Multi-stage Holocene evolution of the River Murray Estuary, South Australia

Abstract

The River Murray Estuary, South Australia exhibits a morphology typical of a wave-dominated estuary and comprises two large, shallow central basin lakes – Lakes Alexandrina and Albert. Contested interpretations of the estuary’s limnological history and uncertainty surrounding the sustainability of current basin water usage practice warrant a robust investigation into how the system has evolved. Here we combine lithostratigraphic, geochemical and sedimentological evidence from a transect of sediment cores to reconstruct the sediment infill history of the system. We uncover multiple stages of sediment infill over the history of the system, associated with (1) the low gradient morphology of the estuary and lower river channel, (2) the mid- to late-Holocene sea-level regression and (3) anthropogenic modifications to the fluvio-estuarine system. We show that while estuarine conditions in the system were fully established during the mid-Holocene highstand (~6.4 kyr BP), central basin facies sedimentation was focussed further inland before prograding with the lowering of base level and shifting of tidal influence as sea-level fell. Central basin facies sedimentation within northern Lake Albert occurred from 5.4 to 4.0 cal kyr BP at ~0.25 cm yr-1. The uppermost accumulation of this unit was eroded by continued reduction in base level until sea-level regression concluded at 3.5 cal kyr BP. Barrage and weir installation (1940 CE) re-initiated and expanded central basin facies sedimentation in the estuary (~0.32 cm yr-1). Recently deposited sediments exhibit geochemical markers of increased trophy and more frequent acid sulfate soil acidification, exposing human impacts on the estuary.

The Monitoring of Sediment Protists in Lake and River Basins Based on Digital Holographic Microscopy

“…(3) Metagenome sequencing Metagenomics is a microbial research method to study microbial diversity, community structure and function, evolutionary relationship and interaction with the environment [11]. The advantage of metagenomics is that it skips the PCR amplification reaction and is no longer limited to pure culture.…”

Legacy archaeology: Aboriginal subsistence response to Holocene environmental changes using faunal evidence from archaeological sites on the Lower Murray, South Australia

“…Between c. 7000 and 3000 BP, the river deposited fluvial clays, silts and fine grained sands of the Coonambidgal Formation over the top of Monoman Formation (Twidale et al, 1978: 40), with the upper layers of the Coonambidgal Formation being described as the ‘Mannum muds’ (Hubble et al, 2014). Sea levels fell slightly between c 6000 and 3500 BP (Job et al, 2021: 61) causing the Murray to incise its floodplain to its current level, creating the Lower Murray River Valley as we know it today.…”

Reply to: A large mid-Holocene estuary was not present in the lower River Murray, Australia

“…Further, sapropelic units derived from the accumulation of freshwater algae (including the described Coorongite 1 ) that underly siliciclastic mud deposits in the Lower Lakes region were likely deposited in freshwater lakes not connected to the primary fluvio-estuarine system during the mid-Holocene 7 and therefore cannot be used to assert freshwater conditions in the estuary 1 . Finally, the assertion that “sub-fossil diatoms in the Lower Lakes also indicate the dominance of freshwater at this time [6,930 ± 150 yr BP]” 1 contradicts evidence of brackish to salty conditions for Lake Albert between 7.9 and 6.0 cal kyr BP 8 .…”