ENGINEERING WITH NATURE:BREAKWATERS FOR

SAV HABITAT CREATION

Nicole Barth

Breakwaters can be used to create living shorelines (with SAV)

WATER FLOW AND SEDIMENT GRAIN SIZE AS CO-VARYING

SAV HABITAT REQUIREMENTS

Becky Swerida

Field Methods

• Wave Climate• Sediment Characteristics• SAV Biomass and Morphology

Calculated Orbital Velocity

Sassa

fras

Susqu

ehan

na

Severn

Iris

hTrip

pe

Solomon

s

Bishop

s

Tangie

r

Fleets

Pianka

tank

Hunga

rs0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35 Vegetated

Unvegetated

Max

Nea

r B

otto

m O

rbita

l Vel

ocity

(m

s-1

)

| Sheltered | Exposed | Sheltered |

*

*

*

**

*

**

NA

Sassa

fras

Susqu

ehan

na

Orbital Velocity at Vegetated Sites

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

0.51

1.52

2.53

3.54

4.5

Orbital Velocity (m s-1)

Num

ber

of S

ites

Sediment Grain Size Distribution

Susqu

ehan

na

Sassa

fras

Severn

Iris

hTrip

pe

Solomon

s

Bishop

s

Tangie

r

Fleets

Pianka

tank

Hunga

rs0

50

100

150

200

250

300

350 VegetatedUnvegetated

Site

D50

Gra

in S

ize

(μm

)

| Sheltered | Exposed | Sheltered |

MS

FS

VFS

ClSi

* * *

*

*

* *

Grain Size in Vegetated Sites0 25 63 75 100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

500

Silt Clay Very Fine Sand

Fine Sand Medium Sand

0

1

2

3

4

5

6

7 20112010

Grain Size (μm)

Num

ber

of S

ites

Z. marina in soft sediment. Photo Evamaria Koch Z. marina in armored sediment. Photo

Chris Pickerel

Bedload Transport

Very fine sand and fine sand

5 to 25 cm/s

10-3

10-2

10-1

100

101

10-4

10-2

100

102

104

106

Grain Size (cm)

She

ar S

tress

(dyn

es c

m-2

)

Initiation of MotionSediment ErosionUnvegetatedVegetated

NA

The percentage of shear stress events meeting or exceeding the Shields derived critical shear stress for the mean D50 at each vegetated and unvegetated site.

Flow-Sediment-SAV Relationship in Controlled Mesocosm Experiment

Sediment Type Water Flow Sediment MotionCoarse Sand 0 cm s-1 Deposition

Coarse Sand 4 cm s-1(±1 SE) Bedload Transport

Coarse Sand 24 cm s-1(± 3 SE) Erosion

Very Fine Sand 0 cm s-1 Deposition

Very Fine Sand 4 cm s-1 (±1 SE) Bedload Transport

Very Fine Sand 24 cm s-1 (± 3 SE) Erosion

Work on Fluid Dynamics by Daily and Harleman

Flow-Sediment-SAV Relationship in Controlled Mesocosm Experiment

Bedload Transport

Suspended Transport

Flow Straightening Levers,

Collimator

Motor

Collimator

Ram

pR

amp

Unvegetated Substrate

Unvegetated Substrate

Z. marina

R. maritimaCoarse Sand

Very Fine Sand

Z. marina

R. maritima

Biomass After 6 Weeks

Zostera CS Zostera VFS Ruppia CS Ruppia VFS-70

-50

-30

-10

10

30

50

70 0424

Bio

mas

s (g

m-2

)

(D) cm s-1

(B) cm s-1

(E) cm s-1

Above-ground

Below-ground

**

**

*

*

* * * *

Shoot and Root Density

Zostera CS Zostera VFS Ruppia CS Ruppia VFS-15000

-10000

-5000

0

5000

10000

1500004

Den

sity

(m-2

)

Shoots

Roots

(D) cm s-1

(B) cm s-1

(E) cm s-1

****

*

*

***

Reproductive Shoot Density

Zostera CS Zostera VFS Ruppia CS Ruppia VFS0

200

400

600

800

1000

1200

14000 424

Rep

rodu

ctiv

e Sh

oots

(m-2

)

0 0 0 0 0 0 0

* *

*(D) cm s-1

(B) cm s-1

(E) cm s-1

10-3

10-2

10-1

100

10-4

10-3

10-2

10-1

100

101

102

103

104

Grain Size (cm)

She

ar S

tress

(dyn

es c

m-2

)Ecological Limitations

Excessively Fine

Excessively Coarse

Excessively Energetic

Excessively Quiescent Limiting boundary layers

Limiting nutrient concentration

Limiting toxicity Limited light,

turbidity

Limited substrate stability

0 2 4 6 8 10 12 140

10

20

30

40

50

60

70

80

90

100

110

Organic Content (%)

