METAALICUS: A Whole-watershed, Stable Isotope Study of the Mechanisms of Net Microbial Methylmercury Production

Academy Of Natural Sciences Philadelphia, Philadelphia PA

Investigators

Abstract

The METAALICUS project is a whole-watershed mercury loading experiment being carried out at the Experimental Lakes Area (ELA) in northwestern Ontario. The study provides a unique opportunity to study the relationship between atmospheric mercury deposition and bioaccumulation of mercury in food webs, at a watershed scale. Mercury is an environmental contaminant that negatively impacts fish and wildlife populations and has resulted in human health advisories worldwide. Mercury emissions reductions have taken place or are being considered in many countries including the U.S. However, the timing and magnitude of a response in fish mercury levels to emissions reductions are unknown. This study seeks to understand those relationships through an experimental addition of mercury to a small lake and its watershed (Lake 658). Some of the important questions being addressed by this study are: 1) Does recently-deposited mercury behave in the same way as mercury deposited in the past? 2) Does mercury deposited to different parts of watersheds behave differently? and 3) Can changes in fish mercury concentrations in response to changes in deposition be adequately modeled? A key process in answering all of the above questions is the production of methylmercury, which is the form of mercury that accumulates in food webs. Methylmercury is produced by natural bacteria found in sediments and wet soils. This study examines how the methylmercury production process responds to changes in mercury deposition. In particular, the study examines how changes in the chemical form of mercury, after deposition and as mercury moves through watersheds, affect the ability of bacteria to take up and methylate mercury. The mercury additions to watershed L658 are being conducted entirely with three stable isotopes of mercury, allowing researchers to track newly deposited Hg separately from the larger existing pools, and to examine its behavior in different parts of the watershed.