Summary of environmental impacts

ALGAE

Ulva

The most obvious and often quoted impact of sewage outfalls in NSW is their effect on the proportion (% cover) of the green alga Ulva lactuca on rocks close to the outfall. Where this has been measured, the % cover of Ulva usually increases quite considerably at the outfall sites and for some distance from the outlet. For example, at Corambirra Point outfall Smith and Simpson (1990) concluded that as a result of the outfall, the cover of Ulva lactuca was increased for the full length of Corambirra Point. Most studies of intertidal algae near outfalls in NSW (and other places) have identified an increase in the cover of Ulva, although the underlying mechanisms for this increase have not been identified. They are likely to be the result of a combination of factors such as toxicity, competition, recruitment, nutrients and perhaps lower salinities.  

Algal Communities

In association with an increase in Ulva lactuca near outfalls , there has usually been a decrease in the diversity of other algal species. The diversity of brown and red algal species in particular, is often reduced in the vicinity sewerage outfalls (e.g. Borowitza 1972, May 1981, 1985, Fairweather 1990, Banwell 1996). In Borowitza’s (1972) study, only 2 species, both of green algae, were present at the outfall site while 41 species, mostly of brown and red algae, were present at a distant site. Areas intermediate between the outfall and polluted sites had intermediate numbers of species. Sewage discharge at Boags Rocks in Victoria has been implicated in a reduction in abundance of two species of brown algae (Hormosira banksii and Durvillaea potatorum) possibly due to interference with normal reproduction and recruitment processes (Doblin and Clayton 1995). In California, Littler and Murray (1975) found a 30% reduction in the number of species of macroalgae near a sewage outfall when compared to unpolluted control sites. Habitat complexity was less at the outfall site because of a reduction in the cover of large algal overstories with a proportionate rise in small algal turf forming species.

Nutrients in Algae

Nutrients in algae have received relatively little attention in NSW; some exceptions are Saenger et al’s (1991) study at Skennars Head and TEL’s (1996a) study at Penguin Head. Considerably more work on nutrients in algae has been done in Queensland (e.g. O’Donohue 1997). No outfall effect was found in terms of metal and nutrient concentrations in kelp plants at Skennars Head (Saenger et al 1991). However, TEL (1996a) studied two species of algae (kelp [Ecklonia] and bubbleweed [Phyllospora]) collected for a pilot study on uptake of nutrients near Penguin Head outfall. Differences were detected between Penguin Head and the reference locations that may be attributable to the release of effluent at Penguin Head. The concentrations of phosphorous and total organic nitrogen (TKN) was greater in algae from Penguin Head compared to reference locations and the concentration of total solids was less in algae from Penguin Head. Further work is being conducted on the relative proportions of nitrogen isotopes (d-N) in algae near Penguin Head, and this may turn out to be useful as an indicator of sewage derived nitrogen. This process has been used successfully in Moreton Bay (O’Donohue 1997) and has the potential to answer questions about the extent of impact around sewage outfalls

(Impac_2) Last updated May 2000