HR: 16:00h
AN: B14B-01 INVITED    [Abstracts]
TI: Estimating Ecosystem Responses to Changes in Mercury Loading: Lessons From the METAALICUS Project
AU: * Krabbenhoft, D P
EM: dpkrabbe@usgs.gov
AF: U.S. Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Tate, M T
EM: mttate@usgs.gov
AF: U.S. Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Harris, R
EM: rharris6@cogeco.ca
AF: Tetra Tech, Inc., 180 Forestwood Drive, Oakville, ON L6J4E6, Canada
AU: Heyes, A
EM: heyes@cbl.umces.edu
AF: University of Maryland, Chesapeake Bay Lab, Solomons, MD 20688, United States
AU: Heyes, A
EM: heyes@cbl.umces.edu
AF: University of Alberta, Department of Biology, Edmonton, AL T6G 2E1, Canada
AU: St. Louis, V
EM: Vince.StLouis@ualberta.ca>
AF: University of Alberta, Dept. of Biology, Edmonton, AL T6G 2E1, Canada
AU: Graydon, J
EM: jgraydon@ualberta.ca
AF: University of Alberta, Dept. of Biology, Edmonton, AL T6G 2E1, Canada
AU: Branfireun, B
EM: brian.branfireun@utoronto.ca
AF: University of Toronto at Mississauga, Dept. of Geography, Mississauga, ON L5L1C6, Canada
AB: The Mercury Experiment to Assess Atmospheric Loadings in Canada and the US (METAALICUS) project is a whole-ecosystem, mercury (Hg) loading experiment specifically designed to examine the relation between atmospheric mercury deposition and fish Hg concentrations. This project was prompted by the observation that we lacked clear evidence whether a changes atmospheric Hg deposition might lead to a corresponding change in fish Hg, and at what time scales. To address this information need, a multi-national team of scientists was formed to devise a whole-ecosystem, Hg-dosing study, whereby mercury would be deliberately added to an entire watershed. The study is being conducted at the Experimental Lakes Area (ELA), which is located in northwestern Ontario, Canada. Whole-ecosystem manipulation studies have a distinct advantage over small-scale (lab scale) studies, in that natural processes and complexities that are present in watersheds are accounted for in the scientific results. Starting in the spring of 2001, the METAALICUS team been dosing the entire Lake 658 watershed with about 20 ug/m2/y (about 4-5 times the current ambient load). However, the applied Hg is in the form of enriched stable isotopes that can be analytically distinguished from previously existing ambient Hg, or currently depositing Hg. Thus, using the applied isotope as a tracer allows for improved insights into process rates occurring in watersheds that have not been possible heretofore. One of the greatest areas of uncertainty for making reliable predictions of the environmental response to changes in atmospheric Hg deposition is quantifying the flux of Hg from terrestrial systems to downstream aquatic ecosystems. This is especially problematic for settings where terrestrial inputs are similar in scale to atmospheric deposition or may exceed it. In these cases, it is critical to understand the details of how Hg is delivered from watersheds and the relative bioavailability of this Hg compared to that from atmospheric deposition. With this information in hand, improved predictive capability of response times of Lake 658 (and other similar lakes) can be achieved. Net accumulation of the applied isotope is reflected in the steadily increasing isotope concentration in terrestrial soils with each year of application (2001- 2004). However, the total soil-mass accumulation of the Hg isotope represents only about a quarter of that which has been applied. The remaining isotope mass is primarily accounted for by reemission from soils and plants, interception and storage in the forest canopy, and runoff. The concentration and overall flux rate of the isotope in runoff has increased about linearly with each year of application, but runoff mass fluxes are small compared to the isotope application rate (about 1-3 percent). By calibrating a simple numerical soil-box model, we can estimate the response time of Lake 658 to changes in Hg load, and if the processes operating in this basin are applicable elsewhere the model will have utility for estimating response times for a wider range of watershed conditions.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0461 Metals
DE: 0466 Modeling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting