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U. S. Geological Survey, Florida Integrated Science Center, Center for Coastal & Watershed Studies
600 4th Street South, St. Petersburg, FL 33701, Phone: 727-803-8747

Gulf of Mexico Estuaries Integrated Science
Tampa Bay Pilot Study
2nd Annual Science Conference, St. Petersburg, FL, Sept. 19, 2002
Poster Presentations: Wetlands Section

Task Leader: Carole McIvor, Email: carole_mcivor@usgs.gov

Poster Title: Intertidal Vegetation Dynamics in the Tampa Bay Estuary

Authors: T.J. Smith III1, N. Silverman2, Jeffrey Dismukes2, G. Peery2, W. Weaver2

   1: USGS/Geological Discipline
   3: ETI Professionals, Inc.

Abstract:

Intertidal vegetative communities such as salt marshes and mangrove forests once covered extensive areas around Tampa Bay. Today only about one-third of the historical acreage remains. The communities comprise important habitats for commercially and recreationally important fisheries, for wading birds and for other wildlife.

The objectives of this work are:

  1. to establish a long-term sampling network in the remaining wetlands of Tampa Bay to assess their health (growth, production, survival, mortality) and measure future changes and trends
  2. provide the scientific insight necessary for enlightened management and restoration of coastal wetlands in the Tampa Bay region.
Our methods involve the establishment of permanent sampling locations that are measured repeatedly over time. We use plots in the mangrove forests and transects in marshes. Sixteen plots have been established to date (8 at Terra Ceia, 8 in the Alafia).

Although only two years old, our sampling has revealed that natural changes have occured. Larger mangrove trees in plots around Moses Hole, at Terra Ceia, suffered mortality during a severe storm event in January 2002. Recruitment into the plots by mangrove stems is low and growth of the trees and saplings is slow. The slow growth we have observed is probably partly attributable to the Region's recent drought.

During the coming year we will resample all of the vegetation plots and transects. Additional plots will be established in the Feather Sound region. We will also place Sediment Elevation Tables (SETs) and soil water wells at a selected number of the permanent vegetation plots. SETs are used to measure changes in the surface elevation of wetlands at small scales. The measures can be related to both physical parameters (groundwater hydrology) and biological aspects of the environment (plant growth). The sampling network will allow us to quickly assess wetland responses to ongoing restoration projects around Tampa Bay.

Introduction:

Coastal wetlands yield important ecosystem services to human societies globally, including habitat for commercially and recreationally important fisheries, providing a buffer from storm surges and improvement of coastal water quality (Ewel et al. 1998, Gautier et al. 2001). Wetland plant communities have been converted to other uses the world over. Mangrove forests have recently been recognized as a threatened habitat in tropical and sub-tropical regions due to conversion by dredging and filling and other activities (Valiela et al 2001). In the Tampa Bay area some 2/3 of the coastal wetlands have been lost due to development, dredge and fill activities or conversion for other human uses.

As part of the Tampa Bay Pilot Study we are:

  1. characterizing the remaining coastal wetlands of Tampa Bay;
  2. studying wetland structure and function;
  3. measuring wetland health;
  4. providing data for sound management of the bay's remaining wetland habitats and for wetland restoration.

Methods:

Initial Plot Set-up: Sampling sites were located using a stratified-random sampling design. Plots were located along the large-scale salinity gradient present in each study area (Figure 1). The mangrove forest plots are circular to mimic the natural canopy gaps that are prominent feature in many forest ecosystems (Harper & White 1974, Kohyama 1993). A PVC rod was driven into the sediment to permanently mark the center of each plot. Stems, greater than 1.4m in height, within a given radius of the center, were identified to species. They were measured for diameter at breast height (DBH) and tagged with an individually numbered aluminum tree-tag (Figure 2). The location on the stem at which DBH is measured is marked with paint to ensure accurate re-measurement. Each stem was mapped by measuring its distance and bearing (E of N) from the center stake (Figure 3). The plot radius is variable and depends on a visual inspection prior to establishment. The radius is large enough to ensure 20 stems. Physical parameters such as soil porewater salinity were measured at each site.

Resurveys of plots: The plots were established in the summer of 2001 and are currently being re-sampled. During a resurvey, DBH is measured at the same spot as previous surveys. Growth is calculated as the simple difference in DBH between surveys. Mortality of stems is recorded and recruitment is noted. We define a recruit as a stem that has attained the size necessary to allow a DBH measurement to be made. In this study a stem recruits when it attains a height of 1.4m.

Future Directions:

Results & Discussions:

Visual observations of all plots have been completed along with quantitative re-sampling at several plots. Recruitment by mangrove stems into the plots was extremely low. Growth has also been very slow. However, increases in DBH have been measured in two plots near the mouth of the Alafia River (plots AT4 and AT4B, see Figure 1B). Both plots are dominated by small stemmed individuals of all species. DBHs are less than 6.0cm in AT4 and less than 3.5cm in plot AT4B. However, over the course of a year, increases in DBH were measured in both plots, especially for Laguncularia at these plots (Figures 4a,b,c,d). Significant mortality was observed at Moses Hole in the Terra Ceia Preserve. The two largest stems (one 6.0cm the other 8.5cm) in plot MHNC-D1 were killed by a severe winter storm in January (Figure 4e,f).

We recognize that two consecutive measurements are not enough to make strong inferences concerning environmental changes in the plots. However, the utility of starting a longer term sampling program in the wetlands of Tampa Bay has been clearly demonstrated by studies in coastal ecosystems elsewhere (Putz & Chan 1986; Smith et al., 1994; Bell 1997).

