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Floating Wetlands Pilot Project: Investigating the Potential for a New Stormwater BMP
Karen Duhring Virginia Institute of Marine Science
Center for Coastal Resources Management
May 24, 2012
Floating Wetlands Pilot Project
• What are Floating Wetlands?
• VIMS Teaching Marsh Project – Objectives
– Design
– Initial Monitoring Results
• Next Steps
WHAT ARE FLOATING WETLANDS?
Manufactured floating platforms
designed to grow plants in open water
Used for water quality & habitat improvements
The islands are engineered to grow any type of plants. Nutrients for plant growth are obtained from the water.
Microbial growth occurs in the matrix and among the
plant roots. Both microbial and plant growth result in
improved water quality.
Hanging network of roots, rhizomes, and
attached biofilms provides surface area
for biochemical & physical processes
Islands function in any depth of water. At least 2.5 ft prevents rooting into benthic substrate during low water levels.
Floating Island Southeast
Potential Applications • Urban stormwater ponds
– TMDL credits
• Wastewater lagoons – Animal feedlots – Fish farms
• Wetland replacement – Fluctuating water levels – Invasive species dominance – Shoreline stabilization
• Aesthetic improvement Photos by Floating Island Southeast
FLOATING WETLAND PILOT PROJECT
William & Mary Sustainability Plan Carbon offset program Facilities management
Energy & water use Transportation
Student Green Fees • $15 per student per semester $225K annually • Project Awards granted by Committee on Sustainability
April 2011 grant award for floating wetlands at 2 locations
VIMS Teaching Marsh & Williamsburg campus
Floating Wetland Pilot Project
• Objectives – Learn how to design & install
– Monitor plant survival & Phragmites invasion
– Monitor water quality before & after deployment (W&M campus only)
– Share experiences with other region projects
– Provide outreach education
– Involve students
VIMS Teaching Marsh Project
• Small shallow pond connected to Coleman Bridge stormwater detention pond
• Phragmites dominates pond edges
• Floating wetlands to increase plant diversity & treatment potential
Freshwater Pond
VIMS Teaching Marsh Project
• Pond surface area approx. 576 sf
• 180 sf floating wetland (+ 30%) – 3 12 x 5 ft sections – Cable together or float separately
• $25/sf for basic design – Cost range $25-30 per sq ft – Cost depends on customization
BioHaven® Floating Island Design Specifications
• Recycled PET plastic matrix 8 inches thick
• Injected marine foam for buoyancy
• Built-in anchor points
• PVC frame with cable to connect island sections together
• Planting holes on 8-inch centers through first 2 layers, 2.5 inch diameter circles
• Can be custom shaped
BioHaven® Floating Island Design Specifications
Inert marine foam provides buoyancy
4 layers in matrix PVC pipe for cable connection
of separate modules
Plant Selection
• Popular, Versatile, and Available native plants for constructed wetlands – as per DCR stormwater
design specification No.13
• Salt tolerance up to 5 ppt – Occasional tidal flooding
Plant Selection
Marsh Hibiscus
Seashore Mallow
Swamp Milkweed
Joe Pye Weed
New York Ironweed
Arrow Arum
Soft Rush
Pickerelweed
Bulltongue Arrowhead
Blueflag Iris Northern & Southern types
Plant Purchase
• Edenton, North Carolina
• Genetically adapted to Carolinas & SE VA
• Container grown in “large plugs”
• $0.94 each
Large plugs, no soil used Approx. 2/3 of the holes planted for budget reasons
Tall flowering plants in center New York Ironweed, Swamp Milkweed, Joe Pye Weed
Shorter plants around edges
Pickerelweed, Peltandra, Bulltongue, Iris
Launch April 30, 2012
Cinder blocks & steel cable for anchors 2 anchor points per section
Launch April 30, 2012
Planted mat with anchors pulled into pond
Anchors set based on proximity to Phragmites
Launch April 30, 2012
Only 2 of 3 sections installed at this time Look smaller in pond than on land
2 Weeks Later – May 12
Noticeable loss of leaves – weather & planting stress No evidence of muskrat grazing
West section floating higher than east section Phragmites rhizomes reaching out but not touching
2 Weeks Later – May 12
Northern blue flag Iris versicolor
Healthy roots with new leaf growth
2 Weeks Later – May 12 Removed dead leaves Pushed viable roots down into holes to make contact with water Recorded species survival
Initial Survival after 2 weeks
Best Condition
• Hibiscus • New York Ironweed • Iris versicolor • Switch grass • Soft rush
Not so good
• Seashore mallow
OK with wet roots
• Iris virginica • Joe Pye Weed • Pickerelweed • Arrow Arum • Bulltongue
Lessons Learned So Far
• Purchasing process took longer than expected
• Delay planting until weather conditions are suitable, keep mats dry in the meantime
• Islands look bigger on land than in the water
• Push plugs all the way into holes
• Add soil if plant plugs are smaller than holes
Other Hampton Roads Projects
• VA Zoological Park, Norfolk
• VA Agriculture Experimental Research Facility, VA Beach
• Elizabeth River Project, Chesapeake
Any others not mentioned here?
Next Steps • Design, plant & launch 3rd section
• Obtain water quality data from main campus project
– What is feasibility for TMDL credits?
• Facilitate network of Hampton Roads projects
– Share lessons learned & monitoring data
– Collaborate outreach efforts
Contact Information:
Karen Duhring Virginia Institute of Marine Science
College of William & Mary PO Box 1346
Gloucester Point, VA 23062 (804) 684-7159
Thanks for Your Interest
Open Discussion • Any upcoming events of interest?
• Any final thoughts or questions?
• Please fill out Workshop Evaluation
• Workshop presentations will be posted to a web site
• Contact list of participants will be e-mailed
– Opt out of e-mail list with Dawn Fleming
Optional Field Trip • Self-guided tour of VIMS Teaching Marsh &
beach • 3 stations with VIMS staff
– Floating Wetlands – Salt Marsh – Beach with Breakwaters and Planted Dune
• Limited facilities, use restrooms here • Walk or drive to Boat Basin area
Parking
Stations
Boardwalk to Beach
