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Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes

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

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Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes

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  1. Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes Heather Burgess1, Andrea Lini1, Milt Ostrofsky2, Suzanne Levine3, Neil Kamman4 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

  3. Significance of Study 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

  5. Proxies • 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

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

  8. Less of the heavier isotopes More of the heavier isotopes 0 +  ‰ -  ‰ 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. 13C/12C)

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

  10. ALGAE ALGAE Terrestrial Plants Increasing productivity Increasing productivity -27‰ -24‰ -30‰ 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 13Carbon

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

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

  13. Phosphorus • Increases due to • Cultural inputs • Upward migration • Biological uptake

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

  15. Field Methods-Summer

  16. Field Methods- Winter

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

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

  19. Case Study: Lake Champlain

  20. Results and Preliminary Interpretations

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

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

  23. Crown Point Stable Carbon Isotope Total Organic Carbon C/N Ratio Total Nitrogen 2002 1982 1958 1849 1781

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

  25. 2000 1980 1959 1917 1811 Cole Bay Total Organic Carbon Stable Carbon Isotope C/N Ratio Total Nitrogen 1760 1711

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

  27. 2001 1996 1979 1964 1926 1859 Mallett’s Bay Total Organic Carbon Stable Carbon Isotope Total Nitrogen C/N Ratio 1819

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

  29. 1991 1840 1668 Savage Island Total Organic Carbon Stable Carbon Isotope Total Nitrogen C/N Ratio

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

  31. 2002 1984 1957 1917 1845 1764 Point Au Roche Stable Carbon Isotope Total Organic Carbon C/N Ratio Total Nitrogen

  32. Total Organic Carbon Total Phosphorus C/N Biogenic Silica d13C Nutrient and Pigment Datafor Crown Point Diatoxanthin Myxoxanthin 2002 1958 1804

  33. Watershed Development

  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

  35. Possible Implications for Lake Management 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

  37. From Schleske and Hodell, 1995 Stable Carbon Isotopes and Bioavailable Phosphorus

  38. Total Phosphorus mg/gdry sediment Savage Island Total Phosphorus

  39. From: Academy of Natural Sciences 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

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

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

  42. Stable Carbon Isotopes • Indicative of: • Changes in productivity • Source of terrestrial or aquatic OM

  43. 13C C/N C/N ratio vs. 13C C/N

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