Izmit Bay (Turkey) ecosystem after Marmara earthquake and subsequent refinery fire: the long-term data

As a part of Marmara Sea, Izmit Bay (Turkey) has been one of the most polluted sites in the region for the last 25 years. On 17 August 1999, a powerful earthquake along the North Anatolian Fault struck the eastern part of the Marmara region including Izmit Bay. The earthquake destroyed many coastal cities. The Bay was also affected by the quake and subsequent fire in the refinery situated on the north-eastern coast of the Bay. Oceanographic characteristics and polycyclic aromatic hydrocarbon (PAH) levels of Izmit Bay (Marmara Sea) have been investigated to find out the degree of contamination. Seawater samples were collected at nine stations of the Bay in April and September 1999 and the results were compared with those obtained in the previous years (1984 and 1994). Monitoring data are presented for plant nutrients (nitrate + nitrate, ortho-phosphate and silicate), dissolved oxygen and chlorophyll a. Surface sediments and mussels, Mytilus galloprovincialis, have been analysed for total PAH (T-PAH) contents in April and September 1999 (before and after the Marmara Earthquake) for the samples collected from eight coastal stations of the Bay. Biomarker (Lysosomal stability and feeding rate) studies at three different sites of the Bay have also been performed to investigate the effect of pollution on mussels. Nitrate + nitrite levels in the upper layer of the eastern part of the Bay increased significantly compared to those measured before the earthquake. Of the samples analysed, the highest o-phosphate concentrations were found in September 1999 in the bottom waters of the Bay. The concentration of chlorophyll a reached its minimum value of the last 15 years. Dissolved oxygen decreased dramatically from 1984 to 1999. Total PAH concentrations measured in April 1999 at both offshore and coastal sites of the Bay were more or less the same (2 micrograms l-1). The subsequent fire after the earthquake caused an increase in the total PAH levels in water column, in sediment and in mussels. Seawater total PAH concentrations ranged between 3.5 and 11 micrograms l-1 at open coast stations and 5-17.5 micrograms l-1 at coastal stations in September 1999. A 2- to 3-fold increase in sediment PAH concentrations (200-5220 mg kg-1 dry weight) was detected after the earthquake. This increase was much more significant in the sediments located around the refinery. More contaminated mussels were detected around the refinery area (110-170 mg kg-1 dry weight). Overall, sediment and mussel PAH concentrations in Izmit Bay are much higher than those found in the other marine systems. In general, the feeding rate and the neutral red retention times of the mussels decreased in some sites of the Bay after the earthquake, but no direct correlation could be detected between the body burden of mussels and biomarkers or between the two biomarker techniques.