The mass flow event resulting from the 1996 flood in the Saguenay region buried the mercury-contaminated indigenous sediments at the head of the Saguenay Fjord under up to 50 cm of postglacial deltaic sediments. This study investigated whether this deposit served as an efficient geochemical barrier to the remobilization of mercury and its availability to the benthic organisms. The vertical distributions of total mercury and methyl mercury (MeHg) in the sediments and pore waters were measured in box cores recovered at three stations along the main axis of the Saguenay Fjord and in the Baie des Ha!Ha!, in successive years between 1996 and 2002. The total solid mercury profile time-series shows that most of the mercury remobilized from the contaminated, indigenous sediments was trapped below or slightly above the former sediment-water interface. Strong correlations with acid-volatile sulphide profiles and extractions of pyrite-associated mercury indicate that most of this mercury was co-precipitated with authigenic iron sulphides. The mercury that was not sequestered by iron sulphides, diffused into the flood layer where it was scavenged by organic matter or methylated. Mercury sequestration at SAG-05 occurred within the older indigenous sediments, in contrast to SAG-09 where it occurred at or above the original sediment-water interface. The sediments are richer in organic matter, more reducing and, thus, establishment of suboxic conditions and precipitation of authigenic iron sulphides occurred more rapidly. The abundance of mercury at the former sediment-water interface and the low dissolved SigmaH2S concentrations, buffered by acid-volatile sulphide precipitation, both favored mercury methylation. A strong correlation between the distribution of acid-volatile sulphides and methyl mercury in the sediment also reveal that the former may serve as a sink for the latter. Throughout the sediment cores, sediment-water partitioning of MeHg as well as Hg(II) is controlled in great part by the residual organic matter content of the sediment.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.97908 |
| Date | January 2005 |
| Creators | Bernier, Geneviève. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Earth and Planetary Sciences.) |
| Rights | © Geneviève Bernier, 2005 |
| Relation | alephsysno: 002338774, proquestno: AAIMR24618, Theses scanned by UMI/ProQuest. |
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