Complex reservoir sedimentation revealed by an unusual combination of sediment records, Kangaroo Creek Reservoir, South Australia

Tibby, J.; Gell, Peter; Hancock, Gary; Clark, M.

Title: Complex reservoir sedimentation revealed by an unusual combination of sediment records, Kangaroo Creek Reservoir, South Australia
Creator: Tibby, John; Gell, Peter; Hancock, Gary; Clark, M.
Date: 2009
Type: Text; Journal article
Identifier: http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/59168
Identifier: vital:1951
Identifier: https://doi.org/10.1007/s10933-009-9349-0
Identifier: ISSN:0921-2728
Abstract: Despite their direct links to human use, reservoirs are not widely utilised, relative to natural lakes, for deriving sediment histories. One explanation is the complex sedimentation patterns observed in water storages. Here a highly unusual combination of sedimentary records is used to determine the sedimentation history of Kangaroo Creek Reservoir, South Australia. We compare contiguous high resolution (0.5Â cm sampling interval) diatom records from an almost 1.3Â m core extracted from the bottom of the reservoir and from a 0.4Â m monolith of sediment perched 15Â m above the reservoir bottom on a disused bridge that was submerged following initial reservoir filling in 1970. The diatom histories are supplemented by evidence provided by other indicators, most notably radionuclide concentrations and ratios. Interestingly, despite the fact that the reservoir has beenÂ >20Â m deep for more than 70% of its recorded history, distinct sections of the reservoir bottom core, but not the bridge monolith, are dominated by non-planktonic diatoms. We attribute the occurrences of these phases to inflows that occur following heavy catchment rains at times when the reservoir is drawn down. These characteristic sections have, in turn, been used to refine the site's chronology. Despite having a length of almost 1.3Â m, a variety of data suggests that the core has not recovered pre-reservoir sediment, but rather spans the period from 1981 (11Â years after first filling) to 2001, when the core was extracted. It is clear, therefore, that sediments in the bottom of the reservoir are accumulating rapidly (>7Â cmÂ year-1), although more than 40% of this deposition occurs in less than 5% of the time. It appears that in the period 1996-2001, quiescent sedimentation rates, both in the perched bridge locality and on the reservoir bottom, slowed in response to reduced stream flow. Our findings indicate that, with caution, complex patterns of sedimentation in water storages can be disentangled. However, it was difficult to precisely correlate diatom sequences from the two records even in periods of quiescent sedimentation, suggesting that reservoir bottom diatom sequences should be interpreted with considerable caution. Furthermore, while storm-derived inflows such as those identified may deliver a substantial proportion of sediment and phosphorus load to storages, the ensuing deposition patterns may render much of the phosphorus unavailable to the overlying waters. © 2009 Springer Science+Business Media B.V.
Relation: Journal of Paleolimnology Vol. , no. (2009), p. 1-15
Rights: Copyright Springer
Rights: Open Access
Rights: This metadata is freely available under a CCO license
Subject: Correlation; Diatoms; Reservoir; Sedimentation rates; Sequence slotting
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