Maritime Accidents

In the Marmara region that covers the Marmara Sea and the Istanbul Strait, approximately 450 maritime accidents have been reported within the last 40 years, of which the prominent reason is collision.

The Istanbul Strait is a 31-km-long waterway between the Black and Marmara seas. It is 36 m deep on the average and varies between 0.7 km and 3.5 km in width. Increased shipping through this narrow passage provides impetus for understanding the dynamics of the two-layer exchange flow through the Bosphorus, which is principally determined by its intricate geometry, bathymetry, sheltering effects of coastal features, and stratification. The narrows and contraction regions cause the surface currents to intensify (Figure 2).

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Transience on various time scales in addition to the spatial features makes the currents highly variable. The strait exhibits a complex nonlinear response to forcing by the net water budget, pressure, and wind setup effects in adjacent basins. The Black Sea level is higher than the Marmara Sea level, which means that the currents have a rapid response to the sea level differences between these adjacent basins (Alpar and Yüce, 1998). The surface current exports less saline waters from the Black Sea to the Marmara Sea, forming a jet near the southern exit. Under this 20- to 40-m layer passes a bottom Bosphorus current that imports more saline Marmara Sea waters into the Black Sea. The velocity of the surface current under normal meteorological conditions doubles the bottom current velocity, which reaches up to 1.5 m/s. The currents also depend on revealing eddies and reversing currents in several embayment and shallow banks as well as turbulent meandering of the main current along the strait. This flow system responds rapidly to changes in time-dependent driving forces that create daily interannual variability in the currents. Extreme conditions result in temporary blocking of the flows in either direction. Southerly winds in winter may pull up water at the southern end of the strait, destroy the layer structure at the surface, and often cause upper-layer blocking. The transient changes in the water budget of the Black Sea or setup by persistent northerly winds can temporarily cause the blockage of the lower layer flow (Andersen et al., 1997).

The Turkish Straits constitute one of the world's major waterways between adjacent seas. Every year, an average of 60,000 vessels, 5500 of which carry oil, LPG, and other dangerous and hazardous cargo, pass via the Turkish Straits through Istanbul, a UNESCO World Heritage City, where more than 10 million people live. The frequency of the traffic is estimated to rise by 50% as a result of the increase in foreign trade of the Black Sea states (Oguzülgen, 1995). The heavy maritime traffic will undoubtedly aggravate the risk of accident because the Istanbul Strait, which is the narrowest (698 m) among the major straits of the world and has strong currents, presents a major challenge for navigation. The U.S. Energy Information Administration (EIA) rates the possibility of accidental oil spill the greatest for tankers moving through the Istanbul Strait (Oguzülgen, 1995). The reasons for accidents are identified as follows:

• Unsuitable meteorological conditions (e.g., restricted visibility)

• Natural structure of the strait (topographical and morphological features)

• Strong two-layer flow

• Heavy navigation

• Inadequate pilotage skills

Ship accidents in the TSS are examined mainly under four categories: collision, grounding, fire, and stranding. Accidents caused by supertankers can result in the release of large volumes of crude oil, and heavy tanker traffic increases this risk, especially along narrow channels, which is the case for the Istanbul Strait (Figure 3). Five major maritime accidents (Independenta 1979, Rab Union-18 1991, Nassia 1994, TPAO 1997, and Volgoneft-248 1999) resulting in oil spills occurred in the past within this region where damage caused by accidental collisions to marine environment and human life was the greatest (Figure 4). One of the largest collisions occurred in 1979 between the Greek cargo ship Evriyali (weight 10,000 t DWT) and the Romanian tanker Independenta (weight 165,000 t DWT), which were carrying 94,000 tons of Libyan crude oil. The collision occurred at the Marmara entrance of the Istanbul Strait. This was by far the largest sea accident in Istanbul, causing heavy air and sea pollution in the Istanbul area and Marmara Sea. Heavy oil contamination formed on the surface of the sea and on the shoreline. It was estimated that 30,000 tons of crude oil was burned, and the remaining amount of 64,000 tons was spilled into the sea. The spilled crude oil sank rapidly to the bottom. An area of the sea bottom approximately 5.5 km in diameter was covered with a thick tar coat of a mean concentration of 46 g/m². In this area, only nine species of benthos were recorded alive, and the mortality rate was estimated at 96% (Baykut et al., 1985).

