A historical reconstruction of organic and inorganic contamination events in the Saguenay Fjord St. Lawrence system from preindustrial times to the present
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abstract
Based on published chronologies of Hg contamination to the Saguenay/St. Lawrence system as well as sedimentary profiles for this heavy metal in the Lower St. Lawrence Estuary, we have established a 100-200 year chronology in the studied sediments and reassessed sedimentation rates for the estuarine system. Our results suggest that sedimentation rates might be higher, by a factor of 1.5-2, than previously assumed for the Lower Estuary. This chronology in parallel with concentrations of Hg and lignin, the latter an unambiguous marker of terrigenous organic matter, were used successfully to describe natural conditions prevailing prior to the late 19th to early 20th century and the changes due to industrial activities (chlor-alkali, pulp and paper mills) that occurred in the first haft of the 20th century. In contrast to earlier studies, no significant relationship was found between Hg and lignin in ancient and recent sedimentary intervals contradicting the hypothesis of a particulate lignin-rich carrier-phase controlling the transport and distribution of Hg within the system. Such a correlation between Hg and lignin was only observed in sediments deposited during a discrete period of high Hg contamination (1940-1975). However, the covariation of Hg and lignin in sediments deposited in this period results from simultaneous loadings of these two compounds following production growth of chlor-alkali and pulp and paper industries, respectively, and conservative dispersal of sediments from the Upper Saguenay Fjord down to the Lower St. Lawrence Estuary.
