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How Might Future Climate Change Affect Lake Temperature, Mixing, Algae, and Small Invertebrates? John T. Lehman University of Michigan 15 June 2001 Climate Change and the Great Lakes What types of Ecological Knowledge do we need to understand and predict the effects of climate change?
Lake Temperature, Mixing, Algae,
and Small Invertebrates?
John T. Lehman
University of Michigan
15 June 2001
What types of Ecological Knowledge do we need to understand and predict the effects of climate change?
What types of Ecological Surprises might occur?
How can we obtain an environmental insurance policy against detrimental effects and surprises?
Do we possess complete catalogs of ecological knowledge about the species now present in the Great Lakes?
Does the knowledge we do possess permit us to make any predictions at all?
Projected duration of thermal stratification under Canadian Climate Centre climate scenario.
Projected maximum temperature of the mixed layer under Hadley Centre climate scenario.
Projected average temperature of the mixed layer under Canadian Climate Centre climate scenario.
Projected average temperature of the lake bottom at average lake depth under Hadley Centre climate scenario.
Projected minimum mixing depth under Canadian Climate Centre climate scenario.
Existing ecological knowledge points to an impending change from fast-growing, opportunistic, rapid-sinking species to slower growing, stress-tolerant, loss-minimizing species.
Rapid-sinking diatom species are presently key to the transfer of energy-rich food from the water column to the sediments, and to the benthic food web.
Most of the Great Lakes are presently optically shallow, in the sense that much light reaches below the mixed layer and permits the growth of metalimnetic and hypolimnetic algal populations.
Climate factors alone will not change this condition. However, if nutrient loading from watersheds and airsheds increase, the optical state could change.
Most of the Great Lakes presently harbor a group of cold stenothermic invertebrate species which cannot tolerate warm temperatures.
Deep, cold water habitat for these species will not disappear. However, the oxygen content of that habitat could become compromised by the end of the thermal stratification period, particularly if nutrient loading were to increase.
Increased foraging and predation by planktivorous fish will result in changes of invertebrate species toward small bodied forms.
The vertical range of zebra mussels may expand, but other benthic invertebrates may suffer from diminished inputs of high quality diatoms as food, and from potential decreases in oxygen.
Further surprises await us regarding the transformations and fates of environmental toxins. Some toxins, such as Mercury or PCBs, become biomagnified up a food chain. Their chemistry, transport, and effects are tied to biology.
For example, elevated UV radiation and elevated temperature could
Science relies on the testimony of evidence rather than the fervor of belief. Observation and theory are the antidotes to ignorance, fear, and doubt.
Thoughtful measurements and analyses can provide an early warning system for changes within the Great Lakes ecosystem.
Regional assessment of Great Lakes response to environmental changes must become a regular activity. This assessment has uncovered many gaps in ecological knowledge that must be filled.
Research and reporting collaborations among federal agencies, academic scientists, and interested citizens require public support.
Special thanks to Art Brooks and the Workshop sponsors. GCM-projected climate data for the Great Lakes were supplied by NOAA-GLERL.