Ph.D. Theses

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Agricultural decision-making in Turkey from climate change perspective :|a new road map for the period of 2021-2050
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2020., 2020.) An, Nazan.; Yenigün, Orhan.; Kurnaz, M. Levent.
The expectation that it can affect basic life resources and particularly food security on a global, regional, and local scale with its impact on the ecosystem has made climate change one of the most urgent issues on the global agenda. Extreme weather events due to climate change may degrade food quality, affect access to food and raise food prices, markedly affecting agricultural productivity. Many countries have already been faced the global impacts of climate change, therefore studies on the effects that may occur on ecosystems are of great importance. As one of the regions that may be most affected by climate change, the Mediterranean Basin is at risk in terms of agricultural production due to temperature increases and precipitation regime changes, and what’s more the increase in the frequency and severity of extreme weather events due to climate change. As a country located in the Mediterranean Basin, Turkey may also suffer from climate change. This situation poses a risk in terms of crop production value and export income, particularly for products with high commercial value grown in Turkey. Therefore, the study has focused two crops of the country i.e., hazelnut and grape with the high commercial value. In the first stage, the climate data for different phenological periods and different variables for each crop was obtained from the regional climate model, RegCM4.4 with the MPI-ESM-MR global climate model under the RCP8.5 pessimistic scenario for the baseline of 1991-2012 and the future period of 2021-2050. In the second stage, the change in hazelnut yield was analyzed by statistical approach, panel data method, and the change in grape yield was analyzed using the crop growth simulation model, STICS. At the last stage, how the climate conditions of hazelnut (88 locations) and grapes (96 locations) will change in the future has been examined by using membership function. However, considering the crop production values of these two crops and export revenue contribution to the national economy, the possibility of new locations where these crops may grow in the future has been analyzed in 923 locations throughout Turkey. Accordingly, at this stage of the thesis, climate suitability index was calculated for hazelnut and grape, and climatic suitability conditions were determined according to 5 classification ranges. In brief, it has been observed that climate change may have a negative impact on both hazelnut and grape yields in the future and it is predicted that there may be significant reductions in climatic suitability conditions in the locations where these two crops grow.
An fmri based method for characterizing superficial layer contamination in fnirs signals
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2014., 2014.) Erdoğan, Sinem Burcu.; Akın, Ata.
Functional near infrared spectroscopy (fNIRS) is a method for monitoring cerebral hemodynamics with a wide range of clinical applications. fNIRS signals are contaminated with systemic physiological interferences from both the brain and superficial tissues, resulting in a poor estimation of the task related neuronal activation. In this study, we introduce an extended superficial signal regression (ESSR) method for cancelling physiology-based systemic interference in fNIRS signals. We apply and validate our method on the optically weighted BOLD signals, which are obtained by projecting the fMRI image onto optical measurement space by use of the optical forward problem. The performance of ESSR method in removing physiological artifacts is compared to i) a global signal regression (GSR) method and ii) a superficial signal regression (SSR) method. The retrieved signals from each method are compared with the neural signals that represent the "ground truth" brain activation cleaned from cerebral systemic fluctuations. We report significant improvements in the recovery of task induced neural activation with the ESSR method when compared to the other two methods with higher spatial localization, lower inter-trial variability, and higher contrast-to-noise (CNR) improvement. Our findings suggest that, during a cognitive task i) superficial scalp contribution to fNIRS signals varies significantly among different regions on the forehead and ii) using an average scalp measurement together with a local measure of superficial hemodynamics better accounts for the total systemic interference. We conclude that maximizing the overlap between the optical pathlength of superficial and deeper penetration measurements is of crucial importance for accurate recovery of the evoked hemodynamic response in fNIRS recordings.|Keywords : Hemodynamic response, systemic interference, functional near infrared spectroscopy, magnetic resonance imaging, physiological artifact removal.
An integrated land use-hydrological model for the Bartın spring watershed
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2009., 2009.) Öztürk, Melih.; Copty, Nadim.; Saysel, Ali Kerem.
