Effects of desalination brine and seawater with the same elevated salinity on growth, physiology and seedling development of the seagrass Posidonia australis.

Desalination has the potential to provide an important source of potable water to growing coastal populations but it also produces highly saline brines with chemical additives, posing a possible threat to benthic marine communities. The effects of brine (0%, 50%, 100%) were compared to seawater treatments with the same salinity (37, 46, 54 psu) for seagrass (Posidonia australis) in mesocosms over 2 weeks. There were significant differences between brine and salinity treatments for photosynthesis, water relations and growth. Germinating seedlings of P. australis were also tested in brine treatments (0%, 25%, 50%, 100%) over 7 weeks followed by 2.5 weeks recovery in seawater. Growth was severely inhibited only in 100% brine. These experiments demonstrated that brine increased the speed and symptoms of stress in adult plants compared to treatments with the same salinity, whereas seedlings tolerated far longer brine exposure, and so could potentially contribute to seagrass recovery through recruitment.

Variable response of three Trifolium repens ecotypes to soil flooding by seawater.

BACKGROUND AND AIMS: Despite concerns about the impact of rising sea levels and storm surge events on coastal ecosystems, there is remarkably little information on the response of terrestrial coastal plant species to seawater inundation. The aim of this study was to elucidate responses of a glycophyte (white clover, Trifolium repens) to short-duration soil flooding by seawater and recovery following leaching of salts. METHODS: Using plants cultivated from parent ecotypes collected from a natural soil salinity gradient, the impact of short-duration seawater soil flooding (8 or 24 h) on short-term changes in leaf salt ion and organic solute concentrations was examined, together with longer term impacts on plant growth (stolon elongation) and flowering. KEY RESULTS: There was substantial Cl(-) and Na(+) accumulation in leaves, especially for plants subjected to 24 h soil flooding with seawater, but no consistent variation linked to parent plant provenance. Proline and sucrose concentrations also increased in plants following seawater flooding of the soil. Plant growth and flowering were reduced by longer soil immersion times (seawater flooding followed by drainage and freshwater inputs), but plants originating from more saline soil responded less negatively than those from lower salinity soil. CONCLUSIONS: The accumulation of proline and sucrose indicates a potential for solute accumulation as a response to the osmotic imbalance caused by salt ions, while variation in growth and flowering responses between ecotypes points to a natural adaptive capacity for tolerance of short-duration seawater soil flooding in T. repens. Consequently, it is suggested that selection for tolerant ecotypes is possible should the predicted increase in frequency of storm surge flooding events occur.