© by PSP Volume 15 – No 12a. 2006 Fresenius Environmental Bulletin 1521 ANTHROPOGENIC POLLUTION IN SEDIMENTS FROM THE GULF OF GEMLIK (MARMARA SEA, TURKEY); CAUSE-RESULT RELATIONSHIP Selma Ünlü 1 , Bedri Alpar 1 , Şenol Aydın 2 , Cengiz Akbulak 3 , Nuray Balkıs 1 , Ipek Barut 1 , Engin Meriç 4 , Abdullah Aksu 1 and Çiğdem Kırbaşoğlu 5 1 Istanbul University, Institute of Marine Sciences and Management, 34116 Vefa, Istanbul, Turkey 2 Turkish Navy, Department of Navigation, Hydrography and Oceanography, 34805 Çubuklu, Istanbul, Turkey 3 Istanbul University, Department of Geography, Beyazit, Istanbul, Turkey 4 Hüseyin Bey Sokak, 15/4, 34710, Moda, Kadikoy, Istanbul, Turkey 5 Turkish Atom Energy Association, Cekmece Nuclear Research and Training Center, Halkali, Istanbul, Turkey SUMMARY A geochemical study of modern sediments across the Gulf of Gemlik in the Marmara Sea, Turkey, was carried out to investigate the main controls on the distribution of anthropogenic pollution. The textural composition, organic carbon content, heavy metal and PAH distribution, and their cause-result relationships from a total of 72 samples (from 6 to 320 m water depths) have been studied. In order to assess the relative importance of productivity, organic car- bon accumulation and preservation, the results were com- pared with two sets of historical data covering the periods of 1990 and 1997. The eastern and southern coasts are mainly influenced by rapid industrial development, mak- ing this semi-enclosed embayment one of the most pol- luted hot spots in the Marmara Sea; an inland sea connect- ing the Black Sea to the Aegean Sea via the Turkish straits. Foraminiferal density and species richness of the assem- blages decrease with an increase in heavy metal and PAH concentration and therefore may be used as pollution in- dicators. The more polluted areas are dominated by the tol- erant pioneer species Amonia tepida and possibly Ammo- nia compacta and Elphidium crispum that may be used as bio-indicator of pollution, mainly in the inner part of the embayment and in the harbors. KEYWORDS: sediment, organic carbon, heavy metals, polycyclic aromatic hydrocarbon, benthic foraminifera. INTRODUCTION The Marmara Sea is a gateway between the Black Sea, the world's largest anoxic basin, and the highly saline Ae- gean Sea (Figure 1). It is controlled by a permanent two- layer flow system; less saline surface outflow coming downwards from the Black Sea and reverse saline subsur- face in-flow coming from the Aegean Sea. The dissolved oxygen (DO) content in the lower layer decreases west to east due to microbial oxidation of organic matter [1]. The only major rivers are from the south and supply nutrient and organic matters to the southern shelf. Between the Black Sea’s high primary plankton production and the Aegean Sea’s low production, the total organic carbon (TOC) content in the western Marmara Sea sediment (0.5- 1.0%) is lower than that in the eastern part (1.0-1.5%) [2]. The Gulf of Gemlik, considered to be one of Turkey’s most industrialized regions, is contaminated by persistent organic and heavy metal pollutants. It is subject to high an- thropogenic pressure due to inputs from rivers, atmosphere, coastal shipping, increasing urbanization and industrial complexes. The total of the house waste water discharge of the highly populated (>130,000) towns of Gemlik and Mudanya into the sea is more than 7.5 million m 3 y -1 [3]. The Kocasu River is the most important sediment source in the west with a mean annual suspended solid discharge of 6.5 x 10 5 t [4], while the Karsak River is the most im- portant pollution source in the east. Many industrial com- plexes use this river and discharge their load directly into the Gemlik port. Its total load varies seasonally and the share of the mostly untreated industrial waste water is high- er (13-to-20 million m 3 y -1 ) [3]. In this study, the distribution, accumulation and cause- result relationships of carbonate and TOC contents, heavy metal and polycyclic aromatic hydrocarbon (PAH) concen- trations in the Gulf’s sediment were investigated. Two ear- lier marine surveys carried out (mainly on TOC and heavy metal) were also considered to estimate the trend of the an- thropogenic pollution in this semi-enclosed basin.