The Bartın spring watershed located in northwestern Turkey supplies the water needs of the Bartın, Amasra and nkumu city centers. Although the water is presently adequate for the spring, autumn and winter seasons, the city centers suffer water scarcity in summer seasons. It is widely recognized that land use changes have a significant impact on the water budget of a watershed. The purpose of this study is to model the land use and hydrological processes within the Bartın spring watershed and simulate the water yield under different future land use scenarios. For this purpose, a coupled land use-hydrodynamics model was developed. The land use dynamic simulation model was built using STELLA dynamic simulation platform while the MIKE SHE computer program was used to simulate the hydrodynamics of the watershed. The link between the two models is through the Leaf Area Index (LAI) and Root Depth (RD) parameters which are generated in the land use model and supplied to the hydrodynamics model. The dynamic land use model represents several forest stand groups and land use categories with their respective acreages and their conversions. The model was structurally validated and analyzed through a series of sensitivity tests. It was calibrated with respect to the historical geographical data and the calibration results are quite satisfactory. The calibration target for the hydrodynamics model was the river discharge at the downstream end of the watershed, while the calibration parameters were the saturated hydraulic conductivity of the deeper soil, the threshold melting temperature values and the RD value. The optimal simulation produced correlation coefficients, R=0.72 and R2=0.52 with a mean error of 0.01 m3/s. Sensitivity analyses of the hydrodynamics model indicate that it is quite sensitive to the land use type; complete agricultural cover would yield 25- 33% higher discharge compared to a completely forested watershed. The hydrodynamics model is also sensitive to the LAI up to a value of 3 and becomes insensitive for higher values. The model however, is not strongly sensitive to hydraulic conductivity of the saturated zone.
Assessment and in silico modelling of the toxicity of selected emerging pollutants to Chlorella Vulgaris
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2017., 2017.) Tuğcu, Gülçin.; Saçan, Melek Türker.
Release of emerging pollutants such as pesticides, phthalates, and substituted phenols and anilines is detrimental threat for the aquatic environment. Registration, Evaluation, Authorization and Restriction of CHemicals (REACH) regulation requires algal toxicity data for regulatory risk assessment purposes. Quantitative Structure–Toxicity Relationships (QSTRs) are well accepted tools for data gap-filling. Therefore, studying the toxic effects of chemicals on algae via experimental and in silico methods would provide invaluable information for the chemicals with no toxicity data; and the knowledge gained through this study forms a scientific basis towards the protection of aquatic ecosystems. In the present study, the 96-h algal toxicity tests were performed with nitro-, chloro-, methoxy-, and methyl- substituted phenols and anilines to Chlorella vulgaris. Merging these data with the previously reported toxicity data of our laboratory enabled a high quality single source algal toxicity data for toxicity modeling. Consequently, models for the prediction of acute toxicity and low-toxic-effect concentrations were developed and verified based on the principles of OECD. Interspecies models were also developed using algae-algae and algae ciliate toxicity data. Developed models displayed decent predictivity and have a high potential to assess the toxicity of untested phenols and anilines on C. vulgaris within the applicability domain of models.
Assessment and modelling of the toxicity of phenols: a comparative study with marine and freshwater algae
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Ertürk, Murat Doğa.; Saçan, Melek Türker.
Algae sustain biodiversity in aquatic ecosystems by producing oxygen and recycling nutrients. In contrast to their key role in the environment, toxicity data of many organic pollutants, such as phenols, on algae, especially for marine algae, are severely limited. On the other hand, the data requirement in algal toxicity is almost impossible to be supplied through exhaustive laboratory testing considering the huge number of chemicals to be assessed. Therefore, the use of alternative methods to laboratory testing, such as the quantitative structure-activity/toxicity relationships (QSARs/QSTRs), can help reduce the data gap in algal ecotoxicity. In this study, novel toxicity data of phenols on marine alga Dunaliella tertiolecta and freshwater alga Chlorella vulgaris were generated and subjected to QSAR analysis. The phenols selected for toxicological assessment are known to elicit toxicity through different modes of toxic action including polar narcosis, respiratory uncoupling and reactive mechanisms; as such, the data set was regarded as a miniature model of industrial chemical space and provided a realistic basis upon which to explore the development of algal QSTRs. Multiple linear regression and counter propagation artificial neural network techniques were used to build internally and externally validated QSTR models. Most of the QSTRs highlighted the importance of hydrophobicity and electrophilicity related parameters among numerous descriptors. Hydrophobicity was found to underpin the toxicity of phenols to algae. On the other hand, pyrogallol, hydroquinones and catechols, which are potentially capable of being oxidized to reactive species, displayed algal toxicity in excess of that predicted by hydrophobicity. The toxicity of these reactive phenols was better described by electrophilicity parameters. The external validation of the models was also verified using a data set obtained from literature comprising the toxicity of phenols and anilines to another freshwater alga, Pseudokirchneriella subcapitata. Consequently, the developed QSTRs were shown to be applicable to data from another algal test system and at least for another class of organic compounds. Apart from the QSTRs, investigation of inter-algal and inter-species toxicity correlations between algae and other aquatic organisms such as bacteria, protozoa, daphnia and fish revealed that the response of aquatic organisms to phenols differentiated above the level of polar narcosis. As a result, for a heterogeneous set of compounds acting through different modes of toxic action, the models developed in this study can be used to predict the toxicity of untested compounds provided that the new chemicals are within the applicability domain of the respective model.
