Salinity tolerance in phytoplankton

Leader

Challenge

Determining the impact of desalination brine discharge on the aquatic environmental is important for the continued societal acceptance of desalination as a technology. Any environmental impacts of the major desalination plants should be investigated, ideally, before and after the operation of the plant. In order to fully identify any impacts on the aquatic environment that are exposed to the brine discharge from the diffusers, the tolerance of local marine organisms to salinity, in particular, should be known.

Phytoplankton communities are the basis of many marine and freshwater food webs and are highly specific to their environment making them a valuable environmental indicator species. Changes in phytoplankton communities can have dramatic implications for the higher species in the food chain and recent studies indicate seawater desalination plants may adversely affect these communities through impingement of organisms on intake screens or by increased salinity levels caused by the discharge.

Current knowledge of a particular phytoplankton species called diatoms, shows they are able of modifying their silica frustule and potentially their silica biogenic proteins as a response to high salinity environments. This has been observed in South Australia’s Coorong Wetlands and is due to localised rises in salinity.

Investigation 

Monitor the diatom communities in the Gulf St Vincent, South Australia, for 12 months at the intake and outfall pipes of the Port Stanvac desalination plant. Determine any morphological and growth changes on the diatoms when exposed to high saline waters.

Outcomes

This was the first study to simultaneously investigate the phytoplankton communities in this area and it established a baseline for any future studies. In total, 147 phytoplankton species were identified and enumerated over 12 months. This community was numerically dominated by nanoflagellates, except in February when Cylindrotheca closterium was the predominant species. The main species contributing to the phytoplankton biomass were: C. closterium, Emiliana huxleyi, Hemiselmis sp. and Plagioselmis prolonga. The results showed that in these shallow waters the phytoplankton communities are affected by wind speed, which directly influence the resuspension of sediment and associated nutrients, and the changing levels of phosphorous and silica. Since nutrient enrichment is generally the main factor driving the succession and composition of phytoplankton communities in coastal waters, further work is now needed to identify the sources of nutrients in this region where river runoff is limited and evaporation is high relative to precipitation.

Seasonal variability of the diatom community was driven by temperature, wind speed/direction and changing levels of phosphorous. Diatom species isolated at the location of the outfall pipe showed varied responses to increased salinity levels, indicating a species-specific response. An increase of 10% found to have no detrimental effect on growth for the majority of the species that were tested. This was likely due to an adaption mechanism, involving a more condensed silicon structure and higher production of proteinaceous materials.

Future Direction

During the 12 month sampling period the desalination plant was not fully operational but has since come online. A before and after impact study could now be undertaken, examining any impact of the brine discharge on the phytoplankton community, by extending the sampling period for a further 12 months. Currents and wind events are critically important for the condition of the coastal waters off Port Stanvac and sampling sites could be established north and south of the diffusers to take into account the water movements in the area.

Partners


 

Total Value: $1,124,725 (cash and in-kind contributions)

Principal Investigator: Dr Sophie Leterme

Title: Nanostructure of diatoms: a predictive model for species sustainability

Length: 24 months

Personnel: 9 collaborators contributing 5.4 FTE

Further Information

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