LEE- Yer Sistem Bilimi-Doktora

Bu koleksiyon için kalıcı URI


Son Başvurular

Şimdi gösteriliyor 1 - 3 / 3
  • Öge
    Distribution of radionuclides in Arıklı region (Çanakkale/Ayvacık) and possible causes
    (Graduate School, 2022-06-28) Top, Gülcan ; Tutay Örgün, Yüksel ; Karahan, Gürsel ; 601112002 ; Earth System Science
    The aim of this thesis is to determine the indoor and outdoor gamma dose rates in Arıklı (Çanakkale/Ayvacık/Turkey) uranium mineralization region, to determine the activity concentrations of 226Ra, 232Th, 40K in selected samples (building materials, rocks, surface soils, beach sands and soil samples collected from excavation ditches), to map the outdoor gamma dose rates and the activity concentrations of the radionuclides specified in the surface soils using geographic information systems, to identify the geological sources that cause high doses and to evaluate the possible health risks for the region based on all these measurement results. The measurement of mass concentrations for U, Th on some selected samples is also included into the study. This study is the first comprehensive study for the region. For this thesis, the Arıklı region was considered as a research area due to the presence of a uranium mineralization zone and the prevalence of felsic volcanic rocks containing above-average uranium, thorium and potassium concentrations. In order to determine the level of radioactivity in the Arıklı uranium mineralization region, preliminary field studies were started in 2015 measuring the outdoor gamma dose taking into account the geological formations. It has been determined that anomalies are especially concentrated in and around the drilling points determined by the General Directorate of Mineral Researches (MTA) to search for uranium.
  • Öge
    Temporal and spatial investigation of maritime accidents in the strait of Istanbul in the perspective of navigational safety
    (Graduate School, 2022-10-24) Kodak, Gizem ; Ünal, Alper ; Acarer, Tayfun ; 601142001 ; Earth System Sciences
    The Strait of Istanbul is located on the primary routes of international maritime transport. The strait, which is the second busiest waterway in the world with average of 50.000 ships per year, has four times more maritime traffic than the Panama Canal and three times more than the Suez Canal. When compared to its peer waterways the biggest threat in the Strait, the risk of accidents created by difficult navigational conditions. Some of the accidents that took place in the strait in the recent past have caused worldwide concern due to the environmental disaster they have caused. Considering that today, ships carrying dangerous goods serve at much larger capacities compared to the past, the maritime traffic in the region poses a risk both for the ships passing and for the city and people of Istanbul, which is densely populated on its shores. In this context, the development of solutions to reduce maritime accidents in the region plays a key role in strengthening navigational safety. In this study, the accidents that took place in the strait were discussed in terms of temporal/spatial and were examined simultaneously with the environmental factors affecting the navigational safety. For this purpose, hourly wind speed and wind direction data of Sarıyer and Atatürk meteorology stations located on the traffic route in the strait were obtained from the Turkish State Meteorological Service and wind dynamics affecting maritime traffic were examined. On the other hand, accidents also were evaluated in terms of the number of ships passing and the effect of maritime traffic on accidents were examined with the regression analysis. In this direction the monthly movement of international ship traffic in the strait was examined on a micro scale with the data of the Directorate General of Coastal Safety and accident rate per passing ship was calculated. In addition to dynamic factors such as wind speed, wind direction and traffic flow, another factor affecting the occurrence of accidents in the strait is the navigational regulations carried out in relation to the traffic order. In this context, the regulations for maritime traffic in the strait were examined chronologically and compared with the accident data. Thus, not only the effects of the regulations regarding navigational safety on the accidents were observed, but also the strengths and weaknesses of the developed solution proposals were revealed. The results of the study have shown that patrol tugs can be an effective solution to prevent accidents when the wind and current dynamics in the region and the spatial distribution of the accidents are evaluated together. In this direction, the response time of the proposed patrol tugboats to a possible accident was calculated and the response options were evaluated under two different scenarios as parallel to the current and antiparallel.
  • Öge
    Fire history and climate change: Black pine forests in Western Anatolia
    (Graduate School, 2022-06-15) Şahan, Evrim Ayşe ; Dalfes, Hasan Nüzhet ; Köse, Nesibe ; 601172003 ; Earth System Science
    Wildfire is a part of the ecological processes that is highly important for the sustainability of forest ecosystems in the Mediterranean Basin. Species adapted to crown fires, such as Turkish pine, are capable of regeneration after a fire and establishing new forests. On the contrary, tree species such as black pine adapted to surface fires have regeneration problems after severe crown fires, and mass extinctions in some regions can be observed. Many studies have revealed that the fire frequency of forests in the Mediterranean Basin is expected to increase due to climate change and the fire regime of black pine forests will shift from surface fires to crown fires. In order to understand the fire regime changes in the black pine forests in the Mediterranean Basin, including Turkey, centuries-long fire records are needed. Thus, dendrochronology is one of the most reliable and effective methods commonly used in fire history studies. In this doctoral thesis, the aims