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Reactive Iron and Iron-Reducing Bacteria in Louisiana Continental Shelf Sediments
Citation:
Devereux, R., D. Beddick, J. Lehrter, D. Yates, J. Mosher, S. Brown, T. Vishnivetskaya, AND A. Palumbo. Reactive Iron and Iron-Reducing Bacteria in Louisiana Continental Shelf Sediments. Presented at ASLO 2013 Aquatic Sciences Meeting, February 17 - 22, 2013.
Impact/Purpose:
Determine distribution of oxidized and reduced iron on Louisiana continental shelf in relation to hypoxic zone. The information will provide important information on effects and extend of hypoxia.
Description:
The Mississippi and Atchafalaya Rivers release sediments containing 15 x 106 t of iron onto the Louisiana continental shelf (LCS) each year. Iron oxides reaching the seafloor may be utilized as electron acceptors by iron-reducing bacteria for organic matter oxidation or become reduced by sulfide from sulfate reduction. 16S rRNA sequence analyses using nearshore sediments suggested Clostridium, Shewanella, and Nitrospira may dominate the iron-reducing community. Distributions of reactive, biologically reducible iron and iron-reducing bacteria in LCS sediments are not well characterized. Oxalate-extractable iron concentrations were measured at twelve stations across the LCS during October, 2010. Stations closest to the Mississippi River delta and furthest offshore (90-115 km offshore) had higher concentrations of total iron in surficial sediments (100 -150 µg-1 dw) than nearshore stations (5-90 km offshore; 50-125 µg-1 dw) and those 260 km westward. Ratios of reduced to total iron in surficial sediments were highest nearshore (0.07-0.38) and lowest offshore (0.03-0.06). Iron-reducing bacterial communities will likely also vary spatially on the LCS with net iron reduction occurring near shore and net iron oxidation occurring further offshore.