• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1532
  • 776
  • 181
  • 48
  • 26
  • 23
  • 20
  • 18
  • 17
  • 17
  • 17
  • 17
  • 17
  • 17
  • 14
  • Tagged with
  • 3429
  • 3429
  • 770
  • 734
  • 705
  • 651
  • 415
  • 386
  • 279
  • 260
  • 253
  • 231
  • 218
  • 210
  • 206
  • 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.
461

The use of selected freshwater gastropods as biomonitors to assess water quality

Moolman, Liesel 14 October 2008 (has links)
M.Sc. / The health of aquatic ecosystems can be severely compromised by a variety of pollutants, such as heavy metals, which are related to anthropogenic activities. Increased recognition is given to the use of organisms, especially molluscs, in the biomonitoring of aquatic ecosystems. This promising approach complements the interpretation of the physico-chemical measurements of water quality. The bioaccumulation of pollutants as well as the resultant biological responses (biomarkers) in organisms can be used in assessing the spatial and temporal trends of chronically polluted environments. The aim of this study was to determine if selected freshwater gastropods (Melanoides tuberculata, Physa acuta, Helisoma duryi and Lymnaea columella) can be used as suitable biomonitors or indicators of water quality. Interspecies differences in metal bioaccumulation and biomarker responses were determined in order to select the most suitable biomonitor/indicator organism to be used. The bioaccumulation of metals was related to the biomarker responses of the organisms. This study was divided into an active biomonitoring (ABM) study and a laboratory exposure study. In the first study, the organisms, M. tuberculata and L. columella were chronically (two, four and six week period) exposed to field conditions. Metal bioaccumulation as well as the biomarker techniques, DNA damage, catalase (CAT) activity, reduced glutathione (GSH) content and cellular energy allocation (CEA) were measured in the organisms. These general biomarkers of exposure and effect, on the biochemical and cellular levels of biological organisation can give a rapid and sensitive assessment of organism health. The second study consisted of exposing the gastropods, M. tuberculata, P. acuta, H. duryi and L. columella to sub-lethal zinc and cadmium concentrations. The uptake and depuration kinetics of these metals were determined in M. tuberculata and H. duryi for a six hour and 48 hour period, respectively. The bioaccumulation of Zn and Cd as well as the biomarkers, DNA damage, CAT activity, GSH content and CEA were measured in all the species, after a two week exposure period. / Prof. J.H.J. van Vuren
462

Perceptions of residents of Hartenbos regarding the status of the water quality of the Hartenbos River

Terblanche, Juan 25 August 2008 (has links)
Having a perception about the water quality of a river can determine its usefulness, as a supply of water and also for recreational purposes. If it is determined that the river water is in a poor state, then it can have an impact on the community’s health, the economy of a settlement, as well as the natural environment along the course of the river. The main aim of this research is to determine what the community of Hartenbos’ opinion is concerning the water quality of the Hartenbos River and what is the true state of the water quality of the Hartenbos River? This could seem as a positive or negative influence on sustainable development and environmental conservation. The town of Hartenbos and the Hartenbos River is situated on the Southern Cape Coast in the Western Cape Province. A questionnaire survey, employing a stratified random sample method, is conducted during the month of April 2005. The Department of Water Affairs and Forestry (Belville) obtain water quality variables from nine sampling points. The results are analysed for a ten-year period (1994-2004) by STATKON, an independent statistical consultant based at the University of Johannesburg (Kingsway Campus). Analysis methods include a repeated measure of variance (ANOVA) and the Wilcoxon Signed Rank Test. These results are compared with the South African Water Quality Guidelines for domestic, recreational and agricultural (irrigation and livestock watering) use. The results show that the state of the water quality of the Hartenbos River is in a good condition and thus acceptable within the modern urban environment. The researched population mainly disagrees with this statement. According to the opinion of the research population, the water quality is in a poor condition, thus unacceptable within the modern urban environment. According to them, human activities within the river and its catchment and poor management are to be blamed. Although the opinion of the research population is genuine and rightful, the opinion is overruled by the water quality results. Economic development such as tourism and residential development will improve the local economy. The local community’s opinion can alter new developments because of their perception regarding the water quality of the Hartenbos River. How the local community’s opinion compare with actual scientific information, will determine its value or correctness and thus, the positive or negative impact on economic development. The state of water quality and the ecosystem must be maintained. An appropriate environmental management plan and enforcement of existing laws will ensure harmony between any existing or future economic development and the conservation of the Hartenbos River. The Hartenbos River with all its functional and aesthetic properties has to be conserved for generations to come. / Dr. P.J. Wolfaardt
463

