Restoration of the Golden Horn Estuary (Halic)

Abstract

Restoration of the iconic Golden Horn Estuary in Istanbul, Turkey was a substantial political, logistical, ecological, and social challenge. Forty years of uncontrolled industrial and urban growth resulted in thick layers of anoxic sediment, toxic bacteria, strong hydrogen sulfide odor, and ecologically unlivable conditions. The major components of restoration, spanning two decades, have included (1) demolition and relocation of industries and homes along the shore, (2) creation of wastewater infrastructure, (3) removal of anoxic sludge from the estuary, (4) removal of a floating bridge that impeded circulation, and (5) creation of cultural and social facilities. Although Turkey is not known as an environmental leader in pollution control, the sum of these efforts was largely successful in revitalizing the area through dramatic water quality improvement. Consequently, the estuary is once again inhabitable for aquatic life as well as amenable to local resource users and foreign visitors, and Istanbul has regained a lost sense of cultural identity. This paper focuses on literature review and personal interviews to discuss the causes of degradation, solutions employed to rehabilitate the estuary, and subsequent physicochemical, ecological, and social changes.

Introduction

Water resources around the world are widely impacted by human activity, especially in developing nations due to perverse financial incentives for development and exploitation, as well as inadequate or absent institutions and infrastructure (Peters and Meybeck, 2000, Pirot et al., 2000). This occurs partially because developing countries are able to spend as little as 1–10% of the sum that buys affluent economies more advanced waste management programs (Brunner and Fellner, 2007). According to the World Bank, up to 3% of a country's gross national product (GNP) can be realistically spent on environmental protection. Thus in low GNP countries (<US$3000/capita), the time required to generate capital investments to meet international standards far exceeds the economic life span of treatment plants and infrastructure (Grau, 1994). In addition to financial limitations, mismanagement of resources, ineffective enforcement, poorly prepared personnel, and limited access to scientific information contribute to the widespread practice of wastewater discharge directly into waterbodies (Kennish, 2002, Massoud et al., 2003, Wagener, 2005). As a result, developing countries are often faced with elevated sewage-borne pathogens, heavy metals, trace elements, organic pollutants, their associated bacteria, resultant oxygen deprivation, and toxic byproducts (Islam and Tanaka, 2004).

In recent years, water resources in Turkey have been severely contaminated by urban and industrial pollution (Burak, 2008). However, the restoration of Istanbul's Golden Horn Estuary (“Halic”) presents a prime example of a developing country ameliorating environmental problems in spite of inadequate management funds, institutions, policy, and legal infrastructure (OECD, 1999, Burak, 2008). Istanbul is the third largest city in the world with a population of over 11 million people, 70% of who are classified as low income (Altinbilek, 2006). Like many developing metropolises, it became subject to chaotic, unplanned urbanization and industrialization when factories began to dominate the iconic estuarine shores. Mismanagement led to serious environmental problems, health and social impacts, as well as local ecological collapse within and around the estuary. However, reorganizing and strengthening municipal institutions proved critical in reversing the effects of pollution by undertaking one of largest rehabilitation efforts of its kind (Dalan, 2006). Over the past 30 years, numerous monitoring studies were undertaken in the Golden Horn by a wide variety of researchers, but they have lacked thorough integration. In this study, the history, causes, and impacts of contamination and restoration efforts are presented by review and synthesis of this data set and supplementary personal interviews.

Estuaries are transitional zones between rivers and seas, and are important ecosystems typically rich in biodiversity. The Golden Horn Estuary supported thriving fisheries until the latter 20th century. It is a 7.5 km long, 200–900 m wide horn-shaped body of water that connects the Alibeykoy and Kagithane Rivers to the Bosphorus strait. Estuarine surface area covers 2.6 km² and maximum depth is 36 m at the mouth, sloping to <1 m near tributary inflow. The shallow inner estuary, defined as the area north of the Valide Sultan/Old Galata Bridge (Fig. 1), is more prone to anoxic conditions given that its depth abruptly slopes to <5 m near the bridge. The water column is a highly stratified product of the Mediterranean Sea (∼38 psu), Black Sea (∼17 psu), and freshwater urban runoff, precipitation, and a small fluvial contribution. Freshwater remains on the surface due to a greater rate of input (300,000 m³ of freshwater enter the estuary annually) than evaporative loss (Ozturk et al., 1998, Alpar et al., 2005). These three layers, separated by strong density gradients, effectively resist mixing of estuarine waters, and movement via tidal mixing or currents is negligible at <10 cm/s (Aksit, 1977). For more oceanographic and related description see Kor, 1963, Gunnerson, 1974, Saydam et al., 1986, Basturk et al., 1988, and Ozsoy et al. (1988). Low velocity surface winds and stable atmospheric conditions contribute to minimal air ventilation in the surrounding area (Incecik, 1986). Thus, both water and air circulation are severely hampered in and around the Golden Horn, which has led to a local environment extremely prone to lasting pollution problems. These conditions are compounded by steep hills lacking foliage, the presence of stone quarries, and the absence of drainage systems, all encouraging substantial erosion and estuarine sedimentation (Aksit, 1977).

