ROBERT E. DEYLE SPECIAL TO THE DEMOCRAT
Alligators – menacing, intriguing, thrilling. As a volunteer river boat tour guide at Wakulla Springs for the past three years, I have shared alligator adventures with visitors from throughout the United States and over 40 nations.
We’ve seen the primeval bellow of an alligator from deep in the swamp; the spine-tingling thrill of seeing and hearing one bellow alongside the boat; 12-foot Joe Junior chasing other males from his domain, snuggling with his girlfriend on the bank, and snagging an unwary white ibis from a rock across from the swimming area. Alligators not only draw visitors to Wakulla Springs, they also are bell weathers of the health of the spring and river ecosystem. Over the past 20 years, wildlife monitoring at the park has documented a 50 percent decline in the annual average number of alligators observed during surveys along the tour route. On a typical boat ride over the past five years, visitors have seen an average of 14 to 17 alligators. Twenty years ago, they would have encountered an average of 35.
This dramatic decline of the top predator in the river food web indicates something is seriously wrong with the ecosystem – total plant and animal abundance has declined, very likely because of dramatic changes in the plants that comprise the foundation of the food web. The likely culprits – too much nitrogen in the ground water flowing into the spring coupled with an alien invasion by the aquarium plant hydrilla.
See Gators, Page 4A
An alligator lurks at Wakulla Springs. Over the past 20 years, wildlife monitoring at the park has documented a 50 percent decline in the number of alligators observed. PHOTOS BY BOB THOMPSON
An alligator with a youngster at Wakulla Springs.
Continued from Page 3A
Humans have generated most of the nitrogen: fertilizing lawns and landscaping, crops, and tree plantations, and discharging wastewater from homes and businesses into the groundwater from municipal sewage treatment plants and private septic systems. In the early 1950s, a St. Louis aquarium-plant farmer imported hydrilla from Asia and sent some to a friend in Tampa who put it in a wire cage in a canal and forgot about it. Within weeks it had taken over the entire water body. Birds and humans spread it throughout Florida over the next 50 years.
Hydrilla first became a problem at Wakulla Spring in 1997. The extra nitrogen fueled its expansion. By 2000 it had taken over the entire spring and the river all the way to the tour boat turnaround, crowding and shading out the native aquatic plants. Mechanical removal could not stop its spread. The Park resorted to applying herbicides annually starting in April 2002.
Herbicides killed back the native plants as well as the hydrilla, but the hydrilla bounced back every year. Some of the native plants grew back as well, but others have largely disappeared. Meanwhile algae proliferated sucking up the nitrogen and colonizing available sand and limestone substrate.
By the mid-2000s, much of the spring and river bottom were covered by dense algal mats mixed with hydrilla. Displacement of the native aquatic plants coincided with major declines of species throughout the food web from invertebrates and fish to birds and alligators. Total animal abundance in the spring and river along the tour boat route has declined by 55 percent over the past 20 years.
One bright spot in the story was an influx of manatees in the mid-2000s, apparently attracted by the prolific hydrilla. Despite heavy grazing by the manatee, herbicide treatments were still needed until Spring 2013 when the hydrilla failed to bounce back. The likely reason – a $225 million overhaul of Tallahassee’s Thomas P. Smith wastewater treatment facility which reduced its nitrogen discharge from the Tram Road spray field to the aquifer by 75 percent.
Hydrilla has not rebounded since 2013 but neither have the native aquatic plants. The spring and river bottom, once carpeted by dense stands of eelgrass and spring tape grass, are now dominated in many places by bare sediments and algae which continue to be fed by excess nitrogen, predominantly from septic tanks.
More than 14,500 septic tanks occupy the Primary Focus Areas, the most vulnerable parts of the spring’s watershed in southern Leon County and northern and central Wakulla County. Properly designed and operating conventional septic tank-leach field systems remove virtually none of the nitrogen from wastewater.
Connecting homes and businesses using septic tanks to existing central sewer systems can greatly reduce nitrogen impacts on the spring and river.
In less densely settled areas, nitrogen- reducing septic systems are needed. Local ordinances on the books and under development in Wakulla and Leon County will require new development within the Primary Focus Areas to install such systems. Property owners with existing septic tanks in areas served by sewers can do their part by connecting to the sewers. Those outside of sewer service areas can take responsibility for their nitrogen impacts to the spring and river by replacing their septic systems with nitrogen- reducing systems.
While septic tanks now account for 51 percent of the nitrogen load to Wakulla Spring, non-agricultural fertilizer use contributes another 5 percent. Property owners can minimize their impacts from this source by eliminating fertilizer use altogether wherever possible; planting grass such as Centipede with low fertilizer needs; and using no more than 1pound of slow-release or water-insoluble nitrogen per 1,000 square feet of lawn when fertilizer is absolutely necessary.
The alligator population at Wakulla Springs appears to have stabilized over the past five years, apparently having attained a new balance with the radically altered food web. Members of the Wakulla Springs Alliance are collaborating with State Park staff to initiate a pilot project to begin to restore native aquatic vegetation in the spring and upper river. They hope that this initiative, coupled with a robust effort to reduce nitrogen from septic tanks, will enable a comeback by Wakulla’s most fearsome predator.
Robert Deyle is a volunteer river guide at Wakulla Springs State Park, vice chair of the Wakulla Springs Alliance, and professor emeritus of environmental planning at Florida State University. Learn more at www.wakullaspringsalliance. org; www.tappwater.org/lawncare. cfm; and cms.leoncountyfl.gov/Portals/ 0/Documents/OnsiteSewageMgt. pdf.
An alligator emerges at Wakulla Springs. BOB THOMPSON