A study of water quality relationships in the Brunette River Basin

McNeill, Brenda Elizabeth January 1978 (has links)
The quality of surface runoff in an urbanized watershed was studied in order to determine the effects of land use and hydrologic conditions. Sampling sites were established so as to be representative of varying land uses and were monitored over a six month period so as to reflect changing flow conditions . Twelve sites, sampled weekly, were established in the Brunette River Basin, an urban watershed located in the Lower Mainland of British Columbia. Water samples, taken at each site, were analyzed for nineteen water quality parameters. Information relating to the hydrology and land uses of the basin was taken from established sources. Multiple regression and analysis of variance techniques were used to relate the land use and hydrology of the basin to the water quality. Total phosphorus, suspended solids and turbity concentrations were directly related to the percentage open space. Specific conductance and the nitrogen compounds were directly related to the percentage residential land. Eight parameters, but particularly turbidity and suspended solids, were dependent on stream discharge. The sensitivity of the data varied from site to site depending on the characteristics of the contributing areas. Discussion was directed toward the spatial and temporal nature of the data, the variance in the data, and the associated problems of scale. / Arts, Faculty of / Geography, Department of / Graduate
464

Determinação química e biológica de carga poluente em lagoa do município de Parintins no Estado do Amazonas / Chemical and biological determination of pollution burden in lagoon from the Parintins municipality in state of Amazon