The Golden Horn lies in the center of the historic city and played a substantial role in Istanbul's culture for thousands of years, particularly for its numerous harbors, abundant fish populations, and recreation grounds. In the mid fifteenth century, it was subject to one of the world's first management policies when Sultan Mehmet the Conqueror limited settlement, encouraged afforestation to combat erosion, banned local agriculture, and encouraged use of alluvial mud by exempting ceramic artisans from taxes (Aksit, 1977, Eroglu, 2001). Similarly, President Mustafa Kemal Atatürk did not allow factories to be built near what was known as the “the most romantic waterway in Europe” in the 1920–1930s. As a result, the most substantial environmental problems upto this point were shipping discharges and accumulation of silt on the floor of the estuary (Inanc et al., 1998, Ozturk et al., 1998).

The allure of industrialization prevailed after World War II, and rural people relocated to Istanbul when the Marshall Plan provided a means to increase infrastructure (Yalpat, 1984). Formerly prestigious and fashionable areas around the Golden Horn were designated for industrial development by the Municipality according to the Prost plan of 1933 (Yerliyurt and Hamamcioglu, 2005). Subsequently, one-third of the estuarine surface area was filled to accommodate factories and their associated tenements with no provision for stability, industrial or domestic waste disposal, or treatment (Eroglu, 2001, Yerliyurt and Hamamcioglu, 2005). By 1975, 696 industrial plants haphazardly occupied a total of 1.6 km² along the estuary and nearby river shores (Fig. 2). Metal smelting, electrical, appliance, machinery, textile, wood, food, and meat production facilities comprised 71% of this area, 28% was shipyards and docks, and 8% supported warehouses (Aksit, 1977).

Subsequently, 200,000 tons of liquid (67% chemical waste, 27% wash water, 4% cooling water, and 2% wastewater) were discharged into the Golden Horn daily. Additionally, wastes from shipping and passenger transport contributed 3.1 million tons of industrial materials and coal per year (Aksit, 1977, Samsunlu, 1988). Furthermore, the shores of both streams feeding the estuary were also developed, leading to the local annual release of 1.9 million tons of liquid and 49,000 tons of solid waste from 364 industries (Tezcan and Durgunoglu, 1977). It has been estimated that in 1980 alone all of these industries discharged 24,000 tons of chromium, 300 tons of copper, 130 tons of nickel, and 7500 tons of zinc (Tuncer et al., 2001). Industrial discharges contained upto 370 times more chromium, 290 times more copper, 45 times more lead, 1.5 times more zinc, 10 times more oil and grease, 14 times more suspended solids, and 18 times higher chemical oxygen demand levels than allowed by discharge standards created in 1995, as well as pH values well outside acceptable ranges (Gunnerson, 1974, Aksit, 1977, Sarikaya et al., 1997). The concentration of detergents in estuarine waters was measured at 1.4 mg/L (Aksit, 1977), whereas after 1995 no nonbiodegradable detergent discharge has been allowed (Sarikaya et al., 1997). Contaminants have also entered the Golden Horn through ship transport, operations, ballasting, storage, washings (gas-freeing operations), and accidents, including a 70,000 ton crude oil spill in 1979 just outside the estuary (Akten, 2003, Akten, 2004, Guven et al., 2005).

Evidence of industrialization has been found in deep sediments of the Golden Horn, due to poor circulation and massive contaminant absorption. The concentration of anthropogenically-derived elements was relatively constant in sediment dated between 1912 and 1950, but dramatically increased after this time, unlike naturally occurring lithophilic elements. The two major sources of anthropogenic metals, especially zinc, copper, and lead, were discharges from an iron and steel plant beginning in 1948 and metalwork industries commissioned in 1959 (Tuncer et al., 2001). Chromium tended to emanate from textile factories and leather tanneries, while nickel was released from electrometal industries, battery plants, and dockyards. Concentrations of chromium and nickel categorize Golden Horn sediment of the late 1980s as moderately contaminated, while zinc, copper, and lead levels are classified as moderately to extremely contaminated, compared to sites around the world (Ergin et al., 1991, Saydam and Salihoglu, 1991).

