Whole-lake experimentation as a tool to assess ecosystem health,response to stress and recovery: the Experimental Lakes Area experience

The rationale and methods for and value of whole-lake experimentation are described using the Experimental Lakes Area (ELA), northwestern Ontario, as the example. The ELA consists of 46 lakes (< 100 ha in surface area), their watersheds, and several streams protected for research purposes in near-pristine boreal forest on the Precambrian Shield near Kenora, Ontario. Over more than 20 y, whole-lake experimentation has provided unique information on the effects on lakes of nutrient additions, acidification, Cd addition, and biomanipulation. Experiments are planned to study the effects of PCB addition and flooding. Recovery, mitigation, and remediation have been explored in some experiments. As well, the fate of radioactive metals in a lake and the effects of acidification on a poor fen and an upland watershed are studied. Comparison between the experimental systems and unmanipulated reference systems has proven to be essential. These reference systems also have a role in defining (absolute) aquatic ecosystem health for small, pristine Precambrian Shield lakes. The ELA experimental data base is available, as well, for calibrating indices of relative aquatic ecosystem health, i.e., environmental degradation, using the dose-responses of lakes to eutrophication, acidification, Cd addition, and other stressors.