**4. Discussion**

DO concentrations of the water column were low in August 1999, after the earthquake, compare to that of other sampling periods. The low DO content was determined in all the stations of İzmit Bay, and particularly in the lower layer waters of the eastern and the central basins, being lower than the detection limit of the method (0.03 mgl-1) (Figure 7b). The negative DO–SDO value along the water column suggested that the oxygen utilization was resulted from the decomposition of organic matter (Figure 5). The limited air-water exchange of free oxygen caused by the spreading petroleum from the refinery fire to the sea surface might be one of the main reason for lowering of DO content in water column. The highest oil concentration was determined in surface water of south of the central basin as 179.2 mgl-1 in August 1999 (Güven et al., 2000, Ünlü et al., 2000). The oil concentrations of the surface water are more than 500 gl-1 in almost half of the western and central basins after the earthquake. In spite of high oil pollution levels of the surface water, the oil concentrations in the lower layer are between 13-55 gl-1in the Bay exception of north of the central basin in August 1999. This oil pollution level decreased to 10.5 mgl-1 in September 1999 and 3.3 mgl-1 in October 1999. The upper layer flows westward to Marmara Sea, while the lower layer flows into the Bay transporting oxygenated Mediterranean originated Marmara Sea waters in September and October 1999 (Güven et al., 2000). This current system provided the removal of the petroleum layer at the sea surface from İzmit Bay to the Marmara Sea and consequently DO concentrations increased in the water column accompanied by phytoplankton bloom (Figure 4a). Phytoplankton bloom was intense in the eastern basin (2,553,000 cell/l, Güven et al., 2000) and possibly the reason for the saturated DO content in this part of the Bay (Figure 5). Since the domestic and industrial wastewater system has been damaged by the earthquake, the nutrient input into the Bay increased, causing the extreme phytoplankton bloom (Okay et al., 2001). In spite of high DO concentrations of the upper layer, DHS is found in the lower layer of the eastern and the central basins (Figure 3). This striking condition clearly indicates the excess organic load that rapidly depositing at the bottom of

Cu (ppm) 0.3-1.1 0.3-1 1.3-4.5 6-26 4-14 Zn (ppm) 0.1-2.3 0.8-37 15-121 14-46 18-98 Fe (%) <0.05 <0.05 0.1-0.6 0.5-1.1 3.8-5.4 Mn (ppm) 1-13 6-51 32-276 32-241 32-176 Co (ppm) 0.1-1.3 0.1-2.2 0.3-3.7 0.2-9 4-9 Cr (ppm) <0.08-4.5 <0.08 1.4-24 2-23 12-51 Al (%) <0.03 <0.03 <0.03 0.1-0.4 2.2-10.9

DO concentrations of the water column were low in August 1999, after the earthquake, compare to that of other sampling periods. The low DO content was determined in all the stations of İzmit Bay, and particularly in the lower layer waters of the eastern and the central basins, being lower than the detection limit of the method (0.03 mgl-1) (Figure 7b). The negative DO–SDO value along the water column suggested that the oxygen utilization was resulted from the decomposition of organic matter (Figure 5). The limited air-water exchange of free oxygen caused by the spreading petroleum from the refinery fire to the sea surface might be one of the main reason for lowering of DO content in water column. The highest oil concentration was determined in surface water of south of the central basin as 179.2 mgl-1 in August 1999 (Güven et al., 2000, Ünlü et al., 2000). The oil concentrations of the surface water are more than 500 gl-1 in almost half of the western and central basins after the earthquake. In spite of high oil pollution levels of the surface water, the oil concentrations in the lower layer are between 13-55 gl-1in the Bay exception of north of the central basin in August 1999. This oil pollution level decreased to 10.5 mgl-1 in September 1999 and 3.3 mgl-1 in October 1999. The upper layer flows westward to Marmara Sea, while the lower layer flows into the Bay transporting oxygenated Mediterranean originated Marmara Sea waters in September and October 1999 (Güven et al., 2000). This current system provided the removal of the petroleum layer at the sea surface from İzmit Bay to the Marmara Sea and consequently DO concentrations increased in the water column accompanied by phytoplankton bloom (Figure 4a). Phytoplankton bloom was intense in the eastern basin (2,553,000 cell/l, Güven et al., 2000) and possibly the reason for the saturated DO content in this part of the Bay (Figure 5). Since the domestic and industrial wastewater system has been damaged by the earthquake, the nutrient input into the Bay increased, causing the extreme phytoplankton bloom (Okay et al., 2001). In spite of high DO concentrations of the upper layer, DHS is found in the lower layer of the eastern and the central basins (Figure 3). This striking condition clearly indicates the excess organic load that rapidly depositing at the bottom of

Fe-Mnoxyhydroxide phase

Organic phase

Residual phase

Carbonate phase

Table 6. Metal distributions in different geochemical phases (%).

