SALT LAKES Palaeolimnological evidence for the independent evolution of neighbouring terminal lakes, the Murray Darling Basin, Australia Jennie Fluin Æ Peter Gell Æ Deborah Haynes Æ John Tibby Æ Gary Hancock Ó Springer Science+Business Media B.V. 2007 Abstract The estuary of the lower River Murray features a complex mosaic of lakes, coastal lagoons and interconnecting channels. The waters of these wetlands are degraded as a result of river regulation, water abstraction, salinisation, sedimentation and the recent constriction of the River mouth. Palaeolimnol- ogial analysis of sediment cores in two wetlands reveals that salinity in the large terminal Lake Alexandrina was only moderately influenced by tidal inflow, particularly over the past ca. 2000 years. It is now largely fresh as a result of isolation by a series of barriers completed by 1940 AD. In contrast, the seaward portion of the Coorong, a back barrier coastal lagoon, was determined to be a subsaline estuary strongly influenced by marine inflows. These findings contrast somewhat with the Coorong’s current Ramsar classification as a saline lagoon. Riverine diatoms, typical of the fossil flora of Lake Alexandrina, are rare or absent in the Holocene sediments of the Coorong, other than for a short period in the late Holocene in the northernmost end of the lagoon. The palaeolimnolog- ical evidence for independent evolution of these wetlands is consistent with geomorphic evidence of a stranded, last interglacial shoreline that acted as a sill limiting the exchange of flows between Lake Alexandrina and the Coorong lagoon. Keywords River regulation  Estuaries  Diatoms  Salinisation  Sedimentation  Eutrophication  Ramsar Introduction Lake Alexandrina is a broad shallow lake, located at the mouth of the Murray River in South Australia (Fig. 1). It has a surface area of over 660 km 2 and volume of 1.66 · 10 6 ML. The Lake is shallow (Z max = 4.05 m; Z mean = 2.86 m) and highly turbid. The Darling River is known to carry a very high- suspended sediment load and this is thought to be the main source of abiogenic turbidity in Lake Alexand- rina although Bourman & Barnett (1995) identified considerable erosion of the littoral zone of the Lake over the last century. The Coorong is a large coastal lagoon complex situated between a Holocene beach—dune barrier, the Younghusband Peninsula, Guest editors: John Tibby, Peter Gell, Lynda Radke, and Michael Reid Salt Lakes: Salinity, Climate Change and Salinisation J. Fluin (&)  P. Gell  J. Tibby Geographical & Environmental Studies, The University of Adelaide, Adelaide, SA 5005, Australia e-mail: jennie.fluin@adelaide.edu.au D. Haynes School of Earth & Environmental Science, The University of Adelaide, Adelaide, SA 5005, Australia G. Hancock CSIRO Land Water, Canberra, ACT 2601, Australia 123 Hydrobiologia (2007) 591:117–134 DOI 10.1007/s10750-007-0799-y