Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth?
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Transcript of Coastal plant communities and sea level rise: Is the sediment suitable for seagrass growth?
Coastal plant communities and Coastal plant communities and sea level rise: Is the sediment sea level rise: Is the sediment suitable for seagrass growth?suitable for seagrass growth?
E. Caroline WicksE. Caroline Wicks
January 23, 2006January 23, 2006
SAV WorkgroupSAV Workgroup
www.dnr.state.md.us
T. CarruthersE. Koch
Outline of talk
• Sea level rise
• My research– Hypotheses
– Methods
– Results
• Conclusions– My research
– The big picture
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
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)
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)
• Mill’s Island, Chincoteague Bay, Maryland– Retreating marsh
shoreline with an eroding dune
– Seagrass bed in subtidal area adjacent to retreating marsh
Study site
www.ian.umces.eduwww.vims.edu/sav
Processes affecting seagrass distribution adjacent to retreating marshes
• Marsh shoreline retreat• Sand from eroding dune
transported along shore• A layered sediment
environment for seagrasses
Old marsh peat
Sand
E. Koch
www.vims.edu/bio/sav
• 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
Field survey at Mill’s Island, Chincoteague Bay
Hypothesis 1: Organic content of sediments adjacent to retreating marshes (i.e. old marsh
peat) is limiting to seagrass growth
Seagrass density decreased with increasing sediment organic content at Mill’s Island
Controlled mesocosm experiment
• 4 seedlings per compartment
• 8 weeks• Quantify biomass,
length and growth rate (Dennison 1990)
Does seagrass growth show a trend with sediment organic content?
0.1%1.2% 4.4%
Seagrass biomass is significantly different between treatments
• One way ANOVA, p < 0.05
• Pairwise comparison using Least Squares Method, p < 0.05
• Sand layer depth measured at 15 points
• Seagrass growth parameters
Old marsh peat
Sand
Hypothesis 2: A thin layer of sand overlaying organic rich sediments adjacent to retreating
marshes allows for seagrass growth
Seagrass density as a function of sand layer depth
Polynomial regression
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
Sand layer depth determines root length
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
Seagrass morphology in different sediments – How does wave energy
affect the plants?
E. Koch
Summary of processes affecting seagrass growth at Mill’s Island, Chincoteague Bay
Seagrass migration towards land may depend on local factors
Thank you!
CommitteeDr. Evamaria KochDr. Bill Dennison
Dr. Court Stevenson
Computer HelpDave Kimmel
IAN GroupLamere Hennessee, MGS
Tom Fisher Greg Radcliffe
Dave Wilcox, VIMS
Field and Lab HelpBill Severn
Ralph KimesGordy Dawson
Lois LaneJack Seabrease
Angie HengstJames Kampmeyer
Blaise Brown
Friends and FamilyShih-nan Chen Angie Hengst
Erin and Chris MarkinDaidipya Patwa
Jeremy TestaJane Thomas