Kimura, Solenise Pinto Rodrigues, 1970- 12 November 2014 (has links)
Orientadores: Melissa Gurgel Adeodato Vieira, Domitila Pascoaloto / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-26T10:26:16Z (GMT). No. of bitstreams: 1 Kimura_SolenisePintoRodrigues_D.pdf: 5566316 bytes, checksum: 8d96b931971d41f62348a0fad4be21f2 (MD5) Previous issue date: 2014 / Resumo: Os recursos hídricos são sistemas dinâmicos que fazem parte do ciclo de sobrevivência de todos os seres vivos, a sua conservação se faz necessária através do controle de qualidade de suas águas. A lagoa da Francesa, localizada na cidade de Parintins/AM, recebe resíduos domésticos e industriais, cuja composição variada vem modificando as características naturais de suas águas. O local de estudo apresenta naturalmente variação no volume de água em determinados períodos do ano. Este trabalho teve como objetivo a identificação e a avaliação das causas de alterações na qualidade da água e de sedimentos da lagoa da Francesa (Parintins/AM), envolvendo o reconhecimento das características locais que possam ter relação com as fontes de poluição responsáveis pela contaminação do corpo hídrico comparando os principais parâmetros de qualidade da água aos limites legais ambientais. Para isso, foram coletadas amostras de água e de sedimento em nove pontos distintos na extensão da lagoa nos meses de março, julho e setembro de 2012 e 2013, período compreendido entre o nível baixo e alto de água da lagoa, respectivamente (período de sazonalidade que é influenciado pelo regime hidrológico do rio Amazonas) e analisados para água os parâmetros físico-químicos e biológicos: temperatura, pH, condutividade, oxigênio dissolvido, turbidez, DBO (Demanda Bioquímica do Oxigênio), DQO (Demanda Química de Oxigênio), COT (carbono orgânico total), clorofila a, coliformes totais e fecais, amônia, nitrito, nitrato, fósforo e nitrogênio total, fosfato, os metais pesados (Cd, Pb, Cu, Ni, Zn e Cr), os elementos ferro total e dissolvido e manganês. Os valores obtidos nos anos foram comparados com intuito de identificar e avaliar as variáveis que afetam a qualidade da água, considerando a variação do regime hidrológico, tendo como padrão de referência os valores legais estabelecidos pela Resolução CONAMA 357/05 para águas de classe 2. Para o sedimento foram avaliadas as variáveis: granulometria, carbono, nitrogênio fósforo, matéria orgânica e os metais (Cd, Pb, Cu, Ni, Zn e Cr), além do ferro e manganês e comparados aos limites legais estabelecidos pela resolução CONAMA 344/04. Os resultados indicam fontes antrópicas que são evidenciadas pelos parâmetros fósforo total, nitrogênio, baixos valores de oxigênio dissolvido e de DBO, condutividade elétrica e altos valores de coliformes totais e fecais na área da lagoa de Francesa, bem como a presença de metais pesados na água e no sedimento. Essa condição é mais acentuada no período de águas baixas, indicando que o regime hidrológico influencia diretamente na qualidade da água da lagoa. Em julho (período de águas altas), a lagoa apresentou capacidade de diluição para alguns parâmetros, que foi evidenciada através da redução de suas concentrações. Foram também identificadas espécies de macrófitas no decorrer do estudo visando à obtenção de um possível bioindicador de qualidade da água. As espécies Eichhornia crassipee e Paspalun repens tiveram maior predominância e são tidas como boas adsorventes de metais pesados. O estudo mostrou que, apesar da contribuição antrópica, a lagoa mantém, ainda, sua capacidade de diluir para a maioria dos constituintes poluentes, principalmente no período de maior volume de água (enchente). Porém, pode-se verificar a necessidade da adoção de medidas preventivas em curto prazo, em função do possível crescimento populacional e suas demandas por produtos e serviços associados / Abstract: Water resources are dynamic systems that are part of the survival of all living beings cycle; its preservation is required by quality control of its waters. The lagoon's volume of water depends on the month. In this work our goal is identify and assess the causes of changes in water quality and sediments of the Lagoa da Francesa (Parintins / AM), involving the recognition of local features that may be related to pollution sources responsible for pollution of the water body in comparing the key parameters of water quality to environmental legal limits. Then, water and sediment samples were taken at nine different points in the extension of the pond during the months of March, July and September 2012 and 2013, the period between the low and high levels, respectively (period of seasonal water level of the pond which is influenced by the regime hydrology of the Amazon river). For water samples we analyzed physico-chemical and biological parameters: temperature, pH, conductivity, dissolved oxygen, turbidity, BOD (Biochemical oxygen Demand), COD (chemical Oxygen Demand), TOC (total organic carbon) , chlorophyll a, total and fecal coliform, ammonia, nitrite, nitrate, phosphorus and total nitrogen, phosphate, heavy metals (Cd, Pb, Cu, Ni, Zn and Cr), the total and dissolved manganese and iron elements. The values obtained were compared with years in order to identify and evaluate the variables that affect water quality, considering the variation of the hydrological regime, taking as reference standard legal values established by CONAMA Resolution 357/05 for Class 2 water. For sediment samples we evaluated the following parameters: particle size, carbon, nitrogen, phosphorus, organic matter and metals (Cd, Pb, Cu, Ni, Zn and Cr), in addition to iron and manganese, and we purchased with the legal limits established by CONAMA Resolution 344 / 04. The results indicate that anthropogenic sources is evidenced by the parameters total phosphorus, nitrogen, low values of dissolved oxygen and BOD, electrical conductivity and high values of total and fecal coliforms in the lagoon area of French, as well as the presence of heavy metals in water and in sediment. This condition is more pronounced in low water period indicating that the hydrological regime directly influences the quality of the pond water. In July (during high water level), the pond showed the capacity of dilution for some parameters, which was evidenced by the reduction of their concentrations. Macrophytes were identified during the study, as a possible biological indicator of water quality. Species Eichhornia crassipee and Paspalun repens had higher prevalence and are seen as good bioadsorbents of heavy metals. The study showed that despite the anthropogenic contribution, the lagoon still maintains its ability to dilute constituents for most pollutants, especially during larger volume of water (flooding). However, there is a need for adopting preventive measures in the short term, due to the possible population growth and demands for their products and associated services / Doutorado / Engenharia Química / Doutora em Engenharia Quimica
465

