The Impact of Multiple Stressors

People often assume that the ecological threats of climate change, acidification, ozone depletion and drought generally have little in common. Contrary to popular opinion, these stressors are intimately linked, and when combined, will likely create conditions detrimental to many organisms. These changes will result in substantial losses of biodiversity and optimal fish habitat, and will decrease water quality across the boreal regions of Canada.

The common link between the above stressors is a compound called dissolved organic carbon (DOC), which is readily abundant in most lakes. DOC is what gives lakes a slightly brownish colour, thus a brown lake contains more DOC than a clear lake. In lakes and streams, DOC acts as a 'shield', filtering out light, harmful ultraviolet radiation, heat, and some harmful side effects of acidification. Lakes with moderate to high concentrations of DOC provide an optimal habitat for many organisms.

Climate change, acidification, ozone depletion and drought can all independently cause reductions of DOC, potentially threatening a wide range of species. There is further concern that when more than one stressor is present (known as multiple stressors), they will simultaneously interact and affect aquatic organisms. Under a scenario of a drought and acidification DOC losses could easily exceed 50%, substantially altering the underwater environment.

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