Element Exchangable

**4. Discussion** 

phase

the Bay. Although no DHS data is available for the previous sampling period (August and September 1999), the establishment of this anoxic condition at the bottom might have started to develop earlier than October 1999. Earlier studies related to the ocenographic features of the Bay have never determined anoxic conditions in the water column (Morkoç, et al., 1988; Tuğrul et al., 1989; Morkoç et al., 1996).

The Marmara Sea water flows as the upper layer into the Bay in December 1999 and the current system is towards the interior of the Bay, whereas the lower layer flows out of the Bay (Güven et al., 2000). The available DHS formation in the eastern and the central basins is reduced or completely disappears in this month by the outflow of the lower layer (Table 2). This current system becomes reversed in February 2000, entering the lower layer and out-flowing the upper layer. The significant increase of DO concentrations of the upper layer in February 2000 might possibly indicate the replenishment of water column in İzmit Bay with oxygenated waters. This is in agreement with the vertical and spatial distribution of DO concentrations in February (Figures 3 and 4b). The thickness of the upper layer increases to 25-30 m suggesting the entrance of waters into the Bay. DO content of the both the upper and the lower layer slightly decreases in May 2000, together with increasing alkalinity (Figures 4b, 7b, 8 and 9). The reducing DO content in this month might be related with the water influx enriched with nutrients into İzmit Bay from the Black Sea (via the Marmara Sea) that receives increasing amount of freshwater inflow during spring (Oğuz and Sur, 1986; Tuğrul and Polat, 1995). In August 2000, DO concentration of the water column is significantly reduced (Figures 4 and 6), suggesting the enhanced consumption of DO by decomposition of high organic materials that possibly from the subsequent death of blooming phytoplanktons. In the eastern basin, the lowest pH is found in this month, supporting the increasing decomposition processes and the formation of DHS (Figure 9).

The formation of DHS leading to anoxia at the lower layer of İzmit Bay occurs in the eastern basin where the depths are shallower than 30 m and also locally in the deep site of the central basin where circulation is restricted (Table 2). After the Earthquake, in the central and the eastern basins, the formation of DHS is resulted from the spreading petroleum from the refinery fire to the surface waters and accumulation of high amounts of organic load from the damaged wastewater systems, and resuspension of bottom sediments releasing the DHS in the anoxic part of the sediment column. This is in agreement with the low DO concentrations of the water column in İzmit Bay during August and September 1999 (Figures 4a, 7a). The removal of anoxia at the bottom of the eastern and the central basins occurred in December 1999 by the replacing of water layers with the oxygenated Marmara Sea waters. DHS exists in the lower layer consistently throughout the sampling period in station 17 (Table 2), however its thickness varies. The reduced bottom current velocities (Algan et al., 1999) and topographic restriction of this small depression might be the reasons for the presence of DHS, by preventing the circulation.

In August 2000, DHS forms again in the eastern basin in low concentrations (Table 2). This re-occurrence of DHS is related with the extreme phytoplankton bloom. A high amount of organic matter produced from their death consumes oxygen for decomposition in the sediment. High decomposition rates might have led the depletion of DO in the overlying water column and consequent formation of DHS. The seasonal circulation pattern and timing of blooms in İzmit Bay were not different than the present as indicated by the

The Effect of Marmara (Izmit) Earthquake on the Chemical

metal distributions along the bay.

**6. Acknowledgements** 

235-250.

MRC Publication.

methods. *Mar. Chem.* 17, 285-300.

Vol. III, Part II and III.

285-334.

**7. References** 

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 269

originated from the occurring anoxic conditions after the Marmara (Izmit) earthquake. Selective extraction studies indicated that the metals were mainly found in the lithogenous, Fe-Mn-oxvhydroxide and organic fractions. The results underlined that the main source of high metal levels in Izmit Bay sediments is of anthropogenic origin. These conclusions reached by the selective extraction studies were supported by the "total"

The Captain, crew, scientists and technicians on board RV *Arar* of Institute of Marine Sciences and Management of Istanbul University, for their help during the collection of

Algan, O., Altok, H.. and Yüce, H., 1999. Seasonal Variation of Suspended Particulate

Altok, H., Legovich, T. and Kurter, A., 1996. A case study of circulation and mixing

Baştürk, Ö., Tuğrul, S., Sunay, M., Balkaş, T., Morkoç, E., Okay, O.S. and Bozyap, A., 1985.

Beşiktepe, Ş.T., Sur, H.İ., Özsoy, E., Latif, M.A., Oğuz, T. and Ünlüata, Ü., 1994. The

Bruland, K. W., Franks, R. P., Knauer, G.A., Martin, J. H., 1979. Sampling and analytical

Bruland, K. W., Coale, K. H., Mart, L., 1985. Analysis of seawater for dissolved cadmium,

DAMOC, 1971. Master plan and feasibility report for water supply and sewerage for

Doğan, E., Sur, H.İ., Güven, K. C., Polat, Ç., Kratl, N., Yüksek, A., Uysal, A., Algan, O.,

Bilimleri ve İşletmeciliği Enstitüsü, Istanbul Üniversitesi. (in Turkish).

nanogram per liter level in seawater. *Anal. Chim. Acta* 105, 233-245.

