# Presentation: 482285

## Paleolimnology as a Tool for Interpreting Ecosystem Changes within Freshwater Lakes

**Heather Burgess****1**, 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

**Notes:**
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)

## 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

| Oligotrophic System | Eutrophic System |
| --- | --- |
|  |  |

- 13Carbon

- High productivity
- Less available DIC
- Less fractionation
- Algae/OM less negative
- Low productivity
- More available DIC
- More fractionation
- Algae/OM more negative

## 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

## 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

## Field Methods-Summer

## Field Methods- Winter

## Glew gravity core

- Preserved sediment-water interface

- Piston core

## Lab Methods

- C/N ratios

- %C and %N

- Elemental Analysis

- Freeze dried samples

- 13C

- Isotopic
- Analysis

- Paleo-pigments and
- Soft Algae

- Nutrients          (P, Silica)

- Sediment Chronology   (210Pb & 14C)

- Other
- Analyses

- Historical Record Search

## Case Study:  Lake Champlain

- Case Study:  Lake Champlain

## Results and Preliminary Interpretations

## Study Sites

- Missisquoi
- Bay

- St. Albans
- Bay

- (VT DEC)

- (VT DEC)

- (VT DEC)

## Crown Point

**Notes:**
Taken north of CP Bridge, near the town of Port Henry, in approx. 9m of water

## Crown Point

- Total Organic Carbon

- Total Nitrogen

- C/N Ratio

- Stable Carbon Isotope

- 1982

- 1849

- 1958

- 2002

- 1781

## Cole Bay

- Modified from LCBP Atlas

- Point Au Roche

- Savage Island

- Crown Point

- Mallett’s Bay

## Cole Bay

- Total Organic Carbon

- Total Nitrogen

- C/N Ratio

- Stable Carbon Isotope

- 1760

- 1711

## Mallett’s Bay

- Modified from LCBP Atlas

- Point Au Roche

- Savage Island

- Cole Bay

- Crown Point

**Notes:**
Taken in outer malletts bayjuly 2002

## Mallett’s Bay

- Total Organic Carbon

- Total Nitrogen

- C/N Ratio

- Stable Carbon Isotope

- 1819

## Savage Island

- Modified from LCBP Atlas

- Point Au Roche

- Cole Bay

- Crown Point

- Mallett’s Bay

## Savage Island

- Total Organic Carbon

- Total Nitrogen

- C/N Ratio

- Stable Carbon Isotope

## Point Au Roche

## Point Au Roche

- Total Organic Carbon

- Total Nitrogen

- C/N Ratio

- Stable Carbon Isotope

**Notes:**
Can I relate decrease in OC and TN at top to decrese P???

## Nutrient and Pigment Datafor Crown Point

- Diatoxanthin

- Myxoxanthin

- 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

## Slide 37

## Stable Carbon Isotopes and Bioavailable Phosphorus

## Savage Island Total Phosphorus

## 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

## Trophic Status and Phosphorus

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

**Notes:**
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...

## Slide 43

## Stable Carbon Isotopes

- Indicative of:
- Changes in productivity
- Source of terrestrial or
- aquatic OM

## C/N ratio vs. 13C

- C/N ratio vs. 13C