Floating Wetland Islands

Raccoon Island, Halsey Island, and Liffy Island have been a part of the Lake Hopatcong landscape for past generations, but a pair of new islands have joined the scene in an effort to keep New Jersey’s largest lake healthy for generations into the future.

Two floating wetland islands—each covering 250 square feet—have been installed in Ashley Cove in the northeast part of Lake Hopatcong as part of a non-point source 319(h) grant that was awarded to the Lake Hopatcong Commission by the New Jersey Department of Environmental Protection and has been recently administered by the Lake Hopatcong Foundation. The islands were installed on July 2 with help from employees of Princeton Hydro LLC (an environmental consulting firm that has worked on numerous Lake Hopatcong water quality projects), Jefferson Township Department of Public Works, and the Lake Hopatcong Foundation. The New Jersey Water Supply Authority’s Watershed Protection Program director Ken Klipstein was also on hand to observe and help with the installation.

Floating wetland islands are made up of woven recycled plastic material that floats, with vegetation planted directly into the material with peat and mulch. They must be planted near shore in a no-wake zone on the lake, which is why Ashley Cove in Jefferson Township, a quiet corner of the lake with no through traffic or lakefront structures, was chosen for the project. The plants then grow on the island, rooting through the plastic material.

According to Dr. Fred Lubnow, a limnologist with Princeton Hydro, these floating wetland island cells will divert some of the existing nutrients in the cove away from the nuisance mat algae and weed and into the plants on the island, creating an excellent habitat for phosphorus removal. As the island plants remove phosphorus from the lake, less phosphorus is available for nuisance aquatic plant growth and algae. As a side benefit, they provide an excellent refuge habitat that attracts beneficial forage fish and can provide shoreline protection.

The islands in Ashley Cove were planted with attractive native vegetation, including sweet-scented joe-pye weed, Hibiscus moscheutos, common rush, New England aster, broadleaf arrowhead, great blue lobelia, and golden zizia.

According to Donna Macalle-Holly, LHF Grant and Program Coordinator, “This is the first of a kind water quality improvement project for Lake Hopatcong.  Each of the islands should remove about ten pounds of phosphorus annually.   It has been well documented in the Lake Hopatcong Water Quality Monitoring report that one pound of phosphorus can generate as much as 1,100 pounds of wet algal biomass.  The islands will require very little maintenance once they are established and should last for 15 years.”

Lake Hopatcong Foundation president Jessica K. Murphy said that the islands are a project that gets right to the heart of the LHF purpose. “We focus a lot on the Lake Hopatcong community and experience, but none of that will matter if the lake itself isn’t healthy,” Murphy said. “Improving the water quality of the lake is truly the centerpiece of our mission, and this is a new and exciting way to do that.”

June 2015 update – Princeton Hydro staff did some replanting on the floating wetland islands on June 23 since the plants did not winter overdue to the harsh conditions during the winter season.  They also installed a different type of fencing to keep waterfowl from feeding on the plants.  The islands will continue to be closely monitored.

Article: ANJEC Report -Winter 2015

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