The Impact of Multiple Stressors

Another concern of multiple stressors is the possibility of synergistic interactions, when the total impact of multiple stressors is more then the sum of its parts. Take a hypothetical example of two stressors, acidification and global warming, and set the damage of each stress to be a loss of 10% of fish biomass. Under a situation where a lake is exposed to acidification and global warming we would predict a loss of 20% fish biomass (i.e. 10 + 10 = 20%). However, because these stressors synergistically interact, the actual loss of fish biomass may be much, much larger than 20%. It can easily be seen that the situation of multiple stressors could be potentially the most serious ecological threat to the integrity and function of freshwater systems in Alberta, Canada and the northern hemisphere.

Unfortunately, very little is currently known about multiple stressors. Aquatic research has focused primarily upon the effects of a single stressor, providing an abundance of important data. However, since these stressors interact with each other, we can not simply predict the effects of multiple stressors using previous data. Experimental evidence of the effects of multiple stressors is required. In the summer of 2004, I will perform the first outdoor experiment testing the impacts of multiple stressors, using global warming, acidification and drought as my stressors. This experiment will be taking place at the Experimental Lakes Area (ELA) in northern Ontario.

This text was written by Michael Christensen, and a longer but similar version was published in Environmental News, an ERSC publication, in February, 2004. It is available for download from the ERSC Site.

Links

• Environmental Lakes Area: University of Manitoba Site
• ELA Canadian Fisheries and Oceans Site

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