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The next largest sea pollution from a collision was generated by the Nassia accident. After this accident dispersed 20,000 tons of oil to the sea, the marine ecosystem has been destroyed, and all bays and beaches around have been covered with oil and pitch. Major concerns are related to potential effects of spilled oil on commercial fisheries and aquaculture products and to the loss and/or change of habitats. Chronic long-term accumulation of hydrocarbons in coastal and estuarine waters and their contribution to a gradual change of ecological systems has been an issue given the fact that oil products are significantly toxic and adversely influence the life activity of the benthos. Total polyaromatic hydrocarbon concentration has decreased gradually in seawater, but it increased in sediments after the accident (Güven et al., 1996). The total oil amount was determined by UVF (RF-1501 Shimadzu) and intensity measured at 310/360 nm (ex/em). After the Nassia tanker accident, oil levels in the tissues of Mytilus galloprovincialis in the Istanbul Strait were as high as 250 μg/g dry weight (Güven et al., 1995). The impact of oil pollution on the species; Merlangius merlangus, Trachurus trachurus, Parapenaeus longirostris and algae Ulva lactuca, Ceramium rubrum, and Cystoseira barbata were investigated after the Nassia tanker accident. The highest oil contamination was found in Parapenaeus longirostris as 253.9 μg/g and in the algae Ulva lactuca as 175.5 μg/g, 1 month and 4 months after the accident, respectively (Güven et al., 1998).

The huge dimensions of marine vessels and subsequent increase in the amount of cargo have introduced new approaches to avert pollution risk from maritime accidents. The most unfortunate example was the collision and sinking of a Lebanon flag vessel Rab Union-18 carrying live sheep near Fatih Bridge in 1991. This vessel sank with 20,000 sheep and its own oil at 32 meters depth, and it has not yet been hauled up onto shore. The sinking of M/S Rab Union-18, after collision with Madonna Lily, carrying so many sheep, has created great anxiety in the public opinion. It was claimed that decay of the bodies of the animals would cause a high degree of pollution in this important waterway. Dissolved O₂ values decreased to 2 mg/L. Furthermore, water turbidity increased, and transparency value decreased to 0.5 m. Red and green algae population existing in the area when the vessel sank died totally. As a result, mass mortality has been determined in such economically valuable fish populations as Gobius spp. Mullus surmuletus, Mullus barbatus, Physis sp. living in the benthic zone. Fish stocks also declined in the incident area. Mass mortality has also been observed in Rapana venosa and Mytilus galloprovincialis, and their fishing catches decreased. Crangon crangon, known as shore shrimp, has totally disappeared; the sudden changes in the food chain have decreased biological diversity (Yurdun et al., 1995).

The other two accidents resulted in historic oil spills with severe adverse impacts on the environment. The TPAO tanker accident that happened in 1997 is one of them. On February 13, 1997, a tanker named TPAO exploded in Tuzla shipyards located on the northeastern coast of the Marmara Sea, resulting in loss of human life and economic damage. During the fire, which took 4 days to extinguish, an estimated 215 tons of oil was spilled into the Aydinlik Bay. The effect of contamination of the seawater was very high for the first 3 months. During the week following the TPAO tanker accident, the sampling required to investigate the impact of oil spill pollution on the marine life could not be carried out in the inner part of the bay because of heavy oil slicks. The investigation shows that the ichthioplankton diversity was low, but the egg numbers were high (Doğan et al., 1998). Especially following the TPAO accident, very high mortality of fish eggs and/or larvae showed the effect of oil and metal pollution in the bay on the biota. The oil pollution level decreased to the normal level as given in the literature nearly 7 months after the accident (Doğan et al., 1998).

