Factors controlling the biogeochemical cycles of trace elements in fresh and coastal marine waters as revealed by artificial radioisotopes
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abstract
Radionuclides in aquatic ecosystems can provide important insights into the way physical, chemical, biological, and sedimentological processes are coupled into networks to control the transfer of major and trace elements within the waterbody itself and across its boundaries. Examples from artificial radionuclide studies in freshwater (Experimental Lakes Area in Northern Ontario, ELA) and coastal marine ecosystem enclosures (MERL tanks at Narragansett Bay, Rhode Island) show the cycling of selected trace elements across the sedimentwater interface as these are influenced by various biogeochemical factors.The approach to meaningful studies using radiotracers should include the separate characterization of the physical transport processes, and preferably a comparison of the fate of radiotracers to those of stable elements in the same system, to allow for kinetic studies of chemical forms. The kinetics of transformation of different chemical species of Co, Hg, Ag, Se, and Cr ions, under variable pH (ELA) or redox (MERL) conditions appeared to be indirectly linked to the kinetics of organic carbon cycling. A better knowledge of the predominant chemical species of trace elements present in these systems will be important in understanding bioavailability, biomagnification, and toxicity of trace elements in aquatic ecosystems.
