The Use of Object-Based Image Analysis for Monitoring 2021 Marine Mucilage Bloom in the Sea of Marmara

Abstract

Global warming threatens ecosystems through rising temperatures, increasing sea levels, drought, and extreme weather conditions. The natural balance of seas and oceans is also at stake with recent outbreaks of mucilage events all over the world. The mucilage phenomenon, which has been frequently observed in the Adriatic and Tyrrhenian seas, has taken place the second time in the Sea of Marmara in Spring 2021. The Sea of Marmara dividing the Asian and European parts of Turkey is an important inland sea with heavy maritime traffic, hosting many industrial zones and surrounded by highly populated cities. This study aims to determine the mucilage formations that were observed intensely all around the Sea of Marmara, focusing on the coasts of Istanbul, Kocaeli, Yalova, and Bursa through classifying Sentinel-2A images dated 19 and 24 May 2021, when the peak period of mucilage bloom, using a new paradigm of object-based image analysis (OBIA) approach. To create representative and homogenous image objects, multi-resolution segmentation was applied, and its result was inputted into a classification process using Random Forest (RF) classifier to generate thematic maps. The produced results were compared with pixel-based classification and a high correlation was estimated. Objectbased classification was found effective for the determination of mucilage-covered areas (> 90% overall accuracy) for both considered dates. More specifically, areas covered with mucilage aggregates were computed as 56.15 km² and 67.51 km² for 19 May and 24 May 2021, respectively, indicating rapid growth in only 5-day period. The resulting thematic maps revealed that mucilage was heavily distributed in the gulfs of Gemlik and Izmit and along the coasts of Darica, Tuzla and Pendik.

Effects of Mucilage on Safety Navigation in the Turkish Straits

“…The study examined the impact of mucilage on specific sectors such as ecology, fisheries, and tourism. Intense mucilage formation in the Sea of Marmara is being investigated by other studies (Balkis et al, 2021;Acar et al, 2021;Kavzoğlu et a., 2021;Hu et al, 2022). The authors imply that due to the excellent mucilage event, the habitat of the sea changed, and unobserved species became dominant.…”

Environmental Statistical Analysis on the Impacts of Marine Mucilage on some Seawater Quality Parameters

“…The study is conducted at the Sea of Marmara, between the coastline of Kadıkoy and Bostanci line, located on the Anatolian side of the Province of İstanbul (Figure 1). This study location is chosen due to the intensive layer of mucilage formations on the sea level (Savun-Hekimoğlu and Gazioğlu, 2021, Kavzoğlu et al, 2021Kavzoğlu et al, -2023Savun et al, 2021, Kömüşcü et al, 2022. Sampling points are marked with an indoor tracking system based on Bluetooth technology GPS (Opoku, 2012) from 0-5 m depth (Tüfekci et al, 2010) from the sea surface.…”

Extraction of Water Bodies from Sentinel-2 Images in the Foothills of Nepal Himalaya

“…For regional studies, images provided by the Landsat TM (Thematic Mapper) and ETM+ (Enhanced Thematic Mapper Plus) proved to be valuable as the imagery has a moderate spatial resolution (30 m), provides multispectral images (seven or eight bands), with a short revisit interval (16 days) and includes decades of records (Du et al, 2016;Masocha et al, 2018;Zhai et al, 2015). Various techniques have been adopted and developed to delineate water bodies in remotely sensed imagery and are commonly grouped into three categories, i.e., Spectral bands (Verpoorter et al, 2012(Verpoorter et al, , 2014Zhai et al, 2015;Kavzoğlu et al, 2023), classification (Acharya et al, 2018;Huang et al, 2018;Talukdar et al, 2020;Kavzoğlu, et al, 2021) and index-based extraction (Acharya et al, 2018;Du et al, 2016;F. Yang et al, 2017;Gazioğlu, 2018).…”