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

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

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

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

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

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

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

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) Less of the heavier isotopes More of the heavier isotopes -  ‰ +  ‰

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

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 Oligotrophic System Eutrophic System -27‰ -30‰ -24‰ ALGAE Increasing productivity Terrestrial Plants 13Carbon

Sediment Chronology Fundamental to Paleolimnology 210Pb 14C 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

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

Phosphorus Increases due to Cultural inputs Upward migration Biological uptake

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

Field Methods-Summer

Field Methods- Winter

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

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

Case Study: Lake Champlain

Results and Preliminary Interpretations

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

Crown Point Point Au Roche Savage Island Mallett’s Bay Cole Bay Modified from LCBP Atlas Crown Point Point Au Roche Savage Island Mallett’s Bay Cole Bay Taken north of CP Bridge, near the town of Port Henry, in approx. 9m of water

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

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

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

Mallett’s Bay Point Au Roche Savage Island Mallett’s Bay Cole Bay Crown Point Taken in outer malletts bay july 2002 Modified from LCBP Atlas

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

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

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

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

Point Au Roche Stable Carbon Isotope Total Organic Carbon Total Nitrogen C/N Ratio 2002 1984 1957 1917 1845 1764 Can I relate decrease in OC and TN at top to decrese P???

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

Watershed Development Date Disturbance Geochemical Trend Prior to 1780 Pre-settlement Stable 1780- early 1900 Settlement, Deforestation, Agriculture Trend toward Eutrophication 1950 Chemical Fertilizer, Development More rapid trend toward eutrophication

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

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

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

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

Savage Island Total Phosphorus Total Phosphorus mg/gdry sediment

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 From: Academy of Natural Sciences

Trophic Status and Phosphorus Trophic state often based on phosphorus concentration (mg/l) Oligotrophic 0-10 Mesotrophic 10-20 Eutrophic >20 Trophic state measurements are often based on phosphorus levels, because P is a limiting nutrient in most lacustrine systems, which essentailly means that as P levels increase, productivity increases. P is measured in mg/L, and defines the 3 states: Oligotrophic lakes have low algae growth and high water clarity, with p levels between 0 and 10 mg/l Mesotrophic lakes have some algae growth and lower water clarity, with P levels between 10-20 mg/l Eutrophic lakes have very high algae growth and very poor water clarity, with P levels greater than 20 mg/l This map shows the different trophic states across lake champain based on P concentrations…

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

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

C/N ratio vs. 13C 13C C/N C/N