Page 106 - Çevre Şehir İklim İngilizce - Sayı 3

The Study of Deoxygenation and Mucilage Formation in The Marmara Sea
Using Novel Oceanographic Approaches in The Frame of Marmod Project

pollution sources, and create actions to protect the Marmara Sea adopting
an ecosystem-based approach. For this purpose, it is required to establish an
ecosystem-based Marmara Integrated Model System specific to the Marmara
Region and to use models that can accurately simulate changing ecological
characteristics (ÇŞB, ODTÜ-DBE, 2017: 136).
The Institute of Marine Sciences of Middle East Technical University (METU-
DBE) has been collecting data from the Marmara Sea within the scope of
various projects since the 1980s. When the data are examined, it is observed
that in the period up to the 2000s, there was dissolved oxygen in the deep
basins of the Marmara Sea in an amount that many marine creatures could
tolerate (>80 µmol/L, hypoxia limit). However, a significant decrease in these
dissolved oxygen levels has been noticed in the following years (ÇŞB, ODTÜ-
DBE, 2017: 136; ÇŞİDB, ODTÜ-DBE, 2021:
91; ODTÜ-DBE, ÇŞİDB, 2021: 103). Oxygen values have fallen below the
hypoxia limit. In addition, it has been observed that there is a decrease in
dissolved oxygen values in the certain zone in Marmara Sea which runs as an
interlayer and covers a depth of 25-40m especially in summer and autumn.
It has been found that oxygen values decreased below the critical threshold
limit for living life defined by scientists, especially from a depth of 20 meters
(ÇŞB, ODTÜ-DBE, 2017: 136; ÇŞİB, ODTÜ-DBE, 2021: 91).
The dissolved oxygen rate observed in the early 1990s, which is important
for marine life, has fallen by less than a quarter today, especially in the eastern
basins (from about 80 μM to lower than 20 µM) (ÇŞB, ODTÜ-DBE, 2017: 136;
ÇŞİDB, ODTÜ-DBE, 2021: 91). The reasons for this
primarily include the impact of nutrient loads coming from the Black Sea
through Danube, and terrestrial inputs that are increasing in parallel with the
population density and the boost in industrialization. In the last decade with
a decreasing trend of nutrient loads from the Black Sea, it is observed from
the measurements and increasingly deteriorating biochemical properties of
Marmara Sea that the “increasing” trend of terrestrial nutrient loads flowing
into the Marmara Sea is still ongoing. This affects us indirectly but especially
the marine life in Marmara (Yücel et al., 2021: 268).
The lack of management of pollution sources in Marmara is perceived from
the current situation of the region. This has led to more deoxygenation in the
lower layer waters of Marmara over the past two decades. In particular, the
oxygen level decreased by 95%, fell below 9.4 μM in the deep basin of the
eastern part, and even deoxygened conditions were observed in the deep
waters below 600m in the autumn period in 2016 (ÇŞB, ODTÜ-DBE, 2017: 136;
Yücel et al., 2021: 268).

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