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Compiled by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland
Department of the Environment, Sport and Territories, Canberra (1995)
ISBN 0 642 17391 5
Marine organisms may be affected by a range of discharges and emissions including nutrients and sediments, heavy metals, organochlorines and litter. Most of these (in the order of 80% according to some commentators(84) enter the sea from the land, from point-sources such as pipes and drains as well as from diffuse sources from catchments and from the atmosphere.
In recent years many of Australia's inland waterways have suffered catastrophic blooms of toxic blue-green algae because of high levels of nutrients from agricultural run-off and urban sewage. Eutrophication, an increase in algal growth because of elevated nutrients, also becomes a problem when polluted waters reach estuaries and enclosed bays. Coastal eutrophication is a growing worldwide problem, and is one of the most serious, large-scale threats to Australia's nearshore marine environment.(42)
Australian coastal ecosystems are particularly vulnerable to eutrophication and sedimentation as they evolved under very low nutrient and sediments regimes and are widely dominated by nutrient-sensitive corals in the north, and seagrass in the south. Estuaries and coastal lagoons whose upper river catchments have been cleared for intensive agriculture and whose lower reaches are subject to major urban and industrial developments are at particular risk.(42)
Clearing of land, overgrazing and cropping have greatly increased soil erosion and, consequently, the amount of sediments entering the sea. Increased sedimentation is the major contributor of nutrients entering the sea. For example, it is estimated in Queensland that four times more sediments, nitrogen and phosphorus now enter the sea each year than in pre-European times.(42)
Fertilisers are a significant source of nutrients in agricultural areas. Because Australia's ancient leached soils are particularly low in phosphorus, superphosphate fertilisers are applied to crops and pastures. Superphosphate use has steadily increased since 1950, and is currently about 350,000 tonnes a year. Application of nitrogenous fertilisers has also steadily increased and is around 370,000 tonnes a year.(42)
Sewage and stormwater run-off are major sources of nutrients in urban areas. Most of Australia's sewage is only secondarily treated and remains high in nutrients. Each year around 10,000 tonnes of phosphorus and 100,000 tonnes of nitrogen are discharged through sewage, much of which finds its way into the marine environment. Tertiary treatment which removes nutrients is now being introduced in inland towns because of eutrophication of rivers. However, stormwater run-off from cities is also high in nutrients from animal and other wastes and may equal that generated from the city sewage.(42)
Many areas around Australia have experienced major changes to marine ecosystems through elevated nutrients. Very large areas of seagrass in southern Australia have suffered die-back from eutrophication and sedimentation(10) (Chapter 1). Nuisance and toxic blooms of seaweeds and phytoplankton are also now common in many southern bays and estuaries(14), (42). Amongst the worst affected areas are the Peel-Harvey system and Cockburn Sound (WA)(42),(56); Holdfast Bay and Barker Inlet (SA)(42),(55); Gippsland Lakes and Port Phillip Bay (Vic)(42),(53); and Lake Illawarra, Lake Macquarie, Tuggerah Lakes, and Georges River (NSW)(42),(52).
There is a growing concern that the Great Barrier Reef lagoon, the body of water between the Reef and mainland, is becoming eutrophic, and that corals on inner reefs may be declining(42). It has also been suggested that elevated nutrients are responsible for outbreaks of crown-of-thorns starfish by increasing the survival rates of their larvae(49). Major research programs are under way on these subjects(69).
The economic costs of reducing eutrophic systems are great. For example, the engineering to reduce algal growth in Cockburn Sound (WA) cost $170 million, in the Peel-Harvey estuary (WA) cost $50 million, and in Tuggerah Lakes (NSW) cost $12 million. The estimated cost of the proposed Sydney Clean Waterways Program was $7.1 billion over 20 years(42).
Figure 89: Elevated sediments and nutrients are a major issue on the Great Barrier Reef. (a) The amounts of sediments entering the sea from Queensland's rivers have increased greatly since European colonisation because of land erosion(42).
Managing nutrients involves controlling point source discharges, rechannelling sewage into better flushed environments, sewage nutrient minimisation, and in extreme cases excavating artificial channels to increase flushing and mechanically removing algae. Management of diffuse sources of nutrients is undertaken in some areas through integrated catchment management to reduce soil erosion and improve fertiliser management. Integrated catchment management is one of the most important initiatives in the management of Australia's terrestrial - and its marine - environments(14), (42).
