Effect of Loading Rate on the Fate of Mercury in Littoral Mesocosms

• Published in: Environmental science & technology 2006-10, Vol.40 (19), p.5992-6000
• Main Authors: Orihel, Diane M, Paterson, Michael J, Gilmour, Cynthia C, Bodaly, R. A. (Drew), Blanchfield, Paul J, Hintelmann, Holger, Harris, Reed C, Rudd, John W. M
• Format: Article
• Language: English
• Subjects: Air Pollutants; Animal, plant and microbial ecology; Applied ecology; Applied sciences; Aquatic ecosystems; Atmospheric chemistry; Biogeochemistry; Biological and medical sciences; Earth sciences; Earth, ocean, space; Ecotoxicology, biological effects of pollution; Engineering and environment geology. Geothermics; Eukaryota - chemistry; Exact sciences and technology; Fresh Water - chemistry; Fresh water environment; Fundamental and applied biological sciences. Psychology; Geologic Sediments - chemistry; Global environmental pollution; Mercury; Mercury - analysis; Methylmercury Compounds - analysis; Pollution; Pollution, environment geology; Water Pollutants, Chemical - analysis
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es060823+

The effects of changes in atmospheric mercury (Hg) deposition on aquatic ecosystems are poorly understood. In this study, we examined the biogeochemical cycling of Hg in littoral mesocosms receiving different loading rates (7−107 μg Hg m-2 year-1). We added a 202Hg-enriched preparation to differentiate the experimentally added Hg from the ambient Hg in the environment. This approach allowed us to follow the distribution and methylation of the isotopically enriched (“spike”) Hg in the mesocosms. Within 3 weeks, spike Hg was distributed throughout the main environmental compartments (water, particles, periphyton, and sediments) and began to be converted to methylmercury (MeHg). Concentrations of spike total Hg and MeHg in these compartments, measured after 8 weeks, were directly proportional to loading rates. Thus, Hg(II) availability was the limiting factor for the major processes of the biogeochemical Hg cycle, including methylation. This is the first study to demonstrate a proportional response of in situ MeHg production to atmospherically relevant loading levels. On the basis of mass balances, we conclude that loading rate had no effect on the relative distribution of spike Hg among the main compartments or on the fraction of spike Hg converted to MeHg. Therefore, loading rate did not change the relative magnitude of biogeochemical pathways competing for Hg within the mesocosms. These data suggest that reductions of Hg deposition to lake surfaces would be equally effective across a broad range of deposition rates.