Figure 4: For both plot sites AT4 and AT4B in the Alafia River Study Area, the second year survey indicates slight growth amongst the adult trees with no emergent growth in the plot areas. At AT4 the calculated mean DBH for Avicennia increased from 3.28 cm in 2001 to 3.36 cm in 2002. Calculated mean DBH for Laguncularia at the same site increased from 1.93 cm in 2001 to 1.96 cm in 2002. There were no Rhizophora species in the AT4 plot. At AT4B, calculated mean DBH increased from 1.21 cm in 2001 to 1.24 cm for the Avicennia species. Calculated mean DBH for Laguncularia increased from 1.96 cm in 2001 to 1.99 cm in 2002. The Rhizophora species at AT4B also showed a net increase in calculated mean DBH from 1.7 cm in 2001 to 1.71 cm in 2002. The final two plots from the MHNC-D1 site in the Terra Ceia Preserve show the result of damage from a severe winter storm in January 2002, which toppled two of the largest Laguncularia at this site, circled in the plot from the first year survey.

Literature Cited:

Bell, D.T. 1997. Eighteen years of change in an Illinois streamside deciduous forest. Bulletin of the Torrey Botanical Society, 124: 174-188.

Boumans, R.O.E. & J.W. Day, Jr., 1993. High precision measurements of sediment elevation in shallow coastal areas using a sedimentation-erosion table. Estuaries, 16: 375-380.

Ewel, K., J.-E. Ong & R. Twilley. 1998. Different kinds of mangrove swamps provide different kinds of goods and services. Global Ecology & Biodiversity Letters, 7: 83-94.

Gautier, D., J. Amador & F. Newmark. 2001. The use of mangrove wetlands as a biofilter to treat shrimp pond effluents: preliminary results of an experiment on the Caribbean coast of Colombia. Aquaculture Research, 32: 787-799.

Harper, J.L. & J. White. 1974. The demography of plants. Annual Review of Ecology & Systematics, 5: 419-463.

Kohyama, T. 1993. Size-Structured Tree Populations in Gap-Dynamic Forests-The Forest Architecture Hypothesis for the Stable Coexistence of Species. Journal of Ecology, 81: 131-143.

Putz, F.E. & H.-T. Chan. 1986. Tree growth, dynamics and productivity in a mature mangrove forest in Malaysia. Forest Ecology & Management, 17: 211-230.

Smith, T.J., III & D.H. Cahoon. 2002. Sediment surface elevation changes in relation to groundwater hydrologic variation in the coastal Florida Everglades. Eos. Trans. AGU, 83(19), Spring Meeting Supple., Abstract H31A-05.

Smith, T.J., III, M.B. Robblee, H.R. Wanless & T.W. Doyle. 1994. Mangroves, hurricanes and lightning strikes. BioScience, 44: 256-262.

Valiela, I., J.L. Bowen & J.K. York. 2001. Mangrove forests: One of the world's threatened major tropical environments. BioScience, 51: 807-815.

Image Captions:

Figure 1. Location of the FY2001 (red) and FY2002 (yellow) study sites.

Feather Sound study site.

Terra Ciea study site.

Alafia River study site.

Figure 2. Noah Silverman (USGS/BRD), measuring diameter at breast height on stems at an Alafia River site.

Figure 3. Schematic diagram of a tree plot.

Figure 4: For both plot sites AT4 and AT4B in the Alafia River Study Area, the second year survey indicates slight growth amongst the adult trees with no emergent growth in the plot areas. At AT4 the calculated mean DBH for Avicennia increased from 3.28 cm in 2001 to 3.36 cm in 2002. Calculated mean DBH for Laguncularia at the same site increased from 1.93 cm in 2001 to 1.96 cm in 2002.

There were no Rhizophora species in the AT4 plot. At AT4B, calculated mean DBH increased from 1.21 cm in 2001 to 1.24 cm for the Avicennia species. Calculated mean DBH for Laguncularia increased from 1.96 cm in 2001 to 1.99 cm in 2002. The Rhizophora species at AT4B also showed a net increase in calculated mean DBH from 1.7 cm in 2001 to 1.71 cm in 2002.

The final two plots from the MHNC-D1 site in the Terra Ceia Preserve show the result of damage from a severe winter storm in January 2002, which toppled two of the largest Laguncularia at this site, circled in the plot from the first year survey.

Fig. A: Alafia River Site #AT4
First Year Survey (2001)
Plot of Diameter at Breast Height vs. Position (n=45)
Laguncularia: (mean DBH = 1.93 cm)
Avicennia: (mean DBH = 3.28 cm)

Fig. B: Alafia River Site #AT4
Second Year Survey (2002)
Plot of Diameter at Breast Height vs. Position (n=45)
Laguncularia: (mean DBH = 1.96 cm)
Avicennia: (mean DBH = 3.36 cm)

Fig. C: Alafia River Site #AT4B
First Year Survey (2001)
Plot of Diameter at Breast Height vs. Position (n=77)
Rhizophora: (mean DBH = 1.70 cm)
Laguncularia: (mean DBH = 1.96 cm)
Avicennia: (mean DBH = 1.21 cm)

Fig. D: Alafia River Site #AT4B
Second Year Survey (2002)
Plot of Diameter at Breast Height vs. Position (n=77)
Rhizophora: (mean DBH = 1.71 cm)
Laguncularia: (mean DBH = 1.99 cm)
Avicennia: (mean DBH = 1.24 cm)

Fig. E: Terra Ceia Preserve Site #MHNC-D1
First Year Survey(2001)
Plot of Diameter at Breast Height vs. Position (n=52)
Rhizophora
Laguncularia
Avicennia

Fig. F: Terra Ceia Preserve Site #MHNC-D1
Second Year Observation (2002)
Plot of Diameter at Breast Height vs. Position(n=50)
Rhizophora
Laguncularia
Avicennia

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