The Relationship Between Shoreline Characteristics and Nearshore Submerged Aquatic Vegetation Bridget Smith, Chris Patrick, Meghan Williams, Don Weller
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The Relationship Between Shoreline Characteristics and Nearshore Submerged Aquatic Vegetation
Bridget Smith, Chris Patrick, Meghan Williams, Don Weller
Submerged Aquatic Vegetation
SAV Decline
Li et al. 2007 Estuaries & CoastsPatrick et al. 2014 Estuaries & Coasts
Shoreline Hardening
Bottom ScourSediment SuspensionWave energy
Shoreline Types Natural Hardened
Mechanisms of change- Suspend sediment, decreasing
water clarity- Scour away sensitive beds- Deepen the adjacent shore through
bottom scour
Slope
0 m
-3 m
0 m
-3 m
Shoreline Hardening and SAV Effects of Shoreline Alteration and Other
Stressors on Submerged Aquatic Vegetation Riprap and bulkhead
negative predictors of SAV abundance at the subestuary scale
Patrick et al. 2014 Estuaries & Coasts
The Relationship Between Shoreline Hardening and Adjacent Submerged Aquatic Vegetation Less SAV directly adjacent to bulkhead Patrick et al. 2014 Estuaries & Coasts (in review)
Shoreline Hardening: Further Questions How does the length of shorelines (natural,
riprap, and bulkhead) influence the abundance of SAV?
How far do these offshore effects extend? Does this differ for different shoreline types?
How are shoreline structures related to nearshore bathymetry?
Subestuary Scale
Shoreline Scale
Shoreline LengthDistance to ShoreDepth
SAV Presence and Mean Density
Presence: The fraction of years SAV is present from 1984 to 2012
<10%
10-40%
40-70%
70-100%
Coverage
SAV Presence and Mean Density
Presence: 0.607Mean Density: 1.714
<10%
10-40%
40-70%
70-100%
Coverage
SAV Presence and Mean Density
Presence: 0.143Mean Density: 0.321
<10%
10-40%
40-70%
70-100%
Coverage
Hypotheses Steeper slopes occur off of hardened
shorelines. SAV adjacent to natural shorelines will have
greater presence and mean density than SAV adjacent to hardened shorelines.
For natural shorelines, there will be a positive relationship between shore length and SAV presence and mean density.
Methods
Data • Shoreline condition: length and location
of shoreline types• SAV spatial extent from 1984 to 2012
from aerial photography
• Bathymetry
Variables
Response Predictor Slope Depth
SAV Presence SAV Mean Density
Shoreline Type
Shoreline Type Depth Shore Length Distance to Shore Salinity Zone
Statistical AnalysesPhysical Characteristics
SAV Presence and Mean Density
ANOVA Categorical variable:
shore type Continuous variables:
depth and slope
ANOVA Categorical variables: shore
type and salinity zones ANCOVA
Categorical variable: shore type
Continuous variables: shore length, distance to shore, depth
If results are significant, run linear regression by shore type
Slope Analysis
SAV Presence and Density Analysis
Results
Results Physical Characteristics
Slope
P value <0.001
Depth
P value <0.001
Results SAV Presence and Mean Density
Shore Type
P value <0.001
Natural shorelines also has the highest mean density of SAV
Depth and Shore Length
Interaction P value = 0.007
Natural Shorelines: Presence by Depth and Shore Length
Bulkhead Shorelines: Presence by Depth and Shore Length
Interaction P value = 0.004Riprap not significant.
Depth Depth
Pres
ence
Pres
ence
Shore Length
Shore Length
Depth and Distance to Shore
Interaction P value < 0.001
Natural Shoreline: SAV Mean Densityby Depth and Distance to Shore
Distance to Shore
Depth
Mea
n De
nsity
Depth and Distance to Shore
Interaction P value < 0.05Interaction P value < 0.001
Riprap Shoreline: SAV Mean Densityby Depth and Distance to Shore
Depth
Mea
n De
nsity
Distance to Shore
Bulkhead Shoreline: SAV Mean Densityby Depth and Distance to Shore
Mea
n De
nsity
Depth Distance to Shore
Salinity
P value < 0.001
Highest presence and mean density in the polyhaline zone
Salinity
Interaction P value < 0.001
Take Away Points More gradual slopes along natural shorelines
Natural shorelines have greater SAV presence and mean density than hardened shorelines
0
3Dept
h
Natural Riprap and Bulkhead
Shoreline Type Presence Density
Length Distance
Natural + + + +Bulkhead - - NS +Riprap - - NS NS
Next Steps Repeat analysis when better bathymetry
becomes available Examine how shoreline length and shore type
are related to slope
AcknowledgementsChris PatrickMeghan WilliamsDonald Weller
Smithsonian Environmental Research Center
Virginia Institute of Marine Science
NOAA
USGS