How Might Future Climate Change Affect

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How Might Future Climate Change Affect
Lake Temperature, Mixing, Algae,
and Small Invertebrates? John T. Lehman Univer
sity of Michigan 15 June 2001
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Climate Change and the Great Lakes
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 insura
nce policy against detrimental effects and
surprises?
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What are the climate forces that are likely to
change?
Air Temperature Humidity Winds Precipitation C
loud Cover
UV Radiation
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What physical features of the lakes are sensitive
to these forces?
Lake surface temperature Evaporation rates Surfa
ce currents and mixing depths Duration of thermal
stratification
Ice cover
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General Types of Ecological Knowledge
Individuals and Single Populations
Population Interactions Communities Materials an
d Energy
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Individuals and Single Populations
Uniqueness of individuals (sexual, asexual
reproduction) Life history and demography
Behavior Genetics and evolution Sex rati
os Dispersion and distribution
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Population Interactions
Predator-Prey (and defense mechanisms)
Parasitism Symbiosis mutualism, commensa
lism Competition (exploitation, interference)
Indirect Effects Fundamental and Realiz
ed Niche
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Communities
Species Composition, Richness, Diversity
Indicator Species Trophic Structure
Keystone Species Stability and Resilience
Invadability Substitutability Ecologic
al Succession
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Materials and Energy
Primary Production Secondary Production
Bioenergetics Biogeochemistry Biolog
ical Magnification or Concentration
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Managing in the Face of Uncertainty
Do we possess complete catalogs of ecological
knowledge about the species now present in the
Great Lakes?
Absolutely not!
Does the knowledge we do possess permit us to
make any predictions at all?
Certainly.
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Projected duration of thermal stratification
under Canadian Climate Centre climate scenario.
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Projected maximum temperature of the mixed layer
under Hadley Centre climate scenario.
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Projected average temperature of the mixed layer
under Canadian Climate Centre climate scenario.
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Projected average temperature of the lake bottom
at average lake depth under Hadley Centre climate
scenario.
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Projected minimum mixing depth under Canadian
Climate Centre climate scenario.
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Ecological Effects on the Algae
Existing theory about algal ecology teaches us
that mixing pattern is a Master Variable for
algal population growth and community
composition. Given extended thermal stratificatio
n and elevated temperatures, what are the
effects on Diatoms? effects on colonial Green
s and Bluegreens?
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Ecological Effects on the Algae
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 present
ly key to the transfer of energy-rich food from
the water column to the sediments, and to the
benthic food web.
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Ecological Effects on the Algae
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.
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Ecological Effects on Lake Invertebrates
Metabolism by invertebrates varies with
temperature. Temperature affects
Growth rate Egg and embryo development
Generation time Feeding, respiration, and excr
etion But temperature also raises the metabolism
and activity of most lake predators on the
invertebrates, as well.
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Ecological Effects on Lake Invertebrates
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.
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Ecological Effects on Lake Invertebrates
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.
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Ecological Surprises
Complex interactions among many species increase
the likelihood of indirect effects, some of which
will lead to ecological surprises.
Species invasions New or invigorated parasi
tes Changes in breeding windows Altered di
stribution patterns
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Ecological Surprises Further surprises await us r
egarding 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.
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Ecological Surprises For example, elevated UV rad
iation and elevated temperature could
Increase rates at which dissolved elemental
mercury is oxidized to ionic mercury
Increase rates of methylation of ionic
mercury Increase accumulation of methyl mercur
y in food chains leading to large fish
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How does the rational Public protect itself from
disaster and surprise?
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 c
an provide an early warning system for changes
within the Great Lakes ecosystem.
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How does the rational Public protect itself from
disaster and surprise?
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 fed
eral agencies, academic scientists, and
interested citizens require public support.
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Special thanks to Art Brooks and the Workshop
sponsors. GCM-projected climate data for the
Great Lakes were supplied by NOAA-GLERL.