Task 3: Wetlands and Seagrass as Indicators of Tampa Bay Health

Tampa Bay, Florida

Coastal wetlands are a critical interface between land and sea providing a habitat and nursery for estuarine organisms and open-marine fish. The TBEP has identified that while the current distribution of wetlands in Tampa Bay is well known, current condition, historical, and pre-historical condition with respect to ecosystem health is not. An understanding of the past history and current conditions of the wetlands will provide the basis for predicting the future for wetlands in Tampa Bay. Groundwater flow is a critical component of wetland health. Both inflow and withdrawal affect water quality and surface gradients that directly affect the health of wetland flora and fauna. Information collected from Tasks 1 and 2 will provide insight into the relation between bathymetry groundwater, salinity gradients, and conditions of the wetlands at each of the study locations (Fig. 1).

Present and Past Health of Tampa Bay Wetlands

Task Participants:
Terry Edgar (USGS-GD), Ellen Raabe (USGS-GD), Carole McIvor (USGS-BRD), Tom Smith (USGS-BRD), Jimmy Johnston (USGS-BRD), Ed Proffitt (USGS-BRD), Rick Oches (USF), Sarah Kruse (USF), Charles Kovach (DEP), Dave Tomasko (SWFWMD-SWIM), Dave Hollander (USF), Roger Johansen (City of Tampa).

An identified need for research to fill an information gap in Tampa Bay is "wetlands health or status". Such an analysis provides the opportunity to integrate several aspects of USGS expertise, i.e., mapping, land-use analysis, water quality, and ecology. The larger wetlands project will include a mapping component consisting of a synthesis of available aerial photos to show patterns of historical wetlands growth or loss as well as land use changes. Detailed bathymetric data will be acquired offshore of the wetlands in the Alafia and Terra Ceia Aquatic Preserve study areas. The product is envisioned as a GIS database onto which other components will be layered, including a water quality layer.

Task 3A: Current Conditions:
The current condition will be determined by an evaluation of ecological indicators such as the composition, quantity, health of vegetation and of animals, and the physical and chemical characteristics of the marsh water. A coordinated effort between characterizing biological components found in the present day environment with indictors of past conditions will be initiated.

Task summary and objectives:

Composition and Abundance: Document/compile existing data of composition and abundance of vegetation. These data will be utilized in a GIS overlay and used as a tool to evaluate health of the wetlands. Data will be compared to historical and pre-historical vegetation data.
Bioindicators: Test the utility of common flora and fauna as indicators of wetland status by comparing their abundance at the study sites with similar salinity regime and known status (little degraded, very degraded). If there appears to be a good relationship, we can then apply our empirical model to wetlands of indeterminate status to test it robustness.

The health of wetlands will be assessed by an indepth characterization of past history, present conditions, and the evolution of the wetlands to present day conditions via a coordinated effort between characterizing biological components found in the present day environment with indictors of past conditions.

Task 3B: Historical Evolution
The historical evolution of wetlands can be established by studying early navigation charts (NOAA-archives), aerial photographs (USGS-BRD, SWFWMD), and multispectral (USGS-GD, DEP) satellite imagery of the bay. The USGS has documented changes for the last 140 years in the Big Bend area of northwestern Florida using these techniques. During this time, sea level rose 1_ feet and human activities changed many aspects affecting the wetlands. With an understanding of the effects of these changes, we are in a better position to manage the coastal region to the benefit of the wetlands, which, in turn, benefits sea life and the quality of life for the public.

Task 3C: Pre-History
The pre-history will be studied from analyses of sediment cores (USGS-GD, BRD) taken along a transect across a wetland. Sediment composition and shallow seismic profiles will be characterized. The cores will be dated using ratios of various isotopes and analyzed to relate changes in vegetation composition and abundance to changes in salinity and temperature (isotope ratios of microscopic shells) in the past. These data will provide guidelines for establishing environmental limits tolerated by wetland vegetation. We shall also determine if these data are applicable to sea grasses. Younger data from the cores can be correlated to results from historical data such as satellite imagery and aerial photographs and long term salinity data (USGS, DEP, Hillsborough County EPC). Determining the pre-anthropogenic condition of wetlands is critical for establishing success criteria for future restoration efforts.

Task 3D: Physical Characteristics of Wetland at the Alafia and Terra Ceia Aquatic Preserve Study Sites
Existing and current data on salinity, water quality and light characteristics from site locations will be compiled and as necessary acquired.

Task 3E: Seagrass as Indicators of Estuarine Health
Tampa Bay Estuary Program, Fish and Wildlife Commission - FMRI representatives have identified the need to examine the condition of seagrass and its distribution around Tampa Bay as a high priority because seagrass is another critical indicator of estuarine health.

Task Summary and Objectives
This effort will develop digital datafiles of seagrass maps and photographs from 1950 to present. These data will assist in the identification of causes for seagrass recovery slowdown in problem areas, historical changes in wetland distribution, assessment of the importance of changes in physical factors (offshore bars, structures affecting seagrasses and wetlands), assessment of changes in seagrass density, and determine the accuracy and precision of historic and current maps. This database will also be used to highlight or depict photographically land use/land cover changes over the past 50 years for selected areas of the Tampa Bay region, including coastal wetlands.