Biogeneration of activated carbon in the treatment of phenolic compounds
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2006., 2006.) Aktaş, Özgür.; Çeçen, Ferhan.
This study aimed to clarify the effect of adsorbability, desorbability, biodegradability and activated carbon type on the extent of bioregeneration in the treatment of phenolic compounds in activated sludge systems combined with activated carbon. Bioregenerabilities of activated carbons preloaded with phenol, 2-chlorophenol and 2-nitrophenol were studied. For this purpose, four different activated carbon types; thermally activated and chemically activated powdered carbons (PAC), and their granular countertypes (GAC) with similar physical characteristics were used. Thermally activated carbons were better adsorbers for phenolic compounds than chemically activated ones. However, apparently higher adsorption irreversibility was calculated in the case of thermally activated carbons. The results suggested that, rather than the physical form, carbon activation type and chemical surface characteristics played a more important role on adsorbability of phenolic compounds and its reversibility. Also, adsorption and its reversibility were highly dependent on the type of the target compound. Bioregeneration of chemically activated carbons was also higher than thermally activated ones. This showed that bioregeneration was controlled by the reversibility of adsorption. The results suggested that carbon activation type was of crucial importance for bioregeneration. PAC and GAC countertypes showed comparable bioregeneration efficiencies indicating that carbon size was not an effective factor. Oxidative polymerization of phenol and 2-chlorophenol was a plausible explanation for lesser bioregeneration of thermally activated carbons. However, bioregeneration efficiencies of thermally activated carbons were much higher than their total desorbabilities. This indicated the presence of exoenzymatic bioregeneration. Bi-solute experiments showed that competition for adsorption sites greatly determined the extent of adsorption reversibility and bioregeneration. Cometabolic biodegradation of 2-chlorophenol and 2-nitrophenol in the presence of phenol resulted in efficient bioregenerability of activated carbons, when they were loaded with non-growth substances together with a growth substrate.
Building resilience to climate change impacts in the Ikel watershed in the Republic of Moldova : a system dynamics approach
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2022., 2022) Ciobanu, Natalia.; Saysel, Ali Kerem.
Climate change threatens social-ecological systems (SES) across the globe. Developing countries where agriculture is a major income source for both local communities and the national economy are especially affected. In conjunction with their reliance on climatic resources, these countries face the challenge of data scarcity. Assessing and building the resilience of these communities to climate change impacts is equally important and challenging. As the relationship between science, policy, and practice changes, the demand increases on research to engage productively with stakeholders and ensure positive outcomes for all parties. Efforts are increasingly focusing on building the resilience of SES to climate impacts. In this research, I design, build and implement a client-based process under data scarcity conditions in a network governance setting within Republic of Moldova. The process includes analyzing a complex socio-ecological problem to identify policies helpful in meeting development objectives: improving crop yields, preserving groundwater resources and securing habitats for biodiversity conservation. To this end, I first develop a computer simulation model – Ikel CliRes – using a participatory approach that combines several methods, techniques and tools from two related fields: system dynamics and resilience of socio ecological systems. I then use Ikel CliRes to design policy interventions that increase the desirable resilience of Ikel SES to some climate impacts. Ongoing implementation of several policies discussed with decision-makers is underway pointing to the effectiveness and usefulness of the process. Results should be regarded within the limitations of the model architecture and of the assumptions underlying both the model and the analysis.
Comparison of traditional and computer - based instruction on the theme of recycling
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2017., 2017.) Canca, Deniz.; Bilgin, Raşit.
