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The accepted thinking around the phenomena of marine pollution has centred around a definition developed by a UN body, the Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP), who define it as the... "Introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazard to human health, hindrance to marine activities including fishing, impairment of quality for use of sea-water, and reduction of amenities."
At Gunnamatta, the effluent discharge causes major damage to the ecosystem.
The effluent acts as a "plume" (a visible pattern) once it is discharged at Gunnamtta. The plume behaves very diversely according to the conditions of wind, tide and swell. It is documented (Lord 1996) that remnants of the plume can round the headland at Cape Schanck approximately 7 km to the south east.
The discharge of effluent influences a number of environmental values and associated beneficial uses of the area. These include:
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Protection of ecosystems - rocky intertidal plant and animal communities
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Recreational Water Quality Aesthetics - discolouration and odour, shoreline litter
(eg. plastic and cotton buds)
The marine environment at Boag's Rocks has been stripped of its original brown algal cover, species of red algae as well as the organisms which depend on them for food and habitat. The two species that were in abundance in this area are Neptune's Necklace (Homosira Banksii) and Bull Kelp (Durvillea). These species were the most obvious marine plant in the area that are noticed in abundance further along the coast at Sorrento and Portsea.
It is documented (Lord 1996) that Neptune's Necklace disappeared at Boags Rocks by 1980 and from St Andrews by 1985.
What is noticed at low tide at Gunnamatta, Fingal Beach and Rye Back Beach on the rocks as a result of the outfall are opportunistic species - growth occurs when dominant species have been impaired.
Species such as green algae and a spionid worm (boccardia proboscieda), higher densities of limpets and gastropods are present but have not made up for the loss the lost species. These replacement species are not able to support the habitat or do the same job that was intended by the lost species.
Damage to the environment at Gunnamatta close to the outfall were considered likely to be caused from a combination of freshwater, ammonia toxicity, and nutrient load.
Laboratory testing revealed ammonia and freshwater as being the most toxic agents to the marine environment. The combined effect of ammonia and freshwater was found to have a synergistic effect - the combined effect is greater than the sum of the individual parts.
The coast between Portsea and Cape Schanck does not contain any natural freshwater streams. The freshwater flow is classed as the major toxic substance from the outfall, as reported by the CSIRO. Even if the effluent was of drinking standard, it would still be toxic as marine life relies on salt water.
The CSIRO study found that unacceptably high levels of ammonia were found in the water. Melbourne Water has undertaken a programme to reduce the amount being discharged to Gunnamatta at as estimated cost of $20 million. Melbourne Water claim the high levels of ammonia were not known about until the results of the CSIRO report were released in 1999 but acknowledge anectodal information has been available regarding the ammonia for 15 years.
Directly at the outfall, the water appears dark brown in colour. A pungent effluent like smell is impregnated in the rocks and in the sand. On certain days depending on the wide and tide conditions the discoloured water is observed further from the outfall at St Andrews to the west and to Cape Schanck to the east.
Tests have been performed to address the question of whether there is contamination to seafood. 1n 1996 the MMBW had wrasse flesh and livers and abalone collected from Boags Rocks and analysed for 10 organochlorine pesticides. The levels were found to be lower than recommended by EPA Standards for human consumption. Further studies were conducted in 1991 on limpets, abalone and the periwinkle. All levels were below EPA standards.
Levels were extremely variable within samples and sites and the data was given to Monash University for statistical analysis. Quinn suggested to estimate the true mean concentrations with 90% confidence was impractical as a sample size of 456 abalone and 641 wrasse were required.
The CSIRO performed studies in the area to measure the effect of the potential effects of effluent on the marine environment. Species studies were bacterium, microalga, macroalgae, invertabrate and fish larvae. Results showed that effluent from the Eastern Treatment Plant was non-toxic to bacteria, 1-3 day old fish larvae and macroalgal fertilization. It was mildly toxic to 4-5 week old fish, and inhibited diatom and macroalgal growth. Scallop larvae was the species to which the effluent was the most toxic.
When the CSIRO undertook the sampling programme for the study, it was considered this level of sampling was inappropriate and ecologically impractical. The EPA and CSIRO decided a sample size of 10 of each species would provide information that indicates the level in contamination. Results of this study are regarded by the CSIRO as "descriptive rather than inferential", which means no hard and fast conclusions or deductions can be made.
In light of emerging evidence regarding the risk to humans and marine environment as a result of effluent that has passed through a secondary process, Clean Ocean Foundation consider that adequate evidence does not exist that can guarantee the safety of fish, or humans that ingest fish caught in the vicinity of the outfall.
Professional fisherman in the area state to Clean Ocean Foundation that "I wouldn't eat the fish caught from near the outfall". |