these ion imbalances on reproduction of freshwater fish were investigated using the fish model species Danio rerio. Five different combinations of elevated ion concentrations adjusted to the current threshold values for the discharge of potash mining effluents in Germany were tested. During a partial life cycle test, adult fish were exposed to the salt combinations for 35 days. Subsequently, the offspring were exposed to the same concentrations until hatch, and the larvae were further reared at the exposure concentrations from hatch until the 8th day post fertilization. Additionally, a standard early life stage test with offspring from unexposed parents was performed. Compared to naturally occurring ion concentrations and ratios in freshwater systems, the fertilization rate of the eggs was significantly lower for all ion combinations, while coagulation and deformation rates were significantly higher. Early life stage tests on embryos and larvae revealed premature and prolonged hatching times, reduced survival rates, increased deformation and heart rates and irregularities in whole body content of K, Mg, Na and Ca and whole body Ca:Mg ratios at elevated ion concentrations and imbalances of ion ratios. Compared to effects on reproduction and development of the offspring, effects on the parental generation were moderate. The results of this dissertation indicate that partial life cycle tests instead of fish egg tests or ELST are needed to examine most sensitively the effects of ion imbalances caused by potash mining effluents on reproduction and early development of freshwater fish. Neither the recent German threshold values nor the future reduced values until 2027 are safe for the reproduction of freshwater fish.
119

Identificação de possíveis áreas afetadas por sais no Perímetro Irrigado de São Gonçalo por meio do sensoriamento remoto. / Identification of possible areas affected by salts in the Irrigated Perimeter of São Gonçalo through remote sensing

OLIVEIRA, Woslley Sidney Nogueira de. 10 May 2018 (has links)
Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-05-10T18:06:15Z No. of bitstreams: 1 WOSLLEY SIDNEY NOGUEIRA DE OLIVEIRA - DISSERTAÇÃO PPGSA ACADÊMICO 2018..pdf: 7059892 bytes, checksum: 1ab51771320e5bbd6c88d3c01b4b7aeb (MD5) / Made available in DSpace on 2018-05-10T18:06:15Z (GMT). No. of bitstreams: 1 WOSLLEY SIDNEY NOGUEIRA DE OLIVEIRA - DISSERTAÇÃO PPGSA ACADÊMICO 2018..pdf: 7059892 bytes, checksum: 1ab51771320e5bbd6c88d3c01b4b7aeb (MD5) Previous issue date: 2018-02-22 / Os perímetros irrigados implantados no Estado da Paraíba são considerados uma alternativa econômica bastante rentável, promove a geração de empregos e aumenta a disponibilidade de alimentos. Devido ao manejo inadequado do solo e da água, isso têm causado perdas na qualidade do solo desses perímetros, degradando-os principalmente por salinização. O sensoriamento remoto é uma alternativa tecnológica de baixo custo, boa frequência temporal e possui a capacidade de mapear áreas em processo de desertificação. Essa pesquisa têm por objetivo identificar possíveis áreas afetadas por sais no Perímetro Irrigado de São Gonçalo (PISG), Sousa- PB, por meio de técnicas de sensoriamento remoto. Para esse estudo foi utilizado imagens do satélite LANDSAT 8/OLI (média resolução espacial), órbita 216 / ponto 65 da data de 23/11/2016; imagem do software Google Earth Pro® da data de 29/02/2016 para servir como imagem auxiliar e registros fotográficos das áreas in loco. Realizou-se a técnica de classificação supervisionada, utilizando o SCP (semi- automatic plugin) no software QGIS (Quantum Gis). A aferição da qualidade da classificação se deu por meio da validação cruzada, utilizando de parâmetros estatísticos como a exatidão do produtor (EP), exatidão do usuário (EU), exatidão global (EG) e índice Kappa. A classe área supostamente salinizada (ASS) apresentou EP e EU de 89.15% e 88.88%, respectivamente. O índice Kappa resultou em um valor de 0.8684, a classe ASS foi classificada como sendo de qualidade excelente. A qualidade geral da classificação é avaliada tanto pela EG que apresentou um valor de 0.9350 como pelo índice Kappa geral com valor de 0.9252, sendo valores que representam uma classificação de qualidade excelente. A classe ASS apresentou os maiores valores mínimos e máximos de fator de refletância em todas as bandas da imagem, destacando a banda 6 de valores 0.47 e 0.67, respectivamente. O valor da área classificada como sendo da classe ASS foi de 1736.75 hectares, 31% da área total do PISG. As imagens analisadas possibilitaram discriminar áreas salinizadas e não salinizadas mediante as diferenças de tonalidade e de refletância. As imagens analisadas com o plugin SCP possibilitaram a realização de um mapa de classificação supervisionada, indicando a variabilidade espacial das áreas propícias ao processo de salinização. No entanto, recomenda- se a análise dos parâmetros físicos e químicos do solo dessas áreas para o aumento da confiabilidade na qualidade desse tipo de mapeamento. / The irrigated perimeters implemented in the State of Paraiba are considered a costeffective alternative quite profitable, promotes the generation of jobs and increases the availability of food. Due to inadequate management of soil and water, that have caused losses in soil quality of these perimeters, degrading them mainly by salinization. Remote sensing is an alternative low-cost technology, good temporal and frequency has the ability to map areas in process of desertification. This research aim to identify potential areas affected by salts in the irrigated perimeter of São Gonçalo (PISG), Sousa-PB, through remote sensing techniques. For this study we used LANDSAT satellite images 8/OLI (average spatial resolution), 216/orbit point 65 of 07/11/2016 date; image of the Google Earth Pro software® from date of 29/02/2016 to serve as auxiliary image and photographic records of the areas on the spot. The supervised classification technique, using the SCP (semi-automatic plugin) in software QGIS (Quantum Gis). The measurement of the quality of the classification took place by means of cross-validation, using statistical parameters such as the accuracy of the producer (EP), accuracy of the user (EU), global (EG) accuracy and Kappa index. The area class supposedly salinated (.ASS) presented EP and I of 89.15% and 88.88%, respectively. The Kappa index resulted in a value of .ASS class 0.8684 was classified as being of excellent quality. The overall quality of the classification is assessed both by EG who presented a 0.9350 value as the Kappa index 0.9252 valued General, being values that represent a rating of excellent quality. The class ASS presented the largest minimum and maximum values of reflectance factor in all the bands in the image, highlighting the band 6 0.47 values and 0.67, respectively. The value of the area classified as being of .ASS class was 1736.75 acres, 31% of the total area of the PISG. The images reviewed discriminate salinated areas and not allowed saline through the variations of shade and reflectance. The images analyzed with the SCP plugin enabled the creation of a map of supervised classification, indicating the spatial variability of the areas prone to salinization process. However, it is recommended that the analysis of the physical and chemical soil parameters of these areas for increased reliability in the quality of this type of mapping.

Page generated in 0.1374 seconds