Freshwater reservoir effect for mollusks in the lower and central Murray River, Australia

Abstract

Since the 1950s, archaeological research conducted along the middle reaches of the Murray River has relied on radiocarbon dating of freshwater mollusk shell to establish the chronology of human occupation within this region as well as support larger models of human occupation timing within Australia. Despite this, there has been no investigation into the potential freshwater reservoir effect (FRE) for the middle reaches of the Murray River. In this research we analyzed historically live-collected freshwater mussel samples from Yorta Yorta, Barkandji, First Peoples of the Millewa Mallee, and First Peoples of the River Murray and Mallee Countries, between Echuca (Victoria) to Morgan (South Australia), to establish the magnitude of the FRE for the lower and central Murray River. We also measured ¹⁴ C content in modern river water and freshwater shell samples from across this region to better understand the source of this FRE offset. The calculated average offset of approximately 138 ± 67 ¹⁴ C years will have a larger impact on archaeological sites for the Late Holocene, with corrections improving overall age accuracy. These results will help the archaeological community develop more robust chronologies in the region and better understand human-mollusk-environment relationships.