Ponds within the Kissimmee Prairie usually exhibited a concentric zonation of vegetation, presumably related to hydroperiod (Figure 2). In the three study ponds the vegetation grows to a density that hides the water from view. The center of most ponds is inhabited by a monotypic stand of Pontederia cordata (pickerelweed) (Figures 3 and 4). The pickerelweed zone is not well defined in pond 1. Surrounding this zone is a dense growth of Panicum hemitomon (maidencane) that grades into a zone of Hypericum fasciculatum (St. John's-wort) accompanied by Utricularia spp., Nymphoides aquatica, Eleocharis spp., Carex spp., Ranunculus spp., and Rhynchospora spp. Dense mats of filamentous green algae form within the pond as water levels recede and vascular vegetation senesces, releasing nutrients.
In the wet prairie transitional zone between the pond and the wiregrass/palmetto prairie is the vegetation community comprised of Drosera spp., Sphagnum spp., Eriocaulon spp., Dichromena spp., Xyris spp., Aristida beyrichiana, Carex spp., Polygonum spp., Rhyncospora spp. etc. Some ponds have a crescent of woody vegetation at the edge such as Persea spp., Myrica cerifera, and Quercus spp. This crescent marks a fire-shadow indicating the direction of the last fire to move through the area (Paul Gray, personal communication). Hypericum fasciculatum and Panicum hemitomon are fire tolerant (VanArman and Goodrick, 1979; Vogl, 1973). Kirkman et al. (1998) found higher species richness for plants in the transitional zone between the longleaf pine/wiregrass community and small seasonal ponds. Winchester et al. (1985) studied the vegetation and substrate of 24 shallow ponds and wet prairie areas in southwestern Florida and found a similar zonation. Several ponds they studied had an accumulation of peat in the center. They believed that fire played an important role in the maintenance of vegetation zonation. They found that the St. John's-wort zone consisted of an inner zone of dead plants during conditions of higher water. This dead vegetation zone was evident in the Kissimmee Prairie ponds after several years of wet conditions. LaClaire (1995) studied the vegetation of 13 seasonal ponds in north, and north-central Florida. She found hydrologic zonation in each pond, and noted the presence of fire-shadows.
The plant species LaClaire (1995) found were also common in the KPS ponds. She made no mention of matting by filamentous algae. She reported that species diversity was higher in ponds that had recently dried out. Greening and Gerritsen (1987) monitored changes in four marsh plant communities under different hydrologic regimes in the Okefenokee Swamp. They found that the highest macrophyte diversity and greatest variability in biomass dynamics were correlated with unpredictable drawdowns. Aquatic vegetation can affect the thermal regime of littoral communities through shading, and reduced water movements (Kushlan and Hunt, 1979), which can lead to thermal stratification. In addition, high water color can increase the rate of heating of shallow water exposed to sunlight (Wetzel, 1985).
In a wetland or lake, water chemistry represents the result of a series of physicochemical and biological processes that determine the concentrations of solutes within the body of water (Dunson et al., 1997). Factors such as pH and specific conductance have an influence on the organisms inhabiting a body of water. For example, due to its greater tolerance of low pH, the pine woods treefrog (Hyla femoralis) out-competes the barking treefrog (Hyla gratiosa) in acidic ponds, in spite of its smaller size (Warner et al., 1993). Calcium ion is important in maintaining low epithelial permeability in fish (Dunson et al., 1997). Alkalinity determines the resistance of water to changes in pH (Wetzel, 1983). Nutrient concentrations influence the species composition of the plant communities inhabiting a body of water.
Organic staining is a variable property of Florida lakes (Shannon and Brezonik, 1972). Water color can be produced in the water and/or imported via drainage, and is considered to be an important component of the metabolism of a body of water (Rich and Wetzel, 1978). Tannins and lignins can inhibit microbial decomposition, especially when combined with low pH (Rich and Wetzel, 1978). The ratios of nitrogen and phosphorus to carbon in aquatic humus are highly variable (Gjessing, 1976; Wetzel, 1983). Humic substances are thought to have a net negative charge, and possess amphiprotic properties, becoming positively charged at low pH (Gjessing, 1976). Humic material has an affinity for mercury and can reduce metals (Zimmerman, 1981). When complexed with aluminum, organic matter is thought to reduce the surface tension of water and thus affect gaseous diffusion and invertebrates that drift in or stride on the water (Hall et al., 1985).
Dissolved organic substances are a source of reduced carbon, and thus energy. Cummins et al. (1972) reported that the microbial community in an artificial lotic system was able to rapidly process leaf leachate. Ultraviolet light breaks apart the more refractory humic compounds, making them available to the biota (Suberkropp et al., 1976; Rich and Wetzel, 1978). Ultraviolet light reduces the color of water, but not necessarily the organic carbon content (Manny et al. 1971). Ultraviolet light liberates nitrite and nitrate from ringed carbon structures. Ultraviolet light can photo-oxidize dissolved organic matter to produce carbon monoxide and carbon dioxide (Zuo and Jones, 1997).
Klosowski (1992) found that some chemical characteristics of water in a littoral zone in a lake in Poland varied significantly within different vegetation zones. For example, pH varied significantly between zones but not within each zone. Klosowski reported (1992) that pH was lowest near shore and increased with water depth. Concentrations of orthophosphate and nitrate decreased towards open water. Dunson et al. (1997) studied the water chemistry and occurrence of fish in southwestern Florida pine flatwoods ponds and found many of the ponds contained soft water. They suggested that differing specific conductances within the ponds were a result of differing degrees of isolation of ponds from surface water inputs.