Influence Of Beggiatoa Bacterial Mats On Chemistry Of Sediment From Hood Canal, Washington

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Abstracts With Programs - Geological Society Of America




Recent fish kills have highlighted the need to better understand the factors that contribute to development of large hypoxic zones in Hood Canal. Among the important questions are whether hypoxic events have occurred in the past and, if so, whether the current events are more extensive, more frequent, or more sustained. The goal of this study is to look for a geochemical signature in sediment cores that could be used to identify whether anoxic conditions existed in the past. In particular we have focused on trace metals in sediment beneath mats of Beggiatoa, sulfide-metabolizing bacteria, that are abundant on the bottom of low-oxygen areas of the canal. Gravity cores were collected from two sites at the southern end of the canal (47 degrees 24'10.96" N, 122 degrees 55'13.22" W and 47 degrees 24'46.07 degrees N, 122 degrees 53'48.44" W), one from a site inside a Beggiatoa mat, the other from a site without Beggiatoa. In the core taken from the Beggiatoa location, the upper 15-25 cm of sediment are noticeably darker in color than the lower layers; no such color change is observed in the other core. ICP-OES analyses of sediment from the Beggiatoa core indicate significant changes in chemical composition within the upper 15-25 cm. Organic content (by LOI), Fe, and Al levels are more variable in this upper section (LOI=11-16%, Fe=13.7-17.0 ppt, Al=8.0-10.1 ppt at the top, and LOI=11-12%, Fe=15.2-16.0 ppt, Al=8.3-8.9 ppt at the bottom), and heavy metals are notably enriched (Zn=24 ppm, Pb=12 ppm in the top, and Zn=2 ppm, Pb=1 ppm in the bottom). These changes in sediment chemistry may reflect variations in sediment input or differences in redox conditions associated with Beggiatoa mats. By comparing the chemistry of the cores from inside and outside Beggiatoa locations we hope to distinguish the relative importance of these factors.









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