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

Karst Lakes and Nutrient Loading to the Aquifer

Sean E. McGlynn, PhD. McGlynn Laboratories Inc. Tallahassee, FL., Destin, FL., Baton Rouge, LA.

The Woodville Recharge Basin is a karst plane that includes several first order springs, numerous sinks and excellent examples of karst lakes (Lakes Jackson, Iamonia, Lafayette, Bradford and Munson). The Watershed Analysis and Management Model (WAMview) was used to assess nutrient loading from surface to ground water. Nitrogen loading was traced to wastewater sources. Phosphorus loading derived from direct surficial inputs into open karst features associated lakes and streams. Popular attention has focused on nitrogen loading but nutrient limitation results suggest that phosphorus loading may have a more serious effect on area springs.

Within the WRB karst lakes periodically disappear into sinkholes. Lost rivers dive into the ground only to reappear as springs. In some areas swaletts are common. These are shallow underground rivers that pop up on the surface for a few hundred feet only to disappear into a sink. Karst features and caves abound. All of these tend to conduct water through a dendritic cavern system to the numerous springs in the area. This study examined nutrient loading and impacts to springs as a result of Landuse.

Wakulla Springs is considered the world’s deepest freshwater spring. Wakulla Springs has experienced significant nutrient enrichment over the past 10 years. Herbicides are now applied at the springshed annually as a drip treatment to keep the springs open. Harmful algae are proliferating. This summer 30 swimmers were treated for toxic shock (this occurred at Ichituknee Springs too) and 37,000 cubic yards of noxious muck washed up at Wakulla Beach.

The Woodville Recharge Basin (WRB) encompasses most of the springshed of Wakulla Springs and the St. Marks Rise. The Floridian Aquifer in the WRB is covered by 10 to 20 feet of sand and is vulnerable. The Floridian Aquifer is a limestone aquifer that transmits water through bedding planes, fractures, tunnels and caverns. The water flows into and out of the springs through the underground caverns of the Floridian Aquifer. The Woodville Recharge Basin (WRB) is experiencing rapid growth. Water quality in the aquifer is deteriorating.

Stormwater flows into Sinkholes and can pass directly to the aquifer without being attenuated. This is has been termed a short circuit to the aquifer. Many compounds like phosphorus, pesticides, herbicides and petroleum hydrocarbons are hydrophobic and are

Session 8B – Page 5

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