Coastal vegetation damage and airborne surfactant deposition in the Barwon Heads area - final report.  J. D. Morris, R. G. Bickford and J. J. Collopy.  January 1991.  26pp. (unpubl.)

SUMMARY

A study of airborne surfactant deposition, foliar chloride concentrations and vegetation damage in coast tea-tree communities was carried out in the Barwon Heads area of southern Victoria. The study was designed to assess the effectiveness of an offshore extension of an existing sewage outfall in reducing the potential for vegetation damage due to surfactant-mediated salt uptake from coastal spray.

The extent of vegetation damage prior to commissioning of the extended outfall was assessed by a transect survey along the coast between Torquay and Queenscliff. Vegetation damage was present to some extent over the whole sampled area, with no evidence of greater damage at sites close to the sewage outfall.

The effect of surfactants on salt uptake from sea water sprayed on the foliage of coast tea-tree seedlings was investigated in a series of glasshouse experiments. The minimum concentration of surfactant which caused enhanced uptake was estimated as 3.4 µg/g of leaf fresh weight. Surfactant concentrations on leaf surfaces decreased by 42% between 1 and 3 days after application, while repeated spraying at two-day intervals caused a steady increase in surfactant concentration. Leaf damage occurred at lower foliar chloride concentrations when leaves were salinised by sea water spraying before application of surfactant, than when surfactant and sea water were applied together.

Surfactant deposition was monitored at seven locations along the coastline during spring and early summer of 1987 and 1989. Surfactant concentrations were assessed on coast tea-tree foliage and on paper collectors from both front- and rear-dune sampling sites. Chloride concentrations in the foliage were also measured. In 1987 deposition was markedly higher at sites close to the sewage outfall, but in 1989 this effect was greatly reduced. Foliar surfactant concentrations in 1989 never reached the level found to be critical for salt uptake, while in 1987 concentrations above this level were common. Foliar chloride levels also tended to be lower in 1989 than in 1987.

A regression modelling approach was used to explore the contribution of weather variations to the difference in surfactant deposition between years, since meteorological records showed that strong onshore winds were more common during the 1987 monitoring period than in 1989. It was concluded that the extended outfall has succeeded in reducing surfactant deposition, but the extent of this reduction in years of strong winds cannot be assessed from the data collected so far.