Terrestrial organic matter biomarkers as tracers of Hg sources in lake sediments
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Terrestrial organic matter (TOM) plays a key role in mercury (Hg) dynamics between watersheds and lakes. In this study we attempts to determine the role of TOM source and quality and not only quantity, in the fate and transport of total Hg (T-Hg) to boreal lakes. Integrating the watershed complexity is a daunting task. Within the scope of this project, we characterized this organic matter at a molecular level in order to determine Hg transfer conditions to the sediments. We sampled ten lakes in the Quebec boreal forest. In each lake, we took a sediment core at the deepest point in addition to analyzing T-Hg and a set of terrigenous biomarkers in recent sediments. Our results show no relationship between TOM quantity and T-Hg concentration in lake sediments. However, [T-Hg] variation is well explained by the increase of 3,5Bd/V ratios (R2 = 0.84; p < 0.0002) and the decrease of C/V ratios (R2 = 0.5; p < 0.0227). Our study shows that TOM source and quality are determinant for Hg loadings in lake sediments. More precisely, increasing TOM derived from humified soil horizons explains most of Hg level variation within sediments.
KeywordsMercury Lignin biomarker Boreal forest lakes Terrigenous organic matter Sediment
We would like to thank Sophie Chen and Isabelle Rheault for their assistance in the laboratory. We also acknowledge Jean Carreau for the sampling work. This research was supported by the Collaborative Mercury Research Network (COMERN), financed by the Natural Sciences and Engineering Research Council of Canada (NSERC). We are grateful to Mark Williams and an anonymous reviewer whose comments greatly improve the manuscript.
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