Download Climate change Interagency Ecological Program Feb 08

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
Context:
Focal Area for Research
SF Bay-Delta Tidal Marshes
Salinity Gradient
Brackish Marshes
Salt
Marshes
Freshwater
Marshes
in the Delta
Historic marshes along gradient
China Camp
Coon Island
Browns Island
Restored marshes along the gradient
Carls
Bull Island
Pond 3
Pond 2A
San Francisco Bay Tidal Marshes
Species Diversity
Brackish Marshes
Salt
Marshes
Freshwater
Marshes
in the Delta
Species Diversity
Species Diversity
Species Diversity
2-22 species
27-65 species
117+ species
San Francisco Bay Tidal Marshes
Annual Primary Production
Brackish Marshes
Salt
Marshes
ANPP
ANPP
200-800
g m-2 yr-1
700-1300
g m-2 yr-1
Freshwater
Marshes
in the Delta
ANPP
1300-2500
g 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 CO2
Rising temperatures
More rain/less snow->reduced snowpack->
reduced water flow in Bay-Delta in late summer
Reduced water flow->increased salinity
Rising 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
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
Temperature effects on wetlands
• Direct
• Indirect
Direct effects-temperature
• Influence on photosynthesis/respiration
balance of dominant plants
rate
respiration
photosynthesis
temperature
Direct effects-temperature
• Influence on photosynthesis/respiration
balance of dominant plants
Increase in ANPP
rate
Decrease in ANPP
temperature
Mortality
Indirect Effects-temperature
• Sierran snow
pack melts
earlier
• Rivers flow
earlier
• Salinity
increases
upstream
Salinity (ppt)
0
5
10 15 20 25 30 35
Projected Salinity Changes Critical
Current Summer
Salinities
Projected Summer
Salinities in 2060
Salinity (ppt)
Figure from Noah Knowles
0
5 10 15 20 25 30 35
Salinity Effects on Tidal Wetlands
• Shifts composition
• Reduces diversity
• Reduces productivity
• Inhibits organic peat production
• Changes soil structure
• Critical thresholds at low salinity levels
Indirect effects, cont.
• Increase in
the rate of
sea level rise
(from IPCC)
Inundation and flooding
current conditions
Marsh Surface Elevations: Percent Time Wet
Restored Sites
120
Bull Island
100
Number of Observations
Reference Sites
300
80
200
60
150
40
100
20
50
0
140
0
160
Pond 2a
120
Browns Island
250
Coon Island
140
120
100
100
80
80
60
60
40
40
20
20
0
100
0
Carl’s Marsh
80
0
10
20
30
40
% time wet
60
40
Restored sites are inundated
longer than natural sites
20
0
0
10
20
30
% time wet
40
50
50
Marsh Surface Elevations: Plant Diversity
12
10
Restored Sites
Bull Island
40
MHW
35
Reference Sites
Browns Island
30
MHHW
8
6
25
20
15
4
10
Number of Species
2
5
0
10
8
0
18
Pond 2a
16
Coon Island
14
12
6
10
8
4
6
4
2
2
0
7
6
0
1.0
Carl’s Marsh
1.4
1.6
1.8
2.0
2.2
elevation (m, NAVD)
5
Diversity peaks at MHHW at
reference sites; lower at restored
sites
4
3
2
1
0
1.0
1.2
1.2
1.4
1.6
1.8
elevation (m, NAVD)
2.0
2.2
Mean high water - MHW
Mean higher high water - MHHW
Coon Island
2.2
0
2.0
10
1.8
1.6
b
c
b
1.4
1.2
b
c
% time wet
elevation (m NAVD)
Within a site, elevation predicts distribution of species
20
1.0
50
Scac
Tyan
Boma Scam Sapa
Species
MTL
MHW
b
b
a
Spfo
Scac
Tyan
Boma Scam Sapa
Species
MHHW
c
30
40
a
Spfo
b
c
Schoenoplectus acutus
tule
Among sites, % inundation time predicts distribution
Larry Allian
0
2.0
a
b
c
10
% time wet
elevation (m NAVD)
2.2
1.8
1.6
1.4
20
40
1.0
50
Bull
Coon
Site
Formerly known as Scirpus acutus
a
a
1.2
Browns
a
30
Browns
Bull
Site
Coon
Bolboschoenus maritimus
Alkali bulrush
2.0
a
0
b
c
1.8
10
d
% time wet
elevation (m NAVD)
2.2
1.6
1.4
20
a
b
c
30
c
40
1.2
1.0
50
Bull
Coon
Pond 2a
Carl's
Site
Formerly known as Scirpus maritimus
Bull
Coon
Pond 2a
Site
Carl's
2.2
0
2.0
10
1.8
1.6
1.4
a
b
c
% time wet
elevation (m NAVD)
Schoenoplectus americanus
Common three-square
20
40
1.0
50
Bull
Coon
Site
Formerly known as Scirpus americanus
b
a
30
1.2
Browns
a
Browns
Bull
Site
Coon
2.2
0
2.0
10
1.8
1.6
a
a
b
c
1.4
% time wet
elevation (m NAVD)
Sarcocornia pacifica
Pickleweed
20
40
1.0
50
Coon
Pond 2a
Carl's
Site
Formerly known as Salicornia virginica
b
c
c
Bull
Coon
Pond 2a
Carl's
30
1.2
Bull
a
Site
40
35
30
25
15
elevation (m NAVD)
Site-level Elevation and
Inundation Patterns
2.2
20
10
5
0
18
16
14
12
10
8
6
2.0
1.8
1.6
1.4
1.2
4
1.0
2
Spfo
0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Scac
Tyan
Boma Scam Sapa
Species
elevation (m, NAVD)
• 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
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
80
While annual productivity
increases with height…
average plant height (cm)
70
60
50
40
30
20
0
200
400
600
800
1000
1200
1400
1600
2
ANPP (g/m )
The pattern with salinity
seems scattered and
complex…
1800
2000
Until well-drained locations are separated
from poorly-drained sites...
2200
well drained plot
poorly drained plot
2000
1800
2
ANPP (g/m )
1600
1400
Well-drained plots
1200
1000
800
600
400
200
Poorly-drained plots
0
10
20
30
40
salinity (ppt NaCl)
50
60
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…
Global Warming Impact on SF Bay-Delta
Increasing
Temperatures
Ppt
Shifts from
Snow to rain
Smaller
Snowpack
Earlier melt
Spring floods
Increased
inundation
Reduced
Peat
formation
Sea level
Rise
Lower
Summer
flows
Increased
Estuarine
salinity
CO2
increases
mixed
these environmental changes
impact the performance of
wetland vegetation:
…and potentially lead to:
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…