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Rotary Happenings: Sanibel employing use of FTWs for Pond Apple Park project

By Staff | Apr 4, 2018

A somewhat simple scientific approach to seemingly complicated problems can turn out to be the best solution overall. This is never more evident than in nature. The Sanibel-Captiva Rotary Club’s guest speaker on March 23 was Dana Dettmar, conservation officer for the city of Sanibel, who discussed the city’s Floating Treatment Wetlands project at Pond Apple Park, off the Bailey Homestead Preserve.

According to Virginia State University, “Floating Treatment Wetlands islands are manmade ecosystems that mimic natural wetlands. FTWs are created using floating rafts that support plants grown hydroponically. The rafts float on a wet pond water surface and can be used to improve water quality by filtering, consuming or breaking down pollutants – nutrients, sediment and metals – from the water. FTWs may represent a relatively low cost and sustainable engineered best management practice for reducing pollution.”

Dettmar described a FTW as basically a floating mat, much like a child’s interlocking foam play mat, laced with pre-cut holes that are planted with a variety of hydroponic plants and placed in a polluted body of water. As the plants grow, they take up unwanted excess nutrients via the root system and store them in plant tissues. The plants compete with the algae for nutrients and diminish algae blooms.

The plants are usually only allowed to grow for a year before harvesting takes place. This is to prevent the decaying of plant material and the re-polluting of the water. Another reason is that younger plants draw the most excess nutrients. After the plants are harvested, the sustainable practice of planting new plants takes place. Repeating the process provides a cycle of optimal nutrient removal from the water, which has proven to be successful in restoring clean water.

According to Beemats, “Positive outcomes are also harvested from the FTWs. They create and enhance wildlife habitat; plants above the surface provides habitat for wading birds, turtles and alligators, while biomass below the water provides a nursery for juvenile fishes.”

Dettmar was appointed a conservation officer for the city in 2015 and soon after took on Phase 1 of the Floating Treatment Wetlands project, which is being funded through a grant acquired by Natural Resources Director James Evans. Dettmar was already familiar with the natural water filtering system and eutrophication because she had written her Florida Gulf Coast University thesis on the topic.

FTWs are proving to be a natural and an inexpensive corrective action for restoring clean water and returning plant and aquatic life at the park. There are other privately owned and maintained FTWs on Sanibel, cleaning up and maintaining the waters in ponds, lakes and along the shorelines. Use by the city and private entities are positive actions toward achieving the goal of cleaning up polluted water. FTWs make sense. An affordable relatively natural solution to a big problem, and cost and maintenance is minimal for them. In this case, a simple solution seems like an extraordinarily good solution.

The plants are harvested periodically from the FTWs, further reducing the nutrients from the waterbody. Some plants grown on FTWs have the ability to release chemicals into the water that deter algal competitors. Furthermore, the submerged portions of FTWs provide substrate for the growth of beneficial nutrient-reducing microbes.

For information about the Sanibel-Captiva Rotary Club, visit sanibelrotary.org or www.facebook.com/sancaprotary. The club meets every Friday at 7 a.m. at the Dunes Golf and Tennis Club, at 949 Sand Castle Road, Sanibel; visitors are always welcome to attend.