Department of Environmental Sciences

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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  Characterization of Biogeochemical Processes Following Sediment Capping: Redox Zone Development and Microbial Colonization
David Himmelheber
Geosyntec Consultants, Columbia, MD

Contaminated aquatic sediments pose health risks to fish, wildlife, and humans and can limit recreational and economic use of surface waters. Subaqueous in situ capping is a promising remedial approach involving the placement of clean material at the sediment-water interface. Little is known, however, regarding biogeochemical processes below a cap and its impact on contaminant fate. This presentation provides an overview of recently-completed laboratory research investigating the influence of capping on biogeochemical processes at the sediment-water interface, and the ability and degree to which microorganisms indigenous to sediment colonize an overlying cap.

Geochemical profiling of capped sediment columns with voltammetric microelectrodes demonstrated that placement of a sand-based in situ cap induced an upward, vertical shift of terminal electron accepting processes into the overlying cap while simultaneously conserving redox stratification. Following dissection of a redox-stratified capped sediment column, quantitative real-time PCR was employed to enumerate multiple metal-reducing, sulfate-reducing, and methanogenic populations. Results indicated that microbes were present in the overlying cap material and population differences among dissected regions of the cap and sediment generally reflected observed redox stratification. Terminal restriction fragment length polymorphism examined community structure within each dissection region and confirmed shifts in bacterial communities were significantly correlated to geochemical gradients and column depth. Collectively, results demonstrate that biogeochemical processes shifted vertically into overlying cap material upon cap placement, and microorganisms indigenous to the sediment formed complex communities within the cap and contributed to redox stratification. Results also suggest that enhanced microbial contaminant degradation in the cap is feasible, thus opening up new avenues for innovative cap design (e.g., capping combined with biostimulation) and active capping technologies.

Last updated: 09/30/2008