The predominantly fresh history of Lake Alexandrina, South Australia, and its implications for the Murray–Darling Basin Plan: a comment on Gell (2020)

Abstract

The pre-European settlement state of Lake Alexandrina, a lake system at the mouth of the River Murray has been the subject of some debate. Fluin et al. (2007) concluded on the basis of diatom evidence from sediment cores that ‘Marine water indicators were never dominant in Lake Alexandrina’. In a report to the South Australian Government, Fluin et al. (2009) stated, consistent with the earlier research, that ‘There is no evidence in the 7000 year record of substantial marine incursions into Lake Alexandrina’. Gell (2020) has argued both that Fluin et al. (2009) is in error and claims that it, and Sim and Muller’s (2004) book that describes early European settler accounts of the lake being fresh, underpin water provisions for Lake Alexandrina under the Murray–Darling Basin Plan. This response demonstrates that all these claims are untrue. Of the three diatom species suggested by Gell (2020) to be indicators of marine waters, Thalassiosira lacustris grows in the freshwater River Murray today, Cyclotella striata was never more than a minor component of the diatom flora and Paralia sulcata has not been detected in the lake in over 3000 years. Water provisions for Lake Alexandrina under The Basin Plan are founded on contemporary environmental water requirements and achievement of agreed socio-ecological-economic objectives, rather than the history of the lake. Nevertheless, the aim to maintain the lake as a freshwater ecosystem under The Murray–Darling Basin Plan is consistent with its history.