Post on 17-Dec-2015
Possible Geomorphic EffectsOf Invasive Spartina alterniflora
in the San Francisco Estuary
Joshua N. Collins, Ph.D
San Francisco Estuary Institute
Josh@sfei.org
Acknowledgments
• US EPA, California Coastal Conservancy• Debra Smith, Katy Zaremba, Shannon Klohr
of the Spartina Project• Donna Morton, SFEI
Laurel Collins, Watershed Sciences• Debra Ayers and Donald Strong, UC Davis• Andrew Cohen, SFEI
Karl-Malamud-Roam, CCMAD
Train of Study Assumptions
1. Function follows form.
2. Form of the intertidal zone is a consequence of interactions between water supply and sediment supply, as mitigated by vascular vegetation.
3. Vascular vegetation is a major structural component of the intertidal zone of the Estuary.
Study Assumptions (cont’d)
4. The geo-ecological effects of plants vary with their architecture through space and over time.
5. NIS Spartina (S. alterniflora and hybrids) has different architecture than any intertidal native plants.
6. Dominance by NIS Spartina will alter the form and function of the intertidal zone.
Fundamental Study Questions
Where does NIS Spartina dominate the intertidal zone?
Based on its dominant location, what might be its effects on geomorphic form?
Given these effects on form, what might be effects on function (questions to answer)?
Synthesis of Study Assumptions and Questions
Interactions between water, sediment, and plants comprise a dynamic
physical template for geo-chemical and ecological processes.
Study Approach
• Map the distribution of NIS Spartina throughout the Estuary.
• Map its distribution relative to other dominant plants along salinity gradients.
• Map its vertical intertidal distribution.
Regional Distribution and Abundance
Regional Abundance and Distribution of
NIS Spartina by Patch Size Class
Distribution Relative toAqueous Salinity:Basic Methods
• Choose local creeks near verified NOS benchmarks.
• Conduct surveys of minimum elevations of NIS Spartina and co-dominant plants throughout local salinity gradient.
• Verify genotype for each NIS Spartina patch surveyed.
Distribution of Low Marsh Plants Alameda Flood Control Channel
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
-500 0 500 1000 1500 2000 2500 3000 3500
Distance Upstream (ft)
Tid
al E
lev
atio
n (
ft b
elo
w L
oca
l M
HW
)
Spartina Hybrids Spartina foliosa Scirpus robustus
Scirpus acutus/californicus Typha sp.
Salicornia
Scirpus robustus
Atriplex Scirpus acutus/californicus
Typha
"Saline" "Brackish" "Fresh"
Distribution of Low Marsh PlantsSan Leandro Creek
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Distance Upstream (ft)
Tid
al E
leva
tion
(ft b
elow
Loc
al M
HW
)
Spartina Hybrids Spartina foliosa Scirpus acutus/californicus Scirpus robustus Typha sp
Salicornia
Scirpus robustus
Distichlis
Scirpus acutus/californicus
Typha
"Brackish" "Fresh"
"Saline"
Extent of aggradation upstream of
cement apron
Degree of Hybridization in Relation to Salinity Regime as Indicated by Distance Downstream from Head of Tide
R2 = 0.39
0
10
20
30
40
50
60
70
80
90
100
0 500 1000 1500 2000 2500 3000 3500 4000
Distance from Head of Tide (ft)
Deg
ree
of
Hy
bri
diz
atio
n
(% a
lter
nif
lora
)
Hybrids Spartina foliosa Spartina alterniflora Linear (Hybridization Trend)
“Fresh” “Brackish” “Saline”
Minimum elevations of NIS Spartina relative to MHW for fresh-brackish tidal reaches of
three creeks of South San Francisco Bay
SiteElevation Relative to
Local MHW (ft)Colma Creek
n = 23 -4.24 0.9
Alameda Flood Channel n = 14 -3.85 0.7
San Leandro Creekn = 13 -3.31 0.6
Distribution vs Aqueous Salinity:Basic Results
• Minimum elevation of NIS Spartina intersects creek bed at about Mean Tide Level.
• NIS Spartina grows lower than other plants throughout salinity gradient.
• Pure S. alterniflora is restricted to fresher conditions near the head of tide.
Vertical Distributionin Saline Intertidal:
Basic Methods
• Choose sites with verified NIS Spartina and NOS benchmarks.
• Map distribution of NIS Spartina relative to intertidal physiography.
