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Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes Heather Burgess 1, Andrea Lini 1, Milt Ostrofsky 2, Suzanne Levine.

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Presentation on theme: "Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes Heather Burgess 1, Andrea Lini 1, Milt Ostrofsky 2, Suzanne Levine."— Presentation transcript:

1 Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes Heather Burgess 1, Andrea Lini 1, Milt Ostrofsky 2, Suzanne Levine 3, Neil Kamman 4 1 Department of Geology, University of Vermont 2 Allegheny College, Biology Department 3 Rubenstein School of Environment and Natural Resources, University of Vermont 4 Vermont Department of Environmental Conservation, Water Quality Division Heather Burgess 1, Andrea Lini 1, Milt Ostrofsky 2, Suzanne Levine 3, Neil Kamman 4 1 Department of Geology, University of Vermont 2 Allegheny College, Biology Department 3 Rubenstein School of Environment and Natural Resources, University of Vermont 4 Vermont Department of Environmental Conservation, Water Quality Division

2 Objectives To determine pre-settlement trophic conditions in Lake Champlain To document changes in trophic state and algal assemblages since European settlement To relate these changes to anthropogenic disturbances within the watershed To determine pre-settlement trophic conditions in Lake Champlain To document changes in trophic state and algal assemblages since European settlement To relate these changes to anthropogenic disturbances within the watershed

3 Significance of Study To better understand: Baseline trophic state of Lake Champlain Anthropogenic impacts on lake ecology Provide information for restoration and management To better understand: Baseline trophic state of Lake Champlain Anthropogenic impacts on lake ecology Provide information for restoration and management

4 Why are Lake Sediments Important? Preserve information about lake history, specifically: Land-use changes in watershed Ecological changes in lake and watershed Preserve information about lake history, specifically: Land-use changes in watershed Ecological changes in lake and watershed

5 Proxies Organic Carbon Total Nitrogen C/N Stable Carbon Isotopes Paleopigments P, Si, metals Diatom Assemblages Organic Carbon Total Nitrogen C/N Stable Carbon Isotopes Paleopigments P, Si, metals Diatom Assemblages

6 Total Organic Carbon (%C) Total Organic Carbon (TOC) Proxy for organic matter Primary productivity Dilution Preservation Total Organic Carbon (TOC) Proxy for organic matter Primary productivity Dilution Preservation (%)

7 C/N Ratio Indicative of organic matter source C/N algae <10 C/N terrestrial >20 Indicative of organic matter source C/N algae <10 C/N terrestrial >20

8 Stable Isotopes Are naturally occurring Do not radioactively decay Reported using the ‘  notation’  ‰ = [(R sample/R standard) -1] x 1000 –where ‘R’ is the ratio of heavy to light isotopes (e.g. 13 C/ 12 C) Are naturally occurring Do not radioactively decay Reported using the ‘  notation’  ‰ = [(R sample/R standard) -1] x 1000 –where ‘R’ is the ratio of heavy to light isotopes (e.g. 13 C/ 12 C) Less of the heavier isotopes More of the heavier isotopes 0 -  ‰ +  ‰

9 Stable Carbon Isotopes and Fractionation Natural abundance of stable carbon isotopes – 12 C 98.9% – 13 C 1.1% Organisms preferentially take up 12 C –Organic matter depleted in 13 C Amount of fractionation based on: –Photosynthetic Pathway –Carbon Availability Natural abundance of stable carbon isotopes – 12 C 98.9% – 13 C 1.1% Organisms preferentially take up 12 C –Organic matter depleted in 13 C Amount of fractionation based on: –Photosynthetic Pathway –Carbon Availability

10 Oligotrophic System Eutrophic System  13 Carbon -27‰ -30‰ -24‰ ALGAEALGAE ALGAEALGAE Increasing productivity Terrestrial Plants Stable Carbon Isotopes and Productivity Change High productivity –Less available DIC –Less fractionation –Algae/OM less negative Low productivity –More available DIC –More fractionation –Algae/OM more negative High productivity –Less available DIC –Less fractionation –Algae/OM less negative Low productivity –More available DIC –More fractionation –Algae/OM more negative

11 Sediment Chronology Fundamental to Paleolimnology –Determine rates of processes/fluxes –Link disturbance to sediment archive –Determine synchronicity of events 210 Pb 14 C –Extrapolate 210 Pb dates, use 14 C to constrain oldest core dates Fundamental to Paleolimnology –Determine rates of processes/fluxes –Link disturbance to sediment archive –Determine synchronicity of events 210 Pb 14 C –Extrapolate 210 Pb dates, use 14 C to constrain oldest core dates

12 Paleopigments Indicative of : –Total algal abundance –Specific algal types –Paleoproductivity Indicative of : –Total algal abundance –Specific algal types –Paleoproductivity Beta Carotene

