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Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth?

Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth?. E. Caroline Wicks January 23, 2006 SAV Workgroup. www.dnr.state.md.us. E. Koch. T. Carruthers. Outline of talk. Sea level rise My research Hypotheses Methods Results Conclusions My research

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Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth?

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  1. Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth? E. Caroline Wicks January 23, 2006 SAV Workgroup www.dnr.state.md.us E. Koch T. Carruthers

  2. Outline of talk • Sea level rise • My research • Hypotheses • Methods • Results • Conclusions • My research • The big picture

  3. Positive effects of marsh-seagrass interactions • Transport of organic matter and nutrients between systems(Whiting et al. 1989) • Marshes reduce eutrophication of shallow waters by filtering out land-based nutrients(Valiela and Cole 2002) • The effect of linked ecosystems for associated fauna(Irlandi and Crawford 1997) www.nwrc.usgs.gov www.deq.state.va.us

  4. TM Marsh Index: Healthy, Moderate Deterioration, Severe Deterioration The ramifications of sea level rise • Relative sea level rise • Enhanced effects of extreme meteorological events (flooding) • Shoreline erosion • 3 mm yr-1 on Maryland’s Eastern Shore • 70% of marshes in Chesapeake Bay are degraded (Kearney et al. 2002) • 31% of Maryland’s coastline (4360 miles) is eroding (State of the Beach 2004)

  5. The impact of sea level rise on seagrasses • Shifts in distribution and community structure(Short and Neckles 1999) • Shallow marine sediment erosion leads to seagrass loss(Duarte 2002) • Seagrasses should be able to colonize newly inundated land, but total coverage should not change(Duarte 2002)

  6. Study site • Mill’s Island, Chincoteague Bay, Maryland • Retreating marsh shoreline with an eroding dune • Seagrass bed in subtidal area adjacent to retreating marsh www.vims.edu/sav www.ian.umces.edu

  7. Sand Old marsh peat Processes affecting seagrass distribution adjacent to retreating marshes • Marsh shoreline retreat • Sand from eroding dune transported along shore • A layered sediment environment for seagrasses www.vims.edu/bio/sav E. Koch

  8. Hypothesis 1: Organic content of sediments adjacent to retreating marshes (i.e. old marsh peat) is limiting to seagrass growth Field survey at Mill’s Island, Chincoteague Bay • 80 cm depth contour through seagrass bed • 15 points along transect to sample the range of sand layer depths • Sediment organic content, seagrass density, biomass, leaf and root length quantified E. Koch

  9. Seagrass density decreased with increasing sediment organic content at Mill’s Island

  10. 1.2% 4.4% 0.1% Controlled mesocosm experiment Does seagrass growth show a trend with sediment organic content? • 4 seedlings per compartment • 8 weeks • Quantify biomass, length and growth rate (Dennison 1990)

  11. Seagrass biomass is significantly different between treatments One way ANOVA, p < 0.05 Pairwise comparison using Least Squares Method, p < 0.05

  12. Sand Old marsh peat Hypothesis 2: A thin layer of sand overlaying organic rich sediments adjacent to retreating marshes allows for seagrass growth • Sand layer depth measured at 15 points • Seagrass growth parameters

  13. Seagrass density as a function of sand layer depth Polynomial regression

  14. Controlled laboratory experiment • 5 treatments • 3 replicates of each, 6 replicates of 0 SLD • 3 seedlings per core • Water change every week • Ran for 8 weeks • Quantify biomass and length

  15. Sand layer depth determines root length

  16. Plant morphology may explain conflicting results • Sediment organic content • Mesocosm experiment shows the sediment organic content adjacent to retreating marshes is not limiting seagrass distribution or growth parameters • Field results suggest the opposite trend • Plant morphology

  17. E. Koch Seagrass morphology in different sediments – How does wave energy affect the plants?

  18. Summary of processes affecting seagrass growth at Mill’s Island, Chincoteague Bay

  19. Seagrass migration towards land may depend on local factors

  20. Committee Dr. Evamaria Koch Dr. Bill Dennison Dr. Court Stevenson Computer Help Dave Kimmel IAN Group Lamere Hennessee, MGS Tom Fisher Greg Radcliffe Dave Wilcox, VIMS Field and Lab Help Bill Severn Ralph Kimes Gordy Dawson Lois Lane Jack Seabrease Angie Hengst James Kampmeyer Blaise Brown Thank you! Friends and Family Shih-nan Chen Angie Hengst Erin and Chris Markin Daidipya Patwa Jeremy Testa Jane Thomas

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