The distributions of Fe, Mn, Ni, Cu, Zn and As in the water column, interstitial waters and associated solid phases in Balmer Lake, Ontario, were determined from samples collected in July and October of 1993, and March and May of 1994, in order to assess the seasonal biogeochemical controls governing trace metal behaviour and mobility. The basin has served as a repository for tailings pond effluents since 1967, and as a result, hosts elevated levels of contaminants in the sediments and lake waters. During the ice-free periods of summer, fall and spring, the water column
is characterized by fully oxygenated bottom waters and homogeneous distributions of all measured parameters. However, reducing conditions develop in deeper areas during the period of ice cover in response to the high biological demand of the organic-rich sediments coupled with restricted atmospheric
exchange. Trace metal profiles collected during winter exhibit considerable lakewide
variation and appear to reflect variability in the duration and extent of bottom water anoxia, and the relative influence of metal-rich lateral inputs from the tailings circuits. Solid-phase profiles indicate that the top decimetre of the sediment
column has received variable contributions of both organic matter- and feldspar-rich
natural detritus, and carbonate-, chlorite- and metal-rich tailings inputs.
High resolution profiles of porewater NO₃⁻, Fe, Mn and SO₄²- illustrate that the
sediments in Balmer Lake become anoxic within a few centimetres of the
sediment-water interface during well-mixed periods. Evidence for the precipitation of a Cu-bearing sulphide phase in the lowermost winter bottom waters suggests that the sulphate redox-cline migrates above the sediment-water interface at some point during ice cover. The seasonal porewater distributions of dissolved Ni, Cu and Zn exhibit pronounced consumption profiles at depths consistent with sulphate reduction zones, suggesting they are sequestered as
metal-sulphide phases. Enrichments of dissolved Ni and Zn in the surficial
sediments at most sites reflect the dissolution of labile particulates at the
sediment-water interface. Diffusive influxes calculated for Zn, Ni and Cu suggest that diffusion mechanisms contribute insignificantly to the accumulation
rates of these metals. Arsenic is remobilized at deeper sediment depths and
appears to be largely governed by the redox geochemistry of Mn. The data collectively demonstrate that trace metal mobility in the Balmer Lake water column/sediment system varies significantly over the course of the
four seasons. With the exception of arsenic, however, dissolved metal fluxes indicate that the underlying contaminated sediments are providing a significant and permanent sink for dissolved metals. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/5882 |
| Date | 05 1900 |
| Creators | Martin, Alan |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Format | 12069535 bytes, application/pdf |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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