**1. Introduction**

30 Will-be-set-by-IN-TECH

246 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

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Dissolved oxygen (DO) content of the marine environment is a crucial parameter for life and water quality as well as playing an important role in biogeochemical processes, and respiration of plants and animals, and decomposition of organic matter by bacteria are the primary processes that consume dissolved oxygen content of water and pore-water in sediments. If the oxygen concentration of water falls below about 2 mg/1, living organisms become stressed and the consequent conditions lead to hypoxia. Persistent hypoxia and increased oxygen uptake accompanies release of hydrogen sulfide. Anoxia occurs in estuaries where high loads of organic matter and/or nutrients are supplied, and in semienclosed water bodies where water mixing and tidal exchanges are strongly restricted. In recent years, aquatic ecosystems have been contaminated by heavy metals; which are of agricultural, industrial, domestic, mining and also natural origins (Ayas and Kolankaya 1996; Han et al., 2002). They are potentially toxic to the aquatic environment; if they exceed natural limits, they will be harmful to the aquatic organisms' environments and human health (Forstner and Witmann, 1981). Organisms need some metals such as Fe, Cu, Zn, Co, Se, Ni and Mn in certain amounts; however, exceeding these amounts may cause toxic effects for these organisms. Some metals such as Hg, Cr, Pb and Cd are toxic to organisms and marine habitat. These metals are dissolved in sea water or suspended in solid materials and absorbed through the gills or skin of marine organisms; they also accumulate in the bodies of organisms through the food chain (Forstner and Witmann, 1981). Mussels, in particular, have been used as biological indicator organisms to monitor marine pollution by toxic heavy metals and potentially toxic chemicals due to their properties of inhabitation (Pempcowiac et al., 1999; Hu 2000).

Izmit Bay (Figure 1) is a semi-enclosed water body and situated in the NE of Marmara Sea. It has been subjected to pollution problems (Orhon et al., 1984; Tuğrul et al., 1989; Morkoç et al., 1996), including eutrophication of the water and inputs of toxic industrial and domestic effluents. Total organic matter load of industrial discharges has been reduced to 80% within the last 10 years, whereas domestic organic loads have been increased in two fold (Morkoç et al., 1996, 2001). The earthquake with a magnitude of 7.4 was occurred at 17th of August 1999, destroying the eastern Marmara Region. The epicenter of the earthquake was found to

The Effect of Marmara (Izmit) Earthquake on the Chemical

**Black Sea**

**Sea of Marmara**

**TURKEY**

metals by Yaşar et al., 2001.

25.00 26.00 27.00 28.00 29.00 30.00

station in İzmit Bay (below).

**2. Material and methods** 

**2.1 Sampling sites** 

and August during 2000.

36.00

37.00

38.00

39.00

40.00

**Aegean Sea**

41.00

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 249

Industrial loads have been reduced by treatment and waste minimization within the last 10 years, but domestic wastes has doubled, due to the increasing population in the Bay. Therefore, the total (domestic + industrial) discharge load into the Bay during the last 10 years has not changed significantly (Morkoç, et al., 2001). The dissolved oxygen content of Izmit Bay decreased dramatically from 1984 to 1999 and reached to a minimum value at 20 m throughout the Bay (Okay et al., 2001). Ergin et al., (1991) suggested that the surface sediments in İzmit Bay are uncontaminated by anthropogenic pollution. However Yaşar et al., (2001) investigated that the heavy metal concentrations are highest in the eastern and central basins. The western basin was also found generally unpolluted with respect to heavy

> 2C R 1C

Fig. 1. The location (left) and bathymetry (above) of the study area. The location of sampling

The water samples were collected from 32 stations in İzmit Bay, including one station located off the western basin (R), on board the R/V Arar (Figure 1). Station (R) represents the characteristics of the Marmara Sea and hence, provides a comparison between the Bay and the Marmara Sea. The sampling stations in İzmit Bay represent the various depths of three basins, with a minimum of 17 m and maximum of 200 m. Sampling was carried out with a Rosette sampler assembled to the Sea Bird CTD System at about 10 m depth intervals through the upper and the lower layers. Sampling period includes August 1999, immediately after the Earthquake and performed monthly in 1999 and in February, May

**Western B.**

28 29 31 30 27 25

**Eastern B.**

**İzmit**

22 23 24 21 20 19 8C 7C 16 15 17 18 14 6C 13 10 12 5C 7 8 9 5 3C 2 4C

**Gölcük**

**Central B.**

be in a small city (Gölcük) located on the southern coast of Izmit Bay. This seismic event caused the destruction of wastewater discharge systems and also dispersal of refined petroleum products onto the sea surface from the subsequent refinery fire. The surface waters of the Bay were partly covered by the thick petroleum layers and partly by a film (Güven et al., 2000, Ünlü et al., 2000). Petroleum layer covering the surface water reduced the transfer of oxygen from air/sea interface and also caused the subsequent death of living organisms. Increasing effluent discharges into the Bay produced an exceptional plankton bloom. Coupling of such factors leading to oxygen deficiency at the sea floor caused the formation of anoxic conditions. Okay et al., (2001) investigated ecological changes in Izmit Bay, however their data is limited with the September 1999.

