Southwest Florida population increases during the winter thanks to a migratory flux of semipermanent (retired) inhabitants. In the eighties, to limit the ecological impacts of such a flux, numerous urban stormwater treatment ponds were mandated to be built in association with urban developments. According to the Chapter 62-40 of the Florida Administrative Code, these ponds are to i) prevent land erosion, ii) provide pollution runoff control via filtration and decantation and iii) reestablish the natural hydropatterns in the region thus allowing aquifer recharge and adequate 80% pollutant free freshwater deliveries to the coasts. Since 2013, a research program was developed to better understand the limnology of these ponds. An investigation involving students was made to account for the total number of ponds, their shape as well as age. This GIS approach was coupled with the limnology of about 50 ponds to in particular study the bathymetry, sedimentology, water quality, groundwater recharge and overall efficiency of some of these ponds. Further, the social behavior of the people was coupled with the resulting limnological state of some of the ponds studied.
Results/Conclusions
About 10,000 ponds (1-40 ha) were found for a combined surface area of 100 km2 thus rivaling by 1.5 times the surface area of the Caloosahatchee River, which drains Lake Okeechobee water to the Gulf. Some ponds were highly convoluted to allow more shoreline urban development, which increased ecological stress. It was found that pond front view properties had indeed a higher real estate value. Because most people surrounding the ponds are accustomed to glacial lakes surrounded by lush lawns, the ponds were forced to be turned into such lakes. Fertilized manicured lawns with little riparian plants thus prevailed around the ponds and this increased the nutrient mass load into the ponds, which, for 90%, turned into eutrophy/hypereutrophy. To mask the symptoms of eutrophication, the water was subsequently treated with algaecides/herbicides, which rendered the ponds inefficient in phyto-remediating nutrient loading. In the ponds of the City of Naples, the resulting average nutrient retention was thus -190%. As a result, the water escaping from some of the ponds via the overflow box had high levels of nutrients associated with (copper-based) algaecides that reached the coasts thus obviating restoration efforts made locally and more inland. Additionally, data on two ponds showed that these two were seepage ponds and did not recharge the aquifer but instead received significant nutrient loads via groundwater.