SUMMARY OF MAJOR RESEARCH PROJECTS AT THE EXPERIMENTAL LAKES AREA DURING 1999 Research activity during 1999 continued to increase as new experimental studies began and background studies for proposed experiments were underway. The first phase of a new laboratory complex was constructed during the winter, and was used during the 1999 field season for water chemistry and other activities. Three new research scientist positions were staffed during the spring and these new personnel were all active on site during the field season. The long-term, ecological research program continued with support from core funding, in recognition of the inherent value of long-term data records on unperturbed systems. Monitoring of lakes recovering from acidification experiments continued, albeit at a reduced level of activity. The investigation of stoichiometric linkages in lakes of different trophic status continued at an active pace, and several other projects investigated the impacts of UV radiation. Although the ELA Reservoir Project and the Lake 226 drawdown study were effectively dormant during 1999, much of the research activity again focused on the effects of reservoirs, as flooding of new upland reservoirs ([4] FLUDEX Project) began in June and continued until October. Mesocosm experiments and baseline measurements were carried out in preparation for two proposed ecosystem-scale experiments; namely, a whole-lake addition of a [5] synthetic estrogen, and a small watershed addition of stable isotopic tracers of mercury ([6] METAALICUS Project). 3. Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS) Why is METAALICUS Necessary? This whole-ecosystem experiment describes research that will directly answer for the first time what happens to fish mercury concentrations when there is a change in atmospheric mercury deposition. Despite the massive amounts of scientific information published on mercury contamination of ecosystems, there remain very basic questions about the environmental behavior and effects of this element. A critical uncertainty is[DEL: :DEL] whether a reduction in atmospheric mercury emissions will reduce mercury concentrations in fish. It is important to answer this question now because controls on industrial emissions of mercury have been proposed that will cost billions of dollars per year if implemented, yet the effectiveness of these controls is unknown. Mercury is the most common contaminant in fish in the United States and Canada. Forty-two states have advisories against fish consumption due to high mercury levels, and unacceptable fish mercury concentrations exist in all Canadian provinces and the Northwest Territories, including remote "pristine" lakes. Ninety-seven percent of closures to fishing in Ontario are due to mercury contamination. Mercury is a neurotoxin. There is a particular concern for prenatal life and infants, for whom safe levels of mercury exposure are lower than in adults. Concern also exists regarding the toxic effects of mercury on reproduction, behavior and survival in fish-consuming birds and marine mammals. Experts agree that the relationship between atmospheric mercury deposition and the mercury in fish can not be understood by examining historical or regional data. This is mainly because empirical attempts to isolate the effects of mercury loading on fish mercury levels are confounded by other environmental factors which cause variations in fish mercury concentrations in lakes. These factors include a wide range of local site conditions and annual weather variability, often combined with poorly documented mercury loads. By contrast, this experiment provides the control necessary to examine the effects of one critical factor: mercury loading. Furthermore, this experiment will also allow us to distinguish newly deposited mercury from background mercury that has accumulated over hundreds of years. [DEL: :DEL] What is METAALICUS? METAALICUS is a whole-ecosystem experiment in which mercury inputs to a headwater lake (example Lake 658) and its watershed will be increased experimentally. An ecosystem approach will be used because the complex pathway of mercury from the atmosphere to fish cannot be simulated in laboratory experiments. The mercury will be added as stable, non-radioactive isotopes of inorganic mercury (Hg(II)). The power of using isotopes lies in the ability to follow the newly deposited mercury separately from the background mercury. Different mercury isotopes will be added to the upland, wetland and the lake surface to determine if the route of entry affects how much is accumulated in the fish . Comprehensive field studies will be carried out to establish site conditions and mercury concentrations in all compartments in the lake and watershed, and how they change with time. Detailed process studies will also be carried out. Movement of the mercury and transformations between mercury forms will be followed through the watershed and lake. Production of methylmercury (MeHg) will be studied in the lake sediments, upland and wetland, as will the bioaccumulation of MeHg into benthic organisms, plankton and fish. Methylmercury will be followed specifically because it is the dominant form in fish and the most toxic form of mercury in the environment. This process-based approach will allow us not only to document what happens, but also to understand why . This is essential if we are to use the results of the study to make predictions for other locations. The approach will also provide critical information for an existing model that predicts fish mercury concentrations in lakes and the effects of remedial actions such as reductions in mercury loading. The study will be carried out in two phases over a 5-year period. Phase 1 has started and involves a series of pilot studies, and background information on the study site. In Phase 2, the mercury loading to the whole ecosystem will be increased. Study Area The Experimental Lakes Area (ELA) is situated in Northwestern Ontario, where atmospheric deposition of mercury is relatively low. Uninhabited research watersheds have been set aside for ecosystem-scale, controlled studies of environmental stressors. ELA lakes and their drainage basins have been used over the past 30 years to provide leading limnological studies in freshwater lakes, including landmark whole-lake studies of the effects of nutrients, acidification and reservoir construction. Other mercury studies at ELA include the completed Experimental Lakes Area Reservoir Project (ELARP) (see 2.1., above) and the ongoing Flooded Uplands Dynamics Experiment (FLUDEX) (2.3., above). These experiments are investigating mercury cycling in natural boreal ecosystems and in experimentally flooded wetlands and uplands. How Much Hg will be Added? Not much