This paper presents the results of one-year monitoring program performed in Izmit Bay after the Earthquake, with the purposes of describing the abrupt changes in chemical oceanography and understanding the mechanism of H2S generation in the Bay which has not been occurred before. Furthermore, the factors controlling metal distributions in water column and surface sediments of the Bay were discussed in this study.

#### **1.1 Study area**

Izmit Bay is an elongated semi-enclosed water body with a length of 50 km, width varying between 2 to 10 km (Figure 1) and has an area of 310 km2. The bathymetry of the Bay constitutes three sub-basin separated by shallow sills from each other. The eastern basin is relatively shallow (at about 30 m) whereas the central basin has two small depressions with depths of 160 and 200 m. The western basin deepens in westward from 150 m to 300 m and connects the Bay to the Marmara Sea. Izmit Bay is oceanographically an extension of Marmara Sea, having a permanent two-layered water system. The upper layer is originated from less saline Black Sea waters (18.0-22.0 psu), whereas the lower layer originated from the Mediterranean Sea waters is more saline (37.5-38.5 psu) (Ünlüata et al., 1990). The permanent stratification occurs at about 25 m in the Marmara Sea (Beşiktepe et al., 1994), however it is highly variable in Izmit Bay (Oğuz and Sur, 1986) (Figure 2). The thickness of the upper layer changes seasonally from 9 to 18 m spring and autumn, respectively (Oğuz and Sur, 1986; Algan et al., 1999). The upper layer enters into the Bay in spring and summer, corresponding to the freshwater inflow changes in the Black Sea, while the lower layer flows to the Marmara Sea from the Bay. However, the upper layer flows towards the Marmara Sea in autumn and winter (Oğuz and Sur, 1986). Vertical mixing of the two layers is restricted and occurs at shallow depths. An intermediate layer develops throughout the year in the water column of the Bay with varying thickness (DAMOC, 1971; Baştürk et al., 1985; Tuğrul et al., 1989; Oğuz and Sur, 1986; Altok et al., 1996). The upper layer of Izmit Bay, in general, is saturated with DO (Tuğrul and Morkoç, 1990). DO concentrations in the lower layer of Izmit Bay has been found to be 2.5-3.0 mgl-1 in winter and spring periods and 0.7-1.5 mgl-1 in summer, in previous studies (Morkoç, et al., 1996). The minimum DO concentrations have been measured locally in the central basin (0.1-0.2 mgl-1) and in the eastern basin (0.5 mgl-1) during spring-summer period (Tuğrul and Morkoç, 1990). Izmit Bay and its surroundings is one of the most industrialized and populated area of Turkey, receiving more than 300 industrial and domestic effluents (Morkoç et al., 1996). Industrial effluents discharges a total of 163,000 m3/day wastewater, 24 tons/day BOD and 19,5 tons/day TSS to Izmit Bay (Morkoç et al., 2001). The eastern basin receives the highest inputs compare to other basins of the Bay. Based on the previous studies, no DHS has been measured in Izmit Bay (Morkoç et al., 1988; Tuğrul et al., 1989; Morkoç et al., 1996).

Industrial loads have been reduced by treatment and waste minimization within the last 10 years, but domestic wastes has doubled, due to the increasing population in the Bay. Therefore, the total (domestic + industrial) discharge load into the Bay during the last 10 years has not changed significantly (Morkoç, et al., 2001). The dissolved oxygen content of Izmit Bay decreased dramatically from 1984 to 1999 and reached to a minimum value at 20 m throughout the Bay (Okay et al., 2001). Ergin et al., (1991) suggested that the surface sediments in İzmit Bay are uncontaminated by anthropogenic pollution. However Yaşar et al., (2001) investigated that the heavy metal concentrations are highest in the eastern and central basins. The western basin was also found generally unpolluted with respect to heavy metals by Yaşar et al., 2001.

Fig. 1. The location (left) and bathymetry (above) of the study area. The location of sampling station in İzmit Bay (below).
