<p>This doctoral research comparatively assesses the biogeochemical properties of suspended aquatic flocs through a integrated field-laboratory approach; providing new insight into the linkages among floc associated bacteria, floc-reactive solid phases and trace metal uptake.</p> <p>Results show flocs to possess a distinct geochemistry, microbiology and composition from bed sedimentary materials in close proximity (III-oxyhydroxide minerals (FeOOH); resulting in localized floc-Fe-mineral precipitates and enhanced reactivity. Further, the Fe-enrichment of floc and of floc bio-mineral constituents in turn provides an important and novel lens through which to examine how environmental microbial communities, microbial metabolism and Fe<sup>III</sup>/Fe<sup>II </sup>redox transformations interact. The results were the discovery of floc-hosted, Fe<sup>III/II</sup>-redox cycling bacterial consortia across diverse oxygenated (O<sub>2</sub><sup>Sat.</sup>=1-103%) aquatic systems, which were not predicted to sustain bacterial Fe-metabolism. Both environmental<em> </em>and experimentally-developed consortial aggregates constituted multiple genera of aero-intolerant Fe<sup>III</sup>-reducing and Fe<sup>II</sup>-oxidizing bacteria together with oxygen consuming organotrophic species. These findings highlight that the implementation of geochemical thermodynamic constraints alone as a guide to investigating and interpreting microbe-geosphere interactions may not accurately capture processes occurring <em>in situ.</em></p> <p><em> </em> Seasonal investigation of microbial Fe<sup>III/II</sup>-redox transformations highlighted the interdependence of floc Fe-redox cycling consortia members, revealing that cold conditions and a turnover in putative Fe-reducing community membership extinguishes the potential for coupled Fe-redox cycling by wintertime floc bacteria. Further, the observed summer-winter seasonal turnover of <em>in situ</em> floc community membership corresponded with an overall shift from dominant Fe to S redox cycling bacterial communities. This significantly impacted observable floc Fe and TE (Cd, Pb) geochemistry, resulting in a shift in floc associated Fe-phases from dominantly Fe<sup>(III)</sup><sub>(s) </sub> to Fe<sup>(II)</sup><sub>(s)</sub>, and, in turn, corresponded to a large decrease of TE uptake by flocs under ice.</p> / Doctor of Science (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/13572 |
| Date | 10 1900 |
| Creators | Elliott, Amy V. C. |
| Contributors | Warren, Lesley, School of Geography and Geology |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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