Paleolimnological History of the Coorong: Identifying the Natural Ecological Character of a Ramsar Wetland in Crisis

Abstract

The Coorong is a back-barrier lagoon that lies at the mouth of the Murray-Darling Basin, Australia. As part of a wider estuarine complex it was successfully nominated as a wetland of international significance under the Ramsar Convention where it was identified as a saline to hypersaline lagoon. Perceived obligations to retain this condition lead to limits on the release of freshwater from the hinterland to the lagoon. The Coorong has been identified as at risk of degradation with declining cover of its primary autotroph Ruppia spp. attributed to increasing salinity. Declining flows through the Murray-Darling Basin and recent drought induced extreme hypersalinity, particularly in the south lagoon. Increases in brine shrimp, declines in its fishery and replacement of a diverse avifauna with Banded Stilt led to calls that the Coorong was in crisis. Diatom-based palaeoecological assessment along the length of the lagoon revealed a natural subsaline, tidal system that shifted, after the commissioning of barrages, to a saline, closed lagoon with extensive sulphidic sediments. The misidentification of the natural character of the lagoon accentuated its degradation. Earlier sediment-based research may have provided for the identification of a more appropriate natural ecological character and an early warning of the degree to which the system had degraded. Palaeolimnological approaches represent a valuable tool to better evaluate the condition of wetlands listed under the Ramsar Convention.