In an attempt to determine the trophic history of the Myall Lakes complex (New South Wales, Australia) ?13Corg, ?15N and Corg:N profiles were determined for bulk organic matter of two short sediment cores from Bombah Broadwater and Myall Lake. 210Pb profiles and sediment types indicate significantly different trophic trajectories during the time periods examined. ?13Corg and Corg:N indicate Bombah Broadwater has been dominated by increasing inputs of terrestrial organic material over the last century, thought to be related to watershed disturbance including agricultural activity. Primary production appears to be dominated by phytoplankton. ?15N remained relatively stable at around 1‰ until the mid-1970s when there was a sharp increase to 4.7‰, interpreted as an influx of sewage-derived material. These observations offer an insight into the recent trophic changes at the site. Sedimentation rates are noticeably lower in Myall Lake and the most recent sediment is a flocculent organic rich deposit overlying mineral clay. ?13Corg and Corg:N values indicate a transition from plankton to macrophyte dominated primary production around 1800AD. ?15N values become increasingly negative from approximately 1900AD. This is interpreted as being due to increasing reliance by macrophytes on nitrogen recycled from decomposing sediments driven by natural infilling and eutrophication in this basin. The contrasting sedimentation rates, sediment types and geochemical profiles suggest the different basins of this water body are subject to substantially different internal and external influences which should be considered in management decisions.
|Publication status||Published - 2008|