Tota

l Bio

mas

s (g

/m2)

V. americana

Z. palustris

R. maritima

Reflected waves may be pushing SAV bed offshore and resuspending sediments

ST. MARYS (August 2012)

1.5 m

NOAA ProjectMultiple stressors in coastal areas

with Lee and other colleagues in MD & VA

Seed dispersal via floating reproductive shoots of

Zostera marina

(preliminary simulation results)

Dale Booth

1. PHYSICAL – BIOLOGICAL PROCESS - On what scale should dispersal of Z. marina reproductive shoots be considered?

2. GENETICS - Are seagrass meadows within given regions of the Chesapeake Bay linked as metapopulations by seed dispersal/recruitment processes?

Research Questions

The Model• The North et al. (2008) LTRANS model was developed to

predict the movements of larval Crassotrea virginica larvae in the Chesapeake.

• By applying similar principals we should be able to use the same model to predict the movements of passive floating Zostera marina shoots, incorporating model parameters based on buoyancy and transport velocities of floating reproductive shoots.

• Once we have model predictions of transport distances, populations identified as connected by transport processes will be tested to determine the degree of relatedness using genetic analysis.

-76.5 -76.3 -76.1 -75.9 -75.7 -75.5 -75.3 -75.136.6

36.8

37

37.2

37.4

37.6

37.8

38

38.2

38.4

Day 1

3

1

2

4

Preliminary Tests • Used arbitrary parameters to

determine how to set up the simulation

• Sites selected based on SAV indicated in VIMS aerial photography.

• 500 initial particles at each site (x’s 4 sites)

• Hydrodynamic data from ROMS model simulations for May 1997

-76.5 -76.3 -76.1 -75.9 -75.7 -75.5 -75.3 -75.136.6

36.8

37

37.2

37.4

37.6

37.8

38

38.2

38.4

Day 2

3

1

2

4

Preliminary Tests • Used arbitrary parameters to

determine how to set up the simulation

• Sites selected based on SAV indicated in VIMS aerial photography.

• 500 initial particles at each site (x’s 4 sites)

• Hydrodynamic data from ROMS model simulations for May 1997

-76.5 -76.3 -76.1 -75.9 -75.7 -75.5 -75.3 -75.136.6

36.8

37

37.2

37.4

37.6

37.8

38

38.2

38.4

Day 4

3

1

2

4

Preliminary Tests • Used arbitrary parameters to

determine how to set up the simulation

• Sites selected based on SAV indicated in VIMS aerial photography.

• 500 initial particles at each site (x’s 4 sites)

• Hydrodynamic data from ROMS model simulations for May 1997

-76.5 -76.3 -76.1 -75.9 -75.7 -75.5 -75.3 -75.136.6

36.8

37

37.2

37.4

37.6

37.8

38

38.2

38.4

Day 6

Preliminary Tests • Used arbitrary parameters to

determine how to set up the simulation

• Sites selected based on SAV indicated in VIMS aerial photography.

• 500 initial particles at each site (x’s 4 sites)

• Hydrodynamic data from ROMS model simulations for May 1997

2013 Field Work

• May-June 2013 we attempted to determine the rate of production of floating reproductive shoots at 3 sites located around Tangier and Smith Island.

• Also performed laboratory experiments on shoot buoyancy and rate of seed dehiscence from mature spathes.

• Once these data are processed we will incorporate the numbers into the simulations and rerun them using more recent hydrodynamic inputs.

Conclusions

30

Breakwaters can sustain SAV populations as long as some habitat requirements are met:

Water quality – regional water quality needs to be good enough to support SAV growth Water depth – deep enough so SAV can remain submersed at low tideSediment – needs to remain sandy (<35% silt+clay) with low organic matter (<5 to 8% organic matter) over time. Sedimentation rates >9mm/yr are also beneficial but no infilling (habitat becomes intertidal) Fetch – breakwaters are most beneficial to SAV in long fetch areas (> 10 km)

Management Recommendations

breakwater construction for SAV conservation and/or restoration

31

Management Recommendations

breakwater construction for SAV conservation and/or restoration

33

Shoreline characteristics also need to be considered:

Eroding Marshes –a layer of sand* needs to be added to cover the marsh peat in

the sub-tidal(*>2cm, Wicks et al.

2009)

Cliffs – base of cliff needs to be

stabilized to reduce sediment input and

shoaling breakwater-

protected area

Sandy Beach – breakwater

beneficial to SAV especially when fetch > 10 km