BOULDER BAY OUTFALL

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Monitoring Results

Indicator Bacteria

In the vicinity of the original (shoreline) outfall median bacteria levels exceeded the NHMRC guidelines for primary contact recreation, while at Fingal Point approximately 1000 m from the original outfall, median levels were reduced to 20 cfu/100ml.

Regular monitoring is now undertaken at local beaches (Boulder Bay, Zenith Beach, Box Beach, Fingal Bay and One Mile Beach) and are all within the guidelines for primary contact recreation and protection of human consumers of seafood (MHL769 1997).

Biological Communities

General findings (studies undertaken prior to the construction of the outfall):

• Comparisons between sites were undertaken (listed below), but these largely represented comparisons between ‘control’ sites and few differences were found.

Methods:

Laurie, Montgomerie & Pettit (1977a) investigated phytoplankton (chlorophyll-a concentrations only - off Boulder Bay, Burwood Beach, Belmont Beach and First Point); zooplankton (off Boulder Bay, Burwood Beach, Belmont Beach and First Point); rocky bottom benthos (First Point, Little Beach Burwood Beach and Boulder Bay); rocky shore ecology (First Point, Little Cove and Little Beach); Soft bottom benthos (Belmont Beach, Burwood Beach, Stockton Beach, Dudley Beach, Merewether Beach, McMasters Beach and Avoca Beach); sandy beach fauna (Belmont Beach, Burwood Beach, Dudley Beach, McMasters Beach and Avoca Beach); fish communities (using otter trawls – Burwood Beach, Belmont Beach and McMasters Beach); and contaminants in fish (McMasters Beach and First Point)

Found that sewage effluent:

• Had an aesthetic impact on the area with turbid water, toilet paper and other debris present in the bay.

But found no effect on:

• the structure of benthic communities.

General findings (not necessarily related to outfall):

• increased the total area occupied by algae at some sites at the expense of sponge and other invertebrates with the greatest changes occurring in the 15m depth range.  These changes, however, were attributed to storm damage.

Methods:

Laxton and Laxton 1979 investigated the benthic communities living in the discharge areas of Nelson Bay, Wanda Head, Corlette, Boulder Bay and Burwood Beach. Data using photo quadrats (rocky bottoms) and sediment core samples (soft bottoms - Corlette only) between 1975 and 1979 (Boulder Bay and Burwood Beach) or between 1977 and 1979 (Nelson's Bay, Corlette and Wanda Head). [A study of settlement on artificial substrates was also conducted at Corlette]. At the time of writing their report, Laxton and Laxton (1979) noted that the proposed outfall and treatment works planned for Boulder Bay had not been built. At that time, however, a temporary outfall was discharging raw sewage into the head of the southern cove. Laxton & Laxton (1979) investigated six sites within Boulder Bay.

General findings (not necessarily related to outfall):

• The only changes detected in south cove since 1977 were those associated with recolonization by algae of areas denuded by the storms of 1974 and 1978.

Methods:

Laxton and Laxton (1982/83) continued monitoring of benthic communities living in the discharge zone of sewage outfalls at Nelson Bay, Wanda Head, Corlette, Boulder Bay and Burwood Beach. They included data from 1975 through to 1982.  In addition, they reported on pre-discharge monitoring of proposed outfall sites at Boat Harbour and Birubi Point. During the period of this monitoring, a number of changes to the Boulder Bay outfall were occurring.  Because of these changes three sites were added to the monitoring study in 1981 and one site dropped in 1982.  

Found that sewage effluent:

• increased the dissolved oxygen concentrations compared to the northern offshore stations. This was suggested to be a result of the dense beds of benthic algae living in Boulder Bay.

•  increased the average concentrations of oxidised nitrogen slightly higher than those obtained at the northern offshore sites over the period of sampling.

• increased the levels of faecal coliforms compared to non-outfall sites, although concentrations of faecal coliforms at Boulder Bay were quite low over most of the period sampled.

General findings (not necessarily related to outfall):

• Surface water at Boulder Bay was found to have similar physical and chemical characteristics to surface water offshore of the Central Coast except for dissolved oxygen concentrations, organic nitrogen concentrations and faecal coliform bacteria levels. Observations of the sewage field from the shore showed that at times it tended to be carried seawards in an anticlockwise direction around the perimeter of south cove. The current carrying the effluent was generated by breaking waves and tidal forces, leaving the cove near the water quality sampling site (located near the isolated rock island). Laxton and Laxton (1987) also analysed the subtidal rocky bottom data gathered over the previous 12 years. The biological effects of outfall construction were assessed and found to be minimal in the long term.

