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Abstract Title: A Whole-Ecosystem Experiment to Assess the Recovery of Mercury-Contaminated Fish Populations
Presenter Name: Paul Blanchfield
Company/Institution: Fisheries & Oceans Canada
Session: Case studies on implementing the Minamata Convention
Co-Authors: Paul Blanchfield

Abstract Information :

The Minamata Convention on Mercury aims to lower concentrations of the potent toxicant methylmercury in fish by controlling mercury emissions, which should then decrease deposition and loading of anthropogenic mercury to aquatic environments. Yet, it is difficult to unambiguously assess the recovery of contaminated fish populations due specifically to mercury control measures because many ecological factors influence both the microbial production and the bioaccumulation of methylmercury in aquatic food webs. In addition, there has until now been no way to evaluate the relative contribution of newly deposited mercury to contemporary methylmercury production. We conducted a novel 15-year whole-ecosystem experiment (METAALICUS) to determine the magnitude and timing of reductions in fish methylmercury concentrations following reductions in mercury additions to a boreal lake and its watershed. During the 7-year addition phase, we applied enriched mercury isotopes to increase local mercury wet deposition rates 5-fold. The mercury isotopes became increasingly incorporated into the food web as methylmercury, predominantly from additions to the lake because most of those added to the watershed remained there. Ceasing isotopic additions to the lake and its watershed, resulted in a ~100% reduction in mercury loading to the lake. The labeled methylmercury quickly diminished in water and lower trophic level organisms. This resulted in rapid methylmercury concentration declines of 38% and 76% in lake whitefish and northern pike populations, respectively, in eight years. While only a small amount of the isotopic mercury added to the upland catchment was detected in fish, this methylmercury also declined quickly once additions to the catchment ceased. This experiment clearly demonstrates that any reduction in mercury loadings to lakes, be they from direct deposition or runoff, will be beneficial to fish consumers.

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