Mercury Fluxes from Watersheds and Responses to Environmental Change: Insights from the METAALICUS Project

David P Krabbenhoft, USGS Upper Midwest Water Science Center, Madison, United States, Michael T. Tate, USGS Wisconsin Water Science Center, Middleton, WI, United States, Vincent L St.Louis, University of Alberta, Department of Biological Sciences, Edmonton, AB, Canada, Jennifer A Graydon, University of Alberta, Edmonton, AB, Canada, Brian A Branfireun, Western University, Department of Biology, London, ON, Canada, John W. M. Rudd, Rudd and Kelly, Inc., Salt Spring Island, BC, Canada and Reed C. Harris, Reed Harris Environmental Ltd., Oakville, ON, Canada

Contact First Author: David P Krabbenhoft; dpkrabbe@usgs.gov

Abstract ID#: 35772

 

English Abstract:
More than decade ago, when the US and many other countries began to consider mercury (Hg) emission regulations, many questioned the potential effectiveness of such actions since soils and sediments were already ubiquitously contaminated, and would potentially fuel this contamination problem indefinitely. To address this concern, a team of scientists was formed to devise a whole-ecosystem, Hg-loading study, whereby Hg would be deliberately added to an entire watershed – The Mercury Experiment to Assess Atmospheric Loadings in Canada and the US (METAALICUS) project. The study is located at the Experimental Lakes Area (ELA), northwestern Ontario, Canada, and the overall project goal is to quantify the magnitude and timing of the watershed response to a change in mercury (Hg) loading.

This paper focuses on the terrestrial (upland forest and wetland) aspects of METAALICUS project. The lake, forests and wetland were dosed with different stable Hg isotopes, which allows for discrimination of the experimentally administered Hg versus ambient Hg brought to the watershed principally from atmospheric deposition. Mercury isotope additions to the watershed were initiated in 2001 and continued through 2006 at a rate of about 5 times measured wet deposition. During the loading phase of the project, the majority of the terrestrially applied Hg isotopes were distributed approximately equally among three major compartments: soils, plants (tree canopy and ground vegetation), and losses to emissions. Much less (about 1%) isotope was measured in runoff that flowed into the downstream lake. With each successive annual dose the isotope pool in soils steadily increased, reaching about 3-4% of the total Hg pool in soils. Isotope concentrations in runoff gradually increased during the loading phase, and continued to increase for a short period after loading ceased. Five years subsequent to cessation the isotope concentrations in soils remained unchanged; however, the isotope abundance in runoff decreased precipitously. This notable divergence in the abundance of isotope in soils versus runoff points to a stabilization process of Hg in soils and a reduced influence of the “old Hg” in soils on Hg in runoff generation.

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