Zicheng Yu Lehigh University Bethlehem, Pennsylvania

1. Millennial-scale Dynamics of Continental Peatlands in Western Canada: Pattern, Controls and Climate Connection Zicheng Yu Lehigh University Bethlehem, Pennsylvania QUEST Workshop on CH4 & Wetlands 14-16 June 2004, Bristol, UK

2. Acknowledgements • Dale Vitt, Kel Wieder, Merritt Turetsky, Dave Beilman, Ilka Bauer, Mike Apps, Celina Campbell, and Ian Campbell for sharing slides, data and ideas. • Climate Change Action Fund (Canada) and National Science Foundation (US) for funding.

3. Outline of Talk • Overview of continental peatlands in western Canada • Accumulation pattern & trajectories • Possible climate & global C cycle connections • Conclusions

4. Peatland Types in Western Canada Bogs (treed) Permafrost peatlands Open fens Treed fens

5. Peatland Distribution % Cover Total peatland area = 365,160 km2 (21% landbase) 63% fens 28% permafrost bogs 9% non-permafrost bogs Vitt et al. (2000)

6. Peatland Carbon Storage 14 Parkland 12 Mid-boreal High boreal 10 Montane 8 Subarctic C Storage (Pg) Arctic 6 4 Total = 48 Pg 2 0 Open fens - patterned Permafrost bogs Treed fens Open fens - nonpatterned Shrubby fens Nonpermafrost bogs Vitt et al. (2000)

7. Fens are more important C pool and have larger area than bogs in continental Canadian peatlands, as well as bigger CH4 emitters, but we know much less about these ecosystems than bogs in general

8. Outline of Talk • Overview of continental peatlands in western Canada • Accumulation pattern & trajectories • Possible climate & global C cycle connections • Conclusions

9. Exponential 120 100 80 Linear Cumulative Mass (g.cm-2) 60 40 20 Logarithmic 0 0 4 8 12 Time (ka) Why accumulation pattern matters? (Convex) Because: Observed pattern  Infer & understand the processes  Projecting future dynamics/trajectories (Concave)

10. Concave Pattern from Oceanic Bogs (assuming constant PAR and decay) “apparent” C accumulation rate

11. Study Sites 5 sites with hi-resolution peat core analysis Basal dates from ~80 paludified peatlands

12. Loss-on-Ignition from Upper Pinto Fen 1-cm LOI n=20 dates also, 2-cm macro 2-cm isotopes Yu et al. 2003

13. Peat Depth-Age Curve: Convex at UPF Opposite to well-documented “concave” pattern Yu et al. 2003

14. What Does This Indicate? • Causes? • decreasing peat-addition rates from acrotelm, and/or • increasing catotelm decomposition rate

15. A Simple Extended Model Yu et al. 2003

16. Sensitivity to Changes in Decay & PAR Yu et al. 2003

17. Change in PAR over Time PAR decrease from initial 192 to eventual 26 g/m2/yr could explain the observed pattern 191.8 g m-2 yr-1 26.0 g m-2 yr-1 Yu et al. 2003

18. Summary I • The model suggests that unidirectional decrease of PAR from 192 to 26 g m-2 yr-1 over that 5400-yr period at UPF could result in the observed convex pattern. • Autogenic drying trend resulted from fen height growth gradually isolates peat surface from water and nutrient sources, causing decreased production, especially for water-demanding rich fen species - esp. in moisture-limiting continental regions. • This analysis indicates that continental peatlands with convex pattern may reach their growth limit sooner than previous model predicts.

19. Convex Pattern @ Other Sites I (Kubiw et al. 1989)

20. Convex Pattern @ Other Sites II Western Canada: Slave Lake Bog (Kurry & Vitt 1996) Southwestern Finland: Pesansuo raised bog (Ikonen, 1993) Western Siberia: Salym-Yugan Mire (Turunen et al. 2001)

21. Convex Pattern from Regional Sites (Yu & Vitt, in prep)

22. Outline of Talk • Overview of continental peatlands in western Canada • Accumulation pattern & trajectories • Possible climate & global C cycle connections • Conclusions

23. Climate Proxy from UPF (Yu et al. 2003)

24. UPF W. Canada (Yu et al. 2003)

25. Global Climate & C Cycle Connections? Chappellaz et al. 1997 Brook et al. 2000 Bond et al. 2001 Indermuhle et al. 1999 Yu et al. 2003

26. Summary II • Peat accumulation in western Canada shows sensitive response to Holocene climate variability at millennial time scale. • Peatland carbon dynamics may connect to change in atmospheric CO2 concentrations (Peatlands in western Canada contain ~50 Pg C, which is equivalent to ~25 ppm CO2 if all remained in the atmosphere). • Are there similar pattern in other peatlands of northern latitudes?

27. Pervasive Climate Controls of Peatland Dynamics A thawed bog shows similar millennial-scale variations Patuanak Bog (internal lawn)

28. Connection of Siberian Peatland Initiations and Atmospheric CH4 N = ~200 Smith et al. 2004

29. Bill Ruddiman’s hypothesis: • CO2 increase since 8 ka: caused by deforestation; • CH4 increase since 5 ka: caused by rice cultivation

30. Allogenic and Autogenic Controls of Peatland Dynamics: a conceptual model Autogenic drying Climate wetting Climate fluctuations Yu et al. 2003

31. Conclusions • The different accumulation pattern observed in continental peatlands suggests these peatlands follow different trajectories historically and may respond to climate change differently (compared to well-studied bogs); • Continental peatlands appear to show sensitive responses to subtle millennial-scale moisture changes during the Holocene; • Fens seem to be more variable in C accumulation and more sensitive (less self-regulating) to climate variations than bogs; • Northern peatlands might have had detectable impacts on atmospheric CO2 and CH4 concentrations during the Holocene.

32. Suggestions • Develop scaling-up models to take advantage of detailed inventory results from western Canada or other regions for regional CH4 emission estimates by peatland types (as a validating tool for global model?); • Confirm the extent of past climate – peatland – global C cycle connections, particularly using multiple proxies from paired lake-peatland approach (lakes for independent climate reconstructions); • Understand implications of permafrost (intact, thawing, and thawed) peatlands (and fen-bog transition) for CH4 emission/budget – permafrost is one of the biggest surprises to come in peatland C dynamics; • Integrate/reconcile down-core paleo data with present-day instrumental C flux measurements.