Climate Change and San Francisco Bay-Delta Tidal Wetlands

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Climate Change and San Francisco Bay-Delta Tidal
Wetlands
V.T. Parker San Francisco State
University and L.M. Schile, J.C. Callaway
M.C. Vasey San Francisco State University and
University of San Francisco
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Context Focal Area for Research
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SF Bay-Delta Tidal Marshes Salinity Gradient
Brackish Marshes
Freshwater Marshes in the Delta
Salt Marshes
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Historic marshes along gradient
Browns Island
China Camp
Coon Island
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Restored marshes along the gradient
Carls
Bull Island
Pond 3
Pond 2A
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San Francisco Bay Tidal Marshes
Species Diversity
Brackish Marshes
Freshwater Marshes in the Delta
Salt Marshes
Species Diversity
Species Diversity
Species Diversity
2-22 species
27-65 species
117 species
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San Francisco Bay Tidal Marshes
Annual Primary Production
Brackish Marshes
Freshwater Marshes in the Delta
Salt Marshes
ANPP
ANPP
ANPP
700-1300 g m-2 yr-1
200-800 g m-2 yr-1
1300-2500 g m-2 yr-1
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SF Bay-DeltaFreshwatergt Salt Marshes

• Freshwater tidal marshes have 5-50 times more
  species than salt marshes
• Freshwater tidal marshes have 3-12 times more
  primary production
• Historic marshes have more species than restored
  marshes

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What happens to these systems under projected
climate change?
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Processes predicted to change
Increases in CO2 Rising temperatures More
rain/less snow-gtreduced snowpack-gt reduced
water flow in Bay-Delta in late summer Reduced
water flow-gtincreased salinity Rising sea level
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Increase in atmospheric CO2 concentration

• Generally good for C3 plants at beginning
• Most wetland plants use C3 photosynthesis
• Generally no improvement for C4 plants (meaning
  net relative loss of productivity)
• Spartina foliosa and Distichlis spicata are two
  common C4 plants in SF Bay-Delta marshes

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Temperature regime increases
6 global climate models for each of 4 different
historic and future scenarios. Northern
California will increase in temperature. The
models are ambivalent about precipitation, but
greater unpredictability
Dettinger 2005
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Temperature effects on wetlands

• Direct
• Indirect

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Direct effects-temperature

• Influence on photosynthesis/respiration balance
  of dominant plants

respiration
photosynthesis
rate
temperature
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Direct effects-temperature

• Influence on photosynthesis/respiration balance
  of dominant plants

Increase in ANPP
rate
Mortality
Decrease in ANPP
temperature
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Indirect Effects-temperature

• Sierran snow pack melts earlier
• Rivers flow earlier
• Salinity increases upstream

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Projected Salinity Changes Critical
Current Summer Salinities
Projected Summer Salinities in 2060
Figure from Noah Knowles
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Salinity Effects on Tidal Wetlands

• Shifts composition
• Reduces diversity
• Reduces productivity
• Inhibits organic peat production
• Changes soil structure
• Critical thresholds at low salinity levels

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Indirect effects, cont.

• Increase in the rate of sea level rise

(from IPCC)
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Inundation and floodingcurrent conditions
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Marsh Surface Elevations Percent Time Wet
Restored Sites
Reference Sites
Browns Island
Bull Island
Coon Island
Pond 2a
Number of Observations
Carls Marsh
Restored sites are inundated longer than natural
sites
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Marsh Surface Elevations Plant Diversity
Restored Sites
Reference Sites
Bull Island
Browns Island
MHW
MHHW
Pond 2a
Coon Island
Number of Species
Carls Marsh
Diversity peaks at MHHW at reference sites lower
at restored sites
Mean high water - MHW
Mean higher high water - MHHW
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Coon Island
Within a site, elevation predicts distribution of
species
c
c
c
c
b
b
b
b
b
b
a
a
MTL
MHW
MHHW
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Schoenoplectus acutustule
inundation time predicts distribution
Among sites,
Larry Allian
c
b
a
a
a
a
Formerly known as Scirpus acutus
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Bolboschoenus maritimusAlkali bulrush
a
b
c
d
a
b
c
c
Formerly known as Scirpus maritimus
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Schoenoplectus americanusCommon three-square
a
a
c
b
b
a
Formerly known as Scirpus americanus
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Sarcocornia pacificaPickleweed
a
c
b
a
c
a
b
c
Formerly known as Salicornia virginica
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Site-level Elevation and Inundation Patterns

• Restored sites differ in length of inundation,
  and elevation at which species diversity peaks
• Elevation important in determining plant
  distributions within sites
• Among sites, inundation patterns for any species
  are relatively similar, but elevations may differ
  
• Salinity another influence needing consideration

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Likely influences of climate change on tidal
wetlands

• Negative impacts
• Increase in inundation
• Increase in salinity
• Increase in temperature?

• Positive impacts
• Increase in CO2
• Increase in temperature?

Restored marshes lagging behind reference sites
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• Given environmental change
• If temperature increases
• If salinity increases
• If marsh substrate accretion fails to keep up
  with sea level rise and inundation increases
• What might be a predictable scenario for SF
  Bay-Delta?

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Sarcocornia pacifica

• Sarcocornia occurs in a diversity of salinity and
  inundation conditions

formerly Salicornia virginica
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Sarcocornia pacifica

• Used spatially variability as a natural
  experiment to ask the question
  What happens to Sarcocornia
  productivity under higher salinities and more
  inundation?

Multiple harvests to assess annual production
under a variety of salinity and inundation
conditions
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While annual productivity increases with height
The pattern with salinity seems scattered and
complex
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Until well-drained locations are separated from
poorly-drained sites...
Well-drained plots
Poorly-drained plots
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Results Natural Experiment

• Increases in salinity and inundation (predicted
  environmental changes) Result
  in significant reductions in wetland productivity
  in the species most likely to expand

low productivity?
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Conclusions

• Reducing the rate of change in wetlands depends
  on maintaining or enhancing freshwater flows into
  the Delta in the summer/fall periods (levee
  protection, less diversion)
• Restoring new marshes sooner might increase their
  likelihood of long-term success and persistence

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What havent I mentioned?

• Temperature, salinity, inundation all strongly
  influence other major ecosystem processes within
  wetlands that have strong links to terrestrial
  and pelagic systems
• Decomposition
• Soil organic matter accumulation
• Every aspect of nitrogen dynamics
• Plant composition shifts, seedling establishment,
  seed bank persistence

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To keep from getting stuck in the details
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Global Warming Impact on SF Bay-Delta
Increasing Temperatures
Smaller Snowpack
Ppt Shifts from Snow to rain
Lower Summer flows
Earlier melt Spring floods
Increased inundation
Reduced Peat formation
Increased Estuarine salinity
Sea level Rise
CO2 increases
mixed
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these environmental changes impact the
performance of wetland vegetation
and potentially lead to
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Acknowledgements CA Parks, CA Fish Game, EB
Regional Park District, a large and excellent
field crew, and colleagues in the IRWM project
meaning marshes may fade to blue
Loss of species, reduction in annual
productivity, with cascading effects on linked
terrestrial and pelagic systems