The most recent major accident in the TSS happened in December 1999 in the Marmara Sea, where Volgoneft-248, a river ship, cracked in two because of bad weather conditions. During the accident, 1578 tons of heavy fuel oil spilled, and ecological damage from this accident was computed as 90% of total mortality of sea life (Moller, 2002). Shellfish were killed, and habitats of local fish destroyed. Most of the migrating fish were not affected directly, but plankton and small organisms, more sensitive to oil pollution, were. Because a breakup in the food chain may force the fish to migrate to other areas, as reported by Otay and Yenigün (2000), this fact is very likely to be a severe disturbance for the migrating fish species. The worst environmental pollution in that case happened at the sea surface, sea floor, within the water column, and along the coast. Within a time span of several hours after the accident, the spilled oil was washed on the shores and contaminated the area between the grounded ship stern off the Florya coast (Alpar and Ünlü, 2007). The sandy beaches, rocks, concrete promenades, fishing ports, and coastal structures located along the shoreline were and continue to be directly affected. It is well known that the petroleum residues from tanker operations, accidents, and other maritime sources continue to contaminate many coastlines and beaches worldwide (Knap et al., 1986). The fate of petrogenic and pyrogenic hydrocarbons in coastal sediments following the Volgoneft-248 oil spill was investigated through a detailed study of chemical markers (Doğan et al., 2000). Fingerprints related to the Volgoneft accident can be detected as tar balls of nearly 5 cm diameter dispersed on the shoreline of the accident location, namely the Florya suburb of Istanbul (Alpar and Ünlü, 2007).

Ballast and Bilge Water Release

Bilge water, wastewater, and oil discharge by vessels contribute to a great extent to marine pollution and have severe adverse impact on water quality of the receiving water. In the course of their passage, these vessels release ballast and bilge waters that result in considerable pollution of the receiving waters. Accumulation of petroleum products is noted in the Black Sea and consequently the Istanbul Strait, an intensive navigation zone on Istanbul–Odessa, Yalta (Ialta)–Batumi maritime line. The oil discharge into the Black Sea was estimated as 410,000 t/a; additionally 110,000 tons of petroleum is annually conveyed into the Black Sea by the Danube waters (Faschuk et al., 1996).

Based on the FAO (1982) standards, which limit the maximum allowable oil concentration to 2.5 μg/L in unpolluted seawater, it can be seen that the results given in Tables 1 and 2 of the monitoring study carried out between 1997 and 2001 are much higher than this acceptable figure. Furthermore, the results show an increasing trend throughout the monitoring period.

Table 1. The highest total oil concentration values in the surface water (μg/L)

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Table 2. The highest total oil concentration values in the surface water (μg/L)

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According to the “Regulations Prohibiting Pollution of the Environment of Turkish Straits, Article 33: No refuse, ballast, bilge water, domestic and industrial waste, ecologically harmful material, oil or other pollutants can be dumped or discharged into the sea in the straits and Marmara Region” (Aybay, 1995). Bilge water discharge is a major problem for the Turkish Straits. So far, increase in petroleum hydrocarbon levels, mainly from oil spills in recent years and ship bilge water, has been observed in the Marmara Sea environment. In the identification of deballasting operations in Tuzla Bay, Güven et al. (1997) used GC/MS and FTIR analyses for the first time. It had been detected that the GC/MS chromatograms and spectra of isoprenoid alkanes (e.g., pristane and phytane) peaks for seawater samples and bilge water samples taken from ships were similar.

Ünlü et al. (2004) showed that the petroleum hydrocarbon pollution was in variable levels in the Istanbul Strait. Petroleum hydrocarbon concentrations in the Istanbul Strait sediment varied between 22.8 and 427.9 μg/g dry weight. This was because of the pyrolytic activity that is a potential threat to the environment and to growing economic activities such as ecotourism and fisheries. Important changes in the PAH accumulation in the eastern Marmara sediment are also attributed to the direct influence of anthropogenic activities, mainly combustion processes of traffic and industrial activities (Ünlü and Alpar, 2004).

Heavy maritime traffic along the TSS connecting oceans to the Black Sea is a reason for enroute pollution caused by transboundary navigation. The major environmental hazard has been identified as the introduction of exotic species to the Black Sea. These are generally carried by tanker ballast water or in fouling of ships hulls. For example, in the late 1960s, Rapana venosa appeared in the Black Sea. This species has been introduced, presumably through ship ballast waters from the Sea of Japan. In the absence of a natural predator in the Black Sea, the population grew rapidly, feeding on mussels, oysters, and clams and expanding into the Marmara Sea and Straits (Öztürk, 1998).

The ctenophore Mnemiopsis leidyi is another species transferred by ballast water of ships, this time from the Atlantic coast of North America to the Black Sea (Vinogradov et al., 1989). This comby jelly badly affected all species of pelagic and benthic communities and caused the collapse of the fishing industry in the Black Sea. Catch in riparian countries fell from 250,000 tonnes to 30,000 tonnes. Consequently, the population of those fish drastically decreased due to this exotic species.