HR: 13:45h
AN: B13A-02    [Abstracts]
TI: A Magnitite Tracer Protocol for Seasonal Measurement of Bed Sediment Biodiffusion Coefficients
AU: * Thibodeaux, L J
EM: thibod@lsu.edu
AF: Louis J. Thibodeaux, Gordon A. and Mary Cain Department of Checical Engineering Louisiana State University, Baton Rouge, LA 70803 United States
AB: Anticipating its use in contaminant remediation this paper describes the development of a particle tracer technique for making short-term,in situ measurements of aquatic bed sediment biodiffusion coefficients. The bioturbation process in the upper sediment layers of streams, lakes, estuaries and the marine environment moves particles and porewater. When present, organic chemcals, metals, colloids, etc., are transported across these layers and exchanges may occur at the sediment water interface. Fickian biodiffusion coefficients that characterize such particle movements,Db (cm2/yr), are used for assessing chemical diagenesis rates and contaminant fluxes and are specific to each site. Chemical fate and transport models, developed for tracking contaminants in aquatic systems, requite a method of measuring in situ Db numerical values. The protocols should be able to detect seasonal and other time or position dependent variations in the coefficients for improved model predictions. Magnetite, a tracer with a long history of use in scientific studies of porous media, particle transport, etc., was chosen. Unlike most tracers it is inexpensive, naturally occuring and readiy available. The steps of the protocol include deployment and retrieval of the tracer, magnitite sepatation and measurement, mathematical model interpretation, an statistical treatment of data. Application of the techinque was tested on South Capitol Lake, a manmade, freshwater lake located in Baton Rouge, Louisiana. The surficial sediment in the lake was found to contain a fairly large population of oglichaete worms in abundances of approximately 18,000 per/m2. Field deployments were conducted in December 2001, January and February 2002, giving biodiffusion coefficients of 0.95, 0.46 and 0.66 cm2/yr. Although the protocol was capable of in situ measurements, testing over one or more calendar years at this and other sites will be needed to determine if the protocol can be used to detect changes in Db with season of the year.
DE: 3022 Marine sediments--processes and transport
DE: 4211 Benthic boundary layers
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4804 Benthic processes/benthos
DE: 4808 Chemical tracers
SC: Biogeosciences [B]
MN: 2005 Joint Assembly