Assessment of raw and treated sewage using in vitro assays

Booysen, Robin Alvin January 2014 (has links)
>Magister Scientiae - MSc / Water scarcity is becoming an increasingly relevant problem for urban centres, especially in Southern Africa. However, water availability is not the only concern for consumers, because water quality is just as relevant. Many studies have revealed adverse health effects in organisms exposed to polluted waters, and the main source of that water pollution was traced back to sewage treatment works (STWs). Physiological systems that are affected include the endocrine system (as well as the reproductive system) and the immune system. Recently, the Stellenbosch STW started upgrading its facility, but this procedure would also affect the STW‘s operations. Stellenbosch STW uses an activated sludge treatment, but also employs trickling filters (biofilters). After screening and grit removal, wastewater enters trickling filters, and then undergoes activated sludge treatment (aerobic basin). After activated sludge treatment (and settling) some water is chlorinated before entering a maturation pond. The other water goes directly to a larger maturation pond (for a longer period), instead. The final effluent then gets discharged into the Veldwagters River. Since STW operations is an important factor in STW effluent quality, this study aimed to investigate the water quality (at Stellenbosch STW) during the upgrade. Specifically, the bacterial quality, the steroidal quality (testosterone, progesterone, estrone: E1, 17 β- estradiol: E2 and 17 α-ethinyl estradiol: EE2) and the potential immunotoxic quality of waters were assessed. Water samples were collected after the grit removal (influent), after the trickling filters (biofilter effluent), while it was leaving the aerobic basin activated sludge effluent) and as it was leaving the maturation ponds (final effluent). To determine bacterial quality a semi-quantitative ReadyCult® assay was performed on raw water samples (detects total coliforms and Escherichia coli). Bacterial levels were high for all influent samples, water from the biofilter, water from the aerobic digester (activated sludge) and the final effluent (most days). The first collection date, however, showed less than 1cfu/mL of both E. coli and total coliforms for the final effluent. Raw water also underwent solid phase extraction, before the steroid concentrations were determined by enzyme-linked immunosorbent assays (ELISAs). Steroid levels were very high in the influent. Each treatment progressively reduced the steroid concentration. However, progesterone concentration increased during the biofilter treatment. The increase in progesterone was probably due to bacterial de-conjugation of hydrophilic-progesterone-conjugates. Nonetheless effluent steroid levels were significantly lower than the influent. Steroid reduction through the Stellenbosch STW was 96%, 95%, 55%, 78% and 87% for testosterone, progesterone, estrone, estradiol and ethinyl estradiol respectively. Much variability in steroid concentrations was noted between sampling dates. The activated sludge treatment was the best at reducing steroid concentration. Nonetheless, the STW still discharged steroids into the environment. Finally, the humoral immune effects of Stellenbosch STW influent and effluent was determined by using hybridoma cells and assessing affects on antibody production. Antibody levels were then detected by ELISA. No adverse effects to antibody synthesis/secretion were noted as a result of exposure to either influent or effluent.
466

Application of system dynamics modeling techniques to an existing stream water quality model

Finley, Allan Michael 16 February 2010 (has links)
<p>From the results of this project and report the following conclusions seem warranted:</p> <p> 1. The actual behavior of any real stream system, subject to a point load, is dependent on an extremely complex and integrated network of events which can occur in series or parallel.</p> <p> 2. The QUAL2E model considers the major events or cycles of a stream system in a fully integrated manner, offers the user many configuration options, and provides for a wealth of essential output data. The documentation provides reasonable explanation as to the means by which the model simulates a stream system. The QUAL2E model can be executed successfully by the first time user with minimal effort.</p> <p> 3. The DYNAMO model can be effectively invoked through the use of differential equations that can be translated into suitable DYNAMO expressions. The model is easy to learn and can be executed by the first time user with minimal effort.</p> <p> 4. Input parameters and initial conditions for the both the QUAL2E and DYNAMO models were reasonable for the purpose intended. That being the comparison of the behavior of the two systems.</p> / Master of Engineering
467

Impact of rainfall events on suspended sediment load and water quality and links to sediment management in Dzindi River Catchment

