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UBC Theses and Dissertations

Dynamics of temporal and spatial mercury contamination in an urban watershed Muraro, Matthew Robert


Mercury is a concern in aquatic environments because it can lead to accumulations of methylmercury in fish, which is the primary source of mercury exposure to humans. The Brunette Watershed is a highly urbanized watershed in metropolitan Vancouver with a rich record of monitoring (1973-2003) trace metal distribution and dynamics. This study was conducted to investigate the 294% increase in Brunette Watershed stream sediment mercury concentrations from 1973-1996. The project conducted analysis of field samples, laboratory experiments and examined previous data to determine if methylcyclopentadienyl manganese tricarbonyl (MMT) may play a role in the increase of mercury in the watershed. Little evidence compiled in this study supported the hypothesis that manganese, iron, sulfur or DOC is associated with mercury throughout the watershed. Thus, it is difficult to conclude or rule out that MMT or manganese oxides play a major role in the transport of total mercury. Laboratory experiments creating summer anoxic conditions released a significant amount of mercury from lake sediment into overlying waters. It seems that this release of mercury may be controlled by sulfate reducing bacteria. The study also found an analysis method used in the study caused 66.8% mean loss of mercury in stream sediment samples when the samples were dried. Temporal and spatial analysis of sediment data revealed that mercury concentrations have started to decrease since 1993. When sediment concentrations were adjusted for the 66.8% loss in stream sediment, 1993 mercury concentrations exceeded the Federal Interm Sediment Quality Guidelines at 12 locations; but in 2003, only 1 site exceeded the same guideline. The decrease in mercury concentrations may be linked to the increased public awareness and a large reduction of emissions from a nearby refuse incinerator. Effective imperviousness and mercury levels in stream sediment are significantly correlated throughout the period of high mercury releases from the incinerator. This may indicate that atmospheric mercury deposited on impervious surfaces connected to waterways may contribute to increases in stream sediment concentrations.

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