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SubmergedAquaticVegetation

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SubmergedAquaticVegetation

  1. 1. The Relationship Between Shoreline Characteristics and Nearshore Submerged Aquatic Vegetation Bridget Smith, Chris Patrick, Meghan Williams, Don Weller
  2. 2. Submerged Aquatic Vegetation
  3. 3. SAV Decline Li et al. 2007 Estuaries & Coasts Patrick et al. 2014 Estuaries & Coasts
  4. 4. Shoreline Hardening Bottom Scour Sediment Suspension Wave energy
  5. 5. Shoreline Types Natural Hardened Mechanisms of change - Suspend sediment, decreasing water clarity - Scour away sensitive beds - Deepen the adjacent shore through bottom scour
  6. 6. Slope 0 m -3 m 0 m -3 m
  7. 7. 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)
  8. 8. 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?
  9. 9. Subestuary Scale
  10. 10. Shoreline Scale Shoreline LengthDistance to ShoreDepth
  11. 11. 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
  12. 12. SAV Presence and Mean Density Presence: 0.607 Mean Density: 1.714 <10% 10-40% 40-70% 70-100% Coverage
  13. 13. SAV Presence and Mean Density Presence: 0.143 Mean Density: 0.321 <10% 10-40% 40-70% 70-100% Coverage
  14. 14. 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.
  15. 15. Methods
  16. 16. Data • Shoreline condition: length and location of shoreline types • SAV spatial extent from 1984 to 2012 from aerial photography • Bathymetry
  17. 17. Variables Response Predictor  Slope  Depth  SAV Presence  SAV Mean Density  Shoreline Type  Shoreline Type  Depth  Shore Length  Distance to Shore  Salinity Zone
  18. 18. Statistical Analyses Physical 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
  19. 19. Slope Analysis
  20. 20. SAV Presence and Density Analysis
  21. 21. Results
  22. 22. Results  Physical Characteristics
  23. 23. Slope P value <0.001
  24. 24. Depth P value <0.001
  25. 25. Results  SAV Presence and Mean Density
  26. 26. Shore Type P value <0.001 Natural shorelines also has the highest mean density of SAV
  27. 27. 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 = 0.004 Riprap not significant. Depth Depth Presence Presence
  28. 28. Depth and Distance to Shore Interaction P value < 0.001 Natural Shoreline: SAV Mean Density by Depth and Distance to Shore Depth MeanDensity
  29. 29. Depth and Distance to Shore Interaction P value < 0.05Interaction P value < 0.001 Riprap Shoreline: SAV Mean Density by Depth and Distance to Shore Depth MeanDensity Bulkhead Shoreline: SAV Mean Density by Depth and Distance to Shore Mean Density Depth
  30. 30. Salinity P value < 0.001 Highest presence and mean density in the polyhaline zone
  31. 31. Salinity Interaction P value < 0.001
  32. 32. Take Away Points  More gradual slopes along natural shorelines  Natural shorelines have greater SAV presence and mean density than hardened shorelines 0 3 Dept h Natural Riprap and Bulkhead Shoreline Type Presence Density Length Distance Natural + + + + Bulkhead - - NS + Riprap - - NS NS
  33. 33. Next Steps  Repeat analysis when better bathymetry becomes available  Examine how shoreline length and shore type are related to slope
  34. 34. Acknowledgements Chris Patrick Meghan Williams Donald Weller Smithsonian Environmental Research Center Virginia Institute of Marine Science NOAA USGS

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