Sydney Harbour – Tainted wilderness Australia’s most well-known estuarine system, is renowned for its complex system of inlets formed by the drowning of a river valley. It has also been drowned in pollution and is slowly recovering from an industrial legacy. The Harbour formed during sea level rise approximately 10,000 years ago. The estuary, which has a complex shoreline and topography, is approximately 30 km long, with a surface area of about 50 km2 and a total catchment of 500 km2. The Parramatta River, Lane Cove and Middle Harbour are major tributaries joining the main estuary channel. In the early days of the colony of New South Wales, the area was sometimes known as Long Cove, presumably for its long narrow shape. The entrance is approximately 3 km wide with a depth of up to 30 m. Then the estuary opens up to form Port Jackson. Before 1788 Sydney was culturally divided between the inland paiendra ‘tomahawk people’ and the harbour side katungal ‘sea people’. The katungal people called themselves Eora. The harbour had an important role in providing food for Aboriginal people and the new settlers, it was also the major transport route. By the second half of the twentieth century there was extensive recreational use of the harbour such as boating and picnicking. At one time there were more than 20 swimming baths along the Parramatta River. As the use of motor vehicles increased, the use of the waterways as a form of transport declined. Altered banks Over time much of the vegetation along urbanised areas was removed, some banks were lined, streams concreted over, marshes reclaimed, and mangroves removed. Sewage poured into the river, carcasses were left to rot, and garbage was dumped along the shore. This estuary is now one of the most modified estuaries in the world, 90% of the catchment is urbanized or industrialized. It is home to a growing urban centre of 4 million people, and more than 50% of the foreshore has been concreted or otherwise armoured. Sydney’s population will grow from 4.5 million to 7 million during the next 45 years. Heavy Metals Waterways still bear the scars of decades of dumped toxic waste before regulations in the 1970s banned the practice. Some areas are badly affected by heavy metal contaminants. The main contaminated areas of the Parramatta River are Homebush Bay, Iron Cove and Breakfast Point. Areas where the water is very shallow or stagnant can experience a build-up of contaminants and algal blooms. At night, when the algae don’t photosynthesise, they take up oxygen supplies needed by fish, making their survival much harder. Stagnant water can contain toxic algae, which is easily eaten by marine animals, including shellfish. In this way, contaminants can work their way up the food chain. Iron Cove Creek (Dobroyd Canal) suffers from organic and hydrocarbon pollutants. In particular, very high levels of copper, zinc, and lead have been detected in the bay. Some of this pollution is contained in road dust, which is washed into the bay in stormwater. Dioxins are a group of persistent environmental pollutants that accumulate in the food chain. The dioxin contamination of Sydney Harbour comes largely from the Union Carbide site at Rhodes adjacent to Homebush Bay. From 1928 until its closure in 1986, the site was used for the manufacture of a wide range of highly toxic chemicals, including timber preservatives, pesticides and plastics. From 1949 until 1976, the site 12 was used to manufacture particularly dangerous herbicides. The soil and groundwater on the site were highly contaminated. In the 1970s, site management was improved to comply with new environmental laws. Dioxins from the site have spread throughout the sediments at the bottom of Sydney Harbour. It is impracticable to remediate the extensive area of the harbour that is contaminated. Fishing Bans Fishing bans have been in place around Homebush Bay since 1989, and were extended to parts of the Parramatta River in 1990. The extent of contamination from the site was not recognised until 2006, when all commercial fishing was banned in Sydney Harbour after tests revealed elevated levels of dioxin in fish and crustaceans in the harbour. Recreational fishing in the Harbour has not been banned but, based on advice from an expert panel, the NSW government recommends that: ? No fish or crustaceans caught west of the Sydney Harbour Bridge should be eaten. ? For fish caught east of the Sydney Harbour Bridge, generally no more than 150 grams per month should be consumed, except for species for which specific higher consumption limits have been established (for example, 1,200 grams of sand whiting). A NSW government study suggested that much of Sydney Harbour will remain contaminated by dioxins at levels that will make eating fish from much of the harbour unsafe for decades [I’d suggest forever]. In context, the report reminded people that Sydney Harbour is only as contaminated as most other harbours in industrialised cities. Marine wilderness Despite this pollution Sydney Harbour hosts a diversity of marine habitats and marine species. Twice the number of fish species have been recorded from Sydney Harbour (550) than for the entire coast of the United Kingdom (200). Powerful flushing events keep the system working. After a large storm, millions of litres of stormwater flow into the harbour and form a freshwater layer above the saltwater. This creates a turbid plume up to two metres deep that flows down the harbour. As the rain stops and the plume slows, it starts to break down and mix with the salt water. Although the plume has temporary negative effects on marine species, the movement of this stormwater into the lower reaches of the harbour dilutes the pollutants to a safe level. Harbour waters then exchange relatively quickly with the open ocean. Water entering from the ocean travels along the sea floor because of its cold temperature, dense consistency and high salt level. Once it has gone past the heads, the force of the ocean dilutes the contaminants to undetectable amounts. Good water exchange with the ocean means that the harbour can be cleansed of pollutants and organisms can easily move in and reproduce. Important wetlands Major wetlands include Bicentennial Park Wetlands and Newington Wetlands There are significant stands of mangroves along the river west of Henley (on the river’s northern shore) and Mortlake (on the river’s southern shore) and in the Lane Cove River. The mangroves have actually colonised areas that were previously salt marsh. Research into historical drawings and writings indicates that the mangroves were far fewer at English colonisation. Council information panels in Glades Bay explain that the bay’s now extensive mangrove stands would once have been open water, sandy beaches and outcrops of rock. Land clearing and development has allowed soil and various nutrients to be washed into the river. This has provided an ideal environment for mangroves to colonise. The excessive siltation of the river is an ongoing problem. Sounds grim? Given the size of the population around Sydney Harbour, it is a relatively clean system. It has a vibrant collection of marine life in the oceanic parts of the harbour, and plenty of things to see and do.