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