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RESEARCH ARTICLE
Contents Vol 61(11)

A novel application of radionuclides for dating sediment cores from sandy, anthropogenically disturbed estuaries

Alexa R. Van Eaton A B , Andrew R. Zimmerman A D , John M. Jaeger A , Mark Brenner A , William F. Kenney A and Jeffrey R. Schmid C
+ Author Affiliations
- Author Affiliations

A Department of Geological Sciences and Land Use and Environmental Change Institute, University of Florida, PO Box 112120, Gainesville, FL 32611, USA.

B Present address: School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.

C Conservancy of Southwest Florida, 1450 Merrihue Drive, Naples, FL 34102, USA.

D Corresponding author. Email: azimmer@ufl.edu

Marine and Freshwater Research 61(11) 1268-1277 https://doi.org/10.1071/MF10028
Submitted: 6 February 2010  Accepted: 24 May 2010   Published: 16 November 2010

Abstract

Reliable sedimentation histories are difficult to obtain in sandy or anthropogenically impacted coastal systems with disturbed sediment profiles and low initial radionuclide activities. This study addresses the problem using radionuclides in sediment cores from Naples Bay estuary, Florida, USA. Non-steady sedimentation and nuclide scavenging processes are shown to limit application of traditional radiometric dating models in this system. Whole-core inventories of excess 210Pb activity (210Pbxs) varied from 21 to 96 dpm cm–2 among sites, and initial sediment 210Pbxs activities were low, decreasing non-uniformly with depth in most cores. Activities of three radioisotopes used for sediment dating (226Ra, 210Pb, and 137Cs) were compared with grain size and organic matter (OM) distributions to assess the factors that influence accumulation of radionuclides. Regression analysis indicated that radionuclide activities were more strongly correlated with OM content than with grain size parameters, and a novel OM-normalisation procedure was developed to correct for preferential nuclide associations. Normalised 210Pbxs profiles provide evidence for shifts in sedimentation rates and episodic erosion events in regions of the estuary where anthropogenic disturbance is known to have occurred. Our results emphasise the need to consider radionuclide scavenging by OM in sandy coastal sediments when establishing sedimentation histories.

Additional keywords: Cs-137, estuaries, grain size effect, organic matter, Pb-210, preferential scavenging, radioisotopes, Ra-226.


Acknowledgements

This research was supported by a grant from The City of Naples to the Conservancy of Southwest Florida. Sincere thanks are extended to Jason Curtis for guidance in the laboratory, to Kathy Worley for field assistance in Naples, and to Michael Macaluso for graphics. We particularly appreciate detailed reviews from Andrew Boulton and anonymous referees, which led to significant improvement of the manuscript.


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