Photoreactions of mercury in the freshwater lakes of Kejimkujik National Park, Nova Scotia
LE3 .A278 2012
Master of Science
Mercury is a globally distributed, toxic environmental contaminant. Divalent mercury (Hg(II)) in freshwater lakes is reduced to volatile elemental mercury (Hg(0)) through reactions with Dissolved Organic Matter (DOM) and energy from solar radiation. Samples were collected from ten lakes in Kejimkujik National Park, Nova Scotia in May, 2008, 2009 and August 2010 and analysed for DOC (ranging 1.4 - 15.4 mg L-1), attenuation, anions, cations, and mercury photoreduction and oxidation rates. An integrated pseudo first order reaction equation was found to fit the gross reduction data extremely well (R2 value of >0.98; p value <0.0001). In all lakes, unfiltered samples (biotic activity included) had a significantly (p <0.01) higher maximum amount of Hg(0) formed (mean = 149 ± 103 pg) than filter sterilized samples lake water samples (mean = 94 ± 75 pg). Gross reduction rate constants for all samples were between 1.63 x 10-3 h-1 to 8.15 x 10-1 h1 (filtered) and 1.29 x 10-3 h-1 to 3.39 x 10-1 h-1 (unfiltered), and rate constants were significantly larger for filtered samples (p = 0.024). We hypothesize that the presence of particles and microbes primarily affects the amount of photo-reducible mercury available. Ultra violet attenuation was measured for each lake and was combined with the measured reduction and oxidation rates to develop a whole lake model for the production of Hg(0) with depth. It was calculated that the lakes studied cumulatively release 115.4 kg of DGM per year, assuming 12 hours of full sun each day
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