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The role of nearshore sediments and vegetation as sources of mercury transfer to yellow perch (Perca flavescens): A study part of the Cornwall Sediment Strategy

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The role of nearshore sediments and vegetation as sources of mercury transfer to yellow perch (Perca flavescens): A study part of the Cornwall Sediment Strategy

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Samenvatting

Mercury is a naturally occurring element but is widely used for industrial purposes. Along the St. Lawrence River in Cornwall, ON, Canada, three plants used to discharge effluents containing mercury among other elements until the beginning of the 70s. It consequently led to the contamination of depositing sediments in several zones along the Cornwall waterfront. Because sediment-associated biota thrives in the depositional zones, mercury (Hg) eventually contaminated invertebrates and fish communities. Methylmercury (MeHg) is the most toxic of Hg species because it has the capacity to bioaccumulates up the food chain with concentrations ultimately harmful to humans.
As a consequence, the International Joint Commission (IJC) designated in 1985 the St. Lawrence River at Cornwall an area of concern (AOC) and was subjected to restrictions on fish consumptions and dredging activities in the contaminated areas. In one of the depositional sites, Zone 1, Hg levels in fish have been reported to be significantly higher than in the other contaminated areas in the Cornwall waterfront despite similar Hg concentrations in the sediments. In summer 2010, a monitoring campaign supervised by the St. Lawrence Institute of Environmental Sciences (SLRIES) took place in Zone 1 to measure Hg concentrations in the sediments, water, amphipods and yellow perch in both nearshore and offshore areas. Biofilm was as well sampled on macrophytes from nearshore. Along with mercury data, carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured to characterize carbon sources and trophic position respectively of biofilm, amphipods and yellow perch (Perca flavescens). Results were compiled in a conceptual model to characterize Hg sources and showed that Hg nearshore was more bioavailable to amphipods in rock baskets likely due to the resuspension of sediments and the input of more contaminated storm water. Yellow perch Hg burden was positively correlated to more littoral carbon sources as a result of diet consisting of more contaminated amphipods as they are young and the consumption of small contaminated fish as they grow. Predicted Hg concentrations via fish bioenergetics modelling confirmed this observation as yellow perch Hg burden increased significantly when their diet shifts from invertebrates to fish when reaching at age 0.5-1 year old.
Hg burden in yellow perch is still important, but only one fish out of 45 had concentrations above provincial guideline for sensitive population. Yellow perch Hg concentrations have been decreasing over the years, but sediments characteristics nearshore in Zone 1 makes it a rather unstable environment to ensure regular deposition of new uncontaminated material (natural recovery). This study proved that Hg is more bioavailable nearshore, and the Cornwall Sediment Strategy (CSS) has to make sure those sediments remain undisturbed through close management and avoid biomagnification.

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OrganisatieHZ University of Applied Sciences
OpleidingWatermanagement/ Aquatische Ecotechnologie
InstituutDelta Academy
PartnersSt. Lawrence River Institute of Environmental Sciences, Cornwall(Canada)
Gepubliceerd in
Datum2011-06-29
TypeBachelorscriptie
TaalEngels

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