In today's development, the general objective is achievement of desired progress on one hand and maintenance of good quality living conditions on the other. The sustainability of these goals depends on our relationship with the environment and how well we take care of it as we progress technologically. In this context, environmental education has crucial importance. This study aims to determine what kind of an instructional design should be implemented for teaching the recycling topic efficiently. This research compares traditional and computer-based instructional designs on the theme of recycling, each having the same content and flowchart. The effects of these two instructional designs on learning are evaluated based on comprehension and attitude outputs of the study group consisting of 3rd grade primary school students. Findings note that the performance of the groups increased with both designs. However, the results show that neither one of the instructional designs lead to a greater impact than the other one on achievement. It is concluded that recycling can be taught in either design, depending on the conditions of the learners and the learning environment.
Contribution of Anatolian bats to genetic diversity of western palaearctic with a particular focus on Kuhl's pipistrelle
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2014., 2014.) Çoraman, Emrah.; Furman, Andrzej.
Identification of intraspecific conservation units and incorporating the distribution of genetic diversity into management plans are crucial requirements for assessing effective protection strategies. The first part of this study investigates the phylogeographic structures of 33 bat species present in the Near East in order to evaluate the conservation implications of their intraspecific genetic diversity. The management requirements of the identified clades and their taxonomical relations were evaluated by analysing their distributions and the levels of their genetic differentiations in mtDNA markers. In 12 species and the large Myotis complex, a total of 15 genetically distinct populations were identified. Comparing the phylogeographic patterns of different taxa indicates that three regions, the Balkans, the Caucasus, and the southern Anatolia, harbour genetically divergent populations and should have higher priority in conservation practices. In the second part, the response of the Pipistrellus kuhlii lineages to climate change was evaluated by analysing their phylogeographical patterns in association to ecological niche models (ENM). The results show that the P. kuhlii clades evolved in separate Pleistocene refugia located in Iberia, the North Africa, and the Middle East, and subsequently colonized Europe. These clades differ on mtDNA and microsatellites, though, are not reproductively isolated. Comparing both the current and the past predictions of ENMs with the observed genetic diversity indicate that the clades had distinct niche identities and should be analysed separately. Apparently, these differences are conserved for long periods of time and will likely to affect their response to current climate change. Nevertheless, we show that the future predictions of the ‘clade only’ models are consistent with the currently observed population expansions. Considering that Turkey has one of the richest bat fauna in the Mediterranean region and the Anatolian populations of various species are genetically distinct, protecting populations in Turkey is critically important for preserving the genetic diversity of the bats in the Western Palaearctic. Both regional and large-scale conservation strategies should incorporate potential differences in climate tolerance among lineages.
Designing a system based environmental instruction program and evaluating its effects on seventh grade students
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Doğança, Zerrin.; Saysel, Ali Kerem.
The present research aimed to test the effects of an environmental instructional design with systems approach on seventh grade students. The main focus was to examine whether systems approach is a more effective way to teach environmental issues that are dynamic and complex. The research was a quasi-experimental study that enabled to compare performances on general systems thinking skills, competence in dynamic environmental problem solving, and success in standard science achievement tests of subjects from different groups. The sample of the study included 42 seventh grade students (12-14 year old). The same pre, post, and delayed tests were applied to both groups. The control group was taught according to the standard unit plan suggested by the Ministry of Education, while the experimental group was taught the same content with activities including, feedback loops, stock and flow diagrams, behavior over time graphs, and computer modeling. It was found that after one month of systems based environmental instruction, the experimental group performed better on systems thinking skills and dynamic environmental scenarios (DES) tests at .05 significance level. Besides, the effects of the system based intervention were more enduring on performance on DES test for the experimental group, when delayed tests were taken into account. No significance difference was found on science achievement level between the two groups. In addition to quantitative results, interviews resulted in higher levels of feedback thinking skills of the selected respondents from the experimental group.
Destruction of analgesic and anti-inflammatory pharmaceuticals in water by catalytic and advanced oxidation processes
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2017., 2017.) Ziylan, Asu.; İnce, Nilsun H.
