Abrupt historical change in the nature of a Ramsar Wetland: Seaford Swamp, greater Melbourne, Australia

<p dir="ltr">Context: Seaford Swamp is a back-of-dune wetland on the eastern side of Port Phillip Bay in greater urban Melbourne. It is a fresh marsh dominated by the reed Phragmites australis that is expanding into open water.</p><p dir="ltr">Aims: Three sediment cores were collected to determine the ecological history of the wetland.</p><p dir="ltr">Methods: The cores were analysed for diatoms and pollen and dated using 14C and 210Pb.</p><p dir="ltr">Key results: The longest core showed an abrupt change from marine–brackish to saline and ultimately the present fresh condition. Saltmarsh declined and was replaced by reed, sedge and rush species. Cores from the centre and south of the wetland showed a similar history, albeit more variable in the south, yet still reflecting a sustained change from marine–estuarine conditions to fresh–brackish. The 7000-year record showed considerable stability despite known climatic and sea-level changes.</p><p dir="ltr">Conclusion: The abrupt change in condition appeared to correspond with hydrological engineering of the site from 1870 for agricultural and urban development. Increased catchment runoff, including from urban areas, are likely to have sustained the freshwater state.</p><p dir="ltr">Implications: The marine–estuarine state represents an alternate condition of the swamp that may broaden options for management under future sea-level rise.</p>