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Transcript of Climate Change and San Francisco Bay-Delta Tidal Wetlands V.T. Parker San Francisco State University...
Climate Change and San Francisco Bay-Delta Tidal Wetlands
V.T. ParkerSan Francisco State University
and
L.M. Schile, J.C. Callaway & M.C. VaseySan Francisco State University
and
University of San Francisco
Context:Focal Area for Research
SF Bay-Delta Tidal MarshesSalinity Gradient
Brackish Marshes
Salt
Marshes
Freshwater Marshesin the Delta
Historic marshes along gradient
China Camp
Coon Island
Browns Island
Pond 2A
Carls
Bull Island
Restored marshes along the gradient
Pond 3
San Francisco Bay Tidal Marshes
Brackish Marshes
Salt
Marshes
Freshwater Marshesin the Delta
Species Diversity
2-22 species
Species Diversity
27-65 species
Species Diversity
117+ species
Species Diversity
San Francisco Bay Tidal Marshes
Brackish Marshes
Salt
Marshes
Freshwater Marshesin the Delta
Annual Primary Production
ANPP
200-800g m-2 yr-1
ANPP ANPP
700-1300g m-2 yr-1
1300-2500g m-2 yr-1
SF Bay-Delta:Freshwater> 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
What happens to these systems under projected climate change?
Processes predicted to change…Increases in CO2Rising temperaturesMore rain/less snow->reduced snowpack-> reduced water flow in Bay-Delta in late summerReduced water flow->increased salinityRising sea level
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
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
Temperature regime increases
Temperature effects on wetlands
• Direct
• Indirect
Direct effects-temperature
• Influence on photosynthesis/respiration balance of dominant plants
rate
temperature
respirationphotosynthesis
Direct effects-temperature
• Influence on photosynthesis/respiration balance of dominant plants
rate
temperature
Mortality
Increase in ANPP
Decrease in ANPP
Indirect Effects-temperature
• Sierran snow pack melts earlier
• Rivers flow earlier
• Salinity increases upstream
Salinity (ppt)
0 5 10 15 20 25 30 35
Salinity (ppt)
0 5 10 15 20 25 30 35
Current Summer
Salinities
Projected Summer
Salinities in 2060
Figure from Noah Knowles
Projected Salinity Changes Critical
Salinity Effects on Tidal Wetlands
• Shifts composition• Reduces diversity• Reduces productivity
• Inhibits organic peat production• Changes soil structure
• Critical thresholds at low salinity levels
(from IPCC)
Indirect effects, cont.
• Increase in the rate of sea level rise
Inundation and flooding
current conditions
0
50
100
150
200
250
300
% time wet
0 10 20 30 40 50
0
20
40
60
80
100
120
140
1600
20
40
60
80
100
120
0
20
40
60
80
100
120
140
% time wet
0 10 20 30 40 50
0
20
40
60
80
100
Marsh Surface Elevations: Percent Time Wet
Restored sites are inundated longer than natural sites
Num
ber
of O
bser
vati
ons
Bull Island
Pond 2a
Carl’s Marsh
Restored Sites
Coon Island
Browns Island
Reference Sites
Bull Island
Pond 2a
Carl’s Marsh
Restored Sites
elevation (m, NAVD)
1.0 1.2 1.4 1.6 1.8 2.0 2.2
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
25
30
35
40
Coon Island
Browns Island
Reference Sites
Diversity peaks at MHHW at reference sites; lower at restored sites
Num
ber
of S
peci
esMarsh Surface Elevations: Plant Diversity
Mean high water - MHW
Mean higher high water - MHHW
MHW
MHHW
Species
Spfo Scac Tyan Boma Scam Sapa
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Coon Island
Species
Spfo Scac Tyan Boma Scam Sapa
% ti
me
we
t
0
10
20
30
40
50
MTL MHW MHHW
c
ab
bc
bc
a
b
bc
b
Within a site, elevation predicts distribution of species
Site
Browns Bull Coon
% ti
me
we
t
0
10
20
30
40
50
Site
Browns Bull Coon
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Larry Allian
Formerly known as Scirpus acutus
Schoenoplectus acutustule
ab c
aa
a
Among sites, % inundation time predicts distribution
Site
Bull Coon Pond 2a Carl's
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
SiteBull Coon Pond 2a Carl's
% ti
me
we
t
0
10
20
30
40
50
Bolboschoenus maritimusAlkali bulrush
Formerly known as Scirpus maritimus
a bc d
a bc c
Site
Browns Bull Coon
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Site
Browns Bull Coon
% ti
me
we
t
0
10
20
30
40
50
Schoenoplectus americanusCommon three-square
Formerly known as Scirpus americanus
ab c
ab
a
Site
Bull Coon Pond 2a Carl's
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Site
Bull Coon Pond 2a Carl's
% ti
me
we
t
0
10
20
30
40
50
Formerly known as Salicornia virginica
Sarcocornia pacificaPickleweed
ab c
a a b cc
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
Species
Spfo Scac Tyan Boma Scam Sapa
elev
atio
n (m
NA
VD
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
elevation (m, NAVD)
1.0 1.2 1.4 1.6 1.8 2.0 2.2
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
25
30
35
40
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
• 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?
Sarcocornia pacifica:
• Sarcocornia occurs in a diversity of salinity and inundation conditions
formerly Salicornia virginica
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
While annual productivity increases with height…
The pattern with salinity seems scattered and complex…
Until well-drained locations are separated from poorly-drained sites...
Well-drained plots
Poorly-drained plots
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?
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
What haven’t 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
To keep from getting stuck in the details…
PptShifts from
Snow to rain
SmallerSnowpack
Earlier meltSpring floods
IncreasingTemperatures
Lower Summer
flows
Global Warming Impact on SF Bay-Delta
IncreasedEstuarine
salinity
Sea levelRise
Increased inundation
ReducedPeat
formation
CO2
increasesmixed
these environmental changes impact the performance of
wetland vegetation:
…and potentially lead to:
Loss of species, reduction in annual productivity, with cascading effects on linked terrestrial and pelagic systems…
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