Another major source of pollution, Istanbul's sewer system consisted of drains dating to Roman and Ottoman periods, as well as isolated cesspools and septic tanks, until the 1980s. Crude housing developments discharged 100,000 m³ of raw domestic wastewater per day into 123 major and at least 500 minor sewers that led to the Golden Horn (Gunnerson, 1974, Dalan, 1988). Explosive urbanization in the second half of the twentieth century and a migration rate as high as 14% in the early 1980s forced Istanbul to further expand, although the city lacked infrastructure necessary to treat subsequent domestic wastes, as seen in Fig. 3 (ISKI, 2006). Domestic discharge of heavy metals increased logarithmically between 1950 and 1985, and in 1980 was estimated to include 50 tons of chromium, 90 tons of copper, 13 tons of nickel, and 120 tons of zinc (Tuncer et al., 2001).

Unplanned, uncontrolled urban development around the Golden Horn and its waste production soon gave rise to anoxic sediment buildup, stifling hydrogen sulfide odor, high concentrations of harmful bacteria, mosquitoes, disease, and a lack of formerly abundant biota (Kor, 1963, Gunnerson, 1974, Karpuzcu, 1974, Karpuzcu and San, 1975, Aksit, 1977, Orhon et al., 1980, Kinaci, 1982, Tuncer et al., 2001, Aslan-Yilmaz et al., 2004, Yuksek et al., 2005). Concentrations of fecal coliform were often 2–5 orders of magnitude greater than levels regarded as hazardous by the United Kingdom (Karpuzcu, 1974). These high bacterial counts contributed to incidents of disease, including 2000 times more cases of typhoid per capita than the United States in the 1960s, and a major epidemic in 1970 (Gunnerson, 1974). Rampant factory emissions also led to a rate of lung cancer approximately ten times greater among residents of the Golden Horn than in surrounding areas (Dalan, 2006).

The third major source of pollution was debris entering the creeks and estuary from industrial waste, largely due to slaughterhouse activities, shipbuilding, repairing, and dockyard operations, as well as erosion via chaotic urbanization, deforestation, and livestock grazing (Dalan, 1988, Kanat, 2004). Ten vertical cm was added to the benthos annually by the entry of 260,000 m³ (50,000 tons) of solid waste high inorganic material, nutrients, heavy metals, and hydrocarbons. Estimated alluvial input was 60,000–80,000 m³/year (Karpuzcu and San, 1975, Aksit, 1977, Inanc et al., 1998, Eroglu, 2001, Alpar et al., 2005). In the outer estuary (Fig. 1) sedimentation was estimated as 3.5 cm/year, which is still greater than most globally reported rates for bays and estuaries (Teksoz et al., 1991, Tuncer et al., 2001). This contributed to 76% of inner and 31% of outer estuarine surface sediments being composed of solid matter in 1995, as well as containing up to 50–80 mg/L hydrogen sulfide (Aksit, 1977, Inanc et al., 1998, Kinaci et al., 2004).

Additional trouble with solid debris stemmed from extensive uncontrolled filling of the Golden Horn's shores with gravel, sand, brick, silt, and clay. Fill material and thickness varied by location, and resulted in differential building settlement, uneven compression, lateral movement, displacement, and massive structural problems. In 1957 a building collapsed, and until they were demolished, the Sutluce livestock sale pavilions, Eminonu vegetable market, and Unkapani chamber of commerce were highly unsound as well (Aksit, 1977, Dalan, 2006).

Another significant problem plaguing natural recovery from pollution was the presence of a floating bridge near the mouth of the estuary. Initially built in 1912, the Galata Bridge (now known as the Valide Sultan/Old Galata Bridge) rested on pontoons that dipped 4 m below the surface, making effective circulation of the upper water column impossible (Inanc et al., 1998, Sur et al., 2002, Alpar et al., 2005). While in place, the top 2–3 m of low density water maintained lower dissolved oxygen and salinity as well as higher temperatures. It also retained large concentrations of suspended matter, effectively occluding light from the rest of the water column (Ozsoy et al., 1988, Sur et al., 2002). Furthermore, floating bridges deliver toxins such as lead, rust, paint, solvents, abrasives, and cleaning products more readily than normal bridges (Alpar et al., 2005).

As a result of these issues, measured water clarity was consistently low, dissolved oxygen levels were always rated “unusable” (<3.5 mg/L) by US EPA standards (Mitchell and Carson, 1981, Luken et al., 1992), almost all aquatic life was rendered locally extinct causing fishery collapse, and a stench that greatly reduced the quality of life around the Golden Horn pervaded (Aksit, 1977, Kinaci, 1982, Kinaci et al., 2004, Yuksek et al., 2005, Yuksek et al., 2006). Local residents tended to be poor and unable to relocate to healthier areas, businesses were space and infrastructure-limited, and the city was disgraced by the state of its formerly prestigious center of culture and recreation. These symptoms prompted one of the world's largest estuary cleaning and rehabilitation projects, given the complexity of the situation and need for a multifaceted, staged approach (Altinbilek, 2006, Dalan, 2006). Restoration was undertaken as a series of solutions to contributing problems, with the knowledge that no single approach would resolve the situation without being part of a larger, long-term plan.