September 1996, Netherlands Centre for Coastal Research, pp. 92-96. Ayas, Z., & Kolankaya, D., 1996. Accumulation of some heavy metals in various

Environmental Contamination and Toxicology, 56, 65-72.

Matter in Two-layered İzmit Bay, Turkey. Estuarine, Coastal and Shelf Science 49,

processes in two-layered water system: İzmit Bay. Eight International Biennial Conference on Physics of Estuaries and Coastal Seas, Extended Abstracts, 8-12

environments and organisims at Göksu Delta, Türkiye, 1991-1993. Bulletin of

Determination of oceanographic characteristics and assimilation capacity of İzmit Bay. NATO TU-WATERS Project, Technical Report. Kocaeli, Turkey. TÜBİTAK-

circulation and hydrography of the Marmara Sea. Progress in Oceanography 34:

methods for the determination of copper, cadmium, zinc and nickel at the

copper and lead: an inter comparison of voltametric and atomic adsorption

Istanbul region. Prepared by the DAMOC Consortium for WHO, Los Angles, CA,

Balks, N., Ünlü, S., Altok, H., Gazioğlu, C., Taş, S., Aslan, A., Ylmaz, N. and Cebeci, M., 2000. Su Kalitesi İzleme Çalşmas. Technical Report. İSKİ. Deniz

water samples. This work was supported by the Turkish Ministry of Environment.

previous studies (Oğuz and Sur, 1986; Tuğrul et al., 1989; Morkoç et al., 1996). DO content has never been fallen below 0.5 mgl-1, and no DHS has been detected in İzmit Bay. Therefore, the re-occurrence of DHS a year after the Earthquake might indicate that İzmit Bay has not been completely return to its regular chemical oceanography. This may be explained by the fact that the amount of organic and possible inorganic wastes into İzmit Bay must have been considerably high and/or must have continued to discharge after the Earthquake. Increasing nutrients, phytoplankton blooms, rapid sedimentation of death organisms and decomposition processes constituted a successive cycle in İzmit Bay and intensified by the Earthquake at 17th August 1999. However, decomposition processes within this cycle might not be completed within a year.

The highest pH values found (8.9) at the upper layer compare to other months in the eastern basin confirms the increasing biological activity in October 1999 (Figure 8). During the respiration of phytoplanktons, dissolved CO2 content of water column increases and consequently CO3-2 and HCO3- anions increase. Increasing carbonate causes enhancement of alkalinity. The pH values become 7.9 at the lower layer (Figure 9) where the anoxic conditions are developed (Figure 3) and indicate the decomposition of organic matter.

Total metal contents in the İzmit Bay sediments increase towards to eastern basin. The eastern basin receives the highest inputs compare to other basins of the Bay (Morkoç 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 found generally unpolluted with respect to heavy metals in this study, also.

Selective extraction studies indicate that the metals are mainly found in the lithogenous, Fe-Mn-oxvhydroxide and organic fractions (Table 6). The results show that the main source of high metal concentrations in the İzmit Bay sediments is of anthropogenic origin. The highest metal values in these fractions are found in eastern basin sediments similar to total metal distributions.

#### **5. Conclusions**

Izmit Bay have been polluted by increasing industrial activities and domestic discharges since early 1980. However this abrupt event caused short-time drastic changes in the water column. Earthquake at 17 August 1999 initiated a fast variation in the chemical oceanography of polluted Izmit Bay. This variation includes the consumption of DO and formation of DHS in the lower layer. The refinery fire and damaged municipal waste effluents caused the reduction of DO in water column by preventing the oxygen transfer from air/ water contact and increasing organic wastes, respectively, and as a result DHS was formed. The increasing wastewater into the Bay stimulated the phytoplankton blooms that causes locally saturated DO concentrations in the eastern basin, however anoxic conditions were prevailing in the lower layer during autumn 1999. The changing circulation pattern during winter provided replenishment of the water column in Izmit Bay and removal of DHS. However, DHS formation established again in August 2000.

The distribution of total metals (Fe, Pb, Cu, Zn, Co, Cr and Cd) in both the water-column and surface sediments showed the influences of terrestrial anthropogenic inputs in the bay. The Mn enrichment in the lower-layer water of the central and eastern basins originated from the occurring anoxic conditions after the Marmara (Izmit) earthquake. Selective extraction studies indicated that the metals were mainly found in the lithogenous, Fe-Mn-oxvhydroxide and organic fractions. The results underlined that the main source of high metal levels in Izmit Bay sediments is of anthropogenic origin. These conclusions reached by the selective extraction studies were supported by the "total" metal distributions along the bay.
