Carbon Sequestration in Tidal Wetlands: Steve Crooks Ph.D.

Transcription

1 Carbon Sequestration in Tidal Wetlands: Steve Crooks Ph.D. Philip Williams and Associates, Ltd South Bay Science Symposium September 25, 2008

2 Overview Carbon trading and wetland GHG cycling Global C sequestration estimates Wetlands of San Francisco Estuary Landscape-level C sequestration trade-offs Back of the envelope storage calculations Impact of sea level rise on C storage Conclusions

3 California s Emission Goals On June 1, 2005, California Governor Arnold Schwarzenegger set forth f his Administration s goal to make California a leader in efforts to reduce global warming. The Governor signed an Executive Order which established statewide greenhouse gas emissions targets and directed the Secretary etary for the California Environmental Protection Agency (Cal EPA) to lead an effort to achieve these targets, which would. By 2010,, reduce statewide GHG emissions to 2000 emission levels; By 2020,, reduce statewide GHG emissions to 1990 emission levels; By 2050,, reduce statewide GHG emissions to 80% below 1990 levels. California emissions, MtC0 2 /yr California emissions, MtC0 Current rate of increase % 2 /yr Current rate of increase % CEC

4 Greenhouse Gases Gas Current (1998) Amount by volume Global warming Potential Percent increase since 1750 Radiative forcing (W/m²) Carbon dioxide CO ppm 1 31% 1.46 Methane CH 4 1,745 ppb % 0.48 Nitrous oxide N 2 O 314 ppb % 0.15

5 Carbon Cap and Trade: Questions Performance standards? At what scale can top down assessments be used before case-by case analysis required? Regulatory additionality? Would carbon storage happen without carbon credits? Baseline Quantification? Can we quantify storage and emissions? Leakages? Does restoration impact C storage nearby? Permanence? Will it be stored for 100+ years? Reliability of storage? Market interest? How much carbon? How to address N 2 O?

6 State of the Science Topic No. Papers Carbon sequestration 5731 C sequestration / forests 2246 C sequestration / wetlands 176 C sequestration / tidal wetlands 6

7 Assessing Carbon Flow and Storage Carbon Flow Curves: trajectories of annual carbon uptake over time Average Carbon Flows: Mean annual increments av. over length of project Cumulative Carbon Capture: Sum of all carbon captured by project Average Carbon Stored: Amount of expanded inventory in sink Conserved Carbon: Measure of carbon emissions avoided (Richard and Stokes 2004)

8 Historic Marshes: a Product of the Holocene 300,000 acres lost 200,000 acres lost

9 SF Estuary Carbon Sequestration: Comparison with Global Estimates (Duarte et al. 2005) SFB: Estimates of gc m -2 a -1 (Callaway and Drexler, unpublished data) The Delta: Estimates of gc m- 2 a- 1 (Fujii, pers. coms)

10 Depth (centimeters) Salt Marsh Carbon Storage Carbon Content (% mass of dry material) C storage dependant on: Plant vigor Soil drainage Tidal range Marsh complexity Grain size Corkscrew Creek, Bair Island 250 Active zone - C turnover Subsurface C storage Data: Elizabeth Watson

11 Sulfate reduction Limits CH4 production Low permeability soils Organics present Saline porewaters Undisturbed (nitrate depleted) Anoxia

12 Methane Production in Salt Marshes Latitude CH flux 4 Site Reference (degrees) (gch 4 m - 2 a - 1 ) Description Saltmarsh 97 Brackish Brackish marsh 1.75 Brackish sandflat Saltmarsh Saline 22.4 Brackish 18.2 Brackish / Fresh Saline marsh Saltmarsh Saltmarsh Saltmarsh (pan) Saltmarsh (creek) Delaune et al, 1983 (east coast USA) Hiroto et al., 2007 (North Japan) (based upon 3 days August) Bartlett et al, 1985 (east coast USA) Bartlett et al, 1987 (east coast USA) Howes et al., 1985 (east coast, USA) Magenheimer et al., 1996 (east coast USA) (based on 150 days of emission) Giani et al., 1996 (German North Sea) Senior et al., 1982 (east England) Compare with estimates of gc m -2 a -1 for carbon storage