Nemapate, Muthuhadini 18 September 2017 (has links)
MESHWR / Department of Hydrology and Water Resources Management / This research was aimed at determining the impact of rainfall events on suspended sediment concentration (SSC) and water quality and links to sediment management in Dzindi River Catchment, Limpopo Province. Rainfall events of different magnitudes and duration erode different sediment volumes resulting in significant variation in sediment loads of receiving water bodies. This affects the water quality of such water bodies. Water samples for water quality and suspended sediment measurements were collected after each rainfall event for periods of six and five months, respectively, in two consecutive rainy seasons. The periods were from October 2012 to March 2013 and December 2013 to April 2014. The samples were collected from selected cross-sections at four sites along Dzindi River. Physical water quality parameters or water quality indicators (pH, Electrical conductivity (EC) and turbidity) were measured with multi 340i/set multimeter and Orion Aqua Fast II turbidity meter, as they are the indicators of the overall status of the water quality. Suspended sediment concentration (SSC) for each sample was measured using evaporation method. SSC at each cross section was computed using the mean discharge-weighted formula. Field survey was undertaken to identify land use activities that promote erosion and hence sedimentation. The relationship between SSC and rainfall magnitude was determined using sediment rating curves. Water quality and sedimentation status at each cross-section together with the information from the GIS map aided in identifying and recommending the best sediment management strategies for different sites in the study area. pH values for October 2012 to March 2013 and December 2013 to April 2014 were both higher in the downstream site of the river catchment, which is Manamani site. Lowest pH was found in the upstream and mid-stream sites, which were Dzindi water treatment works (DWTW) and Tshisaulu, respectively. Tshisaulu had highest EC value and Lwandani had lowest value, respectively, for the period of October 2012 to March 2013. DWTW had the highest EC value and Tshisaulu had the lowest EC value, respectively, for the period of December 2013 to April 2014. Manamani had high turbidity value and Lwandani had low turbidity value for October 2012 to March 2013. Turbidity for DWTW for the period of December 2013 to April 2014 was the highest and Tshisaulu had the lowest turbidity value. Sediment rating curves for DWTW, Tshisaulu and Manamani, respectively, had coefficient of determination (R2) values of 0.185, 0.53 and 0.99, respectively. Different sediment management strategies, including slope and bank protection and minimum and mulch tillage, were recommended based on topography and land use activities and these strategies can prevent soil erosion and minimize transport of sediments into the river.
468

Impact of Animal Waste Best Management Practices on the Bacteriological Quality of Surface Water

Cook, Mary Nicole Jr. 12 June 1998 (has links)
An extensive 10 year monitoring project was initiated in 1986 to examine the effects of a combination of BMPs on surface water quality within a watershed with complex land use. This research specifically examined bacteriological water quality and BMP impacts. Bimonthly grab samples were collected from four surface water monitoring stations, including the watershed outlet, and analyzed for fecal coliform, total coliform, and fecal streptococcus bacteria. Other data compiled from the watershed included hydrologic, meteorologic, geologic and land use data, also collected on a regular basis. Data were collected continuously throughout the project, and thus included both pre- and post-BMP monitoring data. BMP implementation included animal waste storage facilities, nutrient management plans, conservation tillage, alternative water sources for livestock, fences, vegetative filter strips, runoff diversions, and others. Statistical analysis of the monthly precipitation data indicated no significant difference in rainfall quantity between the pre-BMP and post-BMP monitoring periods. Monthly runoff totals increased 39% from the pre- to the post-BMP periods at the watershed outlet. Increases at all of the subwatershed outlets occurred as well (B, 40%; C, 38%; D, 16%). Statistical analysis did not show a significant difference in runoff between the two monitoring periods, except at station C, where post-BMP runoff was significantly greater than the values measured during the pre-BMP period. Overall reductions in the mean (geometric) levels of total coliform, fecal coliform and fecal streptococcus bacteria observed at the watershed outlet were 81%, 30% and 76%, respectively. Both parametric and nonparametric statistical analysis techniques were applied to the bacteriological data. Regression analysis of the fecal coliform data showed an increase during the pre-BMP period followed by a decrease post-BMP and a statistically significant difference between the two periods (p=0.004). No trends were evident. Only one of the four stations had a statistical difference between pre- and post-BMP fecal streptococcus data, however, a downward trend was present at every station. No statistically significant difference between the pre- and post-BMP total coliform bacteria was evident, although a downward trend was present at the watershed outlet. These findings indicate that the combination of BMPs implemented in the watershed were effective in reducing the loss of fecal bacteria to receiving streams via overland flow. / Master of Science
469

