Seagrass restoration in Tampa Bay: a resource-based approach to estuarine management
Johansson, J.O.R.; Greening, H.S. (2000). Seagrass restoration in Tampa Bay: a resource-based approach to estuarine management, in: Bortone, S.A. (Ed.) Seagrasses: monitoring, ecology, physiology, and management. pp. 279-293
In: Bortone, S.A. (Ed.) (2000). Seagrasses: monitoring, ecology, physiology, and management. CRC Marine Science Series, 16. CRC Press: Boca Raton. ISBN 0-8493-2045-3. 318 pp., more
In: Kennish, M.J.; Lutz, P.L. (Ed.) CRC Marine Science Series., more
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| Authors | | Top |
- Johansson, J.O.R.
- Greening, H.S.
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| Abstract |
Historical (pre-1930s) seagrass meadows in Tampa Bay are believed to have covered 31,000 ha of the shallow bay bottom. However, impacts to the bay from increasing population and industrial development of the Tampa Bay area resulted in large seagrass reductions. By 1982, approximately 8,800 ha of seagrass remained. Recently, Tampa Bay seagrass monitoring programs have shown that the trend of seagrass loss has been reversed. The bay-wide seagrass cover in 1997, was estimated at 10,930 ha. In Hillsborough Bay, the bay segment that historically has had the poorest water quality, seagrass increased from near 0 ha in 1984 to about 57 ha in 1998. The Tampa Bay seagrass expansion apparently started in response to water quality improvements that occurred from the late 1970s to the mid-1980s, which included reductions in phytoplankton biomass and water column light attenuation. These improvements followed a nearly 50% reduction in external nitrogen loading from domestic and industrial point-sources, primarily discharging to Rillsborough Bay, that occurred in the early 1980s. However, most recently, high rainfall amounts during the years 1995, 1996, and the 1997-1998 El Nifio event increased nitrogen loading to the bay. Both phytoplankton biomass and light attenuation increased in all major bay segments during this period of high rainfall. These influences on seagrass growth are often detrimental and appear to have reduced the rate of seagrass expansion during the last few years. The reduced rate of expansion is most evident in the Hillsborough Bay section of Tampa Bay for which the most detailed and current seagrass information is available. Recognizing the link between nitrogen loading, water quality, and seagrass protection, local, state, and federal partners working cooperatively through the Tampa Bay National Estuary Program (TBNEP) have agreed to adopt nitrogen loading targets for Tampa Bay based on the light requirements of Thalassia testudinum. A long-term goal has been adopted to achieve 15,400 ha of seagrass coverage, or 95% of the seagrass estimated for 1950. Reaching the goal will require preservation of the approximately 10,400 ha of seagrass present in the bay in 1992 and restoration of an additional 5,000 ha.Field measurements in Tampa Bay indicate that 20-25% of surface irradiance is required for sustained growth of T. testudinum. Two independent water quality models were used to estimate nitrogen loading rates and associated water column chlorophyll a concentrations required to maintain irradiance levels at the apparent maximum depth of seagrass growth in 1950 for each major bay segment. Based on monitoring data, it appears that light levels can be maintained at these depths in most bay segments with the existing nitrogen loading rates. However, to achieve the longterm seagrass restoration goal, increases in nitrogen loading associated with a projected increase in the watershed's human population must be offset.TBNEP partners have, therefore, identified and committed to specific nitrogen load reduction projects to ensure that nitrogen management targets are met. An interagency bay-wide seagrass monitoring program has been established to document the progress of Tampa Bay seagrass protection and restoration. Citizen-based educational and voluntary programs are underway to help reduce propeller scaring of seagrass meadows and to plant seagrass in areas which currently lack vegetation. |
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