department of transportation 

retention ponds

The Florida DOT constructed two retention ponds at the eastern end of the Lytle Avenue Bridge in New Smyrna Beach, Florida.  Run off from the bridge and surrounding causeways enters the eastern most pond, then flows west through large culverts to a shallow pond, with an outfall to Callalisa Creek, a tidal tributary to the Indian River Lagoon. 
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The shallow, western pond was originally designed as a tidal marsh, but failed due to inadequate tidal fluctuation.  Beemats established floating treatment wetlands, with salt tolerant plants (halophytes), to accommodate the high salinity levels.  The water in the eastern pond is somewhat less saline due to freshwater mixing by the roadway run off.  

The mats, pots and roots of the plants have been colonized by bivalve mussels, tube worms, barnacles and oysters. This system has been in place for nine years and has been harvested and replanted four times.  Most of the mats are still in use and the pots have been reused for subsequent replanting efforts.