Determining floodplain sedimentation rates using super(137)Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

• Published in: Journal of environmental radioactivity Vol. 100; no. 10; pp. 858 - 865
• Main Authors: Hughes, Andrew O, Olley, Jon M, Croke, Jacky C, Webster, Ian T
• Format: Journal Article
• Language: English
• Published: 01.10.2009
• Subjects: Catchments; Australia, Queensland
• ISSN: 0265-931X
• DOI: 10.1016/j.jenvrad.2009.06.011

Fallout super(137)Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of super(137)Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total super(137)Cs inventories calculated from the detailed profile data. Information on the rates of super(137)Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection-diffusion model to account of super(137)Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for super(137)Cs being known and without having to assume that super(137)Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total super(137)Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, super(137)Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.