Crude oil and refined petroleum are complex substances made up of hundreds of different compounds of two types alkanes and aromatic hydrocarbons. The former have low toxicity; the latter include environmentally harmful polycyclic aromatic hydrocarbons (PAHs) which are carcinogens and which have been implicated in a wide range of human health problems and diseases in aquatis organisms. PAHs also strongly accumulate in food chains and bind to organic material in sediments.(43)
While the large oil spills from ships (36) grab headlines (Chapter 3), far more oil actually enters the marine environment from industrial, sewage and stormwater discharges from land, and these have a chronic effect on coastal marine life (43, 93)
It is estimated that globally, 36.3% of oil pollution enters the sea from terrestrial sources, 45.2% from shipping (of which 12.5% comes from tanker accidents), 9.2% from the atmosphere, 7.7% from natural sources and 1.5% from offshore oil exploration and production. (93)
In Australia the greatest sources of marine oil pollution are terrestrial outflows from sewage systems and drains, which are estimated at 16,000 tonnes a year, and operational discharges from shipping. The largest number of spills at sea result from accidents during fuelling of vessels in ports. (37, 43)
Figure 91: shore crabs smothered by an oil spill, Cockburn Sound (WA). Source: N. Coleman
Petroleum hydrocarbons are present in different concentrations in water, sediments and biota in the marine environment, but are normally at less than 1 microgram per litre concentrations. Background levels are difficult to establish as many organisms produce natural compounds similar to petroleum hydrocarbons. Waters from areas in Port Phillip Bay and Western Port (Vic), and the Brisbane (Qld), Parramatta (NSW), and Yarra Rivers (Vic) have been contaminated from urban run-off, sewage and petrochemical industries. Sediment concentrations similarly range from background levels in remote areas (e.g. on the Great Barrier Reef) localised contamination in urban areas (e.g. in the Yarra River, parts of Western Port).
Table 8: Occurrence of petroleum hydrocarbons in Australian waters and sediments (43)
|Great Barrier Reef||0.29 petroleum|
|Port Phillip Bay (Vic)||0.2-22.6 petroleum
0.25-07 total hydrocarbon
|Western Port (Vic)||<0.1-7.1 pertroleum|
|Yarra River (Vic)||0.05-0.41 PAHs|
|Parramatta River (NSW)||0.17-0.41 PAHs|
|Brisbane river (Qld)||0.10-0.28 PAHs|
|Great Barrier Reef||0.2-0.8 dry wt hydrocarbons|
|Brisbane River (Qld)||3.9-16.1 dry wt PAHs|
|Parramatta River (NSW)||0.1-13.6% grease|
|Mallacoota Inlet (Vic)||0.80-0.11 PAHs|
|Western Port (Vic)||2.3-5,271 dry wt hydrocarbons|
|Corio Bay (Vic)||0.49-3.0 PAHs|
|Corio/Geelong/||6-1516 petroleum hydrocarbons|
|Port Phillip Bay (Vic)|
|Yarra Estuary (Vic)||0.12-10.9 PAHs|
|Rowley Shelf (WA)||0.015-0.05 dry wt alkanes|
|Background||variable (<1 µg/1)|
Heavy metals such as copper, lead, cadmium, zinc and mercury, as well as tributyl tin (TBT) from antifouling paints, have become serious contaminants in the world's estuaries and coastal waters in recent years. The heavy metals enter the marine environment via urban stormwater run-off, industrial effluents, sediments from mining operations, and atmospheric fall out. Tributyl tin comes from paint on boats' hulls and from slipway operations during repainting. Heavy metals tend to attach to suspended particles in the sea, and ultimately accumulate in bottom sediments.(44)
Heavy metals were identified as a major global pollution threat following a series of eco disasters in the 1960s. The Derwent River in Tasmania was found to be particularly contaminated by metallurgical wastes, pulp mill effluents and partially treated sewage and was then regarded as one of the most polluted places in the world.(44)
Since then significant advances have been made in reducing the problem in Australia through implementation of water quality guidelines and effluent controls. Heavy metals now pose only localised problems, or potential problems, near some of the State capitals and industrial areas like Port Pirie (SA), Lake Macquarie (NSW), and the Derwent and other estuaries in Tasmania. However, concerns remain about the high levels in some sediments, and the long-term effects of moderate but sustained levels through bioaccumulation by fish, molluscs, algae and seagrass. Dredging of contaminated sediments in estuaries is also a problem. Standards for heavy metal levels in dredged sediments do not currently exist in Australia and levels frequently exceed those operating overseas. Australian guidelines are currently under development.(44)
Table 9: heavy metals in selected estuaries, coastal water and sediments
Tributyl tin (TBT) has been widely used in Australia as a poison in antifouling paints since the 1970s. During the 1980s TBT was found to affect the growth of oysters and other molluscs, and a ban was recommended on its use on vessels smaller than 25 metres.(44)
Table 10: Tributyl tin levels* in selected waters in Australia(44)
|Georges River (NSW)||8-40 (pre-ban)
|Kogarah Bay (NSW)||100 (pre-ban)|
|Port Phillip Bay (Vic)||3-23 (pre-ban)|
|Southport (Qld)||45 (pre-ban|
*(nanograms per litre)
Prior to the ban on TBT, levels of concentration in Australian dockyards and marinas were frequently 50 times the guideline. Since the ban, levels have dropped appreciably, to below the guideline. Concentrations are now less in surface sediments than in older sediments below.(44)