John Gunn is a fisheries biologist who has for the past 25 years studied the effects of acid rain, climate change, and a variety of other environmental factors on coldwater fish communities. As the director of the Living with Lakes Centre in Sudbury and Canada Research Chair in Stressed Aquatic Systems, he is now leading a team of researchers in the study of the effects of multiple stressors on Shield ecosystems.
He is also investigating the recovery processes that operate once stressors are removed. Lakes near Sudbury, are particularly important for the recovery studies. Emissions of air pollutants in this area have declined by about 90 per cent in recent decades and many aquatic systems are beginning to recover. Here, he takes time to answer The Star’s 10 questions.
Forests are often described as the lungs of the planet, and freshwater as its lifeblood. Sudbury has plenty of both, although the former was missing for quite a while. Can you talk a bit about the relationship between the two and how regreening has benefited our lakes and rivers?
The recovering forest in Sudbury produces some remarkable interactions with lakes. For example as the trees return to the once-barren landscape (because of cleaner air and trees planted by the many volunteers), the bottom temperatures in the lakes actually begin to cool even while air temperatures rise because of climate warming.
One reason for the cooling effect is that the growing trees create texture and drag on the surface winds, slowing them down by almost 35 per cent, thus reducing the wind’s power to mix warm surface waters into the depths where the cold-water species like lake trout live. As the new forest grows, and sheds leaves and branches, this surface accumulation of litter and rotting vegetation forms a giant “tea bag” of organic matter around the lake.
When water flows through the debris it leaches out organic matter (let’s call it forest tea) into the lake, creating a sunblock substance that shades the bottom waters from the warming effects of the sun’s radiation, as well as blocking the damaging UV rays (yes, providing a natural sunscreen).
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