The present study aims to emphasize the occurrence of pharmaceutical residues in water and their treatability in homogeneous and heterogeneous solutions by advanced oxidation processes utilizing ultrasound and a variety of solid catalysts. Hence, an important part of the study is the synthesis of metallic nanoparticles/nanocomposites and the assessment of their catalytic activity in the destruction of pharmaceuticals in water. One of the main highlights of the study is the higher efficiency of heterogeneous processes that were assisted by ultrasound than homogeneous systems due to the properties of ultrasound accelerating the transfer of organic solutes to the solid surfaces, where they adsorbed and reacted with many different reactive species. A second highlight of the research is the utility of ultrasound in modification of conventional catalysts such as titanium dioxide and alumina to enable the synthesis of platinum, gold and palladium-supported nanocomposites. The method was demonstrated to enhance the catalytic activity of the catalysts via the electron-trapping ability of the co-catalyst, the massive surface area, increased number of adsorption sites and e- transfer from co-catalyst for enhanced rate of OH production. Finally, hybrid processes (e.g. sono-ozonation, sono-photolysis, sono-photo-ozonation) was more efficient than singles leading to the generation of excess radical species.
Destruction of antimicrobial contaminants in water and waste sludge with chemical oxidation processes
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Öncü, Nalan Bilgin.; Balcıoğlu, Işıl.
Destruction of antimicrobial contamination in both water and sewage sludge was investigated in the thesis. In the first part of the study, the effectiveness of three oxidation processes –chlorination, ozonation, and heterogeneous photocatalysis– on the destruction of a resistance carrier bacterial plasmid DNA isolated from E. Coli were compared and the relative superiority of ozonation or heterogeneous photocatalysis over conventional chlorination was demonstrated. Although the nano-fiber-TiO2 that was prepared in the study did not provide better plasmid DNA destruction compared to commercial TiO2-P25, the material is promising for facilitated catalyst separation from the treated water. In the second part of the study, simultaneous degradation of two model antibiotics, ciprofloxacin (CIP) and oxytetracycline (OTC) in secondary sewage sludge, was investigated by the application of (i) ozonation, (ii) hydrogen peroxide oxidation assisted with microwave irradiation (MW/H2O2), iii) persulfate oxidation assisted with microwave irradiation (MW/S2O8 2-), and (iv) persulfate oxidation activated with ferrous iron and conventional heating (Fe2+/heat/S2O8 2-). While under appropriate conditions all of the processes provided >95% antibiotic degradation along with sludge solubilization, they offer different benefits for waste sludge treatment. Ozonation was found to be more effective to treat the sludge with low content of total solid (TS=2.5 g/L), while the desorption of the antibiotics was required to achieve high rate of degradation at high solid content (10 g/L) of the sludge. On the other hand, owing to the desorption ability of MW in the MW/H2O2 and MW/S2O8 2- processes, and owing to the complexation of the antibiotics with iron in the Fe2+/heat/S2O8 2- process, concurrent antibiotic desorption and degradation was achieved in sludge with high TS (10 g/L). MW/S2O8 2- provided exceptional metal solubilization, considerably enhanced sludge filterability within the shortest treatment time. Along with considerable metal solubilization, the Fe2+/heat/S2O8 2- process resulted in phosphorus precipitation, which can potentially increase the fertilizer value of the sludge.
Determination of effects of selected veterinary antibiotics on biogas production in anaerobic digestion systems and analysis of resistance gene promotion
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Türker, Gökhan.; İnce, Bahar Kasapgil.
Animal husbandry developed into a gigantic business sector to meet demands of modern society. Manure produced in animal husbandry is a suitable substrate for anaerobic digestion since it brings solution to the problem of manure accumulation. Although anaerobic digestion is an old and well known process; it is still far from understood completely. Microbial communities and its importance have been revealed recently. A better understanding of operational and microbiological parameters should be reached to modify and reshape anaerobic digestion systems according to demands. In recent years, antibiotic build up has been detected in receiving environments due to common use in treating both men and animals. Due to their persistence, they begin to accumulate in environment. Antibiotics may create a selective pressure on microbial communities. Microorganisms can become resistant to antibiotics when antibiotics are in non-therapeutic concentrations. This study presents results of investigation of many laboratory scale anaerobic digesters operated