Geoökologisches Kolloquium WS 2003/04

Prof. Joel E. Kostka
Department of Oceanography, Florida State University
Thursday, 13.11.2003 16:15, H6

Microbial biogeochemistry in saltmarsh sediments of the southeastern U.S.A

Saltmarshes are among the most productive ecosystems on earth. These wetlands are vital components of coastal marine ecosystems, because the provide important nursery grounds for fish and they limit nutrient-exchange at the land-sea boundary. My research group focuses on quantifying the structure and function of microbial communities catalyzing key C and N cycling reactions across geochemical gradients. We also relate the ecosystem-level ecology of macrobenthos to the rates/ pathways of C and N transformations mediated by microorganisms. Our results have demonstrated the importance of microbial iron respiration to organic matter decomposition in saltmarsh sediments, and Geographical Information Systems (GIS) were utilized to expand estimates of nutrient flow to entire saltmarsh basins over the kilometer scale. We provide the first detailed enumeration and identification of iron-reducing bacteria in marine sediments using a combination of culture-based and molecular techniques. We observed that a rapid iron cycle, facilitated by microbial iron reduction and bioturbation, prevents the poisoning of microbially-mediated nitrogen transformations (nitrification, denitrification) by dissolved sulfide. This new linkage between the nitrogen and iron cycles has been explored in the field and in laboratory incubations. My seminar will present a synopsis of the above recent discoveries at the interface of biology and geochemistry.

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