13 Denitrification NO 3 converted to N 2 and N 2 O (0.5-2%) Suboxic conditions Organics present Fresh or saline NO 3 to quadruple by 2050 Estuaries produce 1/3 of oceanic N 2 0

14 Experience Elsewhere

15 Pre-Mediaeval The Humber Estuary Extensive diked wetlands Post industrial estuary Agricultural run-off Now 405 km of levees 870 km 2 of drained wetlands (San Francisco Bay 769 km 2 of drained wetlands)

16 Restoration Scenario

17 Economics of Flood Defense Realignment (and Restoration) Area restored Capital costs Opportunity costs Maintenance costs Replacement costs (agri) Habitat creation benefits Carbon Sequestration 7,494 ha 812,000 / km 2,110 / ha 3,560 /km/ yr 618,000 /km 621 /ha /yr 7 /tco 2 e

18 Bottom Line Scheme 25 years 50 years 100 years Hold the Line (HTL) Ex. Deep Green (EDG) NPV (EDG-HTL) Values in million GBP

19 Restoring Wetlands to Sequester Carbon High N 2 0 / CH 4 emissions lower N 2 0 / CH 4 emissions Andrews et al. 2006

20 Carbon Storage: Back of the Envelop Calculations

21 Salt Marsh Carbon Storage (preliminary) Area of islands under Examples of most CO 2 agriculture (ha) 5000 fuel efficient emission Rate of accretion (cm) 0.3 cars in class (tco 2 Bulk density of soil (g/cm 3 ) Bulk density of organic matter (g/cm 3 ) 0.07 Hybrid: Toyota Prius 1.93 fraction of carbon (g/g( g/g) Station Wagon: VW Jetta Diesel 3.08 Pick Up: Ford Ranger 4.17 Carbon stored (tc( tc/ha/yr) 2.1 Motor vehicle equivalent Conversion of C to C Hybrid: Toyota Prius 19,912 Station Wagon: VW Jetta Diesel 12,469 C0 2 stored in salt marsh (tco /yr) 38,430 Pick Up: Ford Ranger 9,220 /yr) 38,430

22 How much carbon are we emitting from the Delta? Area of islands under agriculture (ha) 180,000 Rate of subsidence (cm) 2 Bulk density of soil (g/cm 3 ) Bulk density of organic matter (g/cm 3 ) 0.22 fraction of carbon (g/g( g/g) 0.50 Carbon released (tc/ha/yr) 20 (RojstacerRojstacer and Deverel, 1993) Conversion of C to C C0 2 release from Delta (tco 2 /yr) 13,176,000

23 Storage Permanence Living with SLR Tidal marshes continuously sequester and bury carbon in response to sea level rise. Estuaries (saline areas) respond to sea level rise by eroding and redistributing sediment. Freshwater tidal wetlands offer resilience to SLR (need to be maintained in freshwater condition) With high rates of SLR some marshes breakdown. Marsh resilience to SLR depends on sediment supply and salinity.

24 With Too Much SLR or Too Little Sediment salt marshes Drown

25 Elkhorn Slough A Starved Estuary

26 Integrated Sediment & Wetland Management Mudflat Recharge Area Dredging locations (examples)

27 Conclusions Wetlands do sequester carbon, as well as recycle nutrients Storage is more readily calculable than production / flux of GHG biproducts Need better quantification of carbon sequestration by habitat type Need to understand spatial /temporal variation in GHG production (with salinity) How should we account for N 2 O production? Develop estuarine management approaches that support C sequestration Plan for sea level rise: predict the future landscape strategic restoration

28 Recommended Actions Carbon storage by habitat type (e.g. salt marsh, mudflat, eel grass beds, oyster beds, subtidal), GHG emissions by habitat type, Integrated assessment of fertilizer pollution, Forward looking Estuary Management Plans, Case studies for intertidal sediment placement, Case studies of EBM or future estuary assessments, Assess bioregional trade-offs (hotspots, refugia?), Plan for SLR and changing sediment supply (e.g. Delta).

29 Steve Crooks Philip Williams and Associates, Ltd