The Mercury Experiment to Assess Atmospheric Loadings in Canada and the US (METAALICUS) project is a unique, whole ecosystem mercury loading study to test the watershed-scale response to a change in mercury load. The project is based out of the Experimental Lakes Area (ELA:
http://www.umanitoba.ca/institutes/fisheries/) of Ontario, Canada, where there is a long history of whole-ecosystem manipulation studies. The project is an ambitious effort that has as its overall goal to answer a vexing, policy-relevant question: with centuries of relic mercury contamination already residing in soils and sediments across the globe, will proposed regulations have the intended benefit, and if so, what will be the timing and magnitude of ecosystem response?