• Randomly survey minimum elevations of NIS Spartina.
Elevations of NIS SpartinaSan
Leandro Channel
Arrow- head
Marsh
Coyote Point
Marsh
Coyote Hills
Slough
Mean maximum elevation (ft) relative to local
MHHWn = 30
- 0.25 0.3
- 0.44
0.2
- 0.93 0.4
- 0.36
0.4
Mean maximum elevation (ft) relative to maximum elevation of native marsh plants (Grendelia zone)
n = 30
- 0.87 0.4
- 0.91
0.4
- 1.46
0.4
- 1.41 0.5
Mean minimum elevation relative to local MLLW
n = 30
+ 2.68
0.3
+ 2.89
0.3
+ 3.10 0.3
+ 3.26
0.4
Plan Form Details of Distribution
Distribution of NIS Spartina within Arrowhead Marsh
Arrowhead Marsh IR Photo
Arrowhead Marsh IR Photo
Plan Form Details:Basic Results
• Due to channel cross-section form and preferred elevation range, NIS Spartina colonizes channel beds of existing saline tidal marshes mainly in middle reaches of the drainage networks.
• Colonization of an existing marsh by NIS Spartina disconnects headward channels from the rest of the marsh drainage network.
Saline DistributionRelative to Tidal Datums
Mean Minimum Elevation of NIS SpartinaRelated to Mean Tide Range
y = 0.59x - 0.18R2 = 0.81
2.5
2.75
3
3.25
3.5
4.9 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7
Local Mean Tide Range (ft) (MHW - MLW)
Mea
n M
inim
um E
leva
tion
(f
t abo
ve M
LL
W)
Vertical Distribution of NIS Spartina Relative to Tidal Datums and Distance South of Golden Gate
-6
-4
-2
0
2
4
6
Lattitude of NOS Tide Stations
Ele
vatio
n R
elat
ive
to L
ocal
M
ean
Tid
e L
evel
(ft)
Mean High Water Mean Lower Low Water Predicted Minimum Elevation of NIS Spartina
Predicted Minimum Elevation of NIS Spartina Relative to Cumulative Duration of Indundation For Three Tide Stations In San Francisco Bay
0
10
20
30
40
50
60
70
80
90
100-1
.25
-0.7
5
-0.2
5
0.2
5
0.7
5
1.2
5
1.7
5
2.2
5
2.7
5
3.2
5
3.7
5
4.2
5
4.7
5
5.2
5
5.7
5
6.2
5
6.7
5
7.2
5
7.7
5
8.2
5
8.7
5
9.2
5
9.7
5
10
.2
Mid-point of 0.5 ft Height Class
Cu
mu
lati
ve
Du
rati
on
of
Inu
nd
ati
on
(p
erce
nt)
Alameda MTR = 4.43 ft Redwood City MTR = 5.87 ft
Dumbarton Bridge MTR = 6.1 ft
Conclusions
The vertical distribution of NIS Spartina relates to the duration of tidal inundation, or conversely, the duration of exposure above the tides.
Conclusions
NIS cordgrass is likely to invade the upper half of the saline tidal flats and will tend to invade a smaller proportion of the tidal flats in Far South Bay than in South Bay or Central Bay, but plant evolution may change the rules.
Conclusions
NIS cordgrass will probably not dominate the saline high marsh above MHW, but plant evolution may change the rules.
Conclusions
The invasion of existing saline marshes will tend to isolate the headward reaches of their channel networks.
Conclusions
NIS cordgrass can cause the headward channels of marsh drainage systems to retrogress, thus shortening and simplifying intertidal channel networks and the shoreline of the Estuary as a whole.
Conclusions
NIS cordgrass can obstruct tidal flow and upland runoff in the upper tidal reaches of fluvial drainages.
Conclusions
NIS Spartina tolerates fresher conditions than native Spartina, grows lower upstream than downstream in local creeks, and grows lower than other intertidal plants along local salinity gradients.
Conclusions
The upper tidal reaches of local streams can serve as refugia for non-hybrid S. alterniflora and as sources of new recruits for continued invasion around San Francisco Bay.
Major Questions
How low will NIS Spartina grow in Suisun and perhaps the western Delta?
Will NIS Spartina meadows evolve into high marsh with native plants?
How will native plants and animals adjust to the Invasion by NIS cordgrass?
How will the simplification of the intertidal drainage system affect estuarine filtration and material flux?