with cattle manure of OTC vaccinated animal. Excretion pattern of oxytetracycline after treatment was observed and excreted amount of antibiotic was calculated. Anaerobic digestion of cattle manure was monitored and performances were recorded in presence of antibiotic and changing operational parameters. Manure amendment to soil was performed to monitor fate and effect of oxytetracycline and digester microbial communities on soil microbial communities Within the scope of the dissertation, it was found that OTC inhibits digester performance significantly. Effect of OTC was higher on bacterial population rather than archaea. OTC excreted from animal body as at least 18% of initial amount within solid manure. This amount will further increase because of repetitive injections and liquid manure addition. These manures were used as feedstock in anaerobic digesters operated under common operational parameters for farm type anaerobic digesters. 50% inhibition in biogas production was observed. Temperature was most influential parameter of digester performance followed by solid content and mixing rate. Temperature has been also most effective parameter on degradation of OTC. Mixing rate also helped degradation of OTC slightly. Also solid content was in negative relation with OTC inhibition. It has been found that half-life of OTC was ranging from 22-28 days in mesophilic and 16-18 days in thermophilic digesters, respectively. Molecular analyses showed that bacterial community of digesters was dominated by fermentative and hydrolytic bacteria belonging groups of Firmicutes and acidogenic Proteobacteria. Methanobacteriales, Methanomicrobiales and Methanosarcina spp. were found as methanogenic community. FISH analyses indicated an increase in microbial activity after 20 days; after that activity dropped significantly. Manure and digestate were amended to soil to monitor the elimination of antibiotic and its effects on microbial structures. It has been found that the half-life of OTC is far longer (135 days) in soil than in digesters (18-24 days) and microbial structures were changed after amendment. Tetracycline resistance gene analyses showed presence of 104-106 resistance gene copies in digester studies and 103-105 resistance gene copies in soil studies Analyses also showed that ratio of antibiotic resistance genes to bacterial 16S rRNA genes were increased 50 fold in mesophilic digesters and 100 fold in thermophilic digesters. In soil studies ratio don’t showed a significant change.
Dynamic simulation model for long term comprehensive environmental analysis of GAP
(Thesis (Ph.D.)- Bogazici University. Institute of Environmental Sciences, 1999., 1999.) Saysel, Ali Kerem.; Yenigün, Orhan.; Barlas, Yaman.
Integrated development projects based on water resources development, aiming hydropower production and agricultural modernization have many potential impacts on social and natural environments. Southeastern Anatolian Project (GAP), located in Southeast Turkey, comprising 10% of Turkish lands, targeting irrigation schemes on 1.7 million hectare fertile lowlands and 7400 MW hydropower production on Euphrates and Tigris would have many social and environmental consequences. In this study, potential environmental problems suggested by GAP, questions related with utilization of water resources, land degradation, agricultural pollution and land use are analyzed in systems perspective, focusing on the integrity of environmental, social and economic issues. With this aim, GAP S 1M, a dynamic simulation model is developed to trace long term trajectories of selected parameters, representing the relevant aspects of GAP's social, economic and natural environment. Based on a "systemic" problem definition, GAPSIM simulates the development rate of irrigation schemes, hydropower production with respect to changing irrigation releases, water availability on farmlands, crop selection and production, salinization, erosion, pesticide and fertilizer consumption, rangeland and forest quality, urbanization and population dynamics in GAP during 1990-2030 period, which comprises water facilities construction process. GAPSIM is validated, first "structurally", according to the validation tests suggested by the literature and then, model "behavior" is calibrated with respect to data available for the period 1990-1998. GAPSIM provides a dynamic simulation platform where several scenarios and policy analyses concerning GAP environment can be executed in order to arrive at an improved understanding of GAP as a socio-environmental system. Scenario and policy runs on GAPSIM reveal that, increased intensity of the most evapotranspirant crop cotton on GAP fields may cause significant water scarcity, which hinders the development rate of irrigation into new acres and inhibits crop yields by decreased water delivery to individual farms.
Elucidation of the photocatalytic removal pathways of humic substances: progress towards mechanistic explanations
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2005., 2005.) Uyguner, Ceyda Senem.; Bekbölet, Miray.
