Contrasting sedimentation rates in Lake Illawarra and St Georges Basin,two large barrier estuaries on the southeast coast of Australia |
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Authors: | Craig R Sloss Brian G Jones Brendan P Brooke Henk Heijnis Colin V Murray-Wallace |
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Institution: | (1) The Discipline of Biogeoscience, Queensland University of Technology, GPO Box 2434, Brisbane, QLD, 4001, Australia;(2) School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia;(3) Geoscience Australia, GPO Box 1666, Canberra, ACT, 2601, Australia;(4) Australian Nuclear Science and Technology Organisation, Menai, NSW, Australia |
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Abstract: | Sedimentation rates over the last 100 years within two lagoons on the southeast coast of Australia, Lake Illawarra and St
Georges Basin, have been quantified to determine the effects of catchment land use change and native vegetation clearance
on infill rates, and spatial variations in the rate at which the estuaries have filled. Both catchments have similar lake
and catchment area but have experience different degrees of modification due to land clearing for agriculture practices, urbanisation
and industrialisation. Results indicate that in the heavily modified catchment of Lake Illawarra sedimentation rates close
to fluvial deltas can be in excess of 16 mm/year, and between 2 and 4 mm/year in the adjacent central basin. This is approximately
an order of magnitude greater than the pre-European rates. In contrast, at St Georges Basin, where the catchment has experienced
much less modification, sedimentation rates in the central basin appear to have remained close to those prior to European
settlement. However, sedimentation rates in the urbanized margin of St Georges Basin are relatively high (up to 4.4 mm/year).
This rapid modern sedimentation in the margin of the estuarine embayments has been detected in several other estuaries in
the region. However the degree of sedimentation within the bay-head deltas, and more significantly in the central basin appears
proportional to the degree clearance of native vegetation (forest) in the catchment, urban expansion and development of heavy
industry in the respective catchment areas. |
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