1. The impact of a declining water table on observed carbon fluxes at a northern temperate wetland Benjamin N. Sulman A nkur R. Desai * Department of Atmospheric & Oceanic Sciences University of Wisconsin – Madison Bruce D. Cook NASA Goddard Space Flight Center Nicanor Saliendra U.S. Forest Service, Rhinelander, WI D. Scott Mackay Department of Geography State University of New York – Buffalo SWS 2009, Madison, WI

2. Projected climate changes affecting northern wetlands Higher temperatures, more precipitation But: Net drying due to more evaporation Poleward shift of biomes Question: How will changes in hydrology affect interactions between wetlands and climate? Focus: Water table and carbon cycle

3. Wetlands and climate Biogeochemical: Carbon cycle –In Northern Highlands region of Wisconsin, wetlands have over half the carbon pool Biophysical: Evapotranspiration –Atmospheric heat and moisture budgets strongly mediated by surface sensible and latent heat fluxes

4. Northern Highlands Wisconsin Online http://www.wisconline.com/wisconsin/geoprovinces/northernhighland.html

5. Biogeochemical interactions: Existing literature is contradictory Modeling studies have identified a climate feedback (e.g. Ise et al. 2008) Observations have mixed results –Lowering water table increased CO 2 emission or changed wetlands from a carbon sink to a source: (Silvola et al. 1996, Alm et al. 1999, Bubier at al. 2003) –No correlation between water table and CO 2 emission: (Updegraff et al. 2001, Lafleur et al. 2005)

6. Biophysical interactions: How does drying a wetland affect the energy and moisture budgets of the atmosphere? Case 1: High water tableCase 2: Low water table High latent heat loss Low sensible heat loss Low latent heat loss High sensible heat loss

7. Declining water table

8. Long-term drying in N. WI Courtesy of C. Kucharik, UW-Madison SAGE

9. Lost Creek Alder-willow fen Poorly drained sapric muck Flux tower established 2001

10. South Fork and Wilson Flowage Wetland sites SF: Ericaceous bog WF: Grass-sedge-shrub fen Three years (2005- 2007) of growing season flux data with roving tower Switched between sites every two weeks

11. Eddy Covariance Turbulent fluxStorage Equipment: 3D sonic anemometer Open or closed path gas analyzer Multiple level CO 2 profiler 10Hz temporal resolution -> 30 min fluxes

12. Terms Net Ecosystem Exchange (NEE) –Total net carbon flux (measured) Ecosystem Respiration (ER) –Carbon released to atmosphere Gross Ecosystem Production (GEP) –Carbon absorbed from atmosphere Evapotranspiration (ET) –Water / latent heat flux Water table height (WT) Positive = above surface

13. Flux observations Lost Creek Wilson Flowage Willow Creek (forest) ER NEE GEP

14. Lower WT increases ER

15. WT effect is independent of soil temperature

16. Lower WT increase GEP

17. NEE is independent of WT

18. Lower WT decreases ET Water table ET

19. Energy balance is changing Net radiation Latent heat flux Sensible heat flux Heat flux into ground

20. Findings summary Biogeochemical interactions: –Both ER and GEP increased as water table declined –Net ecosystem CO 2 exchange was independent of WT –This supports literature arguing against a strong north temperate wetland water table-carbon feedback Biophysical interactions: –ET declined and energy balance shifted in favor of higher sensible heat flux –This could potentially be a positive feedback to warming and drying trends More results in: –Sulman et al. (2009) Biogeosciences, in press –Mackay et al. (2007) Water Resources Research

21. Ecosystem models simulate wetlands poorly

22. Needs Long-term observations of water table, carbon cycle, energy balance Better characterization of climate trends in wetland extensive areas Improve mechanistic understanding of hydrologic interaction with wetland carbon cycling

23. Models can be made better

24. Acknowledgements Jonathan Thom, UW-Madison Ron Teclaw and Dan Baumann, USDA Northern Research Station, Rhinelander, WI Paul Bolstad, University of Minnesota Jon Martin, Oregon State University Sudeep Samanta, Woods Hole Research Center Bashkar Mitra, SUNY-Buffalo This research was sponsored by the Department of Energy (DOE) Office of Biological and Environmental Research (BER) National Institute for Climatic Change Research (NICCR) Midwestern Region Subagreement 050516Z19.