Detection of mucilage phenomenon in the Sea of Marmara by using multi-scale satellite data.

Marine mucilage outbreaks occurred in the Sea of Marmara in 2021 which severely affected the marine ecosystem. The thick mucilage blankets with different colors became a public concern due to the toxicity potential related to pathogens that accumulate in prolonged presence of mucilage. The mucilage-covered areas in the Sea of Marmara detected by remote sensing data acquired in 2021 were previously reported. However, the areal extents and spectral characteristics of the different colored mucilage types remain unknown. This study presents the spectral characteristics of different types of mucilage in the Izmit Bay in the Sea of Marmara by using medium- (Sentinel-2) and high-spatial resolution (Worldview-3) satellite images. Also, the sea surface temperatures (SST) were studied in relation with the mucilage formation from January 2015 to August 2021 by using NOAA data. Two multispectral satellite sensors Sentinel-2 and Worldview-3 were studied for their potential for mucilage mapping and characterization in the sub-region Izmit Bay. Support vector machine (SVM) classifier was used to detect three different types of mucilage with distinguishable spectral differences in infrared region ranging from 725 to 950 nm. Three different types of mucilage were characterized based on color and texture including (a) the white mucilage aggregates with dispersed patterns which are likely freshly formed, (b) the yellow mucilage accumulations in the coasts that are wind/current transported, and (c) the brown mucilage accumulations that are probably the most-aged. Our results showed that brown mucilage and white mucilage showed similar reflectance values between 425 and 545 nm region, while yellow mucilage showed higher and more distinctive spectral reflectance than white and brown mucilages. The NOAA data showed that average surface water temperature has been increased over the years from 2015 (16.1 °C) to 2021 (17.6 °C). This increase trend in SSTs points out a likely relation with the mucilage formation and hence may suggest a potential of repeating mucilage events in the near future. This study provides a practical methodology for monitoring, classification, and efficient site selection for mucilage cleaning areas in the Sea of Marmara.

Use of remotely sensed data for analysis of land-use change in a highly urbanized district of mega city, Istanbul.

The study forms an example on monitoring and understanding urban dynamics by using remotely sensed data. The selected region is a rapidly urbanizing district of the mega city Istanbul, Gaziosmanpasa, whose population has almost doubled between years 1990 and 2000. The significance of this district besides its urban sprawl is that 61% of its land lies within the boundaries of an important drinking water reservoir watershed of the mega city, the Alibeykoy Reservoir. The land-use/cover changes that has occurred in the years of 1987 and 2001 are analyzed by utilizing a variety of data sources including satellite images (Landsat TM image of September 1987 and Landsat ETM+ image of May 2001), aerial photographs, orthophoto maps, standard 1:25000 scale topographic maps, and various thematic maps together with ground survey. Land-use changes are analyzed on the basis of protection zones of the reservoir watershed and the conversion of bare land and forests to settlements are clearly observed despite the national regulation on watershed protection. The decline of forests within the protection zones was from 69% to 63.6% whereas the increase in settlements was from 0.8% to 3.9%. The associated impact of establishing new residential sites with insufficient infrastructure is then linked with the water quality of the reservoir that has already reached to Class III characteristics regarding the recently revised national legislation stating that any class exceeding Class II cannot be used as a drinking water supply that in turn, had consequences on regulating the water services such as upgrading the existing water treatment plant. The paper aims to help the managers, decision-makers and urban planners by informing them of the past and current land-use/cover changes, to influence the cessation of illegal urbanization through suitable decision-making and environmental policy that adhere to sustainable resource use.

Identification of land-cover changes through image processing and associated impacts on water reservoir conditions.

A temporal assessment of land-cover changes of the province Beykoz in Istanbul has been documented in this article. The study focuses on the acquisition and analysis of LANDSAT 5 TM images that reflect the drastic land-cover changes between the years 1984 and 2001 utilizing aerial photographs, orthophoto maps, standard topographic maps, and ground truth measurements. The status of the province, including its surrounding villages, were examined together with more specialized maps showing only the city center and part of the province that lies within the watershed of the Elmali Drinking Water Reservoir. The land distribution profiles were also calculated for each of the images to help authorities and decision-makers to better understand the main causes of such remarkable changes and to inform them of the changing quality conditions of the reservoir. Rapid, uncontrolled, and illegal urbanization accompanied by insufficient infrastructure has caused degradation of forests and barren lands in the province, especially within the past two decades. The proximity of the province to the reservoir's watershed, downtown Istanbul, and the transportation network has accelerated the land-cover changes whose adverse impacts on the reservoir water quality are sensed. It is intended that the data gathered and processed in this study will provide a basis for future sustainable urban planning and management activities.