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Proactive disclosure Print version   | |  Lake sediment studies, Phase II Metal mobility in lake sediments
Phase II of Lake Sediment Studies within the Geological Survey of Canada (GSC) Metals in the Environment (MITE) Program has (March 2000) provided funding to form a multi-disciplinary research team that includes strong partnerships with government departments and universities in Canada. A major collaboration with the Faculty of Science at the University of Ottawa (UO) has been initiated as a consequence of the GSC study and through funding from the Natural Sciences and Engineering Research Council of Canada (NSERC). As a result, the University of Ottawa and the Geological Survey of Canada have formed a joint study, Lake Sediment Structure and Evolution (LSSE) with several national and international collaborations. This study is possibly the first comprehensive integration of quantitative mineralogy, geochemistry, microbiology, and bio-indicators to infer the processes that control early diagenesis in a freshwater system. Although geochemical profiles of lake sediments can provide a history of chronological metal loading, diagenetic metal remobilization can re-distribute metals within the sediment column. Therefore, interpretations of sediment geochemical profiles can be advanced beyond a chronological record of metal input to incorporate the natural effects of post-depositional re-mobilization (or early diagenesis) on metal concentrations and distributions.
Results from previous reconnaissance surveys of sediments from ~100 lakes in the vicinity of the Horne smelter in Rouyn-Noranda (Quebec, Canada) indicate that metal concentrations are elevated in modern-day sediments in comparison with pre-industrial layers (Kliza & Telmer, in prep). Similar patterns of metal enrichment in surface sediments have been widely reported in the literature (e.g., Nriagu et al., 1982) and have been attributed to increased anthropogenic metal loading or to diagenetic metal remobilization. This study aims to:
The rationale for studying early diagenesis in fresh water systems is to improve our ability to interpret geochemical profiles of lake sediments. The metal distributions observed in sediment cores may not necessarily represent the order of their initial deposition. Results of this study will help identify the causes for higher metal concentrations in surface lake sediments: increases in loading from recent anthropogenic activity and/or natural processes of metal redistribution within the sediment column (e.g., driven by oxidation-reduction reactions). A greater understanding of the processes that lead to metal enrichment in surface lake sediments will aid both government and industry in selecting appropriate risk management strategies to minimize deleterious ecosystem effects.
Kliza, D. A. and Telmer, K.T. Phase I: Lake sediment studies in the vicinity of the Horne smelter in Rouyn-Noranda, Quebec. Geological Survey of Canada Open File D2952, CD-ROM Nriagu, J.O., Wong, H.K.T. and Coker, R.D. 1982. Deposition and chemistry of pollutant metals in lakes around the smelters at Sudbury, Ontario. Environmental Science and Technology 16: 551-560.
In this study, physical methods of quantifying lake sediment mineralogy are coupled with chemical analyses to understand the metal exchange characteristics between the solid and aqueous phases. Since highly reactive Fe and Mn oxides and oxyhydroxides are likely carrier phases for metals, 57Fe Mössbauer spectroscopy is used to identify, quantify and characterize the individual Fe oxide and oxyhydroxide phases. High-resolution X-ray diffraction also enables identification and quantification of mineral phases, including authigenic mineralization that, although thermodynamically favoured, is often undetected by classical dissolution methods. To study metal associations and speciation in the solid phases, additional analytical techniques include scanning electron microscopy, electron microprobe analysis, electron spin resonance spectroscopy, mineral magnetometry, neutron diffraction, micro-Raman spectroscopy, and transmission electron microscopy with selected area diffraction. The LSSE project includes additional advanced and experimental analytical approaches to sediment characterization. Geochemical and microbial investigations are used to examine mineralogical and redox controls on metal distributions in the sediment column. In addition to measurements of bulk sediment geochemistry, metal affinities to various solid phase fractions are being quantified through sequential chemical extractions. Bacterially mediated redox reactions are also being assessed through microbial enumerations (of iron- and sulphate-reducing bacteria and acid-producing bacteria [IRB, SRB and APB]). Organic and inorganic (acid-volatile and chromium-reducible) sulphur phases are being isolated and their isotopic compositions determined to infer lake response to anthropogenic sulphur loading and subsequent S transformations in the sediments. Additionally, pore water chemistry from in-situ dialysis samplers (or peepers) provides clues about diagenetic metal release to the aqueous phase or sequestration in the solid phase. Although lake sediments can provide a chronological record of environmental change, e.g., induced by industrialization, interpretations must consider that diagenetic remobilization can overprint the original depositional record. Historical documentation of the operation of the Horne mine and smelter in Rouyn-Noranda will aid interpretation of geochemical profiles in radiometrically dated lake sediments as a function of changes in industrial emissions. Stable isotope ratios of C, N and S and elemental ratios are measured to assess the source of organic matter, productivity variations in the lakes, and cycling of sulphur and nitrogen. Since diatoms serve as bio-indicators of pH variations in response to natural effects and anthropogenic activity, the history of lake acidity is also being reconstructed.
The structure of the combined companion projects is represented schematically:
Currently, the contributing scientific organizations and their expertise in this project are:
We are seeking industrial, academic, and government partners who are potential users of the reaction transport model (RTM) software that we are developing, for applications involving:
We invite input from potential users during the course of our research and program development. The software will be made available to potential users and information/contact sessions are planned.
We are always open to new industrial, academic, and government collaborators and partners. We are currently seeking new collaborations for:
Please contact Sam Alpay (principal investigator, lake sediment studies, Geological Survey of Canada)
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Participants at the project meeting in December 2001 at the Geological Survey of Canada in Ottawa.
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