The objective of this research was to characterize the spectroscopic properties ofhumic and fulvic acids of different origins as model compounds to represent the naturalorganic matter in aquatic systems. The photocatalytic oxidation of model humic and fulvic acids was carried out using TiO2 Degussa P-25 as the photocatalyst. The degradationkinetics was assessed based on pseudo first order and Langmuir Hinshelwood (L-H)kinetic models. The related data for aquatic and terrestrial humic substances werecomparatively presented in terms of UV-vis parameters such as Color436, Color400, UV365, UV300, UV280, UV254 and total organic carbon (TOC) removal. Furthermore, the molecularand structural characteristics of the humic acid molecule relative to changes duringphotocatalytic oxidation were monitored by spectroscopic techniques.On the basis of their diverse chemical and physical properties such as molecular weight, molecular size, elemental composition and source of origin, substantial differenceswere observed in photocatalytic removal efficiencies of humic and fulvic acids. For all ofthe humic substances, higher removal rates were achieved in terms of UV254 valuescompared to that of Color436. Moreover, humic acids exhibited higher pseudo first order removal rates with respect to that for fulvic acid. The declining trend of the specified UVvisparameters, the related changes in the fluorescence spectra (initial increase of thefluorescence intensities, formation of new fluorophores, shift of the spectra to lowerwavelength region and decline of intensity after long photocatalytic irradiation times), decrease of TOC content during degradation, the spectral changes in FTIR and NMRindicated the oxidative degradation of humic substances.Considering the complexity and polydispersity of the humic macromolecules, theywere fractionated into well defined subcomponents of known molecular sizes usingultrafiltration through membranes in the range of 100-1 kDa. The effect of photocatalyticoxidation on the molecular size fractions of humic substances were also evaluated on acomparative basis by UV-vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the molecular size distributiondata, photocatalytic degradation of humic acid leads to the formation of lower molecularsize (small fractions) and higher UV-absorbing compounds. For fractions less than 10 kDa,UV254 absorbing moieties in treated humic acid samples become higher than that of rawhumic substances designating the generation of new species during photocatalysis.Based on the comparison between the synchronous scan fluorescence spectra ofthe molecular size fractions of raw and oxidized humic substances, it could be concludedthat oxidative cleavage of the molecule leads to a blue shift of the spectra which isindicative to the formation of new fluorophores in each size fraction. It is assumed thatoxidative degradation of the macromolecule occurs through an unselective pathway, by thereaction of .OH radicals with the various moieties within each fraction.
Environmental distribution of polychlorinated biphenyls by topology based characteristic root index
(Thesis (Ph.D.)- Bogazici University. Institute of Environmental Sciences, 1990., 1990.) Saçan, Melek Türker.; İnel, Yüksel.
Relationships between a newly developed index -which is based on topological characteristics ofthe molecules and called the Characteristic Root (CR) index- and the environmentally relevant physicochemical properties of the Polychlorinated Biphenyls, namely, aqueous solubility, vapour pressure, Henry's Law Corastants, and octanol-water partition coefficient are discussed. Correlations performed on the congeners clearly demonstrate that the CR index model accurately predicts the physicochelnicaiproperties of PCBs. Highcorrelationcoefficient (r = 0.998) was calculated for the linear one-parameter correlation between the CR index and molecular total surface area. So, the CR index was used in the prediction of pro2erties dependent on tetal surface area. The quality and reliability of the correlations are show to be high enough for environmental applications. Reported experimental physicochemical data of PCBs are tabulated, Recomended values are given for 58 of the 209 congeners, With the available data, it is possible to estimate what percentage of the chemical will be located in the soil, bottom sediments, water and air. The predicted and experimental physicochemical properties of PCBs were used to predict the environmental compartmentalization of these compounds in an evaluative environment using the fugacity approach.
Evaluation advanced oxidation technologies and nanoscale particles for water and groundwater remediation
(Thesis (Ph.D)-Bogazici University. Institute of Environmental Sciences, 2008., 2008.) Aksoy, Dila.; İnce, Nilsun.; Copty, Nadim.
Advanced Oxidation Processes (AOP) that are based on the in-situ generation of hydroxyl radicals in solution are extremely powerful tools for the destruction of recalcitrant compounds in water and groundwater. Recent research has shown that subsurface injection of nanoparticles may also be a viable technology for the in-situ remediation of contaminated groundwater resources. The purpose of this study was to assess the degradability of typical groundwater contaminants, namely phenol and 2-chlorophenol by advanced oxidation processes, nanoparticles and combinations thereof. Advanced oxidation processes investigated were ozonation, UV irradiation, sonolysis, and sono-Fenton process. In the second part of the research, flow-through reactors were used to test the mobility of the selected nanoparticle solutions in porous media under different flow configurations. Continuous flow experiments mainly focused on the assessment of the mobility of nanoparticle solutions in porous media under different flow configurations. Comparison of the nanoparticle breakthrough curves to that of the conservative tracers showed that the transport of nanoparticles is influenced by their concentration, which strongly controls the particle size and hence, their mobility. Overall, this study has demonstrated that phenolic compounds in contaminated water and groundwaters may be effectively destroyed by use of optimized hybrid processes involving Advanced Oxidation Processes and nanoparticles.|Keywords: advanced oxidation, ultrasound, nanoparticle, groundwater remediation, phenolic compounds
Evaluation of natural organic matter-metal oxide adsorption isotherms under influential structural concepts
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2006., 2006.) Süphandağ, Şerif Altan.; Bekbölet, Miray.
