Seagrass Projects

Because the Section has experience in a wide variety of subjects, the Section was tasked with performing selected seagrass evaluation projects in the Ft. DeSoto Park and Aquatic Habitat Management Area. Two of the most high profile projects include the Seagrass Scar Monitoring Project and the Ft. DeSoto Recirculation Project.

Ft. DeSoto Seagrass Monitoring

Seagrass Scar Monitoring Project in the Ft. DeSoto Park and Aquatic Habitat Management Area. Most people in the Tampa Bay area are now familiar with the protection zones and seagrass recovery efforts that have taken place in the Ft. DeSoto Park and Aquatic Habitat Management Area over the past seven years. The County took the first detailed aerials in 1992 to gather baseline data prior to installing signs delineating the areas or enforcing the seagrass protection ordinance.

The signs were installed in 1993 and aerials were taken on at least an annual basis thereafter. The aerials were then digitized and analyzed to determine the scar rate within each type of the protective areas (non-combustion and seagrass caution) and compared them to the unprotected areas. The County has tracked the prop scar rate over the years and had successfully slowed the increase in accumulated damage.

Hindering our success was the fact that many signs were lost after the first few years. What was once thought to be vandalism turned out to be a galvanic reaction of bird droppings, salt water and dissimilar metals corroding the sign attachment points. Eventually strong winds would pull the signs off the poles. New sign mounting methods resulted in minimal loss of new signs. Better signage, as well as more enforcement, education and experimental seagrass regrowth efforts have resulted in a huge reduction in seagrass scars in the Ft. DeSoto area.

These successes and the fact that the Caution Areas have been about as effective as the Non-Combustion Areas in protecting the seagrass resulted in modifications to the Zones. The Board of County Commissioners recently approved modifications within the Ft. DeSoto Habitat Management Area that change some zones from "Non-Combustion" to "Caution". More significantly, large areas that previously had no protection were designated as "Caution" areas. Discussions are also continuing to extend the seagrass regrowth experiments that have been successful in this area. These efforts should provide faster and more complete recovery of this valuable resource.

Ft. DeSoto Recirculation Project

Work is progressing on the 40-foot span bridges planned for the causeways at Ft. DeSoto Park. This cooperative effort between Pinellas County and the Pinellas-Anclote Basin Board will greatly improve water circulation between the back bays of the park. During the Park's development in the late 1950's and early 1960's the main island was connected to the smaller islands by dredging and filling two causeways, one to provide access to the mainland and the other to create a maintenance area and Park Manager residence.

This activity cut off circulation between the back bays. Data obtained during a 1985 study of water quality, circulation and benthic fauna of the area support the theory that the causeways are restricting flow and reducing water exchange within the back bays of the Park. This study was conducted as a result of the less than optimal operation of the four sewage treatment plants located at the park. Water quality was very bad due to the incomplete treatment of sewage during peak use and suspected entrapment in the back bays.

Tidal surge and flow patterns were mapped to determine if the back bays were flushing or if they were stagnant. As expected, although the tidal flux travels from east to west, the flow patterns merely fill the bays then empty them in a very calm manner not conducive to flushing which led to elevated water temperatures, water quality degradation and seagrass mortality. Although the sewer treatment plants were dismantled and the sewage pumped to mainland treatment plants, water quality still was poor as compared with surrounding waters. Again, stagnant conditions were suspected. Field visits confirmed this and at times one can observe differences in the tidal and wind driven water levels between the bays of Mullet Key.

By opening a channel between the bays pocketing and stagnation would be reduced. Opening the causeways by partial replacement with the 40-foot wide bridges will restore east-west circulation to the semi-enclosed embayments and will improve ecosystem health. The bridges will include fishing areas and maintain the current highly popular bike trail. Pinellas County proposes to perform pre- and post-construction water quality monitoring to document the improved conditions. Allowing the natural tidal flux and wind driven gulf/bay water to pass between the bays will help modulate water temperature and improve water quality by restoring the historic circulation patterns that existed prior to the filling of the passes.

The project directly affects a SWIM priority water body. It affects water quality and habitat value at a regional park facility. The project is consistent with the Pinellas County Comprehensive Plan and with the goals of the National Estuary Program.