210Polonium and 210lead radionucidles in the Delaware and Chesapeake estuarine and coastal regions

Marsan, David
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University of Delaware
One of the primary objectives of this thesis is to present an integrated study of the 210Pb and 210Po radioactive tracers, and assess their use as tracers for particle and trace element export from different estuarine and coastal environments. In order to achieve this main objective, the thesis was split into three sections, each enhancing the understanding of the natural radionuclides 210Pb and 210Po in the estuarine and costal system. Chapter 1 is dedicated to testing the sampling and analytical methods of 210Po and 210Pb extraction from estuarine and coastal waters, specifically comparing the two most widely used scavenging methods, Fe(OH)3 and CoRAPDC. The chapter describes experiments conducted on about 100 samples collected from the Delaware estuary, Chesapeake estuary, Delaware intertidal marsh and an offshore continental slope site. Data in the chapter clarifies the accuracy and reliability of each method and includes suggestions to enhance them. Other details include results of calculations, error propagation, spike calibration, plating efficiency and the MnO2 scavenging method. Chapter 2 presents a synthesis of the estuarine and coastal biogeochemistry of 210Po and 210Pb in the Delaware and Chesapeake estuaries. A single box model is presented using steady state equations to determine residence times of the radionuclides. This chapter presents five highlights: 1) How 210Pb and 210Po dissolved and particulate data can revel key biogeochemical processes and rates in estuaries; 2) Are regional differences in estuaries dominated by a single or compilation of biogeochemical process; 3) Do subRoxic bottom waters affect the distribution of 210Po and 210Pb; 4) Can disequilibria between parent (210Pb) and grandRdaughter (210Po) be used to identify and quantify principle processes; 5) Will a simple mass balance model result in reliable net scavenging residence times for the Delaware and Chesapeake estuaries. Chapter 3 will advance the simple single boxRmodel from chapter 2 to a more complex twoRlayer model. The model will include evaluations of the fate of not only 210Po and 210Pb in the Delaware and Chesapeake estuaries but also the trace elements Fe, Cu, Cd, Ni, Zn, Pb, Cr, Co and Mn. Residences times, presented as halfRlives along with rates and partition coefficients will be identified for the water column including at the sediment water interface. The thesis will revisit the major conclusions obtained from the work presented along with suggestions for future work. Appendix sections include supporting hydrographic data and a compilation of salt marsh trace metal results conducted in Graz, Austria. Trace metal work included a suite of 26 elements measured in a core, two species of mussels, Spartina)alterniflora marsh plant and the sea surface microlayer (SML) from an intertidal Delaware salt marsh.
210 Polomium , 210 Lead , Estuarine and Coastal , Radionuclide Tracers