Unravelling the ecological consequences of discharges of seawater from coastal cooling systems treated with amine and halide-based biocides

Fabiana Moreira (Supervisors: Ass. Prof. Ross Coleman, Dr Mark Browne and Dr Ashley Ward)


Background
Outfall discharge

Billions of tonnes of seawater are used every year to control the temperature inside industrial, commercial and residential coastal buildings. Concerns over dwindling supplies of fossil fuel and freshwater have resulted in the proliferation of buildings using seawater. To prevent organisms growing in the pipes, the extracted seawater is treated with a range of biocides and discharged into marine habitats without treatment. Recently, traditional halide-based oxidants have been replaced by amine-based biocides. There is, however, very little accurate information about the ecological consequences of either of these biocides. Legislation governing the use of these biocides relies on data derived from only a few laboratorial trials with often poorly chosen organisms.
In Sydney harbour, a range of commercial and residential buildings use seawater to cool their buildings and the majority of those use amine-based biocides. The assessment of risk for the amine-based biocides is, however, incomplete and they are not full registered for being used in Australia. Instead each building and company responsible for applying the biocides at the systems has a permit granted by the Australian Pesticides and Veterinary Authority (APVMA). Given that there is no monitoring by the government of possible impacts from these discharges of seawater and biocides from those cooling systems, it is important to investigate possible ecological impacts on animals and plants living in habitats where the seawater is discharged.

Aims

To obtain ecologically relevant data, novel field and laboratorial experiments will be done testing hypothesis across different levels of biological organisation. The ecological effects of seawater discharged from coastal buildings will be examined using assemblages living on wood pilings in Sydney Harbour and also using manipulative field and laboratorial experiments.

Importance
Fouled and non-fouled pilings

This project is the first work investigating the ecological consequences of discharges of biocides from cooling systems across multiple sites. My findings provide better understanding of the effects of these discharges upon biodiversity and how this understanding can be used to improve our management of coastal habitats affected by discharges of seawater from cooling-systems.

Results

Mensurative experiments, used to test hypotheses about differences in the structure of sessile intertidal assemblages at discharge and reference sites, revealed smaller covers of oysters at discharge sites. To understand the mechanisms driving the altered patterns of abundance, I tested hypotheses relating to the recruitment and performance of oysters. Results indicated no pattern related to the recruitment and ongoing experiment is evaluating whether models related to the viability of haemocytes and the feeding behaviour of oysters is compromised.
Mensurative experiments were also used to test hypotheses about differences in the structure of mobile assemblages associated with the matrix of oysters at discharge and reference sites. There was no significant difference in the composition or abundance of mobile assemblages among discharge and reference sites. Experiments using natural assemblages have, however, intrinsic differences (i.e. age of the assemblage or age of the structure) that may hide impacts. Therefore ongoing experiment is evaluating differences in the structure of mobile assemblages developed in standardised units of habitat (plastic pot-scourers) placed among oyster growing on pilings.