The Role of Eutrophication and Sediment Phosphorus Saturation in the Formation of Harmful Cyanobacterial Blooms

Young, Taylor January 2020 (has links)
Harmful cyanobacterial blooms have been a growing concern as global climate change and eutrophication of lakes, rivers, and oceans continually push conditions to favor cyanobacteria over other phytoplankton. Two studies were conducted assessing the impacts of hyper-eutrophication on phytoplankton communities, and phosphorous saturation in the sediments. Excess nutrients available to phytoplankton resulted in dominant cyanobacteria, and predictability of growth, by nutrient limitation, becoming drastically diminished. Sediments were observed to be fully phosphorus saturated, preventing the sequestration of excess phosphorus, and providing a consistent source of phosphorus throughout each season. Extreme saturation of nutrients reduces the predictability of systems and perpetuates the cycles of nutrient release, fueled by the growth and decay of harmful cyanobacterial blooms.
470

Development of a Novel Bioassay and Portable Spectrometer to Assess Inorganic Arsenic Bioavailability in the Environment

Pothier, Martin 24 September 2020 (has links)
Arsenic is a notorious poison due to its high toxicity, worldwide distribution, and lack of any taste and colour once dissolved. The abundance of arsenic in Earth’s crust makes that it can naturally find its way into food and drinking water. Rapid and reliable detection of arsenic, directly in the field, is critical to support evidence-based decision-making in choosing irrigation or drinking water sources. Current cost-effective colourimetric techniques are associated with poor accuracy, health risks, and unacceptable levels of false negatives. Arsenic-specific cellular sensors, or biosensors, may present an inexpensive, safe, and renewable alternative, yet they have long been criticized for unsatisfactory sensing performance, and inconsistency of the outcome. This, in addition to the lack of suitable instruments capable of measuring the signals produced by these biosensors, has led to very few solutions reaching market. The goal of my thesis research was to test hypotheses that improve our fundamental understanding of As species biogeochemistry in simple and complex environmental matrices to then develop a new arsenic monitoring interface, one that would be both simple and accessible to the general public. Using a combination of wild-type and mutant strains, I managed to detail both the internal regulation of arsenic, and the external drivers of arsenic bioavailability. I started by designing a defined exposure protocol that achieved, for the first time, equimolar uptake of over 94% of the added As(III) and As(V) into the cells. By developing this control early into my thesis, I then worked to reintroduce commonly found constituents of environmental waters that are thought to impact arsenic uptake. This direct testing approach uncovered fundamentals of environmental arsenic redox chemistry such as As(III) photooxidation in solution, environmental ligand exchanges, and biological transport pathways. Simplifying a complex exposure protocol for use by the general public required automation of the data analysis steps. This consists of several hundred lines of code, capable of analyzing, normalizing and stabilizing biosensor output to improve the consistency and robustness of this system. These algorithms were then integrated into a new arsenic monitoring interface, one that was built and designed specifically for dehydrated biosensors. This portable, low-cost spectrometer achieved a fluorescent detection range that rivals expensive and sophisticated laboratory equipment at a fraction of the price, and without the need for a computer to compile the measurements. In contrast to highly criticized colorimetric techniques, the biosensor exposure protocol exceeds in operational use, reliability and detection limit. At its core, my thesis research provides a new and complete arsenic testing solution, one capable of measuring both As(III) and As(V) at levels relevant to the World Health Organization and Canadian guidelines for arsenic content in water (10 µg/L). It also provides a new method capable of selectively discriminating between arsenic species, thereby providing an inexpensive and high-throughput arsenic speciation method. I hope this work will help kickstart development of a marketable solution that empowers individuals to test and to monitor the quality of their water sources.

Page generated in 0.0879 seconds