SKENNARS HEAD OUTFALL

Click the photograph for a enlarged view

Monitoring Results

Indicator Bacteria

PRE DISINFECTION (<1994): Extensive monitoring of faecal coliform bacteria in receiving waters indicated that levels were less than the criteria for primary contact recreation within about 100 meters

POST DISINFECTION (>1994): Monthly monitoring since ultraviolet irradiation suggests that faecal coliform bacteria levels are less than the primary contact recreation guideline criteria within 10 m of the outfall.

Biological Communities

INITIAL STUDIES by Saenger et al. (1991)

Found that sewage effluent:

  • altered the community structure of kelp holdfasts

  • increasing the numbers of polychaetes and decreasing the numbers of amphipods (<100m from outfall)

But found no effect on:

  • species composition and abundance in intertidal areas

  • metal and nutrient concentrations in kelp

  • bioaccumulation of metals in invertebrates or fish. 

General findings (not necessarily related to outfall):

  • DDT present in fish from both control and outfall sites

  • Lindane present in fish from the outfall site

In both cases levels were very low and below the recommended level for food consumption (1mk/kg).

Methods: 

Saenger et al (1991) carried out a year long marine environmental study in 1990. This study examined communities of organisms at four locations, two of which (Whites Head & Flat Rocks) were located some distance from Skennars Head outfall and acted as control sites. The other 2 locations were close to the outfall point (site 1 100m north, and site 2 200m north of the outfall) at Boulder Beach south of Lennox Head. Two sampling methods were used; a) phototransects of the intertidal rock surface; and b) examination of the assemblage of animals living in the holdfasts of kelp, Ecklonia radiata. Data were also collected on plant nutrients (nitrogen and phosphorus) in kelp fronds and heavy metals (Zn, Cd, Cu & Pb) in kelp and selected rocky shore invertebrates and offshore fish (Red morwong, Cheilodactylus fuscus). These metals were also examined in animals from the outfall point itself.

Nutrients in kelp at the outfall were compared to two reference areas. One reference area was used for comparison in the intertidal study, three for the holdfast macrofauna, and one, four and three for bioaccumulation in fish, invertebrates and algae, respectively (MHL769 1997).

 

FOLLOW-UP STUDIES  by Holmes and Saenger (1997)

Found:

  • real differences between sites in the holdfast communities (number of species, number of animals and identity of the most numerous species) [however, whether this is due to the outfall cannot be inferred with any confidence with this experimental design] 

  • no effect of the outfall on intertidal communities

  • trace metals and nitrogen in kelp fronds did not differ between sites

  • phosphorus in kelp fronds was highest at Site 1 (closest to outfall) and lowest at Flat Rocks (control site), but this difference was not statistically significant and therefore does not constitute a significant outfall effect

  • in general metals in invertebrates did not vary significantly with site, although copper in Cellana was highest in specimens from the outfall site. Copper levels in the other two molluscs studied (Thais and Morula) showed no significant difference between control and outfall sites

Methods:               

This study was conducted at three sites (the 1990 control site at Whites Head was dropped) at a single time. No examination of metal levels in offshore fish were made, otherwise the same techniques were employed.

Outfall Site

Faecal Coliform

Red Morwong

Banacles

Outfall Site

Mollusc

Scorpion Fish

 
 

 

Skennars Head

  

(Sken_7) Last updated May 2000