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Floating Islands Attract Cranes, Clean Water

In 2000, Citizens for Conservation (CFC) of Barrington added several acres to Flint Creek Savanna preserve, including a two-acre detention pond that serves adjoining Savannah Subdivision. Not content to waste this water feature, CFC set out to turn the usually algae-filled basin into an ecological asset. They deepened the pond and spent three years planting prairie and marsh species in and around the edges. The native plants grew quickly, with the help of a lot of volunteer weed control, and an ecosystem developed.

To increase the complexity of this developing ecosystem, aquatic plants—both fully underwater (submergent) and pushing out of the water (emergent)—were also planted. Unfortunately, the submergent plants were overcome by algae in the water that smothered their roots and blocked sunlight.

To reduce the excess nutrients in the pond that were creating these algal blooms, CFC decided to employ a new technology—floating islands. These islands, made out of recycled pop bottles embedded with Styrofoam for buoyancy, are covered with live plants whose roots penetrate through to the water. The roots and their bacteria absorb common pollutants, such as nitrates and phosphates, at a much higher rate than shoreline plantings.

In spring 2006, islands totaling about 600 square feet were launched in the pond. (See photos of installation.) They were planted with sedges, rushes, and wetland forbs, all of which flourished. Though algae levels appear to have decreased, CFC has been developing a system to measure the islands’ impact on nutrient levels and water quality.

CFC also found that these islands were very aesthetically pleasing and provided important wildlife habitat. Turtles and frogs found safe haven on top of the islands, while fish and invertebrates thrived beneath the islands. Birds found refuge there as well, including sandhill cranes who took their young onto the islands at night for safe roosting. In 2007, the cranes even nested on one of the islands.

Floating islands have been highly successful for CFC’s new wetlands, and are beginning to show how positive environmental planning can impact degraded water quality. For more on floating islands, visit floatingislandinternational.com.

— Tom Vanderpoel