NORAH HEAD OUTFALL

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Monitoring Results

Indicator Bacteria

Extensive monitoring of faecal coliform bacteria indicate that primary contact recreation criteria are satisfied within 100 meters of the outfall. Guidelines for protection of human consumers of seafood are met within a distance of 250 meters of the outfall. 

Biological Communities

General Findings (not necessarily related to outfall):

• spectacular changes occurred in the amount of space occupied by each algal assemblage in response to seasonal storms - the onset of moderate to heavy swells caused large tracts of kelp forest and turfing algae to be stripped from the rocks.

• Areas formerly covered by turfing algae were almost totally denuded in these circumstances.

• Recolonisation of these devastated areas began almost immediately.

Methods:

Laxton & Laxton (1980, 1983b) investigated the benthic component of communities living in the vicinity of the proposed discharge zone of the outfall using photographic samples of the rocky bottom.  These were analysed for the percentage area occupied by each type of benthic organism. Fourteen sampling sites between Bird Island and Pelican point were surveyed during January and August of 1981 and 1982 and during January 1983 (Laxton & Laxton 1983b).

General findings (not necessarily related to outfall):

• comparison of sub-tidal rocky bottom benthic studies between 1981 and 1983 with stations resampled in 1987 showed little change in community structure.

• the fauna on the rock platform sampled conformed to the zone markers and community structure described by Dakin (1952).

• in late 1987, prolific growth of green algae in pools on the rock platform directly above the outfall at Norah Head was noted - this was caused by construction activity.

Methods:

Laxton and Laxton (1988c) resampled many of the stations examined in their earlier (1983) studies. They also undertook a biological survey of four sites on the intertidal rock platform.

Found no effect on:

• algal cover which could be attributed to nutrient enrichment from the outfall (the differences observed between sites were attributed to general seasonal changes.

Methods:

MPR undertook four field surveys between October 1988 and July 1989 after commissioning of the outfall. They used a cover index based on a simplified Braun-Blanquet cover scale and therefore did not repeat the methodology reported in Laxton & Laxton (1988c). Three sites (Norah Head, Little Norah Head and Pelican Point) were surveyed.

General findings (not necessarily related to outfall):

• A small number of organochlorine pesticide residues were above the detection limits.

• Concentrations of DDT, DDD and DDE were found above detection limits in a small number of fish (mostly in red morwong), but the muscle tissue levels recorded were well below the NHMRC recommended limits for human consumption (now superseded by the NFA (Anon 1984) limits).

• Chlordane was detected in the livers of four red morwong samples (maximum 0.1ppm).

• Tunicates (Herdmania sp) from two sites (Broken Head and Wonga Point) had consistently low concentrations of all organochlorine compounds for all replicate samples.  With the exception of chlordane, these concentrations were all below the NHMRC limits for edible fish and shellfish [note that Herdmania is not a fish or shellfish and is unlikely to be used as a food source].

• Concentrations of organochlorine compounds in tunicates at Norah Head and Wybung Head were all below the level of detection.

• Concentrations of PAH compounds and total PAH in red morwong muscle tissue were all below detection limits. Concentrations of individual PAH compounds in liver samples were below detection levels and total PAH concentrations (the sum of individual PAHs) in liver samples were all less than 1.6 mg/g.

• Heavy metal concentrations in the fish muscle tissues were above the detection limits but well below NHMRC recommended levels for human consumption.

• Higher levels of trace metals were often found in the liver tissue samples, but there are no NHMRC (or NFA) recommended levels for fish liver tissue. (Statistical analysis of metal concentrations between sites showed no definitive outfall effect).

Methods:

MPR investigated the bioaccumulation of synthetic organic compounds and heavy metals in a number of marine organisms found at or near the outfall. They collected two species of fish (10 individual red morwong (Cheilodactylus fuscus) and 5 individual rock cale (Crinodus lophodon)) and one species of sessile tunicate (Herdmania sp. – at least 10 individuals) from four sites (Broken Head, Wonga Point (the site of another ocean outfall – see Wonga Point outfall), Norah Head and Wybung Head). Fish muscle and liver tissue and homogenised tunicate tissue were tested for organophosphate pesticides, herbicides and synthetic pyrethroids, carbamates, organochlorine pesticides, PAH compounds and heavy metals.

Found that sewage effluent:

• Significantly increased the species richness of sponge types compared to the locations.

Found no outfall effect on:

• diversity or abundance of kelp, algal or faunal assemblages.

• cover or numbers of individual sponges, including the two most common species Psammopemma sp. and Tedania sp.

Methods:

Roberts and Scanes investigated the macrobenthic assemblages living on hard substrata in shallow water kelp forests. The macrobenthic assemblages were sampled at six locations (Norah Head, North Avoca, Winnie Bay, Bangalley Head, Warriewood and Cape Banks), three of which (Norah Head, Winnie Bay and Warriewood) have ocean outfalls and the other three sites treated as controls. At each location two randomly selected sites were sampled in approximately 6-10m water depth. At each site SCUBA divers estimated abundance of macrobenthos by recording the number and percentage cover of organisms (using the point-intersect method) in 5 randomly placed quadrats (27cm²).

General findings (not necessarily related to outfalls):

• High proportions of green and opportunistic algae and low abundance of red and brown algae were found on settling plates at both outfall and control sites.

Methods:

McNeill (1993) investigated the recruitment of algae and invertebrates to settlement plates at three outfall (Norah Head, Weenie Bay (First Point) and Warriewood) and three control (North Avoca, Bangalley and Cape Banks) sites. Settlement plates were made of sandstone (15 cm X 15 cm X 1cm thick) and were deployed in  March 1993. Settlement plates were retrieved 12 weeks later and the percentage cover of species of algae and species and major groups of sessile invertebrates was estimated using a 100 point grid on the upper surface of the settlement plate.

Found no effect on:

• body condition, wet weight, percentage dry weight, lipid dry weight or mortality of oysters from exposure to the treated, diluted effluent.

• trace metal levels in oysters with respect to outfall and control sites (with the exception of selenium which were found to be similar to other EPA oyster studies and these putative outfall effects require further analysis.).

• no organochlorine pesticides were detected in oysters deployed at the outfall sites.

General findings (not necessarily related to outfall):

• No differences between outfall and control sites were found for extractable organic halogens (EOX) in oysters.

Methods:

Transplanted Sydney rock oysters (Saccostrea commercialis) were also deployed at the same sites as those described by McNeill above.

Outfall Site

Red Morwong

Faecal Coliform

Outfall

Rock Oysters

Norah Head

(Nora_7) Last updated June 2000