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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007


Mandy Livingston-Calley, Jennifer Tallerico BCI Engineering and Scientists Inc. Lakeland, FL Lori McCloud, Pam Livingston SJRWMD Palatka, FL


In an effort to facilitate compliance of the Total Maximum Daily Loads for the lower St. Johns River, a Regional Stormwater Treatment Facility (RST) was constructed in the Tri-County Agricultural Area to treat agricultural runoff from a 1,196-acre watershed. The facility pumps water from an agricultural canal through a 15-acre wet detention pond, then into a 38-acre wetland. Water is then discharged from the wetland into Deep Creek, which empties into the lower St. Johns River. The presence of Hydrilla verticillata, and it’s ability to out-compete native submerged aquatic vegetation (SAV), has caused recent concern that the plant may, over time, completely fill-in the volume of the pond, adversely affecting the pond’s ability to improve water quality. Herbicide application, though effective in treating Hydrilla, would generate a large release of nutrients as the plants die, a result directly in opposition to the goals of the RST. Thick mats have been shown to hinder irrigation operations by reducing flow rates as much as 90% thereby impeding the operation of irrigation structures (Godfrey et al., 1996). The purpose of this project is to monitor the distribution and productivity of Hydrilla verticillata in the pond portion of the RST to evaluate how long it will take, if left untreated, for Hydrilla to completely fill-in the treatment pond.

Hydrilla can grow in almost any freshwater spring, lake, marsh, ditch, pond, river and

tidal zone in water depths ranging from a few inches to 20 ft. Massive amounts of Hydrilla can alter dissolved oxygen, pH, and other water chemistry parameters (Smart and Barko, 1988). The dense mats that form from Hydrilla production interfere with fish and wildlife habitat. Hydrilla has many competitive advantages over other vegetation in that it can grow with less light and it is more efficient at taking up nutrients than other plants. Optimal reproduction temperatures have been reported to be between 68-81 degrees F with a maximum temperature of 86 degrees F (http://plants.ifas.ufl.edu/seagrant/hydver2.html). It has also been suggested that Hydrilla can grow in 1% of surface irradiance or less (www.mass.gov/dcr/waterSupply/lakepond/geir.htm). In order to validate literature values for optimal temperature and light with respect to growth and production for conditions existing in the RST treatment pond, we intend to measure light and temperature in this study, along with the

distribution and productivity.


Traditional methods to monitor SAV such as SCUBA, underwater photography, and hydro-acoustics cannot be utilized in the RST pond, as water depth and high color preclude their

Session 4 – Page 13

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