Lakes as Records of Past Climates

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Lakes as Records of Past Climates

• Carly Fleming

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What is Paleolimnology?

• A scientific subdisipline concerned with
  reconstructing the past environments of inland
  waters

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Why is it Interesting?

• Can learn about past environments
• Can tell us about the impact of climate change
  and human impacts on lake ecosystems
• Can see the difference between human impacts and
  natural processes

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How is it Done?

• Studies usually based on the analysis of sediment
  cores
• Physical
• Chemical
• Mineralogical
• Biological

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Important Biological Indicators

• Diatoms
• -good indicators of water quality and respond
  rapidly to environmental changes
• -well perserved in sediments

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Climate-Driven Regime Shifts in the Biological
Communities of Arctic Lakes

• Within the last 150 years
• Warming will have greater effect on poles
• -glacier retreat
• -sea ice thinning
• -permafrost degradation

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Methods

• 55 sediment cores taken from 48 lakes in
  circumpolar arctic
• Primary paleoindicators Diatoms, Chrysophytes,
  Ciadocerans, Chironomids
• -provide reliable records of changes in water
  quality, habitat, and catchment processes
• Obtained sediments with gravity corers
• samples ages determined by 210 Pb dating
• estimate species turnover in the last 150 years

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Results

• Lengthening of the summer growing season
• Longer ice free periods
• Wider habitat range
• Higher primary productivity
• Increased thermal stratification

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Results

• Change in Diatom life history Diatoms shifted
  from benthic to littoral taxa
• Planktonic diatoms (cyclotella)
• Knocked out other species who are associated with
  cold conditions and ice cover (benthic
  fragilaria)

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Results

• Responses transferred to higher trophic levels
• Increase in Chironomid abundance and diversity
  that is related to increased lake productivity
• Cladoceran microfossils reveal changes toward
  communities dominated by plankonic species
  (expected response to climate warming)

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Results

• Where there was no real change in climate
  records, no real change in diatoms
• eg) Northern Quebec and Labrador

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Location
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Summary

• Large-scale ecological reorganizations or regime
  shifts, have occurred in many arctic lakes and
  these changes are seen at several trophic levels
• widespread species changes and ecological
  reorganizations in algae and invertebrate
  communities since 1850
• Remote northern ecosystems have already been
  affected by human activities
• -not too many more opportunities to study
  arctic lakes unaffected by humans

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Effects of Agriculture, Urbanization, and Climate
on Water Quality in the Northern Great Plains

• Problem Lake eutrophication
• Purpose To determine factors that regulate water
  quality

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Qu Appelle Valley

• Drainage system provides water to a third of the
  population of the Canadian Great Plains
• Poor water quality, excess plant growth, periodic
  fish kills
• Compare climate, resource use and urbanizations
  as controls of aquatic ecosystems

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Methods

• fossil algae (diatoms, pigments), invertebrates
  (chironomids) analyzed in Pasqua Lake
• Annual records of 83 environmental variables
  (1890-1994)
• Historical records of agricutural activity
• Records of urban populations in Regina and Moose
  Jaw

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Biological assemblages in Pasqua Lake

• Pre-agriculture (1776-1890) Eutrophic, had
  cyanobacterial carotenoids, eutrophic diatoms,
  and anoxia-tolerant chironomids
• Land settlement elevated algal biomass, nuisance
  cyanobacteria, and low abundance of deep-water
  zoobenthos

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Summary

• Resource use most important for changes in fossil
  diatoms and pigments
• Resource use and urbanization were stronger
  determinants of algal and chironomid community
  change than were climatic factors
• urban impacts declined with distance from point
  sources so management strategies will vary with
  lake position within the catchment

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References

• Hall, R.I. (1999).  Effects of agriculture,
  urbanization, and climate on water quality in the
  northern Great Plains. Limnology and Oceanography
  44 739.
• Smol, J. P. et al.  (2005) Climate-driven regime
  shifts in the biological communities of arctic
  lakes. Proceedings of the National Academy of
  Sciences of the United States of America, 102,
  4397-4402
• Racki, G. and Cordey, F. (2000). Radiolarian
  palaeoecology and radiolarites is the present
  the key to the past? Earth-Science Reviews 52,
  83-120
• Whiteside. M. C. 1983. The mythical concept of
  eutrophication. Hydrobiologia 103, 107-111