13 Phosphorus Increases due to –Cultural inputs –Upward migration –Biological uptake Increases due to –Cultural inputs –Upward migration –Biological uptake

14 Biogenic Silica Diatoms, chrysophytes Indicator of diatom biomass Diatoms, chrysophytes Indicator of diatom biomass From: Academy of Natural Sciences

15 Field Methods-Summer

16 Field Methods- Winter

17 Glew gravity core Preserved sediment-water interface Glew gravity core Preserved sediment-water interface Piston core

18 Lab Methods C/N ratios %C and %N Elemental Analysis Freeze dried samples  13 C Isotopic Analysis Paleo-pigments and Soft Algae Nutrients (P, Silica) Sediment Chronology ( 210 Pb & 14 C) Other Analyses Other Analyses Historical Record Search

19 Case Study: Lake Champlain

20 Results and Preliminary Interpretations

21 Modified from LCBP Atlas Point Au Roche Savage Island Cole Bay Crown Point Mallett’s Bay Study Sites Missisquoi Bay St. Albans Bay (VT DEC)

22 Modified from LCBP Atlas Crown Point Point Au Roche Savage Island Cole Bay Mallett’s Bay Crown Point

23 Total Organic Carbon Total Nitrogen C/N Ratio Stable Carbon Isotope Crown Point

24 Modified from LCBP Atlas Point Au Roche Savage Island Cole Bay Crown Point Mallett’s Bay Cole Bay

25 Total Organic Carbon Total Nitrogen C/N Ratio Stable Carbon Isotope

26 Modified from LCBP Atlas Point Au Roche Savage Island Cole Bay Crown Point Mallett’s Bay

27 Total Organic Carbon Total NitrogenC/N Ratio Stable Carbon Isotope

28 Modified from LCBP Atlas Point Au Roche Savage Island Cole Bay Crown Point Mallett’s Bay Savage Island

29 Total Organic Carbon Total NitrogenC/N Ratio Stable Carbon Isotope

30 Modified from LCBP Atlas Point Au Roche Savage Island Cole Bay Crown Point Mallett’s Bay Point Au Roche

31 Point Au Roche Total Organic Carbon Total Nitrogen C/N Ratio Stable Carbon Isotope

32 Nutrient and Pigment Data for Crown Point Total Organic Carbon C/N d13C Biogenic Silica Total Phosphorus Diatoxanthin Myxoxanthin

33 Watershed Development DateDisturbanceGeochemical Trend Prior to 1780Pre-settlementStable early 1900 Settlement, Deforestation, Agriculture Trend toward Eutrophication 1950Chemical Fertilizer, Development More rapid trend toward eutrophication

34 Summary Very little change prior to 20th century –Post-1950s Overall increase in organic matter deposition in upper portion of cores Possibly indicative of increased productivity Very little change prior to 20th century –Post-1950s Overall increase in organic matter deposition in upper portion of cores Possibly indicative of increased productivity

35 Possible Implications for Lake Management Historical variability Rates of change Lag time Effects of remediation Historical variability Rates of change Lag time Effects of remediation

36 Thanks USGS Neil Kamman and the VT DEC Vermont Geological Society Andrea Lini, Milt Ostrofsky and Suzanne Levine University of Vermont Geology Department USGS Neil Kamman and the VT DEC Vermont Geological Society Andrea Lini, Milt Ostrofsky and Suzanne Levine University of Vermont Geology Department

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39 Stable Carbon Isotopes and Bioavailable Phosphorus From Schleske and Hodell, 1995

40 Savage Island Total Phosphorus Total Phosphorus mg/g dry sediment

41 Diatom Assemblages Algae with siliceous cell walls Different assemblages based on: –Location in lake, i.e. planktonic vs. benthic –Productivity, pH, DOC within lake Therefore useful indicators of environmental conditions through time Algae with siliceous cell walls Different assemblages based on: –Location in lake, i.e. planktonic vs. benthic –Productivity, pH, DOC within lake Therefore useful indicators of environmental conditions through time From: Academy of Natural Sciences

42 Trophic Status and Phosphorus Trophic state often based on phosphorus concentration (mg/l) Oligotrophic 0-10 Mesotrophic Eutrophic >20 Trophic state often based on phosphorus concentration (mg/l) Oligotrophic 0-10 Mesotrophic Eutrophic >20

43 Total Organic Carbon C/N d13C Biogenic Silica Total Phosphorus Diatoxanthin Myxoxanthin

44 Stable Carbon Isotopes Indicative of: –Changes in productivity –Source of terrestrial or aquatic OM Indicative of: –Changes in productivity –Source of terrestrial or aquatic OM

45 C/N C/N ratio vs.  13C  13C C/N


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