NEW PARTICLE-LABELING TECHNIQUE FOR USE IN BIOLOGICAL AND PHYSICAL SEDIMENT TRANSPORT STUDIES

A new particle-labeling technique is presented that can be used for biological and physical sediment transport studies. The technique improves upon previous methodologies by using natural sediment from the area of interest as tracers. Sediment particles are labeled with noble metals, such as gold or silver, that are present in only trace amounts in most natural settings. The elements are introduced in a liquid phase to the sediment surfaces and are then diffused at a high temperature into the crystalline lattice. Acid etching subsequently removes all unreacted, including surface-adsorbed, metal. The metals can be sensitively detected at low levels (ng/g) using instrumental neutron activation analysis (INAA). Other analytical techniques [e.g., inductively coupled plasma atomic emission spectroscopy (ICPAES), inductively coupled plasma mass spectrometry (ICPMS), and atomic absorption (AA)] would be suitable for this analysis following sediment dissolution and concentration of the dopants. Scanning electron microscopy and energy dispersive X-ray microprobe analysis have been used to examine particles before and after labeling. Neither detectable morphological changes (e.g., size, shape, surface roughness) nor nondiffused surface metals were found following a final etch to remove unreacted dopants. Only minor amounts of particle agglomeration were observed in one sample of the gold-labeled sediments. Sediments labeled by this technique have been used in a study of seasonal and particle-size-dependent bioturbation at a subtidal site in Massachusetts Bay. Application of this technique to the study of other physical transport properties is suggested.