are to develop a high-resolution fire reconstruction of black pine forests in Turkey, determine the seasonality of historical fires, understand the association between climate variability and fire occurrence, understand the variability of spatiotemporal patterns of fires throughout the main distribution areas of black pine forests in Turkey using tree-ring analysis, and monitor the cambium activity in black pine forest. Several spatial and temporal studies are conducted in order to understand the effects of fire management strategies, climate types or geographical gradients on regional fire regimes in the world. A large number of dendrochronology-based studies were conducted, especially in North America, to understand the spatiotemporal patterns in different geographical gradients and different climate types and also corroboration of empirical data. However, in the Mediterranean basin, a few fire history studies based on dendrochronological methods was conducted in Greece, France and Spain to understand the regional fire regime and the relationship between fire and climate. To my knowledge, there is no any conducted fire history study for any species based on tree-ring analysis in Turkey. A total of 211 samples were collected from ten sites throughout western Anatolia. The collected samples were dated by standard dendrochronological methods and the seasonality of each sample was determined. The site-level composite and regional fire chronologies were created for Kütahya, Isparta, Bolu, and western Anatolia. The major fire years were calculated with the criteria that greater than or equal to 25% of recording samples have fire scars on that year in at least two of the samples, while the regular fire years were determined by recording samples have fire scars on that year in at least two of the samples. The relationship between the major fire years and climate was analysed using Superposed Epoch Analsis. Understanding the seasonality of historical forest fires facilitates the development of concepts related to fire as an ecological and evolutionary process. In order to understand the fire regime of a region, determination of the seasonality is a must. In dendrochronology-based fire history studies, the seasonality of fire scars is mostly classified according to the intra-ring position of the fire scars as a classical method. However, studies of cambial phenology are needed to accurately correlate the position of a fire scar with the months in a year. Because the timing of the earlywood and latewood production (cambial cell production) varies according to the species, location and climate. In this context, the aim of this part of this thesis is to determine in which months the cambium activity of black pine forests starts and in which month the early/latewood cells form. In order to monitor cambium activity, a total of 144 microcores were sampled from three sites near the fire history reconstruction sites during a vegetation period (April-November 2021). Monitoring the cambial activity helped to obtain information about which month(s) are risky for forest fires. The first tree-ring based 553-year long fire history reconstruction and cambial activity of black pine forests were presented to improve our understanding of the regional fire regime components with the effect of climate in Turkey. The fire return interval of black pine forests in Anatolia was calculated from a minimum of one year and a maximum of 105-year intervals over the study period. The seasonality of most of the fire scars in western Anatolia occurred in the latewood period. As conducted in a cambial activity study of black pine forests in western Anatolia, latewood tracheid cells are formed from (August in Isparta) from September to November. Since most of the fires in western Anatolia occur in latewood, the risky months for fires in the study area are from (July in Isparta) August to November (the late summer and autumn) based on xylogenesis studies. The relationship between climate and fire years calculated with regional fire chronologies showed that the major fires in Kütahya and Bolu are associated with dry years, while the wet conditions two years prior to major fire events in Isparta. The decrease in fire frequency was observed in the late 19th and early 20th centuries due to human-induced fire suppression activities. That can cause the accumulation of combustible material and pose a risk for more intense fires. Based on future climate projections, as a result of increased drought frequency, we will face extended fire seasons that may shift the fire regime from the surface to crown fires and even cause mega fires. A large number of simultaneous fires were recorded in the period between the mid-1800s and the early 1900s. The decrease in fire frequency after the early 1900s coincides with the first forest protection law in 1937. As a result of the comparison of fire years in western Anatolia, Spain, and Greece, more common fire years were found in studies of Greece than in Spain. The differences in climate conditions of the eastern and western Mediterranean due to frontogenesis or depressional activity might explain these different common fire years. The year 1879 was the most extensive fire year in Greece in the 19th century and it was recorded as one of the most common fire years in western Anatolia. The year 1945 was the only common fire year in the Mediterranean region sites. Results in this study showed that the fires in 1945, observed simultaneously in Anatolia, Greece, and Spain, occurred in the most severe and widespread drought among the spatially visualized common fire years. In this study, long-term fire history data were developed by using dendrochronological methods to understand the fire regime of black pine forests for the first time in Turkey. These fires were analyzed with a new approach with the determination of the seasonality by taking samples with microcores. Unlike studies only current fires are analyzed or fire history reconstructions, the results were obtained by integrating both ecological and statistical methods.