Methods:

Studies of the water column, water chemistry, pelagic biology and benthic communities of sedimentary and rocky bottoms commenced in January 1985. For the rocky bottom community studies in Boulder Bay, two areas of sloping rocky bottom were selected with approximately the same degree of exposure to wave attack, depth range and zonation patterns. One site located in north cove away from the influence of the outfall was designated as the control area. The other site located in south cove was designated as the experimental area. Photo-quadrats were used to measure sub-tidal rocky benthic communities and initial sampling frequency was set at once every six months. [Sampling of rocky bottoms also occurred at Burwood Beach, Swansea, Nelson Bay and Wanda Head].

Water quality studies were located as close to each outfall as possible and at a location seaward of the outfall (approximately 2km). Control stations, both an inshore and an offshore site, were located at the far northern and far southern ends of the study area (between Port Stephens and Catherine Hill Bay).  Laxton and Laxton (1987) also analysed the water quality data gathered over two years for coastal waters between Port Stephens and Catherine Hill Bay. These data were compared to data obtained for Boulder Bay.

General findings (not necessarily related to outfall):

• the colonisation of one site close to the outfall by the ascidian Pyura stolonifera (Laxton and Duell 1990), however, this change might not have been entirely due to the effluent discharge since this animal was also observed at control sites.

Methods:  

Benthic sampling at Boulder Bay 1989-1990.

General findings (not necessarily related to outfall):

• three organochlorines (technical chlordane, DDE and DDD) were detected in deployed oysters. However, because of the low frequency of detection no impact versus control comparisons could be made.

• Trace metal concentrations in oysters were within or below the range of concentrations found in oysters deployed offshore of Sydney and naturally occurring in other estuarine areas of NSW.

• Trace metal concentrations in sediments were comparable to concentrations found in Sydney with the exception of zinc, lead and manganese at an offshore dumpsite (spoil ground) and the entrance to Newcastle Harbour.

• At certain times manganese levels at Burwood Beach were higher than the range of concentrations found in Sydney.

• All mean trace level concentrations were below the concentrations considered to have the potential for adverse biological effects (with the exception of manganese levels in three sediment samples – 2 at Burwood Beach and 1 at the Spoil Ground)

Methods:

The Hunter EMP involved bioaccumulation studies (using deployed oysters and sediments) over the period 1992 to 1996.  During the first two years of the Hunter EMP, oysters (Crassostrea commercialis) were deployed at potential contaminant sites (including the outfall sites of Boulder Bay, Burwood Beach and Belmont Beach) and at a number of control sites. Retrieval of oysters occurred twice a year at which time sediment samples were also collected by divers using corers. These samples were analysed for 17 organochlorine and 12 trace metal levels.

Found that sewage effluent:

•  increased the abundance of both adult and juvenile kelp plants immediately after the commissioning of the extended outfall.

Methods:

Ajani et al investigated the effect of the Boulder Bay sewage discharge on Sydney rock oysters (Crassostrea commercialis) and kelp (Ecklonia radiata). Sydney rock oysters were deployed at outfall and control locations for three months, after which time they were retrieved and analysed for trace metal and organochlorine concentrations. This process was repeated every six months for a total of eight sampling times (3 times before the commissioning of the extended ocean outfall and five times after its commissioning). The results for oysters are also described in the Hunter EMP report and have already been summarized above (see section describing the results of Ajani and Wansborough 1996). The abundance and recruitment of adult and juvenile kelp plants were also investigated.

Found that sewage effluent:

• decreased the abundance of the eastern hulafish (Trachinops taeniatus), yellowtail (Trachurus novaezelandiae) and the urchin (Centrostephanus rodgersii).

• decreased the abundance and species richness of fish at the outfall compared to fish assemblages at the control locations.

•  increased the abundance of some cryptic (small, cave dwelling or camouflaged) fish species over time at the outfall.

Methods:

Smith et al investigated the abundance and species richness of temperate rocky reef fish and the abundance of sea urchins (Centrostephanus rodgersii) at the site of the offshore Boulder Bay outfall. A before/after/control/impact (BACI) design over three periods (before commissioning, immediately post-commissioning and one year post commissioning) were investigated.

Found that sewage effluent:

• significantly reduced the cover of crustose and foliose algae at the outfall location compared to control (Port Stephens and Tomaree Head) locations within 3 months of the commissioning of the outfall.

• decreased the cover of several species of sponge, including Cymbastela concentrica, Geodinella sp. and Spongia sp., however, declines in the cover and number of species of sponges or total fauna did not change significantly.

•  increased the cover of a nondescript matrix comprising silt and microorganisms doubled its representation to almost 60%.

• changed the overall composition of the community at the outfall from one in which algae and sponges were well represented to an assemblage dominated by silt and ascidians.

Methods:

Roberts et al investigated the cover and number of species in encrusting macrobenthic assemblages inhabiting temperate rocky reefs in the vicinity of the offshore Boulder Bay outfall. Photographic samples were taken over three periods (before commissioning, immediately post-commissioning and one year post commissioning).

Faecal Coliform

Ulva

Kelp

Cunjevoi

Boulder Bay

(Boul_7) Last updated May 2000