The adsorption of molecules onto a surface is a necessary prerequisite to any surface mediated chemical process. Therefore, the mechanism of binding of humic acids to TiO2 surface has to be addressed in order to improve the understanding of photocatalytic degradation. From the fundamental point of view, natural organic matter (NOM) for water scientists can be perceived as very complex entities both in terms of chemistry and comprehension. Especially the fulvic (FA) and humic acids (HA), the soluble portions of NOM, are often considered as oligomeric and polymeric materials. In literature, there are ongoing discussions regarding the high molecular mass is due to aggregation of small units, as in micelles, or due to covalently bound units, as in polymers. The essence of this thesis is to evaluate the adsorption under the light of these two debatable approaches and bring reasonable interpretations of the observed isotherm patterns through the use of proposed structures. In this dissertation the isotherms of humic acid (HA) on titanium dioxide are analyzed at acidic, neutral, and basic pH. Combined effects of pH and increasing ionic strength were evaluated in order to asses the effect of changing solution matrix on the molecular structure of humic acid.|Keywords: humic acid, titanium dioxide, adsorption, natural organic matter, metal oxides
From riverscape to energyscape: Constructing the space of hydroelectricity production in the İkizdere River Valley, Turkey.
(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2017., 2017.) Eren, Ayşen.; Yenigün, Orhan.; Dove, Michael R.
This dissertation examines the processes, relations, and practices by which all the involved parties construct, sustain and contest the space of hydroelectricity production in the İkizdere River Valley, Turkey. Beginning with the first hydroelectricity plant built in 1950s, the İkizdere HES, the study traces historical small-scale hydroelectricity development in the valley, and then focuses on "the sustainable development" of hydroelectricity program launched in 2003. The thesis explores how the program came about on the national scale and materialized on the İkizdere River Valley with the emergence of five private hydroelectricity plants. It also seeks to explain how the emerging hydroelectricity plants have contributed to the deterioration of the once-positive local perception toward hydroelectricity production. Moreover, this thesis focuses on the water-electricity nexus in order to better understand the hydroelectricity development and to demonstrate the real scale of its environmental and social consequences in the valley. The thesis follows an interdisciplinary methodology, integrating multi-sited fieldwork with a mixed-method design. It employs Lefebvre's the theory of space together with the concepts of relations of production and infrastructure in analyzing the processes and relations. In addition, the thesis uses a post-structuralist approach in examining the policies, regulations, and practices constituting hydroelectricity development program.
Impacts of land use change on soil respiration and elemental carbon in the forests of Karasu district
(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2010., 2010.) Oral, Hasan Volkan.; Onay, Turgut T.; Yenigün, Orhan.
In recent years, expansion of agricultural activities in the Karasu region which is located in northwest Turkey has led to significant deforestation. As a result, deforestation in this region is one of the most critical in Turkey. The purpose of this study is to evaluate the impact of land use change on soil respiration, soil elemental carbon in the Karasu District. The study also assess the potential seasonal changes on these three key parameters. To achieve this purpose, field trips were carried out over four seasons in 2008-2009. In total 900 soil samples from forested and deforested lands were collected. Geographical Information Systems (GIS) Remote Sensing Technologies (RST) were employed in conjunction with in situ measurements, laboratory experiments and statistical analyses. Soil respiration was measured in situ while soil samples were collected for the laboratory determination of soil elemental carbon (C) and nitrogen (N), C:N ratio, microbial respiration, soil organic matter (SOM), electrical conductivity, gravimetric moisture content, pH and soil textural structure. Analysis of the collected data indicated that the differences in mean soil respiration and elemental carbon due to land use and seasonal variations were statistically significant. The average annual soil respiration and elemental carbon in forested lands was about 27% and 34% higher than that from deforested lands. The statistical analyses also showed that the clay content exhibited high correlations with soil respiration and, particularly, with elemental carbon. Geostatistical analysis was conducted to calculate the spatial average values of soil respiration, surface elemental carbon. The data analyses and interpretation methods developed in this study can serve as an example for future studies in other geographical regions involving the evaluation of soil carbon content and emissions.

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