Limnology of Ponds in the Kissimmee Prairie Tim Kozusko Environmental Management, United Space Alliance, 8550 Astronaut Blvd., USK-T28, Cape Canaveral, FL 32920 E-mail: [email protected] John A. Osborne UCF Department of Biology, 4000 Central Florida Blvd., Orlando, FL 32816-2368 Paul Gray Audubon of Florida, 100 Riverwoods Circle, FL 33857 ABSTRACT We studied the physicochemical features of three ponds in the Kissimmee Prairie, Okeechobee County, Flor- ida, between January and August 1997, and May and August 1998. Data collected included pH, specific con- ductance, water temperature and depth, turbidity, water color, alkalinity, tannin, dissolved oxygen, and concentrations of nitrogen and phosphate. We found the ponds to be acidic, poorly buffered, moderate to high in water color, and low in mineralized nitrogen and phosphorus. There were statistically significant differences in water chemistry between the inner zones of ponds and the outermost wet prairie zones. Water in the wet prairie zones had significantly lower pH, higher specific conductivity, and greater water color and tannin con- centrations than did water in the inner zones of ponds. INTRODUCTION fasciculatum Lam. with Utricularia, Eleocharis, Carex, Ra- nunculus, and Rhynchospora species. In the wet prairie The National Audubon Society’s Ordway-Whittell transitional zone between the pond and the wiregrass/ Kissimmee Prairie Preserve (KP), now part of the Kissim- palmetto prairie, the vegetation community is principally mee Prairie Preserve State Park, managed by the Florida comprised of Drosera sp., Sphagnum sp., Eriocaulon spp., Department of Environmental Protection, is located in Rhynchospora, Aristida stricta var. beyrichiana (Trin. & Ru- north-central Okeechobee County, Florida. The Sanctu- pr.) D. B. Ward, Carex spp., and Rhynchospora spp. ary (hereafter KP) represents a portion of the lower Kiss- We studied the limnological characteristics of Kissim- immee River watershed that contains unaltered wetlands mee Prairie ponds to determine if there were significant and numerous small ponds ranging in area from less than differences in water chemistry among the ponds and 1 ha to greater than 5 ha. among the vegetation zones within each pond. We used KP is composed of nearly level Pleistocene marine ter- monthly mean precipitation data from Fort Drum, 1961- race deposits (Webb 1990). The substrate is of well-sorted 1990 (Owenby and Ezell 1992) to characterize precipita- fine quartz sands. These marine sands are drought-prone tion for the area. Fort Drum is located approximately 16 yet poorly drained due to level topography and presence km east of KP. of an organic and/or calcareous pan that can impede ver- tical water movement (Pettry et al. 1965, McCollum and METHODS AND MATERIALS Pendleton 1971). In shallow surface waters water chemistry is strongly in- fluenced by soil composition (Wetzel, 1983). Marine ter- The study ponds are located at latitude 27° 33’ N, lon- race deposits in Florida generally favor formation of the gitude 81° 59’ W. Surveys of the property indicate the wet- Spodosol soil order (Brown et al., 1990). Spodosols are typ- lands are near the top of their watershed (P. Gray, unpub. ified by an illuvial soil horizon enriched in oxides of iron data), thus should be unaffected by flows from off the and aluminum, and organocomplexes that have leached property. Native-range cattle grazing was the previous use down from the soil surface (Allen and Fanning 1983, of the property, but cattle had been removed for 17 years Brown et al. 1990). The spodic horizon in Florida soils gen- at the commencement of the study. erally follows the contour of the ground and is related to We monitored pond depth using a 2.54-cm-diameter water table depth (Pettry et al. 1965, Yuan 1966). Spodic gauging post driven into the sediment. Water depth was also horizon development is thought to be inhibited by condi- determined at each sampling site. We performed water sam- tions of permanent soil saturation (McKeague et al. 1983). pling along a transect with three stations in each of four veg- The spodic horizon is not present under the ponds. etation zones. We withdrew water samples for laboratory Ponds within the KP exhibit a concentric zonation of analyses using PVC pipe, 1 m long and 2.5 or 5 cm in diam- vegetation, presumably related to hydroperiod. The cen- eter (2.5 cm for deep samples, 5 cm for shallow samples). ter of most ponds is inhabited by a monotypic stand of The pipe was fitted with a shut-off valve. This device was used pickerelweed, Pontederia cordata L. Surrounding this zone to isolate a section of the water column. Two columns were is a dense growth of maidencane, Panicum hemitomon withdrawn from each station and mixed in a larger contain- Schult. grading into a zone of St. John’s-wort, Hypericum er from which the sample bottle was filled. Land of Fire and Water: The Florida Dry Prairie Ecosystem. Proceedings of the Florida Dry Prairie Conference. Reed F. Noss, editor. 2006. 182 We measured hydrogen ion concentration in situ with RESULTS AND DISCUSSION an Oakton pH Testr 2. We measured specific conductance and water temperature in situ with a Hach Model 150 spe- cific conductivity meter. Water color and tannin/lignin The study ponds had areas <1 ha, maximum depths < 60 concentrations were determined spectrophotometrically cm, and surface area to volume ratios > 50:1. Dense vegeta- (APHA 1975). We determined dissolved carbon dioxide tion shaded the water, retarded mixing, and decreased the and alkalinity by titration (APHA 1975) and Lind (1979), effects of wind on the water surface. In the less-shaded areas respectively. Dissolved oxygen was determined using the of the ponds, heating was intensified by high water color. modified Winkler method (APHA 1975). Water between 20 and 50 cm deep was isothermal at dawn, A certified commercial laboratory performed nutri- yet stratified by afternoon. In late spring through summer, ent analyses on composite samples (n = 27) using EPA the surface of the water column was generally 10° C warmer laboratory procedures. These included ammonium than the bottom, and temperatures of water less than 20 cm (EPA 350.1), nitrate (EPA 353.1), total Kjeldahl nitrogen deep exposed to full sunlight commonly exceeded 40° C. (EPA 351.2), nitrite (SM4500NO2B), orthophosphate The highest temperature recorded was 46° C. (EPA 365.2), and total phosphorus (EPA 365.2). In 1998 The normal rainfall pattern for the study area is a wet the updated version (365.4) was used to determine total summer and fall, followed by a dry winter and spring. The phosphorus. The wet prairie zone was not included in the seasonal rainfall pattern was abnormal in 1998, with above composite samples for nutrient analysis because this average precipitation during February and March. This re- would over-represent this small component of the pond sulted in flooded conditions throughout the prairie dur- volume. Beginning in July 1998, nutrient analyses includ- ing late winter and spring. When the normal rainy season ed composites of the four vegetation zones. would have begun, the area was struck by a drought that re- Kruskall-Wallace analysis of variance was used to com- sulted in the study ponds drying out in June. pare sample medians with a confidence level of p = 0.05. During 1997 there was no significant difference in the All calculations involving pH were performed by first con- pH of water in the pickerelweed and maidencane zones verting pH to hydrogen ion concentration. We assigned (Table 1). However, the St. John’s-wort zone pH was sig- the detection limit value to concentrations found to be nificantly lower than the two inner zones, and the wet below detection limits, allowing calculation of means and prairie pH was significantly lower than the St. John’s-wort confidence limits. zone. In 1998 the pH of each zone ranged much lower, Table 1. Mean pH values, ranges, and sample sizes within the vegetated zones of Kissimmee Prairie study ponds between January and August 1997, and May and August 1998. Vegetated Zone Pickerelweed Maidencane St. John’s-wort Wet Prairie 1997 Pond 1 Mean pH 4.7 4.6 4.5 4.3 Range 4.6 - 4.9 4.4 - 4.8 4.3 - 4.9 4.1 - 4.4 Sample Size 42 42 42 24 Pond 2 Mean pH 4.5 4.5 4.4 3.7 Range 4.3 - 4.7 4.3 - 4.7 4.1 - 4.7 3.3 - 4.1 Sample Size 42 42 42 30 Pond 3 Mean pH 4.3 4.4 4.3 4.0 Range 4.1 - 4.6 4.2 - 4.7 4.0 -4.7 3.7 - 4.2 Sample Size 42 42 42 30 1998 Pond 1 Mean pH 4.5 4.5 4.5 4.6 Range 4.1 - 4.9 4.1 -4.9 4.0 - 4.9 4.0 - 5.8 Sample Size 27 27 27 21 Pond 2 Mean pH 4.3 4.3 4.2 3.8 Range 3.5 - 4.7 3.5 - 4.9 3.4 - 4.7 2.9 - 4.5 Sample Size 27 27 27 21 Pond 3 Mean pH 4.3 4.2 4.0 3.9 Range 4.1 - 4.6 3.9 - 4.7 3.8 - 4.5 3.5 - 4.3 Sample Size 27 27 24 21 183 though there were no significant differences in any zone Riekerk and Korhnak (1992) report that the pH values from 1997 to 1998. The extremely low values are from the of runoff water from undisturbed pine flatwoods were one sampling period right after the ponds had re-filled. In nearly one pH unit less than the pH of rainfall, and these 1998 the inner three zones had no significant differences in authors attributed the lower pH of runoff to organic acids pH, but the wet prairie zone had a significantly lower pH leached from soil humus.