Lake Alexandrina, located at the terminus of the Murray River, is listed under the Ramsar agreement as a wetland of international significance and is thus afforded special protection by both the South Australian and Federal governments. Part of this protection means that water is allocated to the lower lakes system in an attempt to prevent further ecological decline. The allocation of this water represents an opportunity cost to potential upstream users and is therefore contested. In this context, the natural salinity regime of the lake has been debated for more than two decades. Existing and new data from lake sediments are used to infer the salinity history of Lake Alexandrina. Complementary data from Lake Albert will also be presented
Despite its connection to the ocean, the central basin of Lake Alexandrina has been predominantly fresh for the last 7,500 years. Notably, the lake was fresh during a time when sea levels were higher than at present. The potential for oceanic incursion during this time appears to have been balanced by higher inflows from the River Murray.
The second part of this talk will focus on ongoing research inferring the flooding history of the Murray River. In the northern section of Lake Alexandrina, close to the inflow of the Murray River, finely laminated lake sediments have accumulated over the past 4,000 years. We will provide a preliminary interpretation of the climate history of the Murray drainage basin using high resolution sediment geochemistry, diatom data, total carbon to total nitrogen (C/N) ratios and carbon isotope composition from this core. This research will eventually provide insight into the long term “drivers” of Murray River discharge such as the El-Niñ0 Southern Oscillation and the Southern Westerly Winds.