1. Carbon and Energy Flow Dynamics in a Coastal Salt Marsh Dissertation defense 29 th May 2008 James Chacko Kathilankal

2. Environmental forcings on CO 2 flux from a salt marshes

3. Hypothesis Intertidal salt marshes are the major sinks of atmospheric carbon in the land-ocean interface and are the most susceptible ecosystems to regional and global climate changes. Intertidal salt marshes are the major sinks of atmospheric carbon in the land-ocean interface and are the most susceptible ecosystems to regional and global climate changes. The magnitude of the CO 2 assimilation rates by the salt marsh is strongly modulated by tidal activity. The magnitude of the CO 2 assimilation rates by the salt marsh is strongly modulated by tidal activity.

4. To understand the leaf level assimilatory response of Spartina alterniflora to changes in the physical environment To quantify the atmospheric forcings on the seasonal rates and amounts of carbon assimilation by a Spartina alterniflora dominated inter-tidal salt marsh using tower- based eddy covariance studies on a continuous and long term basis. Objectives

5. Objectives To study the response of salt marsh ecosystem to tidal activity in terms of carbon assimilation and energy partitioning. To develop numerical models (biophysical) which can predict the carbon dynamics of a salt marsh in response to prevailing environmental conditions and perturbations, such as tropical storms and sea level rise.

6. Objective-Plant physiology Plant physiological measurements using Li-6400 Plant physiological measurements using Li-6400 Measurements were made through out the peak growing season (June- August). Measurements were made through out the peak growing season (June- August). Measurements were made at the tower site and other similar locations on different morphological forms. Measurements were made at the tower site and other similar locations on different morphological forms.

7. Light Curves-(An-PAR) A) MorningB) Noon C) Evening

8. A-Ci Curves analysis Morning Noon Evening

9. Temperature relationships-plant physiology parameters V cmax25= 44.25 μmol m -2 s -1 Peak value 105 at 38°C V pmax25= 13.03 μmol m -2 s -1 Peak value 80.6 at 35°C

10. Temperature relationships-light limited assimilation weak temperature relationship Jmax25= 108.08 μmolm -2 s -1 Peak values

11. Spartina alterniflora-A-Ci curve characteristics Initial slope of A-Ci curve is not as steep as observed For C4 plants-seems more like C3-C4 intermediate type (Adapted from S. von Caemmerer (1999))

12. Conclusions  Spartina alterniflora exhibits light saturation at low light levels.  Higher temperature optimum for carboxylation reactions-with greater rubisco activity than PEP carboxylase.  The possibility of a C 3 -C 4 intermediate mechanism exists.

13. Flux tower –construction TOWER SETUP INSTRUMENTATION SETUP SOLAR PANEL INSTALLATION

14. NEE trends-May-October 2007 Peak assimilation rates observed from June to July System reverting to respiratory state in October

15. NEE-influence of sky conditions NEE-influence of sky conditions Spartina exhibits higher assimilation rates under cloudy conditions Photo-inhibition is observed under clear sky high irradiance conditions

16. Carbon fixed through atmospheric exchanges for growing season 2007 ∑NEE =132.65 gCm -2

17. Role of Tidal activity-Some basic questions Are tides affecting carbon assimilation rates? Mechanism of CO 2 exchange under submerged conditions-Air-sea transfer? Are there changes in redistribution of available energy?

18. Quantification of CO 2 flux loss by tidal activity Fourth order Fourier curve was used to fit to the CO 2 flux data avoiding data points when water level was above 0.25 m Loss in CO 2 assimilation capacity can be between 3- 91 percent (0.009 to 2.44 g CO 2 m -2 d -1 ) Average loss due to tidal influence can exceed 46 % of total CO 2 fixed during a day

19. Relative electron transport rates under submergence ETRMAX=29.96 Spartina alterniflora do have the ability to photosynthesize under submerged conditions as evidenced by fluorescence measurements LOW-TIDE-EXPOSED HIGH TIDE-SUBMERGED ETRMAX=74.14 ETRMAX=29.96

20. Ecosystem respiration-temperature relationships *Weak relationship between soil temperature and Ecosystem respiration

21. Canopy controls on evapo-transpiration observed bulk stomatal conductance values were lower compared to other ecosystems indicating water stress

22. PAR reflectivity greatly increased in October indicating senescence α= LE/LE eq Priestly-Taylor coefficient values get above 1 during month of august indicating maximum evaporation rates comparable to equilibrium rates Canopy controls on evapo-transpiration.cont

23. Conclusions-Objective 2 & 3 Conclusions-Objective 2 & 3 Inter-tidal salt marshes can fix considerable amounts of CO 2 during the growing season. Inter-tidal salt marshes can fix considerable amounts of CO 2 during the growing season. Maximum carbon fixed by the system was in the month of June and the system started loosing carbon by October Maximum carbon fixed by the system was in the month of June and the system started loosing carbon by October High tide events can greatly reduce the assimilation capacity of the system and they will affect the redistribution of available energy High tide events can greatly reduce the assimilation capacity of the system and they will affect the redistribution of available energy Decreased CO 2 assimilation rates from coastal salt marshes can be a consequence of sea level rise Decreased CO 2 assimilation rates from coastal salt marshes can be a consequence of sea level rise

24. Modeling surface-atmosphere co 2 exchange Carbon exchange Micromet data Canopy-Leaf area distribution Source/Sink distribution Dispersion of scalars (Turbulent diffusion) Sediment respiration and algal assimilation Biophysical model –C4 *Stomatal conductance *Leaf energy balance *Carboxylation model Profiles of scalars Canopy Microclimate *Wind profiles *Radiation profiles (Shortwave and long wave) Tidal activity

25. Model comparison Clear vs Cloudy days Clear day Cloudy day

26. Model comparison-Tidal activity impacts High tide Low tide

27. Comparison between measured and Modeled CO 2 Fluxes-effects of tide

28. Conclusions-Objective 4 Modeled NEE agrees well with estimated NEE values under low tide conditions. Modeled NEE agrees well with estimated NEE values under low tide conditions. Air-water CO 2 transfer processes should be incorporated in the modeling procedure for better representation of physics. Air-water CO 2 transfer processes should be incorporated in the modeling procedure for better representation of physics. Tidal inundation can lead to changes in plant physiological activity and source/sink distribution in the canopy. Tidal inundation can lead to changes in plant physiological activity and source/sink distribution in the canopy.

29. Summary Inter-tidal coastal marshes do fix a modest amount of atmospheric CO 2 (8-10 μmol m -2 s -1 ) Tidal activity affects net ecosystem exchange and distribution of available energy. Plant physiology is greatly influenced by environmental forcings which has consequences on ecosystem level fluxes of CO 2 and energy Inter-tidal salt marshes are complex systems and they are vulnerable to sea level rise associated with global climate change

30. Acknowledgments  Advisory committee: Jose D Fuentes, Paolo D’Odorico, Karen Mcglathery, Jay Zeiman and Irina Mitrea  Tower crew-S. Chan, Tymchack,M., Karen.V, Kendra, D  Collaborators: Tom Mozdzer, Davon Upsher, Ben  Lab group members  VCR-LTER staff- Art, Chris, David, Donna, Kathleen  John Porter  My fellow countrymen  Friends  Funding : NSF-VCR-LTER and University of Virginia